Canada - English - Health Canada
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Acyclovir Oral Suspension USP, 200 mg /5 mL
Acyclovir Tablets USP, 200, 400, and 800 mg
7333 Mississauga Road
Date of Revision:
September 10, 2008
Submission Control Number: 123012
2008 GlaxoSmithKline Inc. All Rights Reserved
ZOVIRAX, WELLSTAT PAC and ZOSTAB PAC are registered trademarks, GlaxoSmithKline Inc.
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Table of Contents
PART I: HEALTH PROFESSIONAL INFORMATION.........................................................3
SUMMARY PRODUCT INFORMATION ........................................................................3
INDICATIONS AND CLINICAL USE..............................................................................3
WARNINGS AND PRECAUTIONS..................................................................................4
DRUG INTERACTIONS ....................................................................................................9
DOSAGE AND ADMINISTRATION..............................................................................10
ACTION AND CLINICAL PHARMACOLOGY ............................................................12
STORAGE AND STABILITY..........................................................................................14
DOSAGE FORMS, COMPOSITION AND PACKAGING .............................................14
PART II: SCIENTIFIC INFORMATION ...............................................................................16
PART III: CONSUMER INFORMATION..............................................................................37
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PART I: HEALTH PROFESSIONAL INFORMATION
SUMMARY PRODUCT INFORMATION
Dosage Form / Strength
Clinically Relevant Non-medicinal
200 mg/5 mL
200 mg, 400 mg and 800 mg
200 mg Tablets contain lactose.
For a complete listing see Dosage Forms,
Composition and Packaging section.
INDICATIONS AND CLINICAL USE
(acyclovir) is indicated for the following conditions:
The treatment of initial episodes of herpes genitalis.
The suppression of unusually frequent recurrences of herpes genitalis (6 or more
episodes per year).
The acute treatment of herpes zoster (shingles) and varicella (chickenpox).
The results of clinical studies suggest that some patients with recurrent genital herpes
may derive clinical benefit from the administration of oral ZOVIRAX
if taken at the
first sign of an impending episode. Those most likely to benefit are patients who
experience severe, prolonged recurrences; such intermittent therapy may be more
appropriate than suppressive therapy when these recurrences are infrequent.
Early treatment of acute herpes zoster (shingles) in immunocompetent individuals with
resulted in decreased viral shedding; decreased time to healing; less
dissemination; and alleviation of acute pain.
Treatment of varicella (chickenpox) in immunocompetent patients with oral ZOVIRAX
reduced the total number of lesions, accelerated the progression of lesions to the crusted
and healed stages, and decreased the number of residual hypopigmented lesions. In
decreased fever and constitutional symptoms associated with
The prophylactic use of acyclovir in chickenpox has not been established.
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Geriatrics (≥ 65 years of age):
Use in the geriatric population may be associated with
differences in safety due to age-related changes in renal function and a brief discussion
can be found in the appropriate sections (see WARNINGS AND PRECAUTIONS).
Pediatrics (< 2 years old):
No data is available.
(acyclovir) is contraindicated for patients who develop hypersensitivity or
who are hypersensitive to acyclovir, valacyclovir or any other components of the
formulations of ZOVIRAX
. For a complete listing, see Dosage Forms, Composition
and Packaging section of the product monograph.
WARNINGS AND PRECAUTIONS
Care should be taken to maintain adequate hydration in patients receiving high oral doses
Suppressive therapy of herpes genitalis with ZOVIRAX
(acyclovir) should be
considered only for severely affected patients. Periodic evaluation of the need for
continued suppressive therapy is recommended. In some patients, there is a tendency for
the first recurrent episode to be more severe following cessation of suppressive therapy.
In severely immunocompromised patients, the physician should be aware that prolonged
or repeated courses of acyclovir may result in selection of resistant viruses associated
with infections which may not respond. Thrombotic thrombocytopenic
purpura/haemolytic uremic syndrome (TTP/HUS), which has resulted in death, has
occurred in immunocompromised patients receiving ZOVIRAX
The recommended dosage and length of treatment should not be exceeded (see DOSAGE
AND ADMINISTRATION). The decision to prescribe a course of suppressive therapy
should be weighed in the light of our present knowledge about the long-term effects of
and must clearly relate to the condition of the patient.
Whereas cutaneous lesions associated with herpes simplex infections are often
pathognomonic, Tzanck smears prepared from lesion exudate or scrapings may assist in
the diagnosis. Positive cultures for herpes simplex virus offer the only absolute means
for confirmation of the diagnosis. Appropriate examinations should be performed to rule
out other sexually transmitted diseases. All patients should be advised to take particular
care to avoid potential transmission of virus if active lesions are present while they are on
therapy. Genital herpes can also be transmitted in the absence of symptoms through
asymptomatic viral shedding.
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The clinical status of the patient and the adverse event profile of ZOVIRAX
borne in mind when considering the patient’s ability to drive or operate machinery.
There have been no studies to investigate the effect of ZOVIRAX
performance or the ability to operate machinery. Further, a detrimental effect on such
activities cannot be predicted from the pharmacology of the active substance.
Although chickenpox in otherwise healthy children is usually a self-limited disease of
mild to moderate severity, adolescents and adults tend to have more severe disease.
Treatment was initiated within 24 hours of the typical chickenpox rash in the controlled
studies, and there is no information regarding the effects of treatment begun later in the
disease course. It is unknown whether the treatment of chickenpox in childhood has any
effect on long-term immunity. However, there is no evidence to indicate that treatment
of chickenpox with ZOVIRAX
would have any effect on either decreasing or increasing
the incidence or severity of subsequent recurrences of herpes zoster (shingles) later in
Carcinogenesis and Mutagenesis
has caused mutagenesis in some acute studies at high concentrations of the
drug (see Part II, TOXICOLOGY).
Renal insufficiency or acute renal failure has been observed in patients taking
at the recommended dosage and/or with no previous renal conditions and
may be associated with renal pain (see ADVERSE REACTIONS, Post-Market Adverse
Acyclovir is eliminated by renal clearance, therefore the dose must be reduced in patients
with renal impairment (see DOSAGE AND ADMINISTRATION, Patients with Acute or
Chronic Renal Impairment). Elderly patients are likely to have reduced renal function
and therefore the need for dose reduction must be considered in this group of patients.
Both elderly patients and patients with renal impairment are at increased risk of
developing neurological side effects and should be closely monitored for evidence of
these effects. In the reported cases, these reactions were generally reversible on
discontinuation of treatment (see ADVERSE REACTIONS).
Caution should be exercised when administering to patients receiving potentially
nephrotoxic agents since this may increase the risk of renal dysfunction.
In a study of 20 male patients with normal sperm count, oral acyclovir administered at
doses of up to 1 g per day for up to six months has been shown to have no clinically
significant effect on sperm count, motility or morphology. There is no information on the
effect of acyclovir oral formulations on human female fertility.
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Teratology studies carried out to date in animals have been negative
in general. However, in a non-standard test in rats, there were fetal abnormalities such as
head and tail anomalies, and maternal toxicity; since such studies are not always
predictive of human response, ZOVIRAX
should not be used during pregnancy unless
the physician feels the potential benefit justifies the risk of possible harm to the fetus.
The potential for high concentrations of acyclovir to cause chromosome breaks
should be taken into consideration in making this decision.
A post-marketing acyclovir pregnancy registry has documented pregnancy outcomes in
women exposed to any formulation of ZOVIRAX
. The registry findings have not
shown an increase in the number of birth defects amongst subjects exposed to
compared with the general population, and any birth defects showed no
uniqueness or consistent pattern to suggest a common cause.
Acyclovir concentrations have been documented in breast milk in
2 women following oral administration of acyclovir and ranged from 0.6 to 4.1 times
corresponding plasma levels. These concentrations would potentially expose the nursing
infant to a dose of acyclovir up to 0.3 mg/kg per day. Caution should therefore be
exercised when ZOVIRAX
is administered to a nursing woman.
: Safety and effectiveness in children less than 2 years of age have not been
The possibility of renal impairment in the elderly must be considered and the
dosage should be adjusted accordingly (see WARNINGS AND PRECAUTIONS, Renal,
and DOSAGE AND ADMINISTRATION, Patients with Acute or Chronic Renal
Impairment). Adequate hydration of elderly patients taking high oral doses of acyclovir
should be maintained.
Adverse Drug Reaction Overview
The most frequent adverse reactions associated with the use of ZOVIRAX
are headache and nausea.
Neurological side effects have also been reported in rare instances. Elderly patients and
patients with a history of renal impairment are at increased risk of developing these
effects. In the reported cases, these reactions were generally reversible on
discontinuation of treatment (see WARNINGS AND PRECAUTIONS and ADVERSE
REACTIONS, Post-Market Adverse Drug Reactions).
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Clinical Trial Adverse Drug Reactions
Because clinical trials are conducted under very specific conditions the adverse
reaction rates observed in the clinical trials may not reflect the rates observed in
practice and should not be compared to the rates in the clinical trials of another
drug. Adverse drug reaction information from clinical trials is useful for
identifying drug-related adverse events and for approximating rates
Treatment of Herpes Simplex:
Short-term administration (5-10 days): The most
frequent adverse reactions reported during clinical trials of treatment of genital herpes
with oral ZOVIRAX
in 298 patients are listed in Table 1.
Adverse Reactions Reported in Clinical Trials of
Treatment of Genital Herpes with Acyclovir
Nausea and/or Vomiting
Suppression of Herpes Simplex:
Long-term administration: The most frequent adverse
events reported in a clinical trial for the prevention of recurrences with continuous
administration of 400 mg (two 200 mg capsules) 2 times daily are listed in Table 2.
Adverse Reactions Reported in a Clinical Trial for the
Prevention of Recurrences of Genital Herpes with Acyclovir
Evidence so far from clinical trials suggests that the severity and frequency of adverse
events is unlikely to necessitate discontinuation of therapy.
The most frequent adverse reactions reported during three clinical trials
of treatment of herpes zoster (shingles) with 800 mg of oral ZOVIRAX
5 times daily for
7 or 10 days or placebo are listed in Table 3.
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Adverse Reactions Reported in Clinical Trials of
Treatment of Herpes Zoster
The most frequent adverse events reported during three clinical trials of
treatment of chickenpox with oral ZOVIRAX
or placebo are listed in Table 4.
Adverse Reactions Reported in Clinical Trials of Treatment
Less Common Clinical Trial Adverse Drug Reactions
Other adverse reactions reported in less than 1% of patients receiving ZOVIRAX
clinical trial included: abdominal pain, anorexia, constipation, dizziness, edema, fatigue,
flatulence, inguinal adenopathy, insomnia, leg pain, medication taste, skin rash, sore
throat, spasmodic hand movement and urticaria.
Abnormal Hematologic and Clinical Chemistry Findings
No clinically significant changes in laboratory values have been observed in clinical trials
for the treatment of chickenpox and zoster, and for the treatment and suppression of
genital herpes with ZOVIRAX
Post-Market Adverse Drug Reactions
The following events have been reported voluntarily during post-market use of
in clinical practice. These events have been chosen for inclusion due to
either their seriousness, frequency of reporting, potential causal connection to
or a combination of these factors. Post-market adverse events are reported
spontaneously from a population of unknown size, thus estimates of frequency cannot be
Fever, headache, pain, and peripheral edema.
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Dizziness, paresthesia, agitation, confusion, tremor, ataxia, dysarthria,
hallucinations, psychotic symptoms, convulsions, somnolence, encephalopathy and coma
have been reported. These events are generally reversible and usually reported in patients
with renal impairment, or with other predisposing factors (see WARNINGS AND
PRECAUTIONS). These symptoms may be marked, particularly in older adults.
Diarrhea, gastrointestinal distress, nausea.
Hematogical and Lymphatic:
Anaemia, leukopenia, lymphadenopathy and
Hypersensitivity and Skin:
Alopecia, erythema multiforme, Stevens-Johnson
syndrome, toxic epidermal necrolysis, rashes including photosensitivity, pruritus,
urticaria, dyspnoea, angioedema and anaphylaxis.
Hepatobiliary Tract and Pancreas:
Reports of reversible hyperbilirubinemia and
elevated liver related enzymes. Hepatitis and jaundice.
Elevated blood creatinine and blood urea nitrogen (BUN). Acute renal
failure, renal pain and hematuria have been reported. Renal pain may be associated with
renal failure (see WARNINGS AND PRECAUTIONS).
No clinically significant interactions have been identified.
Acyclovir is eliminated primarily unchanged in the urine via active renal tubular
secretion. Any drugs administered concurrently that compete with this mechanism may
increase acyclovir plasma concentrations. Probenecid and cimetidine increase the area
under the curve (AUC) of acyclovir by this mechanism, and reduce acyclovir renal
clearance. Similarly increases in plasma AUCs of acyclovir and of the inactive
metabolite of mycophenolate mofetil, an immunosuppressant agent used in transplant
patients have been shown when the drugs are coadministered. However, no dosage
adjustment is necessary because of the wide therapeutic index of acyclovir.
There is no known interaction with food (see ACTION AND CLINICAL
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Interactions with herbal products have not been established.
Drug-Laboratory Test Interactions
Interactions with laboratory tests have not been established.
DOSAGE AND ADMINISTRATION
The dosage of ZOVIRAX
(acyclovir) should be reduced in patients with
impaired renal function.
Therapy should be initiated as soon as possible after a diagnosis of chickenpox or
herpes zoster, or at the first sign or symptoms of an outbreak of genital herpes.
The recommended dose and duration of use is dependent on the indication.
and Dosage Adjustment
Treatment of Initial Infection of Herpes Genitalis:
200 mg (one 200 mg tablet or one
teaspoonful of suspension [5 mL]) every 4 hours, 5 times daily for a total of 1 gram daily
for 10 days. Therapy should be initiated as early as possible following onset of signs and
Suppressive Therapy for Recurrent Herpes Genitalis:
The initial recommended dose
is 200 mg (one 200 mg tablet or one teaspoonful of suspension [5 mL]) three times daily.
This can be increased if breakthrough occurs up to a dosage of one 200 mg tablet or one
teaspoonful [5 mL] of suspension, five times daily. If necessary, a dose of 400 mg (one
400 mg tablet [two 200 mg tablets] or two teaspoonfuls of suspension [10 mL]) given
twice daily may be considered. Periodic re-evaluation of the need for therapy is
Administration of ZOVIRAX
for intermittent therapy is 200 mg (one 200 mg tablet or
one teaspoonful [5 mL] of suspension) every 4 hours 5 times daily for 5 days. Therapy
should be initiated at the earliest sign or symptom (prodrome) of recurrence.
Treatment of Herpes Zoster:
800 mg (one 800 mg tablet, or 800 mg of another oral
dosage form), every 4 hours, 5 times daily for 7 to 10 days. Treatment should be initiated
within 72 hours of the onset of lesions. In clinical trials, the greatest benefit occurred
when treatment was begun within 48 hours of the onset of lesions.
Treatment of Chickenpox:
20 mg/kg (not to exceed 800 mg) orally, 4 times daily for
5 days. Therapy should be initiated within 24 hours of the appearance of rash.
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Patients With Acute or Chronic Renal Impairment:
Caution is advised when
administering acyclovir to patients with impaired renal function. Adequate hydration
should be maintained.
Comprehensive pharmacokinetic studies have been completed following intravenous
acyclovir infusions in patients with renal impairment.
Based on these studies, dosage adjustments are recommended in Table 5 for genital
herpes and herpes zoster indications.
Dosage Modification for Renal Impairment
Adjusted Dosage Regimen
Normal Dosage Regimen
Dosing Interval (hours)
every 4 hours, 5 x daily
200 mg every 4 hours
every 12 hours
every 12 hours
400 mg every 12 hours
every 12 hours
Every 4 hours, 5 x daily
every 8 hours
800 mg every 4 hours
every 12 hours
For patients who require hemodialysis, the mean plasma half-life of
acyclovir during hemodialysis is approximately 5 hours. This results in a 60% decrease
in plasma concentrations following a six-hour dialysis period. Therefore, the patient's
dosing schedule should be adjusted so that an additional dose is administered after each
No supplement dose appears to be necessary after adjustment of the
If a dose of ZOVIRAX
is missed, the patient should be advised to take it as soon as
he/she remembers, and then continue with the next dose at the proper time interval.
For management of a suspected drug overdose, contact your regional Poison
Activated charcoal may be administered to aid in the removal of unabsorbed drug.
General supportive measures are recommended.
Acyclovir is only partly absorbed in the gastrointestinal tract. Patients have ingested up
to 20 g acyclovir on a single occasion, with no unexpected adverse effects. In clinical
studies, the highest plasma concentration observed in a single patient at these doses was
10.0 μg/mL. Accidental, repeated overdoses of oral acyclovir over several days have
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been associated with gastrointestinal effects (such as nausea and vomiting) and
neurological effects (headache and confusion).
Intravenous doses administered to humans have been as high as 1200 mg/m
3 times daily for up to 2 weeks. Peak plasma concentrations have reached 80 μg/mL.
Overdosage of intravenous acyclovir has resulted in elevations of serum creatinine, blood
urea nitrogen and subsequent renal failure. Neurological effects including confusion,
hallucinations, agitation, seizures and coma have been described in association with
Patients should be observed closely for signs of toxicity. Hemodialysis significantly
enhances the removal of acyclovir from the blood and may, therefore be considered a
management option in the event of symptomatic overdose. Precipitation of acyclovir in
renal tubules may occur if the solubility (2.5 mg/mL) in the intratubular fluid is exceeded.
In the event of renal failure and anuria, the patient may benefit from hemodialysis until
renal function is restored (see DOSAGE AND ADMINISTRATION).
ACTION AND CLINICAL PHARMACOLOGY
Mechanism of Action
(acyclovir), a synthetic acyclic purine nucleoside analog, is a substrate with
a high degree of specificity for herpes simplex and varicella-zoster specified thymidine
kinase. Acyclovir is a poor substrate for host cell-specified thymidine kinase. Herpes
simplex and varicella-zoster specified thymidine kinase transform acyclovir to its
monophosphate which is then transformed by a number of cellular enzymes to acyclovir
diphosphate and acyclovir triphosphate. Acyclovir triphosphate is both an inhibitor of,
and a substrate for, herpesvirus-specified DNA polymerase. Although the cellular α-
DNA polymerase in infected cells may also be inhibited by acyclovir triphosphate, this
occurs only at concentrations of acyclovir triphosphate which are higher than those which
inhibit the herpesvirus-specified DNA polymerase. Acyclovir is selectively converted to
its active form in herpesvirus-infected cells and is thus preferentially taken up by these
cells. Acyclovir has demonstrated a very much lower toxic potential
uninfected cells because: 1) less is taken up; 2) less is converted to the active form; 3)
cellular α-DNA polymerase has a lower sensitivity to the action of the active form of the
drug. A combination of the thymidine kinase specificity, inhibition of DNA polymerase
and premature termination of DNA synthesis results in inhibition of herpes virus
replication. No effect on latent non-replicating virus has been demonstrated. Inhibition
of the virus reduces the period of viral shedding, limits the degree of spread and level of
pathology, and thereby facilitates healing. During suppression there is no evidence that
acyclovir prevents neural migration of the virus. It aborts episodes of recurrent herpes
due to inhibition of viral replication following reactivation.
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The pharmacokinetics of acyclovir after oral administration have been evaluated in
6 clinical studies involving 110 adult patients.
In one study of 35 immunocompromised patients with herpes simplex or
varicella-zoster infection given ZOVIRAX
Capsules in doses of 200 to 1000 mg every
4 hours, 6 times daily for 5 days, the bioavailability was estimated to be 15 to 20%. In
this study, steady-state plasma levels were reached by the second day of dosing. Mean
steady-state peak and trough concentrations following the last 200 mg dose were
0.49 μg/mL (0.47 to 0.54 μg/mL) and 0.31 μg/mL (0.18 to 0.41 μg/mL), respectively and
following the last 800 mg dose were 2.8 μg/mL (2.3 to 3.1 μg/mL) and 1.8 μg/mL (1.3 to
2.5 μg/mL). In another study, 20 immunocompetent patients with recurrent genital
herpes simplex infections given ZOVIRAX
Capsules in dose of 800 mg every 6 hours,
4 times daily for 5 days, the mean steady-state peak and trough concentrations were
1.4 μg/mL (0.66 to 1.8 μg/mL) and 0.55 μg/mL (0.14 to 1.1 μg/mL).
In a multiple-dose crossover study where 23 volunteers received ZOVIRAX
200 mg capsule, one 400 mg tablet and one 800 mg tablet 6 times daily, absorption
decreased with increasing dose and the estimated bioavailabilities of acyclovir were 20,
15 and 10%, respectively. The decrease in bioavailability is believed to be a function of
the dose and not the dosage form. It was demonstrated that acyclovir is not dose
proportional over the dosing range 200 mg to 800 mg. In this study, steady-state peak
and trough concentrations of acyclovir were 0.83 and 0.46 μg/mL, 1.21 and 0.63 μg/mL,
and 1.61 and 0.83 μg/mL for the 200, 400 and 800 mg dosage regimens, respectively.
In another study in 6 volunteers, the influence of food on the absorption of acyclovir was
A single oral dose bioavailability study in 23 normal volunteers showed that ZOVIRAX
Capsules 200 mg are bioequivalent to 200 mg acyclovir in aqueous solution. In a
separate study in 20 volunteers, it was shown that ZOVIRAX
bioequivalent to ZOVIRAX
Capsules. In a different single-dose bioavailability/
bioequivalence study in 24 volunteers, one ZOVIRAX
800 mg Tablet was demonstrated
to be bioequivalent to four ZOVIRAX
200 mg Capsules.
Plasma protein binding is relatively low (9 to 33%) and drug interactions
involving binding site displacement are not anticipated.
Following oral administration, the mean plasma half-life of acyclovir in
volunteers and patients with normal renal function ranged from 2.5 to 3.3 hours. The
mean renal excretion of unchanged drug accounts for 14.4% (8.6 to 19.8%) of the orally
administered dose. The only urinary metabolite (identified by high performance liquid
chromatography) is 9-[(carboxymethoxy)methyl]guanine.
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Special Populations and Conditions
In general, the pharmacokinetics of acyclovir in children is similar to adults.
Mean half-life after oral doses of 300 mg/m
and 600 mg/m
, in children aged 7 months
to 7 years, was 2.6 hours (range 1.59 to 3.74 hours).
Orally administered acyclovir in children less than 2 years of age has not yet been fully
In the elderly, total body clearance falls with increasing age, associated with
decreases in creatinine clearance, although there is little change in the terminal plasma
half-life. Dosage reduction may be required in geriatric patients with reduced renal
function (see DOSAGE AND ADMINISTRATION).
The half-life and total body clearance of acyclovir are dependent
on renal function.
A dosage adjustment is recommended for patients with reduced renal function (see
DOSAGE AND ADMINISTRATION).
STORAGE AND STABILITY
Tablets should be stored at controlled room temperature (15° to 25°C) in a
dry place and protected from light.
Suspension should be stored at controlled room temperature (15° to 25°C).
DOSAGE FORMS, COMPOSITION AND PACKAGING
Suspension: Each teaspoonful (5 mL) of ZOVIRAX
Suspension contains 200 mg
acyclovir and the non-medicinal ingredients banana flavor, cellulose, glycerin,
methylparaben, propylparaben, sorbitol, vanillin, and water.
Tablets: Each ZOVIRAX
200 Tablet contains 200 mg acyclovir and the non-medicinal
ingredients cellulose, indigotine, lactose, magnesium stearate, povidone, and sodium
400 Tablet contains 400 mg acyclovir and the non-medicinal
ingredients cellulose, iron oxide, magnesium stearate, povidone and sodium starch
800 Tablet contains 800 mg acyclovir and the non-medicinal
ingredients cellulose, indigotine, magnesium stearate, povidone and sodium starch
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Suspension is available in bottles of 125 mL* and 475 mL. Each
teaspoonful (5 mL) of off-white, banana-flavoured suspension contains 200 mg acyclovir.
*125 mL bottle not available in Canada
200 Tablets are available in bottles of 100 tablets. Each blue, shield-shaped,
bevel-edged, compressed tablet contains 200 mg acyclovir, and is imprinted with
"ZOVIRAX" on one side and a triangle on the reverse.
400 WELLSTAT PAC
are available in cartons of 56 blister-packed tablets.
Each pink, shield-shaped, bevel-edged, compressed tablet contains 400 mg acyclovir, and
is imprinted with "ZOVIRAX 400" on one side and a triangle on the reverse.
800 ZOSTAB PAC
are available in cartons of 50 blister-packed tablets.
Each blue, biconvex, elongated, scored compressed tablet contains 800 mg acyclovir, and
is imprinted with "ZOVIRAX 800" on one side.
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PART II: SCIENTIFIC INFORMATION
Physicochemical properties: Acyclovir is a white, crystalline powder with a
maximum solubility in water of 1.3 mg/mL at 25°C.
Initial Genital Herpes
Double blind, placebo controlled studies have demonstrated that orally administered
significantly reduced the duration of acute infection and duration of lesion
healing. The duration of pain and new lesion formation was decreased in some patient
Recurrent Genital Herpes
In a study of patients who received ZOVIRAX
400 mg twice daily for 3 years, 45%,
52%, and 63% of patients remained free of recurrences in the first, second, and third
years, respectively. Serial analyses of the 3 month recurrence rates for the patients
showed that 71% to 87% were recurrence free in each quarter.
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Herpes Zoster Infections
In a double blind, placebo controlled study of immunocompetent patients with localized
cutaneous zoster infection, ZOVIRAX
(800 mg 5 times daily for 10 days) shortened the
times to lesion scabbing, healing, and complete cessation of pain, and reduced the
duration of viral shedding and the duration of new lesion formation.
In a similar double blind, placebo controlled study, ZOVIRAX
(800 mg 5 times daily
for 7 days) shortened the times to complete lesion scabbing, healing, and cessation of
pain; and reduced the duration of new lesion formation.
Treatment was begun within 72 hours of rash onset and was most effective if started
within the first 48 hours. Adults greater than 50 years of age showed greater benefit.
Three randomized, double-blind, placebo controlled trials were conducted in 993
pediatric patients aged 2 to 18 years with chickenpox. All patients were treated within
24 hours after the onset of rash. In 2 trials, ZOVIRAX
was administered at 20 mg/kg
4 times daily (up to 3,200 mg per day) for 5 days. In the third trial, doses of 10, 15, or
20 mg/kg were administered 4 times daily for 5 to 7 days. Treatment with ZOVIRAX
shortened the time to 50% healing; reduced the maximum number of lesions; reduced the
median number of vesicles; decreased the median number of residual lesions on day 28;
and decreased the proportion of patients with fever, anorexia, and lethargy by day 2.
Treatment with ZOVIRAX
did not affect varicella zoster virus specific humoral or
cellular immune responses at 1 month or 1 year following treatment.
See Part I, ACTION AND CLINICAL PHARMACOLOGY.
The quantitative relationship between the
susceptibility of herpes simplex virus
(HSV) and varicella-zoster viruses (VZV) to acyclovir and the clinical response to
therapy has not been established in man, and virus sensitivity testing has not been
standardized. Sensitivity testing results, expressed as the concentration of drug required
to inhibit by 50% the growth of virus in cell culture (ID
), vary greatly depending upon
the particular assay used, the cell type employed, and the laboratory performing the test.
of acyclovir against HSV-1 isolates may range from 0.02 μg/mL (plaque
reduction in Vero cells) to 5.9-13.5 μg/mL (plaque reduction in green monkey kidney
[GMK] cells). The ID
against HSV-2 ranges from 0.01 μg/mL to 9.9 μg/mL (plaque
reduction in Vero and GMK cells, respectively).
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Using a dye-uptake method in Vero cells, which gives ID
values approximately 5 to 10-
fold higher than plaque reduction assays, 1417 HSV isolates (553 HSV-1 and 864 HSV-
2) from approximately 500 patients were examined over a 5-year period. These assays
found that 90% of HSV-1 isolates were sensitive to ≤0.9 μg/mL acyclovir and 50% of all
isolates were sensitive to ≤0.2 μg/mL acyclovir. For HSV-2 isolates, 90% were sensitive
to ≤2.2 μg/mL and 50% of all isolates were sensitive to ≤0.7 μg/mL of acyclovir. Isolates
with significantly diminished sensitivity were found in 44 patients. It must be
emphasized that neither the patients nor the isolates were randomly selected and,
therefore, do not represent the general population. Most of the less sensitive HSV
clinical isolates have been relatively deficient in the viral thymidine kinase (TK). Strains
with alterations in viral TK or viral DNA polymerase have also been reported.
against VZV ranges from 0.17-1.53 μg/mL (yield reduction, human foreskin
fibroblasts) to 1.85-3.98 μg/mL (foci reduction, human embryo fibroblasts [HEF]).
Reproduction of EBV genome is suppressed by 50% in superinfected Raji cells or P3HR-
1 lymphoblastoid cells by 1.5 μg/mL acyclovir. Cytomegalovirus (CMV) is relatively
resistant to acyclovir with ID
values ranging from 2.3-17.6 μg/mL (plaque reduction,
HEF cells) to 1.82-56.8 μg/mL (DNA hybridization, HEF cells). The latent state of the
genome of any of the human herpesviruses is not known to be sensitive to acyclovir.
Prolonged exposure of HSV to subinhibitory concentrations (0.1 μg/mL) of acyclovir in
cell culture has resulted in the emergence of a variety of acyclovir resistant strains. The
emergence of resistant strains is believed to occur by "selection" of naturally occurring
viruses with relatively low susceptibility to acyclovir. Such strains have been reported in
pre-therapy isolates from several clinical studies.
Two resistance mechanisms involving viral thymidine kinase (required for acyclovir
activation) have been described. These are: (a) selection of thymidine-kinase-deficient
mutants that induce little or no enzyme activity after infection, and (b) selection of
mutants possessing a thymidine kinase of altered substrate specificity that is able to
phosphorylate the natural nucleoside thymidine but not acyclovir. The majority of less
susceptible viruses arising
are of the thymidine-kinase-deficient type which have
reduced infectivity and pathogenicity and less likelihood of inducing latency in animals.
However, an acyclovir-resistant HSV infection in an immunosuppressed bone marrow
transplant recipient on extended acyclovir therapy was found to be due to a clinical
isolate which had a normal thymidine kinase but an altered DNA polymerase. This third
mechanism of resistance involving herpes simplex virus DNA polymerase is due to the
selection of mutants encoding an altered enzyme, which is resistant to inactivation by
VZV appears to manifest resistance to acyclovir via mechanisms similar to those seen in
Page 19 of 39
However, limited clinical investigation has revealed no evidence of a significant change
susceptibility of VZV with acyclovir therapy, although resistant mutants of this
virus can be isolated
in a manner analogous to HSV. Analysis of a small number
of clinical isolates from patients who received oral acyclovir or placebo for acute herpes
zoster suggests that
emergence of resistant VZV may occur infrequently.
Prolonged acyclovir treatment of highly immunocompromised patients with acquired
immunodeficiency syndrome and severe VZV may lead to the appearance of resistant
Cross-resistance to other antivirals occurs
in acyclovir-resistant mutants. HSV
mutants which are resistant to acyclovir due to an absence of viral thymidine kinase are
cross-resistant to other agents which are phosphorylated by herpesvirus thymidine kinase,
such as bromovinyldeoxyuridine, ganciclovir and the 2'-fluoropyrimidine nucleosides,
such as, 2'-fluoro-5-iodoarabinosyl-cytosine (FIAC).
The clinical response to acyclovir treatment has usually been good for patients with
normal immunity from whom HSV having reduced susceptibility to acyclovir has been
recovered, either before, during or after therapy. However, certain patient groups, such
as the severely immunocompromised (especially bone marrow transplant recipients) and
those undergoing chronic suppressive regimens have been identified as being most
frequently associated with the emergence of resistant herpes simplex strains, which may
or may not accompany a poor response to the drug. The possibility of the appearance of
less sensitive viruses must be recognized when treating such patients, and susceptibility
monitoring of clinical isolates from these patients should be encouraged.
In summary, the quantitative relationship between the
susceptibility of HSV and
VZV to acyclovir and the clinical response to therapy has not been clearly established in
man. Standardized methods of virus sensitivity testing are required to allow more precise
virus sensitivity and clinical response to acyclovir therapy.
Acute Toxicity Studies
Adult Mice and Rats:
The acute toxicity of oral acyclovir was determined as shown in
Acute Toxicity Studies
Page 20 of 39
Neonatal, Immature, and Adult Rats:
Groups of 10 male and 10 female Charles River
CD (Sprague-Dawley) rats were given single large doses (5 different dose levels) of a
solution (pH 11.0) of acyclovir by subcutaneous injection when they were 3, 10, 28 and
71 days of age. They were observed for 14 days after treatment and LD
calculated by the Litchfield and Wilcoxon method (see Table 7 below). This study was
done to determine if age at exposure affects the acute toxicity of acyclovir; there was no
evidence that young rats were more sensitive than older rats to the acute toxic effects of
LD50 in Rats
(mg/kg body weight)
Age When Treated
There was no apparent relationship between length of survival after treatment and age at
which treatment was given. Clinical signs for the rats treated at 3 and 10 days of age
included red and purple cutaneous blisters, blue areas, scabs, scars, necrotic and sloughed
skin, open wounds, body tremors and alopecia. Decreased activity, lacrimation, closed
eyelids, red-brown or brown material around the eyes, nose and mouth, ataxia,
prostration, body tremors, urine stains around the abdomen or genital area, scabbed or
necrotic areas and alopecia were observed in rats treated at 28 and 71 days of age.
Subchronic Oral Toxicity Study
Four groups each consisting of 28 male and 28 female Charles River CD-1 (ICR)
mice were orally dosed by stomach tube for 33 days with suspensions of acyclovir. Daily
dose levels were 0, 50, 150 and 450 mg/kg. Hematology and clinical chemistry
measurements were made on an additional 8 male and 8 female mice per group (dosed in
the same manner) after the first and fourth weeks of dosing and during the 3rd postdose
Plasma drug concentrations were measured in pooled samples from an additional 4 male
and 4 female mice per group on dose days 1, 15 and 30.
Based on preliminary experiments with rats and mice, the high dose of 450 mg/kg was
selected to produce the highest drug plasma levels attainable, in a practical manner, by
oral dosing in a rodent species. Averaged drug plasma concentrations ranged from
approximately 3.4 (at the low dose) to 11.0 (at the high dose) μg/mL of plasma one hour
after oral dosing.
Page 21 of 39
No changes in health, growth rate, hematology and clinical chemistry measurements
occurred that could be definitely attributed to dosing with acyclovir. Gross and
histopathologic examinations of 16 male and 16 female rats from the high-dose and
control groups at the end of the dose period revealed nothing remarkable.
Chronic Toxicity Studies
Lifetime Oral Toxicity Study in Rats Given Acyclovir by Gastric Intubation:
Charles River CD (Sprague-Dawley) rats were given suspensions of acyclovir by gavage.
There were 50 male and 50 female rats at each of the following dose levels: 0, 50, 150
and 450 mg/kg. After 30 and 52 weeks of treatment, 10 male and 10 female rats from
each group were necropsied. The remaining rats were dosed each day until natural
mortality decreased a group size to approximately 20% of the number of animals of that
sex present in the test groups when the study was started. All remaining rats were killed
and necropsied when the 20% cut-off point was reached. This was during week 110 for
the male rats and week 122 for the female rats. Tissues from control rats and those in the
high-dose group were evaluated by light microscopy. Tissues from rats in the low and
mid-dose groups having masses, nodules or unusual lesions were also examined by light
microscopy. Fixed tissues from rats that were found dead during the first 52 weeks of the
study were also evaluated by light microscopy.
No signs of toxicosis were observed. Plasma samples were collected 1.5 hours after
dosing on days 7, 90, 209, 369, 771 (males only) and 852 (females only). Mean plasma
levels found in high-dose males (450 mg/kg/day) at the times indicated above were as
follows: 1.54, 1.63, 1.39, 1.60 and 1.70 μg/mL (6.84, 7.26, 6.17, 7.10 and 7.56 μM).
Corresponding mean plasma levels for the high-dose females for the corresponding time
periods were 1.76, 2.38, 2.12, 1.71 and 1.81 μg/mL (7.82, 10.58, 9.44, 7.62 and
8.03 μM). Plasma levels in both males and females at all dose levels after one year of
treatment were generally comparable to plasma levels obtained at earlier samplings.
Values for laboratory tests including hematology, clinical chemistry and ophthalmoscopy
were all within the normal range. There were no drug-induced gross or microscopic
lesions and there was no evidence that acyclovir affected survival.
Lifetime Oral Carcinogenicity Study in Rats:
There were no signs of toxicosis in
Charles River CD (Sprague-Dawley) rats (100 rats/sex/dose group) given acyclovir by
oral gavage at 50, 150 and 450 mg/kg in a lifetime oral carcinogenicity study. Mean
plasma levels obtained in high-dose males 1.5 hours after dosing at various sampling
times during the study were as follows: 1.54, 1.63, 1.39, 1.60 and 1.70 μg/mL (6.84,
7.26, 6.17, 7.10 and 7.56 μM) at days 7, 90, 209, 369 and 771, respectively.
Corresponding mean values for the high-dose females were 1.76, 2.38, 2.12, 1.71 and
1.81 μg/mL (7.82, 10.58, 9.44, 7.62 and 8.03 μM) at days 7, 90, 209, 369 and 852,
Page 22 of 39
Values for clinical laboratory tests including hematology, clinical chemistry, urinalysis,
body weight, food consumption and ophthalmoscopy were all within normal ranges.
There were no drug-induced gross or microscopic lesions and there was no evidence that
acyclovir affected survival, temporal patterns of tumor incidence or tumor counts for
benign or malignant neoplasms.
Most of the relatively few rats found dead or moribund during the first 52 weeks of this
study suffered dosing accidents as evidenced by postmortem findings of esophageal
perforation causing pleural effusion, pneumonia, or mediastinitis.
Lifetime Oral Carcinogenicity Study in Mice:
There were no signs of toxicosis in
Charles River CD-1 (ICR) mice (115 mice/sex/dose group) given acyclovir by oral
gavage at 50, 150 and 450 mg/kg/day in a lifetime oral carcinogenicity study. Mean
plasma levels obtained in high-dose males 1.5 hours after dosing at various sampling
times during the study were as follows: 2.83, 3.17 and 1.82 μg/mL (12.59, 14.10 and
8.10 μM) at days 90, 365 and 541, respectively. Corresponding mean values for the
high-dose females were 9.81, 5.85 and 4.0 μg/mL (43.60, 26.0 and 17.79 μM).
Values for clinical laboratory tests including hematology, body weight and food
consumption were all within normal ranges. There were no drug-induced gross or
microscopic lesions. Female mice given 150 and 450 mg/kg acyclovir survived
significantly longer than control female mice; survival of treated males was comparable
to survival of control males. Patterns of tumor incidence and tumor counts for benign or
malignant neoplasms were not affected by treatment with acyclovir.
Chronic 12-Month Oral Toxicity Study in Dogs:
Purebred Beagle dogs were given 0,
15, 45 or 150 mg/kg/day of acyclovir each day for the first two weeks of a 1-year study.
There were 9 male and 9 female dogs in each test group. The dogs were given gelatin
capsules that contained the appropriate dose. They were treated t.i.d., hence the dosages
administered at each of three equally spaced dose periods were 0, 5, 15 and 50 mg/kg.
The 45 and 150 mg/kg dose levels induced diarrhea, emesis, decreased food consumption
and weight loss in both male and female dogs during the first two weeks of the study.
For this reason, during the third week of the study the decision was made to decrease the
mid- and high-dosage levels to 30 and 60 mg/kg/day (10 and 20 mg/kg t.i.d.). The low
dose of 15 mg/kg/day (5 mg/kg t.i.d.) was unchanged. Dogs given 60 mg/kg/day
occasionally vomited and occasionally had diarrhea but did well for the duration of the
test, and values for body weight gain and food consumption were comparable to control
Page 23 of 39
During the toxicosis induced by the larger doses of acyclovir, plasma levels of the drug
were likely very high (as indicated by initial mean values of 24.0 μg/mL (106.6 μM) for
high-dose males and 17.4 μg/mL (77.2 μM) for high-dose females when determined
1 hour after the third dose on day 1 of the study). When measured on day 15, plasma
levels of acyclovir in high-dose dogs (150 mg/kg/day) were still very high but they
decreased later when the dosages were decreased. Values for plasma levels after
12 months of treatment were generally comparable to values recorded after 1, 3 and
6 months of treatment. Thus, there was no indication of enhanced metabolism of
acyclovir as a result of chronic treatment.
During the 13th week, some male and female dogs at both the mid- and high-dosage
levels had the following signs: tenderness in forepaws, erosion of footpads, and breaking
and loosening of nails. Regeneration of lost nails began a few weeks later. Nails
regenerated by 6 months (when 3 males and 3 females from each group were killed for an
interim sacrifice) and by the end of the study were of generally good quality. There were
never any signs of an effect on paws or nails in dogs in the low dose group
It is accepted that injury of the corial epithelium that produces nail keratin can result in
arrested production of keratin and production of abnormal keratin. The transient
toxicosis induced by the large doses (45 and 150 mg/kg/day) of acyclovir given during
the first two weeks of the study may have affected the corial epithelium. If there was a
transient effect on the corial epithelium (possibly related to direct effects or secondary to
drug-induced illness during the first two weeks of the study) later loss of the nail could be
a sequella. No discernible effects upon other keratin-producing or keratin-containing
tissues were observed. It should be emphasized that the alterations in the nails appeared
to be related to the transient toxicosis induced by dose levels of 50 and 150 mg/kg/day
tested during the first two weeks of the study and not to the 30 and 60 mg/kg/day dose
levels tested subsequently.
There were no important drug-induced alterations in values for serum biochemical tests,
urinalyses and electrocardiographic tests done at appropriate intervals during this study.
Values for serum albumin and total protein were slightly decreased in dogs treated at 30
and 60 mg/kg/day for 6 and 12 months. However, all values for these parameters
remained within limits accepted as normal.
With the exception of residual alterations in old keratin at the tips of the claws, there
were no signs of treatment-related effects in any of the tissues examined by light
microscopy. Nor were there meaningful alterations in values for the organs weighed at
necropsy. Thus, dose levels up to 60 mg/kg/day were well tolerated for one year. The
"no dose effect" dose level of acyclovir was 15 mg/kg/day (5 mg/kg t.i.d.); however, the
only adverse effects at 30 or 60 mg/kg/day were changes in nails and footpads (30 and
60 mg/kg/day) and mild gastrointestinal signs (60 mg/kg/day).
Page 24 of 39
Teratology – Rats:
Acyclovir was administered to pregnant A.R.S. Sprague-Dawley
female rats by subcutaneous injection during the period of organogenesis (day 6 through
day 15 of gestation) at dose levels of 0.0, 6.0, 12.5 and 25.0 mg/kg body weight twice
Criteria evaluated for compound effect included maternal body weights, weight gains,
appearance and behavior, survival rates, eye changes, pregnancy rates, and reproduction
data. Offspring viability and development were also evaluated.
In addition to the above measurements, designated animals were sacrificed 1 hour after
the first dose on day 15 in order to collect samples of maternal blood, amniotic fluid and
fetuses for measurements of drug concentration. Mean values from these samples are
listed in Table 8.
Acyclovir Concentrations in a Teratology Study in Rats
(nmoles/g wet wt)
The values obtained for plasma would represent about 30% of initial plasma levels as
judged by the plasma half-life in rodents.
No effects attributable to the administration of acyclovir were noted in comparisons of
maternal body weight values, appearance and behavior, survival rates, pregnancy rates, or
implantation efficiencies. In addition, no compound-related differences were noted in
evaluations of fetal size, sex, and development.
Although the incidences of resorption and fetal viability were within the range of normal
variability in all of the groups, slightly greater incidences of resorptions were noted in the
high-dose animals sacrificed on days 15 and 19 of gestation; however, clear dose-related
trends did not eventuate.
Therefore, acyclovir was not considered teratogenic or embryotoxic when administered
to rats at levels up to 50.0 mg/kg of body weight per day during organogenesis.
Teratology – Rabbits:
A teratology study was done in New Zealand White rabbits using
essentially the same experimental design as in the rat, except that dosing was from day 6
through day 18 of gestation. Also, collection of fetuses, amniotic fluid and samples of
maternal blood occurred on day 18 rather than day 15.
Page 25 of 39
No signs of maternal toxicity were observed at any dose, but there was a statistically
significant (p<0.05) lower implantation efficiency in the high-dose group. While there
were a few terata observed in the study (in both control and treated animals), there was
no apparent association with drug treatment. There was, however, an apparent dose-
related response in the number of fetuses having supernumerary ribs. No similar effect
was noted in the rat teratology study (see above) or in a reproduction-fertility experiment
Concentrations of acyclovir were detected in plasma and amniotic fluid samples, as well
as in homogenates of fetal tissues. All samples were taken one hour after the first dose
on day 18 of gestation. Drug concentrations in amniotic fluid were substantially higher
than that of plasma (see Table 9).
Acyclovir Concentrations in a Teratology Study in Rabbits
Acyclovir Concentrations (Mean and S.E.)
(nmoles/g wet wt)
Reproduction – Fertility:
Acyclovir was shown not to impair fertility or reproduction
in groups of 15 male and 30 female mice in a two-generation fertility study. The mice in
this study were given acyclovir by gastric intubation at dosage levels of 50, 150 and
450 mg/kg/day. Males were dosed for 64 consecutive days prior to mating and females
for 21 days prior to mating.
In a rat fertility study where groups of 20 male and 20 female rats were given 0, 12.5,
25.0 and 50.0 mg/kg/day by subcutaneous injection, acyclovir was shown not to have an
effect on mating or fertility. The males were dosed for 60 days prior to mating and until
their mating schedule was completed. Female rats were dosed for 14 days prior to mating
and until day 7 of pregnancy. At 50 mg/kg/day s.c. there was a statistically significant
increase in post-implantation loss, but no concomitant decrease in litter size.
In 25 female rabbits treated subcutaneously with 50 mg/kg/day acyclovir on days 6 to 18
of gestation, there was a statistically significant decrease in implantation efficiency but
no concomitant decrease in litter size. There was also a dose-related increase in the
number of fetuses with supernumerary ribs in all drug-treated groups. This increase was
not dose-related when the incidence of supernumerary ribs per litter was examined.
In 15 female rabbits treated intravenously with 50 mg/kg/day acyclovir on days 6 to 18 of
gestation, there was no effect on either implantation efficiency or litter size.
Page 26 of 39
In a rat peri- and postnatal study (20 female rats per group), acyclovir was given
subcutaneously at 0, 12.5, 25 and 50 mg/kg/day from 17 days of gestation to 21 days
postpartum. At 50 mg/kg/day s.c. there was a statistically significant decrease in the
group mean numbers of corpora lutea, total implantation sites and live fetuses in the F1
generation. Although not statistically significant, there was also a dose-related decrease
in group mean numbers of live fetuses and implantation sites at 12.5 mg/kg/day and
25 mg/kg/day s.c.
In a dose-range finding study with 5 female rabbits the intravenous administration of
acyclovir at a dose of 100 mg/kg/day from days 6 to 8 of pregnancy, a dose known to
cause obstructive nephropathy, caused a significant increase in fetal resorptions and a
corresponding decrease in litter size. At a maximum tolerated intravenous dose of
50 mg/kg/day in rabbits there were no drug-related reproductive effects.
In a subchronic toxicity study where groups of 20 male and 20 female rats were given
intraperitoneal doses of acyclovir at 0, 20, 80 or 320 mg/kg/day for one month, and
followed for a one-month postdose period, there was testicular atrophy. Some histologic
evidence of recovery of sperm production was evident 30 days postdose, but this was
insufficient time to demonstrate full reversibility.
Groups of 25 male and 25 female rats were administered intraperitoneal doses of
acyclovir at 0, 5, 20 or 80 mg/kg/day for 6 months. Ten male and 10 female rats in each
group were continued undosed for 13 weeks. Testicular atrophy was limited to high-dose
rats given 80 mg/kg/day for 6 months. Organ weight data and light microscopy defined
full reversibility of the testicular atrophy by the end of the postdose recovery period.
In a 31-day dog study (16 males and 16 females per group) where acyclovir was
administered intravenously at levels of 50, 100 and 200 mg/kg/day, testicles were normal
in dogs at 50 mg/kg. Doses of 100 or 200 mg/kg/day caused death of some dogs due to
cytostatic effects (bone marrow and gastrointestinal epithelium) and aspermic testes or
testes with scattered aspermic tubules. It cannot be ruled out that the testicular change
may have been primary, however, similar changes can be observed secondary to severe
stress in moribund dogs.
Page 27 of 39
Developmental Toxicity Studies
Neonatal Rats - Subchronic Study:
Acyclovir dissolved in 0.4% sterile saline was
given by subcutaneous injection to Charles River CD (Sprague-Dawley) neonatal rats for
19 consecutive days, beginning on the 3rd post-partum day. The dose levels tested were
0, 5, 20 and 80 mg/kg body weight. There were 12 litters (each consisting of 5 male and
5 female neonates nursing the natural dam) at each dose level. The dams were not
treated. Neonates were removed from each group for necropsy and microscopic
evaluation of a wide variety of tissues, including eyes and multiple sections of brain, after
they had been treated for 5, 12 or 19 days and after a 3-week postdose drug-free period
(at which time they were 45 days of age). Hematologic (hemoglobin, packed cell
volume, RBC, WBC and differential cell counts) and clinical chemistry (BUN) tests were
done after 16 days of treatment and repeated 18 days after the last (19th) dose was given.
Blood was collected from some neonates 30 minutes after treatment on day 1, on day 9
and at the end of the dose period for the determination of concentrations of acyclovir in
plasma. The largest concentration of acyclovir in plasma was 99.1 μg/mL (440.5 μM)
found in pooled plasma collected from 6 female high-dose (80 mg/kg) neonates
30 minutes after the first dose was given. Treatment with acyclovir did not increase
mortality in the neonatal period.
Rats in the low-dose group gained as much body weight as the respective control rats.
Significant (p<0.05) reductions in mean body weight values were observed in mid- and
high-dose group male and female neonates during the treatment period. Rats in the high-
dose group partially compensated by gaining significantly more body weight than the
controls during the postdose recovery period. There was a minimal but significant
increase in BUN for male (p<0.01) and female (p<0.05) neonates in the high-dose group
on dose day 16. This finding may be of biological importance because there were
minimal accumulations of nuclear debris in renal collecting ducts and loops of Henle in
kidney sections taken from high-dose neonates after 19 days of treatment and examined
by light microscopy. This was the only time period (and the kidney was the only organ)
in which minimal effects on developing organ systems were detected. Thus, 5 mg/kg was
clearly a no effect dose level and 20 mg/kg caused only minimal decreases in body
Eye examinations and light microscopy did not reveal adverse effects on ocular
development. It should be emphasized that there was no morphologic or functional
evidence of adverse effects on developing brain or other portions of the central nervous
system. Thus, acyclovir is distinctly different than cytosine arabinoside which was
reported to produce prominent cerebellar and retinal dysplasia in neonatal rats.
Mutagenicity and Other Short-Term Studies
Acyclovir has been tested for mutagenic potential in a number of
Page 28 of 39
Acyclovir was tested for mutagenic activity in the Ames Salmonella plate
assay; in a preincubation modification of the Ames assay; in the Rosenkrantz E. coli
DNA repair assay; and in the eukaryote S. cerevisiae, D-4. All studies were
performed both in the presence and absence of exogenous mammalian metabolic
activation. Acyclovir gave no positive responses in any of these systems.
The previous Salmonella studies were extended to extremely high concentrations in order
to achieve toxicity. No positive effects were observed either in the presence or absence
of exogenous mammalian metabolic activation, at concentrations of acyclovir up to
300 mg/plate or 80 mg/mL.
Acyclovir was tested for mutagenic activity in cultured L5178Y
mouse lymphoma cells, heterozygous at the thymidine kinase (TK) locus, by measuring
the forward mutation rate to TK-deficiency (TK
; additional studies were
performed at the HGPRT locus and at the Ouabain-resistance marker in these same cells.
All studies were performed in the presence and in the absence of exogenous mammalian
metabolic activation. The test compound was mutagenic at the TK locus at high (400 -
2400 μg/mL) concentrations. (By comparison, the upper limit of acyclovir peak plasma
levels following oral dosing of 200 mg q4h is 0.9 μg/mL). It was negative at the HGPRT
locus and Ouabain-resistance marker. Identical results were obtained with and without
Inconclusive results with no apparent dose-related response were obtained when
acyclovir mutagenicity was studied at each of 3 loci (APRT, HGPRT and Ouabain-
resistance) in Chinese hamster ovary (CHO) cells, both in the presence and absence of
exogenous metabolic activation.
Acyclovir, at a concentration of 50 μg/mL (222 μM) for a 72-hour exposure, has been
shown to cause a statistically significant increase in the incidence of morphologically-
transformed foci resulting from treating BALB/C-3T3 cells
in the absence of
exogenous metabolic activation. The morphologically transformed foci have been shown
to grow as tumors following transplantation into immunosuppressed, syngeneic, weanling
mice. Tumour tissues were diagnosed as being either undifferentiated sarcomas or
Acyclovir at concentrations between 8 μg/mL and 64 μg/mL for 18 hours' exposure did
not induce any morphologically-transformed foci among C3H/10T 1/2 cells treated
in the absence of exogenous metabolic activation.
Acyclovir, at concentrations of 62.5 and 125 μg/mL for a 48-hour exposure, did not
induce any chromosome aberrations in cultured human lymphocytes in the absence of
exogenous metabolic activation. At higher concentrations - 250 and 500 μg/mL for
48 hours exposure - acyclovir caused a significant increase in the incidence of
chromosome breakage. There was also a significant dose-related decrease in mitotic
index with exposure to acyclovir.
Page 29 of 39
Acyclovir, at doses of 25 and 50 mg/kg/day i.p. for 5 consecutive days, did not produce a
dominant lethal effect in male BKA (CPLP) mice. Further, there was no evidence of a
dominant lethal effect on Charles River CD-1 (ICR) male and female mice treated orally
at dose levels of 50, 150 and 450 mg/kg/day as summarized for the Two Generation
Reproduction/ Fertility Study.
Acyclovir, at single intraperitoneal doses of 25, 50 and 100 mg/kg, failed to induce
chromosome aberrations in bone marrow cells of Chinese hamsters when examined
24 hours after dosing. At higher nephrotoxic doses (500 and 1000 mg/kg), a blastogenic
effect was seen. (An intraperitoneal dose of 500 mg/kg produces mean peak plasma
levels in Chinese hamsters of 611 μg/mL (2.72 mM) which is 680 times higher than the
upper limit of human peak plasma levels during oral dosing of 200 mg q4h).
Acyclovir, at single intravenous doses of 25, 50 and 100 mg/kg, failed to induce
chromosome aberrations in bone marrow cells of male and female rats when examined at
6, 24 and 48 hours after treatment.
Thus, all these studies showed that acyclovir does not cause single-gene mutations but is
capable of breaking chromosomes.
Acyclovir was subjected to a number of
tests, lymphocyte-mediated cytotoxicity and neutrophil chemotaxis,
acyclovir showed no inhibitory effects at concentrations as high as 135 μg/mL (600 μM).
The compound inhibited rosette formation approximately 50% at 0.9 μg/mL (4 μM).
tests in mice which measured cell-mediated immunity (complement-
dependent cellular cytotoxicity, complement-independent cellular cytotoxicity, delayed
hypersensitivity and graft vs. host reaction) acyclovir showed no inhibitory effects at
single doses up to 200 mg/kg given on day 2 after antigenic stimulation.
Four daily doses of 100 mg/kg/day had no significant effect on Jerne hemolysin plaques
or circulating antibody on day 7 after antigenic stimulation. When the Jerne hemolysin
plaques and antibody titers were examined four days after antigenic challenge and one
day after the last drug dose, 100 mg/kg showed only a slight suppressive effect.
However, 200 mg/kg produced some weight loss (-2.2 g), a moderate reduction in the
number of Jerne hemolysin plaques (PFC/spleen were reduced to 33% of control,
PFC/107 WBC to 46.5% of control). However, there was only a small reduction in the
circulating hemagglutinin titer (from 8.3 to 6.5) and the circulating hemolysin titer (from
9.5 to 8.3) at 200 mg/kg.
Page 30 of 39
In experiments in mice designed to test whether acyclovir would potentiate the
immunosuppressive effect of azathioprine on antibody formation, it was found that the
effects of the two drugs were no more than additive. Only the 200 mg/kg dose of
acyclovir showed an increased suppression of antibody response when given in
combination with azathioprine at doses above 25 mg/kg.
Studies were carried out to evaluate the influence of acyclovir
lymphocyte function. Inhibitory effects on blastogenesis were seen only in assays
examining peak concentrations of potent mitogens, phytohemagglutinin (PHA) and
concanavalin A (Con A), and only at concentrations of drug above 50 μg/mL (222 μM)
and were much less with monilia and tetanus toxoid antigens, where the blastogenic
response is characteristically less vigorous. There was very little effect on cytotoxicity or
LIF production except at concentrations of 200 μg/mL (890 μM) where there has already
been demonstrated to be a direct cytotoxic effect. These inhibitory concentrations are far
in excess of anticipated levels from doses selected for clinical application and over 1000-
fold higher than the concentration required to inhibit herpesvirus multiplication
The effect of acyclovir on human cells was measured. A concentration of 11.2 -
22.5 μg/mL (50-100 μM) inhibits the division of fibroblasts to a variable extent,
depending on the experimental design and the confluency of the monolayer. The
magnitude of this effect was less than that caused by adenine arabinoside or human
leukocyte interferon when these three antiviral agents were compared at clinically
relevant concentrations. Acyclovir also inhibited thymidine incorporation by peripheral
blood mononuclear cells stimulated by PHA or three different herpesvirus antigens. A
linear dose-response curve was observed with these cells, and their proliferation was 50%
inhibited by 22.5 μg/mL (100 μM) acyclovir. Inhibition was exerted on T-cell
proliferation without apparent effect on the release of lymphokines or on monocyte
It should also be mentioned that there was no evidence of adverse effects on the immune
system in the detailed subchronic and chronic animal tests covered earlier in this
summary except at excessively high doses (50 to 100 mg/kg b.i.d.) in dogs where marked
lymphoid hypoplasia occurred.
Balfour HH, Jr., Kelly JM, Suarez CS, Heussner RC, Englund JA, Crane DD et al.
Acyclovir treatment of varicella in otherwise healthy children. J Pediatr 1990;
Balfour HH, Jr., Rotbart HA, Feldman S, Dunkle LM, Feder HM, Jr., Prober CG
et al. Acyclovir treatment of varicella in otherwise healthy adolescents. The
Collaborative Acyclovir Varicella Study Group. J Pediatr 1992; 120(4 Pt 1):627-
Page 31 of 39
Barry DW, Blum MR. Antiviral drugs: acyclovir, in Recent Advances in Clinical
Pharmacology. Turner P, Shand DG (eds) Churchill Livingstone, Edinburgh
Barry DW, Nusinoff-Lehrman S. Viral resistance in clinical practice: summary of
five years experience with acyclovir. Pharmacological and Clinical Approaches to
Herpesviruses and Virus Chemotherapy, Aiso, Japan, September 10-13 1984.
Barry DW, Nusinoff-Lehrman S, Ellis MN, Biron KK, Furman PA. Viral
resistance, clinical experience. Scand J Infect Dis Suppl 1985; 47:155-164.
Barry DW, Nusinoff-Lehrman S. Viral resistance in clinical practice: summary of
five years experience with acyclovir. Proceedings of the International Symposium
on Pharmacological and Clinical Approches to Herpes Viruses and Virus
Chemotherapy, Elsever, Amsterdam 1985;269-270.
Biron KK, Elion GB. Effect of acyclovir combined with other antiherpetic agents
on varicella zoster virus in vitro. Am J Med 1982; 73(1A):54-57.
Boelaert J, Schurgers M, Daneels R, Van Landuyt HW, Weatherley BC. Multiple
dose pharmacokinetics of intravenous acyclovir in patients on continuous
ambulatory peritoneal dialysis. J Antimicrob Chemother 1987; 20(1):69-76.
Bryson YJ, Dillon M, Lovett M, Acuna G, Taylor S, Cherry JD et al. Treatment
of first episodes of genital herpes simplex virus infection with oral acyclovir. A
randomized double-blind controlled trial in normal subjects. N Engl J Med 1983;
Burns WH, Saral R, Santos GW, Laskin OL, Lietman PS, McLaren C et al.
Isolation and characterisation of resistant Herpes simplex virus after acyclovir
therapy. Lancet 1982; 1(8269):421-423.
Christophers J, Sutton RN. Characterisation of acyclovir-resistant and -sensitive
clinical herpes simplex virus isolates from an immunocompromised patient. J
Antimicrob Chemother 1987; 20(3):389-398.
Cole NL, Balfour HH, Jr. Varicella-Zoster virus does not become more resistant
to acyclovir during therapy. J Infect Dis 1986; 153(3):605-608.
Collins P, Bauer DJ. The activity in vitro against herpes virus of 9-(2-
hydroxyethoxymethyl)guanine (acycloguanosine), a new antiviral agent. J
Antimicrob Chemother 1979; 5(4):431-436.
Collins P, Oliver NM. Sensitivity monitoring of herpes simplex virus isolates
from patients receiving acyclovir. J Antimicrob Chemother 1986; 18 Suppl
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Collins P. Viral sensitivity following the introduction of acyclovir. Am J Med
Collins P, Larder BA, Oliver NM, Kemp S, Smith IW, Darby G. Characterization
of a DNA polymerase mutant of herpes simplex virus from a severely
immunocompromised patient receiving acyclovir. J Gen Virol 1989; 70 ( Pt
Crumpacker CS, Schnipper LE, Zaia JA, Levin MJ. Growth inhibition by
acycloguanosine of herpesviruses isolated from human infections. Antimicrob
Agents Chemother 1979; 15(5):642-645.
Crumpacker CS, Schnipper LE, Marlowe SI, Kowalsky PN, Hershey BJ, Levin
MJ. Resistance to antiviral drugs of herpes simplex virus isolated from a patient
treated with acyclovir. N Engl J Med 1982; 306(6):343-346.
Darby G, Inglis MM, Larder BA. Mechanisms of resistance to nucleoside
analogue inhibitors of herpes simplex virus. 6th Int Congr Virol 1984;(Abstract
De Clercq E, Descamps J, Verhelst G, Walker RT, Jones AS, Torrence PF et al.
Comparative efficacy of antiherpes drugs against different strains of herpes
simplex virus. J Infect Dis 1980; 141(5):563-574.
De Clercq E. Comparative efficacy of antiherpes drugs in different cell lines.
Antimicrob Agents Chemother 1982; 21(4):661-663.
Dekker C, Ellis MN, McLaren C, Hunter G, Rogers J, Barry DW. Virus resistance
in clinical practice. J Antimicrob Chemother 1983; 12 Suppl B:137-152.
Douglas JM, Davis LG, Remington ML, Paulsen CA, Perrin EB, Goodman P et
al. A double-blind, placebo-controlled trial to the effect of chronically
administered oral acyclovir on sperm production in men with frequently recurrent
genital herpes. J Infect Dis 1988 Mar; 157:588-93.
Douglas JM, Critchlow C, Benedetti J, Mertz GJ, Connor JD, Hintz MA et al. A
double-blind study of oral acyclovir for suppression of recurrences of genital
herpes simplex virus infection. N Engl J Med 1984; 310(24):1551-1556.
Dunkle LM, Arvin AM, Whitley RJ, Rotbart HA, Feder HM, Jr., Feldman S et al.
A controlled trial of acyclovir for chickenpox in normal children. N Engl J Med
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Ellis MN, Keller PM, Martin JL, Strauss SE, Nusinoff-Lehrman S etal.
Characterization of an HSV-2 clinical isolate containing an ACV-resistant mutant
which produces a thymidine kinase with altered substrate specificity. Ninth Int
Herpesvirus Workshop, Seattle, Washington, August 24-29 1984.
Ellis MN, Keller PM, Fyfe JA, Martin JL, Rooney JF, Straus SE et al. Clinical
isolate of herpes simplex virus type 2 that induces a thymidine kinase with altered
substrate specificity. Antimicrob Agents Chemother 1987; 31(7):1117-1125.
Englund JA, Zimmerman ME, Swierkosz EM, Goodman JL, Scholl DR, Balfour
HH, Jr. Herpes simplex virus resistant to acyclovir. A study in a tertiary care
center. Ann Intern Med 1990; 112(6):416-422.
Erlich KS, Jacobson MA, Koehler JE, Follansbee SE, Drennan DP, Gooze L et al.
Foscarnet therapy for severe acyclovir-resistant herpes simplex virus type-2
infections in patients with the acquired immunodeficiency syndrome (AIDS). An
uncontrolled trial. Ann Intern Med 1989; 110(9):710-713.
Erlich KS, Mills J, Chatis P, Mertz GJ, Busch DF, Follansbee SE et al. Acyclovir-
resistant herpes simplex virus infections in patients with the acquired
immunodeficiency syndrome. N Engl J Med 1989; 320(5):293-296.
Field HJ, Darby G, Wildy P. Isolation and characterization of acyclovir-resistant
mutants of herpes simplex virus. J Gen Virol 1980; 49(1):115-124.
Field HJ. The problem of drug-induced resistance in viruses, in Problems of
Antiviral Therapy. Stuart-Harris CH, Oxford J (Eds) Academic Press, London
Fyfe K. Recurrence patterns of genital herpes after cessation of more then 5 years
of chronic acyclovir suppression. VIII Int Conf AIDS/III Std Wrld Cong
Huff JC, Bean B, Balfour HH, Jr., Laskin OL, Connor JD, Corey L et al. Therapy
of herpes zoster with oral acyclovir. Am J Med 1988; 85(2A):84-89.
Jacobson MA, Berger TG, Fikrig S, Becherer P, Moohr JW, Stanat SC et al.
Acyclovir-resistant varicella zoster virus infection after chronic oral acyclovir
therapy in patients with the acquired immunodeficiency syndrome (AIDS). Ann
Intern Med 1990; 112(3):187-191.
Kaplowitz LG, Baker D, Gelb L, Blythe J, Hale R, Frost P et al. Prolonged
continuous acyclovir treatment of normal adults with frequently recurring genital
herpes simplex virus infection. The Acyclovir Study Group. JAMA 1991;
Page 34 of 39
Krasny HC, Liao SH, de Miranda P, Laskin OL, Whelton A, Lietman PS.
Influence of hemodialysis on acyclovir pharmacokinetics in patients with chronic
renal failure. Am J Med 1982; 73(1A):202-204.
Kurtz T. Safety and efficacy of long-term suppressive cyclovir treatment of
frequently recurring genital herpes: year 5 results. 30th Intersci Conf Antimicrob
Agents Chemother 1990;270.
Laskin OL, Longstreth JA, Whelton A, Krasny HC, Keeney RE, Rocco L et al.
Effect of renal failure on the pharmacokinetics of acyclovir. Am J Med 1982;
Lau RJ, Emery MG, Galinsky RE. Unexpected accumulation of acyclovir in
breast milk with estimation of infant exposure. Obstet Gynecol 1987; 69(3 Pt
Lehrman SN, Douglas JM, Corey L, Barry DW. Recurrent genital herpes and
suppressive oral acyclovir therapy. Relation between clinical outcome and in-vitro
drug sensitivity. Ann Intern Med 1986; 104(6):786-790.
Marlowe S, Douglas J, Corey L, Schnipper L, Crumpacker C. Sensitivity of HSV
genital isolates after oral acyclovir. 24th Interscience Conf Antimicrob Ag
Chemother, Washington, DC, October 8-10 1984.
Mattison HR, Reichman RC, Benedetti J, Bolgiano D, Davis LG, Bailey-
Farchione A et al. Double-blind, placebo-controlled trial comparing long-term
suppressive with short-term oral acyclovir therapy for management of recurrent
genital herpes. Am J Med 1988; 85(2A):20-25.
McLaren C, Sibrack CD, Barry DW. Spectrum of sensitivity of acyclovir of
herpes simplex virus clinical isolates. Am J Med 1982; 73(1A):376-379.
McLaren C, Ellis MN, Hunter GA. A colorimetric assay for the measurement of
the sensitivity of herpes simplex viruses to antiviral agents. Antiviral Res 1983;
McLaren C, Corey L, Dekket C, Barry DW. In vitro sensitivity to acyclovir in
genital herpes simplex viruses from acyclovir-treated patients. J Infect Dis 1983;
Mertz GJ, Critchlow CW, Benedetti J, Reichman RC, Dolin R, Connor J et al.
Double-blind placebo-controlled trial of oral acyclovir in first-episode genital
herpes simplex virus infection. JAMA 1984; 252(9):1147-1151.
Page 35 of 39
Mertz GJ, Jones CC, Mills J, Fife KH, Lemon SM, Stapleton JT et al. Long-term
acyclovir suppression of frequently recurring genital herpes simplex virus
infection. A multicenter double-blind trial. JAMA 1988; 260(2):201-206.
Mertz GJ, Eron L, Kaufman R, Goldberg L, Raab B, Conant M et al. Prolonged
continuous versus intermittent oral acyclovir treatment in normal adults with
frequently recurring genital herpes simplex virus infection. Am J Med 1988;
Meyer LJ, de Miranda P, Sheth N, Spruance S. Acyclovir in human breast milk.
Am J Obstet Gynecol 1988; 158(3 Pt 1):586-588.
Mindel A, Weller IV, Faherty A, Sutherland S, Hindley D, Fiddian AP et al.
Prophylactic oral acyclovir in recurrent genital herpes. Lancet 1984; 2(8394):57-
Morton P, Thomson AN. Oral acyclovir in the treatment of herpes zoster in
general practice. N Z Med J 1989; 102(863):93-95.
Naib ZM, Nahmias AJ, Josey WE, Zaki SA. Relation of cytohistopathology of
genital herpesvirus infection to cervical anaplasia. Cancer Res 1973; 33(6):1452-
Nilsen AE, Aasen T, Halsos AM, Kinge BR, Tjotta EA, Wikstrom K et al.
Efficacy of oral acyclovir in the treatment of initial and recurrent genital herpes.
Lancet 1982; 2(8298):571-573.
Nusinoff-Lehrman S, Hunter G, Rogers J, Corey L, Davis G. The in vitro
acyclovir sensitivity of herpesvirus shed by patients receiving suppressive oral
therapy. 24th Interscience Conf Antimicrob Ag Chemother, Washington, DC,
October 8-10 1984;(Abstract #1015).
O'Brien JJ, Campoli-Richards DM. Acyclovir. An updated review of its antiviral
activity, pharmacokinetic properties and therapeutic efficacy. Drugs 1989;
Pahwa S, Biron K, Lim W, Swenson P, Kaplan MH, Sadick N et al. Continuous
varicella-zoster infection associated with acyclovir resistance in a child with
AIDS. JAMA 1988; 260(19):2879-2882.
Parker AC, Craig JI, Collins P, Oliver N, Smith I. Acyclovir-resistant herpes
simplex virus infection due to altered DNA polymerase. Lancet 1987;
Page 36 of 39
Parris DS, Harrington JE. Herpes simplex virus variants restraint to high
concentrations of acyclovir exist in clinical isolates. Antimicrob Agents
Chemother 1982; 22(1):71-77.
Preblud SR, Arbeter AM, Proctor EA, Starr SE, Plotkin SA. Susceptibility of
vaccine strains of varicella-zoster virus to antiviral compounds. Antimicrob
Agents Chemother 1984; 25(4):417-421.
Reichman RC, Badger GJ, Mertz GJ, Corey L, Richman DD, Connor JD et al.
Treatment of recurrent genital herpes simplex infections with oral acyclovir. A
controlled trial. JAMA 1984; 251(16):2103-2107.
Shah GM, Winer RL, Krasny HC. Acyclovir pharmacokinetics in a patient on
continuous ambulatory peritoneal dialysis. Am J Kidney Dis 1986; 7(6):507-510.
Sibrack CD, Gutman LT, Wilfert CM, McLaren C, St Clair MH, Keller PM et al.
Pathogenicity of acyclovir-resistant herpes simplex virus type 1 from an
immunodeficient child. J Infect Dis 1982; 146(5):673-682.
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suppress recurring herpes simplex virus infections in immunodeficient patients.
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Suppression of frequently recurring genital herpes. A placebo-controlled double-
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Acyclovir suppression of frequently recurring genital herpes. Efficacy and
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Intravenous acyclovir to treat mucocutaneous herpes simplex virus infection after
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IMPORTANT: PLEASE READ
Page 37 of 39
PART III: CONSUMER INFORMATION
This leaflet is Part III of a three-part "Product Monograph"
published when ZOVIRAX
(acyclovir) was approved for
sale in Canada and is designed specifically for Consumers.
This leaflet is a summary and will not tell you everything
. Contact your doctor or pharmacist if you
have any questions about the drug.
ABOUT THIS MEDICATION
What the medication is used for and what it does:
(acyclovir) is an antiviral medicine.
Treatment of shingles (herpes zoster)
is used to treat shingles (herpes zoster)
infections. Shingles is caused by the varicella-zoster virus.
The virus multiplies in and eventually destroys affected skin
stops the virus from multiplying and
therefore from spreading to neighbouring healthy cells. It
cannot replace a cell which has been damaged by the
multiplying virus, but it will facilitate the process of healing.
Treatment of chickenpox (varicella)
is used to treat chickenpox (varicella) which is
caused by the varicella-zoster virus. See the “Information for
Parents” section at the end of this leaflet.
Treatment and suppression of genital herpes
is used to treat initial episodes of genital herpes.
Genital herpes is a sexually transmitted infection caused by
the herpes simplex virus (HSV). HSV causes small, fluid-
filled blisters in the genital area which break down into
ulcers/sores which may be itchy or painful. The fluid in these
blisters contains the virus which causes the disease. It is a
feature of all herpes viruses that once in the body, they stay
there throughout life alternating between active (outbreak) and
When taken on a daily basis, ZOVIRAX
can also be used to
prevent the HSV infection from coming back. This type of
treatment is called suppressive therapy.
When it should not be used:
You should not use ZOVIRAX
if you are allergic to or react
badly to acyclovir or valacyclovir or any other components of
the formulation of ZOVIRAX
(see “What the non-medicinal
ingredients are” section). Tell your doctor if you have ever
had an allergic reaction to any of these ingredients.
What the medicinal ingredient is:
Suspension and Tablets contain the active
What the non-medicinal ingredients are:
Suspension contains the non-medicinal ingredients
banana flavor, cellulose, glycerin, methylparaben,
propylparaben, sorbitol, vanillin, and water.
200 mg Tablets contain the non-medicinal
ingredients cellulose, indigotine, lactose, magnesium stearate,
povidone, and sodium starch glycolate.
400 mg Tablets contain the non-medicinal
ingredients cellulose, iron oxide, magnesium stearate, povidone
and sodium starch glycolate.
800 mg Tablets contain the non-medicinal
ingredients cellulose, indigotine, magnesium stearate, povidone
and sodium starch glycolate.
What dosage forms it comes in:
is available in oral suspension containing 200 mg
of acyclovir per 5 mL.
is available in tablets containing 200 mg, 400 mg
or 800 mg of acyclovir.
WARNINGS AND PRECAUTIONS
Before using ZOVIRAX
, tell your doctor if:
You have kidney problems or if you are 65 years of
age or older. Your doctor may give you a lower dose
You are pregnant, planning to become pregnant, or
When using ZOVIRAX
for suppression of genital herpes,
your doctor may periodically stop your drug therapy in order to
reassess your need for continuous treatment. The effect of
long-term use in humans has not been fully assessed. Prudence
is therefore suggested when choosing continuous, long term
therapy with ZOVIRAX
. Suppression of recurrent genital
herpes is therefore, only recommended in those who are
severely affected. Some patients experience increased severity
of the first episode of genital herpes after stopping treatment.
Genital herpes is passed from one person to another through
direct intimate contact. To reduce the risk of transmission,
wash your hands immediately if you touch your skin sores, and
do not touch other parts of your body until you have done so.
Especially avoid intimate contact with others when the disease
is visible. Herpes virus particles may also be released when
IMPORTANT: PLEASE READ
Page 38 of 39
you do not have blisters or sores. For this reason, it is safest
to believe that you can spread the infection to your partner
even when sores are not present.
Although decreased sperm counts were observed in animals
treated with high doses, these effects did not occur in humans.
PROPER USE OF THIS MEDICATION
Medication should not be shared with others. The prescribed
dosage should not be exceeded.
Usual dose for shingles:
For the treatment of shingles (herpes zoster), the usual dose of
is 800 mg every 4 hours, 5 times daily for 7 to 10
must be taken as early as possible within
72 hours of the onset of lesions.
Usual dose for chickenpox:
For the treatment of chickenpox (varicella), the usual dose of
is 20 mg/kg (not to exceed 800 mg) 4 times daily
for 5 days. ZOVIRAX
must be taken as early as possible
within 24 hours of the appearance of rash.
Usual dose for genital herpes:
For the treatment of an initial episode of genital herpes, the
usual dose of ZOVIRAX
is 200 mg every 4 hours, 5 times
daily (maximum 1 g daily) for 10 days. ZOVIRAX
taken as early as possible following onset of signs and
For the suppression of genital herpes, the usual dose of
is 200 mg 3 to 5 times daily or 400 mg twice
daily. You should follow dosing instructions carefully. The
objective is to keep enough of the drug in the body at all times
to prevent the herpes virus from multiplying. Your doctor
will try to prescribe the minimum dose required to do this in
your case and may therefore increase or decrease your dose
during the first few weeks. Follow your doctor's instruction
carefully to ensure that you get the best possible response to
For the treatment of recurrent episodes of genital herpes, the
usual dose of ZOVIRAX
is 200 mg every 4 hours 5 times
daily for 5 days. ZOVIRAX
must be taken at the earliest
sign or symptom (prodrome) of recurrence.
It is important to follow the dosage instructions on the label of
your medicine. In the event of an overdose, you should
contact either your doctor, the nearest
hospital emergency department or poison control centre.
If you forget to take a dose, take it as soon as you remember.
Then continue with the next dose at the proper time interval.
Do not double doses.
SIDE EFFECTS AND WHAT TO DO ABOUT THEM
As with any widely prescribed medication, adverse events in
association with the use of ZOVIRAX
are reported from time
to time. The common ones are listed below; they have rarely
been severe enough to make it necessary to stop taking the
Headache, nausea, diarrhea, skin rash and upset stomach.
If you experience any of the following side effects, contact
your doctor as soon as possible:
Pain in the side (between ribs and hip) or kidney area of
Unusual bruising or bleeding.
Tell your pharmacist or doctor if you notice other side effects
from your medicine which are not mentioned here. A complete
listing of adverse events that have been reported is contained in
the Product Monograph supplied to your doctor and
HOW TO STORE IT
Tablets and Suspension at room temperature
(15° to 25°C). ZOVIRAX
Tablets should be stored in a dry
place and protected from light.
Keep your ZOVIRAX
Tablets and Suspension in a safe place
where children cannot reach them.
CHICKENPOX – INFORMATION FOR PARENTS
Chickenpox is one of the most
infections in otherwise
healthy children. It usually occurs in children before the age of
ten, but anyone who has never had chickenpox can become
infected - irrespective of age.
Chickenpox is caused by a virus called "varicella zoster" and it
. Family members often give the disease
to each other. For reasons that are not known, often the second
or third child who catches it from a brother or sister will be
sicker than the first child. Also, the disease tends to be more
severe in teenagers than in younger children.
IMPORTANT: PLEASE READ
Page 39 of 39
The disease can be mild with few pox or mild symptoms -
alternatively, it could be severe with hundreds of pox. The
pox can occur both outside and inside the body. There is
way to predict the severity
Recognizing the Disease
The early symptoms of chickenpox may be vague and could
include fever, itching, headache, aching joints and muscles,
sore throat, general malaise: loss of appetite, listlessness and
irritability. After that, itchy, small, red spots (the "pox")
appear, and become blisters within a few hours. New spots
and blisters continue to appear for about five days. The
blisters start to dry up and within six or seven days turn into
Not all who are exposed come down with the disease. The
incubation period may extend from one to three weeks after
exposure. The virus is spread through the air when: (1) a
person with chickenpox scratches the blisters, allowing the
virus to become airborne; or (2) a person with chickenpox
coughs or sneezes within close contact of others. The disease
is most contagious shortly before the rash appears, through the
early stages of the rash, and until all the blisters have dried. A
contagious once all the blisters have become
Early consultation with your doctor
If you think your child has been exposed to chickenpox, be on
the lookout for symptoms described above.
At the first sign
of rash, CALL YOUR DOCTOR.
There are more treatment
options available when the infection is caught this early. Your
doctor may prescribe a medication which could offer the child
less discomfort, and possibly a faster recovery.
Tips to bear in mind
It is important to follow the doctor's orders with all
medications prescribed - even if the patient seems to feel
Never use medications containing acetylsalicylic
acid (ASA) in children with fever and chickenpox.
Acetaminophen may be given to reduce fever.
The rash can be soothed by coating with an anti-itch product
such as calamine, or other medications that your doctor
recommends. The discomfort of itching can be relieved
temporarily by baths and wet compresses. Bathing daily with
soap and water can also help prevent infection.
Do not use
on the sores; rather
consult your doctor
might prescribe an antibiotic if necessary. Since infection or
scarring can occur at scratch sites, it is important to
discourage scratching and spreading of virus particles through
the air. Keep the rash clean and dry. If possible keep the nails
cut short, cover the hands and feet with cotton gloves, mitts or
socks to discourage children scratching at sleep time.
Complications are rare in the healthy child. The people who
are at greatest risk of complications are: pregnant women,
newborn babies, or people being treated for cancer, arthritis,
asthma, or after organ transplants - where medicine is
suppressing their immune systems. If anyone in your family
falls within these groups
inform your doctor
so that the
preventive measures can be taken.
REPORTING SUSPECTED SIDE EFFECTS
To monitor drug safety, Health Canada through the
Canada Vigilance Program collects information on serious
and unexpected side effects of drugs. If you suspect you
have had a serious or unexpected reaction to this drug you
may notify Canada Vigilance:
By toll-free telephone: 866-234-2345
By toll-free fax: 866-678-6789
By email: CanadaVigilance@hc-sc.gc.ca
By regular mail:
Canada Vigilance National Office
Marketed Health Products Safety and
Effectiveness Information Bureau
Marketed Health Products Directorate
Health Products and Food Branch
Tunney’s Pasture, AL 0701C
Ottawa ON K1A 0K9
NOTE: Should you require information related to the
management of the side effect, please contact your health
care provider before notifying Canada Vigilance. The
Canada Vigilance Program does not provide medical advice.
This document plus the full product monograph, prepared for
health professionals can be found at:
http://www.gsk.ca or by contacting the sponsor,
7333 Mississauga Road
This leaflet was prepared by GlaxoSmithKline Inc.
Last revised: September 10, 2008
2008 GlaxoSmithKline Inc. All Rights Reserved
ZOVIRAX is a registered trademark, GlaxoSmithKline Inc.