Main information

  • Trade name:
  • Isofane 100% w/ w Inhalation Vapour, Liquid
  • Pharmaceutical form:
  • Inhalation vapour, solution
  • Prescription type:
  • POM-V - Prescription Only Medicine – Veterinarian
  • Medicine domain:
  • Animals
  • Medicine type:
  • Allopathic drug



  • Available in:
  • Isofane 100% w/w Inhalation Vapour, Liquid
    United Kingdom
  • Language:
  • English

Therapeutic information

  • Therapeutic group:
  • Cats, Dogs, Horses, Mice, Ornamental Birds, Rabbits, Rats, Reptiles
  • Therapeutic area:
  • Neurological Agent general anaesthetic


  • Source:
  • VMD - Veterinary Medicines Directorate
  • Authorization status:
  • Authorized
  • Authorization number:
  • 37071/4001
  • Authorization date:
  • 28-06-1999
  • Last update:
  • 15-05-2018

Summary of Product characteristics: dosage, interactions, side effects

Revised: December 2017

AN: 01761/2017




Isofane 100% wlw Inhalation vapour, liquid.



Active substance: Isoflurane 100% w/w

For a full list of excipients, see section 6.1



Inhalation vapour, liquid

A clear colourless liquid with a characteristic odour.



Summary presentation of the active substance: Isoflurane is a volatile liquid

halogenated hydrocarbon. Although the exact mode of action is poorly

understood it is thought that, in common with other general anaesthetics,

isoflurane acts by competing with endogenous ligands for binding to

specific neuroreceptors.


Target species

Horses, dogs, cats, small mammals, ornamental birds and reptiles.


Indications for use, specifying the target species

To induce and maintain anaesthesia in all types of veterinary surgery.



Do not use in animals sensitive to isoflurane or other halogenated or

inhalation anaesthetic agents. Do not use in animals with a known

susceptibility to malignant hyperthermia.


Special warnings for each target species

Horses: Recovery from isoflurane anaesthesia is generally smooth and


However, one report suggests that horses recovering from isoflurane

anaesthesia may appear un-coordinated. It is important to provide

adequate post-anaesthetic analgesia since isoflurane anaesthetised horses

may become aware of their surroundings more rapidly than horses

recovering from halothane anaesthesia.

Other species: none


Special precautions for use

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Special precautions for use in animals

None known

Special precautions for the person administering the veterinary

medicinal product to animals

Do not breathe the vapour. The Occupational Exposure Standard

(OES) for isoflurane has been set at 50 ppm on an 8-hour weighted


Operating rooms and recovery areas should be provided with

adequate ventilation or scavenging systems to prevent the

accumulation of anaesthetic vapour.

All scavenging/extraction systems must be adequately maintained.

To protect the environment it is considered good practice to use

charcoal filters with scavenging/ventilation equipment.

Avoid using masking procedures for prolonged induction and

maintenance of general anaesthesia. Use cuffed endotracheal

intubation when possible for the administration of Isofane during

maintenance of general anaesthesia.

Care should be taken when dispensing isoflurane, with any spillage

removed immediately using an inert and absorbent material e.g.


Pregnant and breast-feeding women should avoid exposure to the

product and should avoid operating rooms and animal recovery


Wash any splashes from skin and eyes immediately and avoid

contact with the mouth.

In the event of severe accidental exposure; remove the operator

from the source of the exposure and seek urgent medical assistance

and show this label.

Halogenated anaesthetic agents may induce liver damage. In the

case of isoflurane this is an idiosyncratic response very rarely seen

after repeated exposure.

Advice to doctors: maintain a patent airway and give symptomatic

and supportive treatment. Note that adrenaline and catecholamines

may cause cardiac dysrhythmias.


Adverse reactions (frequency and seriousness)

Heart rate usually remains stable with isoflurane, however both respiration

and blood pressure are depressed in a dose-related manner. Pulse and

respiration should be assessed for both rate and character in all patients.

Consideration should be given to supplemental ventilation, especially in

animals which have sustained injuries which may lead to increased CO

levels or a depressed heart rate. In animals with head injuries consider

supplemental ventilation to maintain normal circulating CO

levels such that

cerebral blood flow does not increase. Blood pressure should be assessed

throughout anaesthesia. Hypotension, if related to depth of anaesthesia,

can be corrected by a reduction in delivered isoflurane concentration. In

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horses, as with all anaesthetic agents, it may sometimes be necessary to

administer an ionotropic agent in hypotension. Isoflurane appears to

sensitise the myocardium to the dysrhythmogenic effects of circulating

catecholamines to a lesser extent than halothane.


Use during pregnancy, lactation or lay

Isoflurane has been successfully used in pregnant animals, including the

horse, dog and cat, for Caesarean section. Reproduction studies in mice,

rats and rabbits show no evidence of effect on foetal malformation

specifically attributable to isoflurane at clinically relevant doses.

However,specific studies in the target species to show the effect on

pregnant, lactating or breeding animals have not been undertaken.


Interaction with other medicinal products and other forms of


Muscle relaxation with isoflurane is normally adequate for the majority of

surgical procedures. If a more profound muscle relaxation is required, e.g.

for thoracic surgery, additional muscle relaxants may be employed. All

commonly available non-depolarising muscle relaxants are potentiated by

isoflurane and the effects will be maintained for longer than is usual with

these agents. In dogs, care should be taken if administering a

midazolamketamine combination to an animal already anaesthetised with



Posology and method of administration

The product should only be used in an accurately calibrated isoflurane

specific vaporiser.

Pre-medication: The pre-medication should be chosen according to the

type and condition of the animal and the surgical procedure planned.

Isoflurane has been shown to be compatible with the most commonly used

veterinary premedicant agents. The use of sedative or analgesic drugs is

likely to reduce the concentration of isoflurane required to induce or

maintain anaesthesia.

Induction: The dose for induction of anaesthesia will vary according to

species, but is generally between 2% and 5% concentration in an oxygen,

or oxygen/nitrous oxide mixture. The table below presents a guide to the

concentrations required for induction of anaesthesia by species based on

use of Isofane with oxygen. When used in conjunction with oxygen/nitrous

oxide a lower concentration of isoflurane may be required. Speed of

induction and the concentration of isoflurane required may vary according

to several different influences, including the health and medication status of

the patient.

Observation of effect and clinical judgement will be required to determine

the most appropriate induction dose in each case.

Maintenance: A guide to maintenance dose by species based on use of the

product with oxygen is presented in the table below. When used in

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AN: 01761/2017

conjunction with oxygen/nitrous oxide a lower concentration of isoflurane

may be required. The specific dose required may vary according to several

different influences, including the health and medication status of the


Clinical judgement will be required to determine the most appropriate dose

in each case.

Recovery: Recovery from anaesthesia is generally rapid, uneventful and


Guide to induction and maintenance of anaesthesia by species

(Isofane concentration in oxygen)










3.0 – 5.0


1.5 – 2.5


Up to 5.0

1.5 – 2.5

Up to 4.0

1.5 – 3.0




Up to 5.0

2.0 – 3.0


2.0 - 4.0

1.0 – 3.0

Small Mammals

2.0 – 3.0

0.25 – 2.0

Rabbit 2.05

Mouse 1.34

Rat 1.38 – 2.4

* Minimum Alveolar Concentration at which 50% of anaesthetised patients

show no response to a stimulus.


Overdose (symptoms, emergency procedures, antidotes), if


Isoflurane causes dose related respiratory and cardiovascular depression.

It is important that both respiration and cardiovascular function is monitored

for both rate and character. Respiratory arrest should be treated by

assisted ventilation, preferably with oxygen supplementation. Maintain a

patent airway and adequate tissue oxygenation throughout the period of



Withdrawal periods

Not to be used in animals intended for human consumption.

Treated horses may never be slaughtered for human consumption.

The horse must have been declared as not intended for human

consumption under national horse passport legislation.

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Pharmacodynamic properties

In common with other anaesthetics, increasing concentrations of isoflurane

produce respiratory depression characterised by decreased respiratory rate

and/or tidal volume and by concurrent increases in arterial CO

tension and

respiratory acidosis in all species. Cardiovascular effects are more varied,

including falls in arterial pressure, total peripheral resistance and baroreflex

sensitivity. Heart rate tends to remain stable or increase and cardiac output

remains stable in cats and dogs but falls in horses. Prolonged anaesthesia

causes initial respiratory depression but parameters remain stable


In the horse, heart rate, left ventricular work and arterial pressure may

increase. Otherwise, these and other cardiovascular parameters tend to

remain stable. Isoflurane also protects against atrial fibrillation and

sensitises the myocardium to catecholamine-induced arrhythmias to a

lesser degree than other anaesthetics. The effects on the CNS include loss

of consciousness, analgesia and muscle relaxation. Cerebral

autoregulation in response to changes in PaCO

or blood pressure at high

isoflurane concentrations is depressed, as are cerebral vascular resistance

and metabolism. The cerebral blood flow tends to increase.

There are no signs of CNS irritability or increased cerebrospinal fluid

production in dogs; in cats there are signs of mild CNS irritability (possibly

due to hypocapnia) and a small increase in intracranial pressure. Isoflurane

has no clinically significant effects on the liver and kidneys or on blood

chemistry or cell counts.

5.2 Pharmacokinetic properties

Isoflurane is administered by inhalation. Absorption takes place across the

alveolar exchange membranes at a rate determined by the rate and depth

of respiration, by the cardiac output and by the solubility of isoflurane in the

blood. Isoflurane has a low blood/gas partition coefficient (i.e. it is poorly

soluble) and equilibration between alveolar gas and the circulation is

therefore rapid, in the order of 30 minutes. Distribution of isoflurane is

dependent on cardiac output and the partition coefficients of the various

tissues. Again these tend to be low so distribution is rapid.

Isoflurane is very stable and metabolism is minimal. 95% or more is

excreted unchanged, the remainder is believed to be metabolised by the

liver to fluoride ions, trifluoroacetic acid and HCI. Peak serum fluoride ion

concentrations stay well below the levels considered to be harmful for the


Excretion occurs mostly via the lungs and is dependent on the same

parameters determining absorption and distribution. In dogs, 92-96% of

absorbed isoflurane is excreted unchanged via the lungs with a half-life of

150±42 minutes. The metabolites of isoflurane are excreted in the urine.



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6.1 List of excipients


6.2 Incompatibilities

Isoflurane has been reported to interact with dry carbon dioxide absorbents

to form carbon monoxide. In order to minimise the risk of this in rebreathing

circuits, and the possibility of elevated carboxyhaemaglobin levels,

absorbents should not be allowed to dry out.

6.3 Shelf life

Shelf life of the veterinary medicinal product as packaged for sale: 5 years

6.4 Special precautions for storage

Do not store above 25°C.

Keep the container tightly closed.

Protect from light.

6.5 Nature and composition of immediate packaging

Glass, amber, Type IV bottles, with black phenolic screw caps with aconical

low density polyethylene liner.

Pack sizes of 100ml and 250ml.

Not all pack sizes may be marketed.

6.6 Special precautions for the disposal of unused veterinary medicinal

product or waste materials derived from the use of such products, if


Any unused veterinary medicinal product or waste materials derived from

such veterinary medicinal products should be disposed of in accordance

with local requirements.



Piramal Critical Care Limited

Suite 4, Ground Floor

Heathrow Boulevard - East Wing

280 Bath Road

West Drayton, UB7 0DQ

United Kingdom




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AN: 01761/2017



28 June 1999



December 2017

Approved: 07 December 2017

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