POM-V Prescription Required Companion Animal

IsoFlo 100% w/w Inhalation Vapour, Liquid

Active ingredient: Isoflurane

Form

Inhalation vapour, liquid

Species

Cats Chinchilla Dogs Ferrets Gerbil Guinea Pig Hamster Horses Mouse Ornamental Birds Rat Reptiles

Manufacturer

Zoetis Belgium S.A.

VMD MA No.

60021/3072

What it's used for

Induction and maintenance of general anaesthesia.

Full indications, dosage and side effects ↓

View official SPC (PDF)

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2

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Clinical information

IsoFlo 100% w/w Inhalation Vapour, Liquid — SPC Details

Source: VMD Summary of Product Characteristics (SPC). Last updated 27 Mar 2026.

Induction and maintenance of general anaesthesia.

Isoflurane should be administered using an accurately calibrated vaporiser in
an appropriate anaesthetic circuit, since levels of anaesthesia may be altered
rapidly and easily.
Isoflurane may be administered in oxygen or oxygen/nitrous oxide mixtures.
The MAC (minimal alveolar concentration in oxygen) or effective dose ED50
values and suggested concentrations given below for the target species
should be used as a guide or starting point only. The actual concentrations
required in practice will depend on many variables, including the concomitant
use of other drugs during the anaesthetic procedure and the clinical status of
the patient.
Isoflurane may be used in conjunction with other drugs commonly used in
veterinary anaesthetic regimes for premedication, induction and analgesia.
Some specific examples are given in the individual species information. The
use of analgesia for painful procedures is consistent with good veterinary
practice.
Recovery from isoflurane anaesthesia is usually smooth and rapid. The
analgesic requirements of the patient should be considered before the
termination of general anaesthesia.
HORSES
The MAC for isoflurane in the horse is approximately 1.31%
Premedication:
Isoflurane may be used with other drugs commonly used in veterinary
anaesthetic regimes. The following drugs have been found to be compatible
with isoflurane: acepromazine, alfentanil, atracurium, butorphanol,
detomidine, diazepam, dobutamine, dopamine, guaiphenesin
morphine, pentazocine, pethidine, thiamylal, thiopentone and xylazine. Drugs
used for premedication should be selected for the individual patient.
However, the potential interactions below should be noted.
Interactions:
Detomidine and xylazine have been reported to reduce the MAC for isoflurane
in horses.
Induction:
As it is not normally practicable to induce anaesthesia in adult horses using
isoflurane, induction should be by the use of a short acting barbiturate such as
thiopentone sodium, ketamine or guaiphenesin. Concentrations of 3 to 5%
isoflurane may then be used to achieve the desired depth of anaesthesia in 5
to 10 minutes
Isoflurane at a concentration of 3 to 5% in a high flow of oxygen may be used
for induction in foals.
Maintenance:
Anaesthesia may be maintained using 1.5% to 2.5% isoflurane.
Recovery
Recovery is usually smooth and rapid.
DOGS
The MAC for isoflurane in the dog is approximately 1.28%.
Premedication:
Isoflurane may be used with other drugs commonly used in veterinary
anaesthetic regimes. The following drugs have been found to be compatible
with isoflurane: acepromazine, atropine, butorphanol, buprenorphine,
bupivacaine, diazepam, dobutamine, ephedrine, epinephrine, etomidate,
glycopyrrolate, ketamine, medetomidine, midazolam, methoxamine,
oxymorphone, propofol, thiamylal, thiopentone and xylazine. Drugs used for
premedication should be selected for the individual patient. However, the
potential interactions below should be noted.
Interactions:
Morphine, oxymorphone, acepromazine, medetomidine, medetomidine plus
midazolam have been reported to reduce the MAC for isoflurane in dogs.
The concomitant administration of midazolam/ketamine during isoflurane
anaesthesia may result in marked cardiovascular effects, particularly arterial
hypotension.
The depressant effects of propranolol on myocardial contractility are reduced
during isoflurane anaesthesia, indicating a moderate degree of β-receptor
activity.
Induction:
Induction is possible by face mask using up to 5% isoflurane, with or without
premedication.
Maintenance:
Anaesthesia may be maintained using 1.5% to 2.5% isoflurane.
Recovery:
Recovery is usually smooth and rapid.
CATS
The MAC for isoflurane in the cat is approximately 1.63%.
Premedication:
Isoflurane may be used with other drugs commonly used in veterinary
anaesthetic regimes. The following drugs have been found to be compatible
with isoflurane: acepromazine, atracurium, atropine, diazepam, ketamine, and
oxymorphone. Drugs used for premedication should be selected for the
individual patient. However, the potential interactions below should be noted.
Interactions:
Intravenous administration of midazolam-butorphanol has been reported to
alter several cardio-respiratory parameters in isoflurane- induced cats as has
epidural fentanyl and medetomidine. Isoflurane has been shown to reduce
the sensitivity of the heart to adrenaline (epinephrine).
Induction:
Induction is possible by face mask using up to 4% isoflurane, with or without
premedication.
Maintenance:
Anaesthesia may be maintained using 1.5% to 3% isoflurane.
Recovery:
Recovery is usually smooth and rapid.
ORNAMENTAL BIRDS
Few MAC/ED50 values have been recorded. Examples are 1.34% for the
Sandhill crane, 1.45% for the racing pigeon, reduced to 0.89% by the
administration of midazolam, and 1.44% for cockatoos, reduced to 1.08% by
the administration of butorphanol analgesic.
The use of isoflurane anaesthesia has been reported for many species, from
small birds such as zebra finches, to large birds such as vultures, eagles and
swans.
Drug interactions/compatibilities:
Propofol has been demonstrated in the literature to be compatible with
isoflurane anaesthesia in swans.
Interactions:
Butorphanol has been reported to reduce the MAC for isoflurane in cockatoos.
Midazolam has been reported to reduce the MAC for isoflurane in pigeons.
Induction:
Induction with 3 to 5% isoflurane is normally rapid. Induction of anaesthesia
with propofol, followed by isoflurane maintenance, has been reported for
swans.
Maintenance:
The maintenance dose depends on the species and individual. Generally, 2
to 3% is suitable and safe.
Only 0.6 to 1% may be needed for some stork and heron species.
Up to 4 to 5% may be needed for some vultures and eagles.
3.5 to 4% may be needed for some ducks and geese.
Generally, birds respond very rapidly to changes in concentration of
isoflurane.
Recovery:
Recovery is usually smooth and rapid.
REPTILES
Isoflurane is considered by several authors to be the anaesthetic of choice for
many species. The literature records its use on a wide variety of reptiles (eg.
various species of lizard, tortoise, iguanas, chameleon and snakes).
The ED50 was determined in the desert iguana to be 3.14% at 35˚C and
2.83% at 20˚C.
Drug interactions/ compatibilities:
No specific publications on reptiles have reviewed compatibilities or
interactions of other drugs with isoflurane anaesthesia.
Induction:
Induction is usually rapid at 2 to 4% isoflurane.
Maintenance:
1 to 3% is a useful concentration.
Recovery:
Recovery is usually smooth and rapid.
RATS, MICE, HAMSTERS, CHINCHILLAS, GERBILS, GUNIEA PIGS AND
FERRETS
Isoflurane has been recommended for anaesthesia of a wide variety of small
mammals.
The MAC for mice has been cited as 1.34%, and for the rat as 1.38%, 1.46%
and 2.4%.
Drug interactions/ compatibilities:
No specific publications on small mammals have reviewed compatibilities or
interactions of other drugs with isoflurane anaesthesia.
Induction:
Isoflurane concentration 2 to 3%.
Maintenance:
Isoflurane concentration 0.25 to 2%.
Recovery:
Recovery is usually smooth and rapid.
SUMMARY TABLE CONTAINING ANAESTHESIA INDUCTION AND
MAINTENANCE DATA BY SPECIES
SpeciesMAC (%)Induction
(%)
Maintenance
(%)
RecoveryHorses1.313.0 – 5.0 1.5 – 2.5Smooth
and rapid
Dogs1.28Up to 5.01.5 – 2.5Smooth
and rapid
Cats1.63Up to 4.01.5 – 3.0Smooth
and rapid
Ornamental
birds
See posology3.0 – 5.0 See posologySmooth
and rapid
ReptilesSee posology2.0 – 4.0 1.0 – 3.0Smooth
and rapid
Rats, mice,
hamsters,
chinchillas,
gerbils, guinea
pigs and
ferrets
1.34 (mouse)
1.38/1.46/2.40
(rat)
2.0 – 3.0 0.25 – 2.0Smooth
and rapid

Do not use in cases of known susceptibility to malignant hyperthermia.
Do not use in cases of hypersensitivity to the active substance.

Horse, dog, cat, ornamental bird, reptile, rat, mouse, hamster, chinchilla,
gerbil, guinea pig and ferret.
Rare (1 to 10 animals / 10,000
animals treated)
bradycardia
, arrhythmiasVery rare
(<1 animal / 10,000 animals
treated, including isolated
reports):
cardiac arrest, respiratory arrest,
malignant hyperthermia
Undetermined frequencyhypotension
, respiratory depression
1
Transient.
Susceptible animals.
Dose-related.
Reporting adverse events is important. It allows continuous safety monitoring
of a veterinary medicinal product. Reports should be sent, preferably via a
veterinarian, to either the marketing authorisation holder or its local
representative or the national competent authority via the national reporting
system. See also the last section of the package leaflet for respective contact
details.

The ease and rapidity of alteration of the depth of anaesthesia with isoflurane
and its low metabolism, may be considered advantageous for its use in
special groups of patients such as the old or young, and those with impaired
hepatic, renal or cardiac function.

Special precautions for safe use in the target species:
Isoflurane has little or no analgesic properties. Adequate analgesia should
always be given before surgery. The analgesic requirements of the patient
should be reviewed again before the general anaesthesia has ended.
Isoflurane causes depression of the cardiovascular and respiratory systems.
It is important to monitor pulse quality and rate in all patients. The use of the
product in patients with cardiac disease should only be considered after a
benefit risk assessment by the responsible veterinary surgeon. In the case of
cardiac arrest, complete cardiopulmonary resuscitation should be performed.
It is important to monitor respiratory rate and quality. It is also important to
maintain an open airway and to properly oxygenate tissues during the
maintenance of anaesthesia. Respiratory arrest should be treated by assisted
ventilation.
The metabolism of isoflurane in birds and small mammals can be affected by
decreases in body temperature that may occur secondary to a high surface
area to body weight ratio. Therefore body temperature should be monitored
and kept stable during treatment.
Drug metabolism in reptiles is slow and highly dependent upon environmental
temperature. Reptiles may be difficult to induce with inhalation agents due to
breath holding.
When using isoflurane to anaesthetise an animal with a head injury,
consideration should be given as to whether artificial ventilation is appropriate
to help avoid increased cerebral blood flow by maintaining normal CO2 levels.
Special precautions to be taken by the person administering the veterinary
medicinal product to animals:
Do not breathe the vapour. Users should consult their National Authority for
advice on Occupational Exposure Standards for isoflurane.
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.
Adverse effects on foetuses and pregnant animals were observed in
laboratory animals. Pregnant and breast- feeding women should not have any
contact with the product and should avoid operating rooms and animal
recovery areas. Avoid using masking procedures for prolonged induction and
maintenance of general anaesthesia.
Use cuffed endotracheal intubation when possible for the administration of
IsoFlo 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. sawdust. Wash any
splashes from skin and eyes, and avoid contact with the mouth. If severe
accidental exposure occurs remove the operator from the source of exposure,
seek medical advice immediately and show the package leaflet or the label to
the physician.
Halogenated anaesthetic agents may induce liver damage. In the case of
isoflurane this is an idiosyncratic response very rarely seen after repeated
exposure.
To the Physician: Ensure a patient’s airway and give symptomatic and
supportive treatment. Note that adrenaline and catecholamines may cause
cardiac dysrhythmias.
Special precautions for the protection of the environment:
Although anaesthetics have a low potential for damage to the atmosphere, it
is good practice to use charcoal filters with scavenging equipment, rather than
to discharge them into the air.

interaction
The action of muscle relaxants in man, especially those of the
nondepolarising (competitive) type such as atracurium, pancuronium or
vecuronium, is enhanced by isoflurane. Similar potentiation might be
expected to occur in the target species, although there is little direct evidence
to this effect. Concurrent inhalation of nitrous oxide enhances the effect of
isoflurane in man and similar potentiation might be expected in animals.
The concurrent use of sedative or analgesic drugs is likely to reduce the level
of isoflurane required to produce and maintain anaesthesia.
Some examples are given in section

Do not store above 25 C.
Store in the original bottle.Keep the bottle in the outer carton
Keep the bottle tightly closed
Protect from direct sunlight and heat.

and rapid
Dogs1.28Up to 5.01.5 – 2.5Smooth
and rapid
Cats1.63Up to 4.01.5 – 3.0Smooth
and rapid
Ornamental
birds
See posology3.0 – 5.0 See posologySmooth
and rapid
ReptilesSee posology2.0 – 4.0 1.0 – 3.0Smooth
and rapid
Rats, mice,
hamsters,
chinchillas,
gerbils, guinea
pigs and
ferrets
1.34 (mouse)
1.38/1.46/2.40
(rat)
2.0 – 3.0 0.25 – 2.0Smooth
and rapid
3.10 Symptoms of overdose (and where applicable, emergency
procedures and antidotes)
Isoflurane overdose may result in profound respiratory depression. Therefore,
respiration must be monitored closely and supported when necessary with
supplementary oxygen and/ or assisted ventilation.
In cases of severe cardiopulmonary depression, administration of isoflurane
should be discontinued, the breathing circuit should be flushed with oxygen,
the existence of a patent airway ensured, and assisted or controlled
ventilation with pure oxygen initiated. Cardiovascular depression should be
treated with plasma expanders, pressor agents, antiarrhythmic agents or
other appropriate techniques.
3.11 Special restrictions for use and special conditions for use,
including restrictions on the use of antimicrobial and antiparasitic
veterinary medicinal products in order to limit the risk of
development of resistance
Not applicable.
3.12 Withdrawal periods
Horses:
Meat and offal: 2 days
Not authorised for use in mares producing milk for human consumption.
4.

This information is sourced from the official Summary of Product Characteristics (SPC) published by the Veterinary Medicines Directorate (VMD). It is provided for informational purposes only and does not replace professional veterinary advice. Always consult your vet before administering any medication.