Introduction

Virbac AH Logo Blue

Company name: Virbac Limited

Address: Woolpit Business Park

Windmill Avenue

Woolpit

Bury St Edmunds

Suffolk

IP30 9UP

Telephone: 01359 243243

Fax: 01359 243200

Website: www.virbac.co.uk

Presentation

A clear, colourless, volatile liquid containing 100% isoflurane USP. It is stable, non-flammable, non-explosive and has a mildly pungent odour. Its chemical structure is 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether.

Uses

A non-irritant, inhalation agent for induction and maintenance of surgical anaesthesia in dogs and cats.

Dosage and administration

Isoflurane is a potent anaesthetic agent of low solubility, allowing rapid changes to be made to the level of anaesthesia. For this reason it should only be administered using an adequately calibrated vaporiser in an appropriate anaesthetic circuit. Isoflurane should be used to effect by a suitably skilled anaesthetist. Administration may be performed in oxygen only or in a mixture of nitrous oxide and oxygen at a ratio of 2:1.

Minimum alveolar concentration The MAC value of isoflurane is 1.28% in the dog and 1.63% in the cat.

Premedication A preanaesthetic regime should be chosen to suit the patient. Isoflurane use has been shown to be compatible with common preanaesthetic agents such as acepromazine, opioids, benzodiazepines, alpha-2-adrenoreceptor agonists (and their reversal agents) and anticholinergics.

Induction of anaesthesia Dogs and cats may be induced by inspired isoflurane concentrations between 2 and 4%. Premedication and/or concurrent use of nitrous oxide reduces the concentration of isoflurane required.

If anaesthesia is induced with an injectable agent, an initial isoflurane concentration slightly above that required for maintenance should usually be administered to aid the transition to gaseous anaesthesia.

Maintenance of anaesthesia As a general rule, concentrations of around 1.5 MAC are necessary for anaesthetic maintenance. In practice, levels of 1.5-2.5% in the dog and 1.5-3.0% in the cat are used. Again, premedication and/or concurrent use of nitrous oxide reduces the concentration of isoflurane required.

Contra-indications, warnings, etc

For use in dogs and cats only.

The product should not be used in animals with a known sensitivity to isoflurane or a known susceptibility to malignant hyperthermia.

The lowest effective dose should be administered. Concurrent use of a premedicant, sedative or analgesic drugs may reduce significantly the required concentration of isoflurane.

Isoflurane causes dose-dependent depression of respiratory rate and depth.

Isoflurane causes a dose-dependent reduction in systemic blood pressure. In general though, it is less detrimental to cardiac function than halothane and is less likely to predispose the heart to arrhythmias.

If cardiopulmonary parameters are overly depressed by the agent, reducing the inspired concentration will normally be sufficient to correct this.

The use of non-depolarising muscle relaxants is potentiated by isoflurane, leading to increased duration of neuromuscular blockade.

For the anaesthesia of a patient with a head injury, high concentrations (over 1.5MAC) cause increases in cerebral blood flow and intra-cranial pressure. Use of artificial ventilation to maintain normal CO2 levels can attenuate this.

In the event of severe overdosage, cease isoflurane administration. An endotracheal tube should be passed of one is not already in place and positive pressure ventilation with oxygen commenced.

Isoflurane may react with dessicated carbon dioxide absorbents to form carbon monoxide, and therefore create a risk of elevating carboxyhaemoglobin levels in a rebreathing circuit. To avoid this, absorbents should be regularly checked and not allowed to dry out.

Operator warnings

Do not breathe vapour. Isoflurane has a recommended Occupational Exposure Standard of 50 ppm as an 8 hour time-weighted average. Operating areas should be equipped with active extracting/scavenging systems that are adequately and regularly maintained and checked for leaks. Induction and recovery areas should be well ventilated. To protect the environment, it is considered good practice to use charcoal filters with scavenging equipment.

Care should be taken when dispensing isoflurane, with any spillage absorbed immediately.

Wash any splashes from skin and eyes and avoid contact with mouth.

If severe accidental exposure occurs remove the operator from the source of exposure, seek medical advice and show this label.

Note that adrenaline and catecholamines may cause cardiac dysrythmias.

Pharmaceutical precautions

Store below 25°C tightly closed original container.

Protect from direct sunlight.

Any unused product or waste material should be disposed of in accordance with advice from a local waste regulatory authority.

Keep out of reach of children.

Legal category

POM-V

Packaging Quantities

250 ml bottle.

Further information

Isoflurane is minimally metabolised (less than 0.2%) and almost all excreted unchanged by the lungs.

It causes good muscle relaxation for standard surgical procedures. Due to its rapid elimination, it provides neglible analgesia post recovery, and the use of an analgesic agent should be considered.

Isoflurane has been safely used for caesarean section in the dog and cat. Fully comprehensive data on isoflurane use during pregnancy and lactation in the target species have not been obtained.