Steroid Agents
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The only available steroid anaesthetic for use in veterinary patients is alfaxalone. It is a progesterone derived neurosteroid.
Mechanism of Action
Neurosteroids act similarly to other anaesthetic agents by acting at the GABAa receptor chloride channels to enhance the inhibitory effect of GABA. This produces hypnosis and muscle relaxation.
Pharmacological Considerations
Alfaxalone can be administered intravenously and intramuscularly. It is available as either a single agent solution at 10mg/ml, or in combination with alfadolone with polyoxyethylated castor oil as a solvent. It has a rapid onset of action, inducing anaesthesia with 30-60 seconds when given intravenously. Its duration of action is dose dependent. If given intramuscularly, onset of anaesthesia is within 7-10 minutes. However, it has a varying degree of effect and may only sedate the patient. Recovery is dependent on metabolism via glucuronidation processes, rather then redistribution.
Contraindications and Side Effects
Cardiovascular Effects
- Dose dependent decrease in arterial blood pressure thought to be due to myocardial contractility and stroke volume.
Respiratory Effects
- Minimal respiratory effects.
Other Effects
- Histamine release leading to swollen paws and face of dogs that have received agents in polyoxyethylated castor oil. This also makes it contraindicated in cats with asthma or mast cell tumours.
Uses
Alfaxalone can be used for induction of anaesthesia in dogs and cats.