ATCvet code: QN01AX05.
Pharmacodynamics
Alfaxalone (3-α-hydroxy-5-α-pregnane-11,20-dione) is a neuroactive steroid molecule with properties of a general anaesthetic. The primary mechanism for the anaesthetic action of alfaxalone is modulation of neuronal cell membrane chloride ion transport, induced by binding of alfaxalone to GABAA cell surface receptors.
Pharmacokinetics
In cats following a single intravenous dose of alfaxalone at 5 mg/kg bw, the mean plasma elimination half-life (t1/2) is approximately 45 minutes. Plasma clearance is 25 ml/kg/min. Volume of distribution is 1.8 L/kg.
In dogs following a single intravenous dose of alfaxalone at 2 mg/kg bw, the mean plasma elimination half-life (t1/2) is approximately 25 minutes. Plasma clearance is 59 ml/kg/min. Volume of distribution is 2.4 L/kg.
In rabbits following a single intravenous dose of alfaxalone at 5 mg/kg bw, the mean plasma elimination half-life (t1/2) is approximately 46 minutes. Plasma clearance is 56 ml/kg/min. Volume of distribution is 3.6 L/kg.
In dogs, cats and rabbits the elimination of alfaxalone demonstrates non-linear (dose-dependent) pharmacokinetics.
In vitro cat and dog hepatocyte studies show that alfaxalone experiences both Phase I (cytochrome P450 dependent) and Phase II (conjugation dependent) metabolism. Both cats and dogs form the same five (5) Phase I alfaxalone metabolites. The Phase II metabolites observed in cats are alfaxalone sulphate and alfaxalone glucuronide, while alfaxalone glucuronide is observed in the dog.
Alfaxalone metabolites are likely to be eliminated from the dog, cat and rabbit by the hepatic/faecal and renal routes, similar to other species.