Alfaxalone

Alfaxalone, also known as alphaxalone or alphaxolone and sold under the brand name Alfaxan, is a neuroactive steroid and general anesthetic which is used in veterinary practice as an induction agent for anesthesia and as an injectable anesthetic. Though it is more expensive than other induction agents, it often preferred due to the lack of depressive effects on the cardiovascular system. The most common side effect is respiratory depression; when premedications aren't given, patients also become agitated and hypersensitive when waking up. Alfaxalone, also known as alphaxalone or alphaxolone and sold under the brand name Alfaxan, is a neuroactive steroid and general anesthetic which is used in veterinary practice as an induction agent for anesthesia and as an injectable anesthetic. Though it is more expensive than other induction agents, it often preferred due to the lack of depressive effects on the cardiovascular system. The most common side effect is respiratory depression; when premedications aren't given, patients also become agitated and hypersensitive when waking up. Alfaxalone works as a positive allosteric modulator on GABAA receptors and, at high concentrations, as a direct agonist of the GABAA receptor. It is cleared quickly by the liver, giving it a relatively short terminal half-life and preventing it from accumulating in the body, lowering the chance of overdose. Alfaxalone is used as an induction agent, an injectable anesthetic, and a sedative in animals. While it is commonly used in cats and dogs, it has also been successfully used in rabbits, horses, sheep, pigs, and exotics such as red-eared turtles, axolotl, green iguanas, marmosets, and koi fish. As an induction agent, alfaxalone causes the animal to relax enough to be intubated, which then allows the administration of inhalational anesthesia. Premedication (administering sedative drugs prior induction) increases the potency of alfaxalone as an induction agent. Alfaxalone can be used instead of gas anesthetics in surgeries that are under 30 minutes, where it is given at a constant rate via IV (constant rate infusion); this is especially useful in procedures such as bronchoscopies or repairing tracheal tears, as there is no endotracheal tube in the way. Once the administration of alfaxalone stops, the animal quickly recovers from anesthesia. Alfaxalone can be used as a sedative when given intramuscularly (IM), though this requires a larger volume (and not all countries allow alfaxalone to be administered IM). Despite its use as an anesthetic, alfaxalone itself has no analgesic properties. Though alfaxalone is not licensed for IM or subcutaneous use in the United States (as both cause longer recoveries with greater agitation and hypersensitivity to stimuli), it is routinely used IM in cats, and is licensed as such in other countries. Alfaxalone is dissolved in 2-hydroxylpropyl-β cyclodextrin (which is toxic to people). The cyclodextrin is a large, starch-derived molecule with a hydrophobic core where alfaxalone stays, allowing the mixture to be dissolved in water and sold as an aqueous solution. They act as one unit, and only dissociate once in vivo. The lack of preservatives in alfaxalone vials gives them an extremely short shelf-life once the seal has been broken, as microbes can grow inside the vial. Official instructions in the U.K. are to take up enough alfaxalone into a syringe as needed and to discard the rest immediately. In the United States, a vial of alfaxalone can be kept up to six hours after its first use. In New Zealand and Australia, a used vial can be kept in a fridge for up to seven days. Alfaxalone has been used to perform c-sections in pregnant cats; though it crosses the placental barrier and had some effects on the kittens, there is no respiratory depression and no lasting effect. Alfaxalone has also been found to be safe in young puppies and kittens.