Introduction

Azaperone is a pyridinylpiperazine and butyrophenone neuroleptic drug with sedative and antiemetic effects, which is used mainly as a tranquiliser in veterinary medicine. It is uncommonly used in humans as an antipsychotic drug.

Azaperone acts primarily as a dopamine antagonist but also has some antihistaminic and anticholinergic properties as seen with similar drugs such as haloperidol. Azaperone may cause hypotension and while it has minimal effects on respiration in pigs, high doses in humans can cause respiratory depression.

Veterinary Use

The most common use for azaperone is in relatively small doses as a “serenic” (to reduce aggression) in farmed pigs, either to stop them fighting or to encourage sows to accept piglets. Higher doses are used for anaesthesia in combination with other drugs such as xylazine, tiletamine and zolazepam. Azaperone is also used in combination with strong narcotics such as etorphine or carfentanil for tranquilising large animals such as elephants. Use in horses is avoided as adverse reactions may occur.

The European Medicines Agency has established a maximum residue limit for azaperone when administered to pigs.

Azaperone (under the brand name Stresnil) was approved for use in pigs in the USA in 1983, under NADA 115-732.

Synthesis

The alkylation of 2-chloropyridine with piperazine gives 1-(pyridin-2-yl)piperazine 67980-77-2. The attachment of the sidechain by reaction with 4-chloro-4′-fluorobutyrophenone 3874-54-2 completed the synthesis of azaperone.

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