The applied pharmacology of azaperone in ponies

The butyrophenone tranquilliser, azaperone, was administered intramuscularly to ponies in five series of experiments, using a dose level of 0-4 mg/kg once and 0-8 mg/kg four times. An excellent or good sedative effect was usually obtained with both dose levels, but the response was more consistent with the higher dose. The onset of sedation was apparent within 10 min of administration, the maximal effect usually occurring between 20 and 60 min while sedation was no longer apparent after 2 to 6 h. Body temperature was reduced in all animals for at least 2 h and respiratory rate was increased in some ponies but not in others. A mild tachycardia occurred in the first hour after administering azaperone (0-8 mg/kg) and arterial blood pressure was reduced for at least 4 h. The hypothesis that azaperone reduced blood pressure by blocking alpha-adrenoceptors, thereby decreasing vasomotor tone, was tested by measuring the ability of azaperone (0-8 mg/kg) to antagonise the action of standard intravenous doses of adrenaline (1-5 mug/kg) on blood pressure, Azaperone partially antagonised the pressor action of adrenaline and in comparative studies the phenothiazine tranquilliser, acepromazine (0-1 mg/kg), also exerted a similar blocking effect.