The metabolism of promazine and acetylpromazine in the horse.

Promazine hydrochloride and acetylpromazine maleate were administered intravenously at clinical dose levels to horses. In urine from horses given promazine hydrochloride, the parent drug and four metabolites were detected. The two major metabolites, present as conjugates were identified after hydrolysis by beta-glucuronidase/arylsulfatase as 3-hydroxypromazine and 3-hydroxydesmonomethyl-promazine. Conjugated 3-hydroxypromazine has been previously identified as a major metabolite in the horse. Two minor metabolites isolated in this study were primaizine N-oxide and promazine N-oxide sulfoxide. At the administered dosage, promazine sulfoxide was not found to be the major nonconjugated metabolite, as had been reported elsewhere. In urine from horses given acetylpromazine maleate, only three metabolites were found. Two were identified after hydrolysis by beta-glucuronidase/arylsulfatase as 7-hydroxyacetylpromazine and 2-(1-hydroxyethyl)-7-hydroxypromazine. The third, nonconjugated metabolite was 2-(1-hydroxyethyl)promazine sulfoxide.