ANTIHISTAMINICS AND APOMORPHINE-INDUCED VOMITING

Abstract

The experiments reported were undertaken to investigate pharmacologically certain claims that some antihistaminics are antemetic in man and capable of inhibiting or preventing apomorphine-induced vomiting in animals. Diphenhydramine hydrochloride, diphenhydramine-8-chlorotheophyllinate, and diphenhydramine- 8-bromotheophyllinate, administered to cats in rotation, by mouth, in doses of from 0.5 to 20 mgm. per kgm. body weight 0.5 hr. before subcutaneous injection of 20 to 50 mgm, per kgm. of apomorphine hydrochloride, had no effect upon the vomiting syndrome. Doses of from 0.5 to 40 mgm. Per kgm. of the same three derivatives of diphenhydramine were administered orally to dogs in rotation and at intervals of 0.5, 1,2, and 4 hr. before intramuscular injection of 0.05 mgm. per kgm. of apomorphine hydrochloride, with no effect upon the incidence of vomiting and no effect upon the frequency of vomiting and retching except partial inhibition at convulsant and subconvulsant doses. Similar results were obtained from administration of promethazine hydrochloride orally to dogs in doses of from 0.5 to 40 mgm. per kgm. one hour before intramuscular injection of 0.05 mgm. per kgm. of apomorphine hydrochloride, and the same procedure, substituting methapyrilene hydrochloride and methapyrilene-8-chlorotheophyllinate for promethazine hydrochloride, did not affect the vomiting syndrome whatsoever. The results indicate that in amounts corresponding to usual human therapeutic doses, none of these antihistaminics has any ability to prevent apomorphine-induced emesis in dogs and cats.