The effect of antihistaminics on cataleptogenic action of analgesics and haloperidol.

We investigated the effect of benzhydramine, thenalidine, mepyramine (H1 receptor antagonists) and cimetidine (H2 receptor antagonist) on cataleptogenic action of morphine, codeine, fentanyl, and haloperidol. Benzhydramine antagonized the catalepsy induced by analgesics (particularly by codeine). The antagonistic effect of thenalidine was weaker (but also very prominent for codeine catalepsy). Mepyramine did not affect the catalepsy induced by analgesics. All three H1 receptor antagonists attenuated the catalepsy induced by haloperidol. Cimetidine, injected intraventricularly, did not affect the catalepsy induced either by analgesics or by haloperidol. It is suggested that the antagonistic action of benzhydramine and thenalidine against analgesic catalepsy is related rather to their antiserotonin properties, while the anticataleptic activity of all three H1 receptor antagonists against haloperidol catalepsy is caused by their anticholinergic and antiserotonin properties.