Antihistaminic and anticholinergic activities of mequitazine in comparison with clemizole.

The antihistamine and anticholinergic properties of mequitazine have been investigated and compared with those of clemizole. Both mequitazine and clemizole antagonized the effect of histamine in guinea-pig ileum competitively, the pA2 values calculated by Schild plot were 9.95 +/- 0.44 for mequitazine and 10.54 +/- 0.44 for clemizole. Mequitazine at 10(-7) M produced a parallel shift of the dose-response curve to acetylcholine in the rat duodenum, clemizole and the lower doses of mequitazine failed to modify the effect of acetylcholine. The potency of mequitazine and clemizole as H1-histamine blockers is similar, but only mequitazine at highest concentration used showed anticholinergic activity.