Comparative study of anticholinergic effects of H1-receptor antagonists

ABSTRACT

Anticholinergic effects of various H1-receptor antagonists [Promethazine, diphenhydramine, cyclizine, clemastine, antazoline, cholorpheniramine, pheniramine, terfenadine, astemizole] were studied by observing their antagonism to the contractile response of the rabbit isolated ileum preparation to acetylcholine. Four doses of acetylcholine were selected from the linear part of log dose response curve, constructed by recording isotonic contractions of rabbit ileum on kymograph. The effects of these 4 doses of acetylcholine alone and in the presence of three increasing doses of HI-receptor antagonist in the organ bath were compared. Experimental data was statistically analysed. Diphenhydramine, promethazine and cyclizine showed prominent anticholinergic effects. Clemastine, antazoline and pheniramine had moderate anticholinergic effect. Chlor- pheniramine had mild anticholinergic effect whereas terfenadine and astemizole were devoid of anticholinergic effect