Effect of mifentidine on histamine-stimulated human atrium "in vitro": comparison with ranitidine and cimetidine.

The new H2-antagonist mifentidine was tested on human atrium, in comparison with cimetidine and ranitidine, for its activity against histamine-induced inotropic effect. Mifentidine was found to be 10 times more potent than ranitidine and 100 times more potent than cimetidine. The kinetics of the three compounds are typical of a competitive antagonism and the pA2 value was of 8.60, 6.35, 5.94 for mifentidine, ranitidine and cimetidine, respectively. Our data confirm previous findings in another isolated heart preparation, namely the guinea-pig papillary muscle.