Abstract: Aim ＆ Methods The effect of pseudoephedrine hydrochloride mixture, a compound consisting of pseudoephedring hydrochloride, dextromethorphan hydrobromide and chlorpheniramine, on the histamine-induced cont raction of guinea pig bronchial smooth muscle was studied in vitro by the method of receptor kinetics.Results ＆ Discussion The result showed that H1 receptor of histamine in isolated bronchial smooth muscle was competitively blocked by chlorpheniramine and noncompetitively blocked by pseudoephedring hydrochloride. Though the significant antagonism on the H₁ receptor was not observed with dextrome hydrobromide alone, synergetic asthma-relieving effects were shown as the medicine was simultaneously administ rated with pseudoephedring hydrochloride or chlorpheniramine.furthermore, when these three drugs were simultaneously administ rated, the most obvious synergetic could be observed.

Key words: pseudoephedrine hydrochloride mixture, trachea, guinea pig