DEXTRORPHAN AND DEXTROMETHORPHAN - COMPARATIVE ANTITUSSIVE EFFECTS ONGUINEA-PIGS

Dextromethorphan, alter administration, is rapidly and extensively tra nsformed into dextrorphan. The aim of this study was to compare the co ugh-suppressing activity of 6, 12, 24, 48 mg/kg, i.p., of dextrorphan (dextro rotatory isomer of racemorphan) with that of dextromethorphan, using the model of citric acid-induced coughing in the unanaesthetize d, unrestrained guinea pig. A significant dose-effect relationship of dextrorphan in reducing citric acid-induced cough was observed. This e ffect was comparable with that of dextromethorphan. However, at 48 mg/ kg, i.p., dextromethorphan had a toxic effect while dextrorphan did no t. Because dextrorphan is the major metabolite of dextromethorphan and has antitussive activity comparable to that of dextromethorphan, clin ical use of dextrorphan is suggested.