Antitussive Activity Directed Isolation of Compounds from Onosma hispidum

The chemical investigation of the ethanolic extract of the root bark of Onosma hispidum following antitussive activity directed isolation led to the isolation of 4-hydroxy-3-methoxy cinnamic acid (mCA) and 4-hydroxy-3-methoxy benzoic acid (mBA) which have been reported for the first time in this species. Antitussive activity of the compounds was evaluated by reduction in frequency of cough induced by SO₂ gas in mice. In addition to these compounds, the crude ethanolic extract and methanolic fraction showed highly significant antitussive activity (p< 0.001, Students t test) compared to control. A dose-dependent inhibition of cough was observed with the extracts and the pure compounds and the results were also comparable with the effect produced by dextromethorphan- a standard antitussive drug.