Anticough and antimicrobial activities of Psidium guajava Linn. leaf extract

The anticough activity of Psidium guajava Linn. (guava) leaf extract was evaluated in rats and guinea pigs. The results showed that water extract of the plant at doses of 2 and 5 g/kg, p.o. decreased the frequency of cough induced by capsaicin aerosol by 35 and 54%, respectively, as compared to the control, within 10 min after injection of the extract, (P < 0.01). However, the anticough activity is less potent than that of 3 mg/kg dextromethorphan which decreased frequency of cough by 78% (P < 0.01). An experiment on isolated rat tracheal muscle showed that the extract directly stimulated muscle contraction and also synergized with the stimulatory effect of pilocarpine. This effect was antagonized by an atropine. Moreover, growth of Staphylococcus aureus and beta-streptococcus group A, as determined by the disc diffusion method, was inhibited by water, methanol and chloroform extract of dry guava leaves (P < 0.001). The LD50 of guava leaf extract was more than 5 g/kg, p.o. These results suggest that guava leaf extract is recommended as a cough remedy.