Analgesic activity of crude aqueous extract of the root bark of zanthoxylum xanthoxyloides.

OBJECTIVE The analgesic activity of crude aqueous extract of the root bark of Zanthoxylum xanthozyloides was studied in mice and rats with the view to verifying the claim in folklore medicine that the extract has analgesic activity. METHOD The extract was obtained by Soxhlet extraction and rotatory evaporation, followed by freeze-drying. Groups of rats and mice were, respectively, assigned randomly to treatment groups. The animals received three different treatments orally: 0.9% saline (control), the extract (400mg/kg and 800mg/kg for mice; 1000mg/kg and 2000mg/kg for rats) and indomethacin (5mg/kg and 10mg/kg for mice; 10mg/kg and 20mg/kg for rats). Each group of animals was rotated through the entire treatment groups such that each animal served as control as well as received all the treatments. The hot-plate and paw-pressure methods were used to study pain perception in the treated animals. Analysis of variance was used as the statistical test. RESULTS In both methods, the extract and indomethacin caused dose-dependent elevation in pain threshold. At the peak of activity, 400mg/kg and 800mg/kg extract caused 74% and 95% increase in the reaction time respectively whilst 5mg/kg and 10mg/kg indomethacin gave 97% and 116% increment respectively. Similarly, 1000mg/kg and 2000mg/kg extract caused 65% and 84% increase in pain threshold whilst 10mg/kg and 20mg/kg indomethacin caused 95% and 113% increment respectively. CONCLUSION It was concluded that the extract induced analgesia, probably, by inhibiting prostaglandin production, just as did indomethacin.