Evaluation of analgesic activities of methanolic extract of Callichilia stenosepala root bark

Callichilia stenopetala is a medicinal plant and its root is used as chewing stick in the treatment of toothache and fever in south-east of Nigeria. The methanolic extract of its root bark and fractions obtained after successive liquid-liquid partitioning (hexane, chloroform, ethyl acetate and methanol fractions) of the crude extract were investigated for analgesic activities in animal (mice) using hot plate and acetic acid – induced writhing models. Doses of 250 and 500 mg/Kg of the extract were used orally while a single dose of 500 mg/Kg was used for the fractions. The extract, in hot plate model, exhibited analgesic activity by significantly (P < 0.01) increasing the pain reaction time, PRT (64.8 and 85.70%) respectively in a dose dependent manner comparison to reference drugs, aspirin and morphine. In the acetic acid- induced writhing model the extract significantly (P < 0.01) reduced the number of writhes (56.34 and 84.06%) respectively compared to the control. The percentage of writhe inhibition of the fractions is as follows, ethyl acetate (93.27%), methanol (50.63%) hexane (17.72%) chloroform (2.53%). There was no record of animal death when the extract was administered orally up to 8000 mg/Kg.

The observed pharmacological activities in this study demonstrated a good level of antinociceptive activities in the models used and this suggests that there is a scientific basis for the folklore use of the plant in management of acute toothache and ethyl acetate fraction being more potent.

Key words: Callichilia stenopetala, analgesic, pain reaction time (PRT), acetic acid, hot plate