Analgesic and Antioxidant Activities of Stem Bark Extract and Fractions of Petersianthus macrocarpus

Background: Petersianthus macrocarpus (Lecythidaceae) is widely used in the folk medicine in Nigeria to relieve pain and fever associated with malaria. This study evaluated the analgesic and antioxidant activities of the methanol extract and fractions of the stem bark of the plant. Materials and Methods: The analgesic activity was determined in mice using hotplate and acetic acid‑induced writhing models. Morphine sulphate (5 mg/kg, i.p.) and aspirin (100 mg/ml, p.o.) were used as reference analgesic agents. The antioxidant potential was evaluated using 1,1‑diphenyl‑2‑picrylhydrazyl (DPPH) radical; reducing power, iron chelating properties and determination of total phenolic content. Results: The extract at 200 and 500 mg/kg, produced an insignificant (P > 0.05) increase in pain threshold in hotplate but a significant (P < 0.05) increase at 1000 mg/kg. The extract significantly (P < 0.05) reduced the writhing induced by acetic acid in mice in a dose dependent manner. Fractionation increased the analgesic activities significantly (P < 0.05) in ethyl acetate and aqueous fractions (200 mg/kg). The extract demonstrated strong DPPH radical scavenging activity with IC₅₀ 0.05 mg/ml, good reducing power and weak iron chelating activities. The total phenol content was 142.32 mg/gin term of gallic acid. The antioxidant effects were more pronounced in ethyl acetate and aqueous fractions. Conclusion: The findings of the study suggested that the extract has strong analgesic and antioxidant activities which reside mainly in the polar fractions thus confirming the traditional use of the plant to alleviate pains.