Context Landolphia owariensis P. Beauv. (Apocyanaceae) leaf is used in southeast Nigeria to treat malaria. Objective This study evaluated the antiplasmodial activity of L. owariensis leaf extract and fractions, also the phytoconstituents were standardized and analyzed. Methods The effects of daily, oral administrations of 200, 400 and 800 mg/kg of L. owariensis leaf extract (LOE), its hexane (LOHF), ethyl acetate (LOEF) and methanol (LOMF) fractions on early, established and residual infections in Plasmodium berghei-infected albino mice were evaluated in vivo. The extract and fractions were subjected to phytochemical analysis and HPLC fingerprinting, and the acute toxicity of LOE was evaluated. Results The extract and fractions elicited 29-86, 18-95 and 75-96% significant (p < 0.001) suppression of parasitemia in early, established and residual infections, respectively. The ED50 values for suppressive activity of LOE, LOHF, LOEF and LOMF were 266.56, 514.93, 392.95 and 165.70 mg/kg, respectively. The post-day 30-survival index was 16.7-50, 16.7, 16.7-66.7 and 50-83.3% for LOE, LOHF, LOEF, and LOMF, respectively. Extract-treated mice significantly (p < 0.001) gained weight and had reduced mortality compared with negative control (untreated) mice. An oral LD50 value >5000 mg/kg in mice was established for LOE. The LOMF showed the greatest antiplasmodial activity in all the models, suggesting that the antimalarial activity of the plant may be attributed to alkaloids, flavonoids, saponins and tannins present in the fraction. Conclusion Results demonstrate the antiplasmodial activity of L. owariensis leaf, and provide a pharmacological rationale for its ethnomedicinal use as an antimalarial agent.
Keywords: Antiplasmodial; Rane test; curative activity; early infection; repository test; suppressive activity; white rubber vine.