Synergy and Antagonism in Antimalarial Crude Extract Combinations

Background Malaria accounts for around 4.8% of all recorded fatalities in Tanzania. Medicinal plants such as Caesalpinia bonducella, Azadirachta indica, and Annickia kummeriae have demonstrated promise in treating many diseases, including malaria. However, their combined activity against malaria has not been documented. Combination therapy using some medicinal plants with antimalarial activities may enhance safety and efficacy and reduce the evolution of parasite resistance. Objectives This study aimed to investigate antiplasmodium activities of different combinations of crude extracts from selected medicinal plants. Azadirachta indica leaves, Annickia kummeriae and Caesalpinia bonducella were extracted using dichloromethane (DCM). Methods An in vivo acute toxicity study of both individual and combined crude extracts was carried out according to Chinedu et al., 2015. The in vivo antiplasmodial activity of individual and combined crude extracts was performed in mice inoculated with Plasmodium berghei (ANKA strain) using Peters’s 4-day suppressive test. Results Individually, Caesalpinia bonducella crude extracts exhibited the highest in vivo antiplasmodial efficacy (91% parasite suppression) than A. kummeriae (73% parasite suppression) and A. indica (60% parasite suppression) at 800 mg/kg/day. The A. indica and A. summarize combinations and A. indica and C. bonducella demonstrated higher antiplasmodial activity (synergism-combination index 0.29 and 0.97, respectively) than their constituents. However, combining A. kummeriae and C. bonducella produced the lowest antiplasmodial activity (antagonism- combination index 40.67) than its extracts. The high antiplasmodial potencies (ED50) demonstrated by AiAk and AiCb are significant and critical results for traditional, complementary and alternative medicine. Conclusion Therefore, these preliminary findings suggest that AiAk and AiCb are potential antiplasmodium herbal therapies. Further research should be undertaken to investigate the antiplasmodium effect of AiAk and AiCb in humans.