Antimalarial activity of some Kenyan plants used in traditional medicine
Wamakima, Francis Muregi
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Plasmodium falciparum, the commonest etiological agent for human malaria is becoming increasingly resistant to standard antimalarial drugs in many malaria endemic areas. This necessitates a continuous effort to search for new and novel antimalarial drugs. Plants have always been a rich source for new drugs and many antimalarial drugs such as quinine and artemisinine were either obtained from plants, or developed using their chemical structures as templates. One hundred and fifteen aqueous and organic extracts of 22 plant species from 15-taxonomical families from Kisii District were prepared and screened for their in vivo antimalarial activity against four laboratory-adapted P. falciparum isolates. In the preliminary screening, the extracts were screened against K39, a chloroquine (CQ) sensitive strain and the extracts which had high activity (IC50<20 g/ml) were subsequently screened against ENT 30, V1/S and NF 54. Data were expressed in terms of mean 50% inhibitory concentration. The effect of combining CQ with selected plant extracts against the multi-drug resistant V1/S was also investigated. Out of the 22 plants screened against P. falciparum isolate K39, 15 plant species showed an activity of IC50<100g/ml. Of these, 5 plant species were highly active with IC50 values ranging from 1.01-19.15 g/ml against all strains of P. falciparum tested (K39, NF 54, ENT 30 and V1/S). The best activities were from extracts of Vernonia lasiopus whose IC50 values ranged from 1.01-4.13 g/ml for both CQ-sensitive and CQ-resistant isolates. In addition, several extracts in combination with CQ exhibited good synergistic effects against V1/S. The lower IC50 values exhibited by many extracts against both chloroquine-sensitive and -resistant isolates suggested that there was no cross-resistance to chloroquine. The active principles could therefore be isolated and used to standardize a popular drug based on traditional use of these medicinal plants as antimalarials. The potentiation of CQ by some extracts suggested that the active principles in medicinal plants could be used in combination with standard antimalarials to enhance its activity. These results could account for the ethnopharmacological use of the plants investigated as antimalarials.