Abstract

Fresh leaves of Citrus limon, Psidium guajava, Carica papaya, Cymbopogon citratus and Vernonia amygdalina were investigated. These plants are used singly and in combination in the traditional treatment of malaria in Nigeria. The dried leaves of plants were sequentially extracted with solvents of different polarities. We investigated the in vitro activities of selected extracts singly and when combined against the chloroquine sensitive and resistant strains of P. falciparum. Cytotoxic activities as well as the fractional inhibitory concentration of extracts were further evaluated. Most of the single extracts showed equipotent activity against both strains of the parasite. However, it was apparent that there were slight increases in parasite survival in the resistant strain as compared to the sensitive strain. Interestingly, when the extracts were investigated in combination, we observed that the potency of most of the extracts was enhanced. In this study, C. papaya extract was demonstrated to enhance the activities of component extracts in the combination. The dominant effect of C. papaya activity could be traceable to its high selectivity index for the sensitive and the resistant strain of the parasites. We envisage that the escalating challenge posed by parasite resistance, to existing antimalarials could be averted by combination treatments.

Key words: Citrus limon, Psidium guajava, Citrus papaya, Citrus citratus, Vernonia amygdalina, in vitro, antimalarial, combination.