RESUMO
Background: drug resistant malaria is spreading inexorably to areas with drug sensitive malaria parasites. This study compared the in vitro sensitivities of Plasmodium falciparum fresh parasite isolates; to some standard antimalarial drugs; in Makurdi and Masaka located over 300 km apart; in north central Nigeria. Methods: The in vitro responses of P. falciparum isolates; 43 and 39 in Makurdi and Masaka were evaluated by the standard schizonts growth inhibition assay in children aged 2-14 years. Results: The geometric mean effective concentration-EC50; EC90 and EC99 of quinine between Makurdi and Masaka differed significantly (P 0.05). A similar difference (P 0.05); was observed with the artesunate antimalarial at EC90 and EC99 levels; but not at EC50. No significant difference (P 0.05) was observed in the EC values of amodiaquine between the two locations. 5.13(2/39) of parasites at Masaka were in vitro resistant to amodiaquine with EC50 80 nM. The rest of the isolates were sensitive to the three antimalarial drugs at both locations. Conclusion: The results demonstrated low in vitro resistance of P. falciparum to amodiaquine in the region. Constant monitoring and intervention is needed to curtail the spread of resistance to antimalarials in Nigeria