Comparative assessment of Plasmodium falciparum sensitivity to chloroquine and amodiaquine in vitro

Abstract

The in vitro sensitivity of Plasmodium falciparum isolates to chloroquine and amodiaquine were assessed in children with symptomatic uncomplicated malaria in Ibadan, Nigeria. The WHO standard in vitro micro-test method was employed for the study. A total of one hundred and two children were admitted into the study. Inhibition of schizont maturation at varying concentration of the study drugs was used as an index for drug activity. Effective concentrations by probit analysis of log dose/response for 50, 90 and 99% (EC50, EC90and EC99) inhibition were 0.37, 2.38 and 5.76 mol/l, respectively, for chloroquine and 0.06, 0.26 and 0.59 mol/l, respectively, for amodiaquine. Forty isolates of P. falciparum were tested for chloroquine sensitivity. Eighty percent (32/40) showed schizont maturation at 1.6 mol/l and were classified as resistant, while 39% (14/36) of isolates tested for amodiaquine matured at 0.4 mol/l and were also classified as resistant. This shows that amodiaquine is significantly more effective than chloroquine. While this data provides no absolute demonstration of chloroquine resistance, it underlies the need for continuous monitoring of the susceptibility of P. falciparum to chloroquine in southwest Nigeria.