[Variability of in vitro activity of proguanil and cycloguanil on erythrocyte stages of Plasmodium falciparum as a function of culture conditions].

The in vitro activity of proguanil, cycloguanil (active metabolite of proguanil), pyrimethamine, and chloroquine was determined for 14 isolates of Plasmodium falciparum and the chloroquine-resistant W2 clone. In vitro assays were performed by using different types of RPMI 1640 culture medium and incubation period. The use of the standard RPMI medium or RPMI medium containing low concentrations of folate and para-aminobenzoic acid increases the 50% inhibitory concentrations of cycloguanil and pyrimethamine, as compared with the use of folate- and para-aminobenzoic acid-free RPMI medium. The concentrations of folate and para-aminobenzoic acid did not affect the in vitro activity of proguanil and chloroquine. However, prolongation of the incubation period from 42 to 66 hours decreased the 50% inhibitory concentrations of all test compounds. The weak antagonism in vitro between chloroquine and proguanil or cycloguanil does not seem to have any repercussion on the in vivo efficacy of chloroquine-proguanil combination.