Plasmodium falciparum-malaria: resistance to chloroquine, but sensitivity to mefloquine in the Gabon. A prospective in-vitro study.

A determination of the sensitivity to chloroquine and to mefloquine was carried out in malaria patients of the Albert Schweitzer Hospital, Lambarene, Gabon, by using the schizont maturation test. The chloroquine testing showed in 6 of 31 cases a schizont maturation at 1.14 pmol/microliter of blood and more; this means an in-vitro resistance in 19% of the cases. The evaluation of the effective concentrations (i.e. concentrations producing the appropriate inhibition of schizont maturation) with the probit analysis yielded for chloroquine an EC50 of 0.2537 X 10(-6) mol/l of blood and an EC90 of 0.8317 X 10(-6) mol/l of blood. In the testing of mefloquine, schizont maturation was found in 3 of 31 cases in concentrations of 1.6 pmol/microliter of blood, the probit analysis, however, showed effective doses in the normal range with an EC50 of 0.2192 X 10(-6) mol/l of blood and an EC90 of 0.7863 X 10(-6) mol/l of blood. These results demonstrate the alarming observation of Plasmodium falciparum strains resistant in-vitro to chloroquine in a region where in vivo resistance has not been observed hitherto.