Chemotherapy of malaria and resistance to antimalarial drugs in Guayana area, Venezuela.

Resistance to antimalarial chemotherapy is one of the greatest difficulties for the control of malaria transmission. Seventy patients with Plasmodium falciparum malaria were included in a study of resistance to chloroquine and sulfadoxine-pyrimethamine therapy. Resistance levels RI, RII, and RIII were established. Eighteen infections (51%) cleared after chloroquine treatment and did not recur within 28 days of follow-up; these were classified as sensitive. Ten infections (29%) were resistant at the RI level. Resistance at level RII was observed in 5 (14%) cases, and RIII resistance was demonstrated in 2 infections (6%). With sulfadoxine-pyrimethamine, 28 (80%) infections were classified as sensitive. Six infections (17%) showed resistance at level RII, and 1 (3%) infection was resistant at the RI level. Resistance at level RIII was not observed. In a microtest for chloroquine and sulfadoxine-pyrimethamine sensitivity in vitro, schizont development was accomplished successfully in 70 blood samples. In vitro resistance to chloroquine was demonstrated in 15 of 70 (21%) of all isolates. Eight of 70 (11%) of all isolates showed resistance to sulfadoxine-pyrimethamine. Diversity of response of P. falciparum to the studied antimalarial drugs in the Guayana area of Venezuela is considered a problem restricting the control of malaria in this geographical area. A constant evaluation program monitoring P. falciparum drug sensitivity is necessary for preserving the efficacy of the established treatment.