Clinical and parasitological response of Plasmodium falciparum to chloroquine and sulfadoxine/pyrimethamine in rural Uganda.

Following the WHO protocol for in-vivo tests in areas with intense transmission of uncomplicated falciparum malaria, a randomized comparison of the invivo efficacy of chloroquine alone, sulfadoxine/pyrimethamine alone, and their combined administration was carried out in the third quarter of 2001 in Kaberamaido District, northeastern Uganda. Malaria in the study area is hyper-endemic, with a high prevalence of Plasmodium falciparum. The patients were infants and young children with a median age of 15 months. Of the 117 originally enrolled patients, 104 had a complete follow-up with presentation at all scheduled examinations. In the chloroquine group (n = 42), 55% were classified as adequate clinical response, 26% as early treatment failure, and 19% as late clinical failure. In the sulfadoxine/pyrimethamine group (n = 30), the respective figures were 83%, 13% and 3%, and in the group with combined treatment (n = 32), 88%, 6% and 6%. In terms of clinical cure rate, speed of clinical relief and parasite clearance the combined treatment proved to be the most effective of the three drug regimens. In the patients with adequate clinical response, a significant post-therapeutic increase of the haematocrit was observed, which was particularly marked in patients who had also cleared their parasitaemia. Increase of the efficacy of chloroquine with age indicates the early development of semi-immunity in the study area, with conserved efficacy of chloroquine in semi-immune persons.