Therapeutic responses to different antimalarial drugs in vivax malaria

The therapeutic responses to the eight most widely used antimalarial drugs were assessed in 207 adult patients with Plasmodium vivax malaria. This par asite does not cause marked sequestration, so parasite clearance can be use d as a direct measure of antimalarial activity. The activities of these dru gs in descending order were artesunate, artemether, chloroquine, mefloquine , quinine, halofantrine, primaquine, and pyrimethamine-sulfadoxine (PS), Th erapeutic responses to PS were poor; parasitemias did not clear in 5 of the It PS-treated patients, whereas all the other patients made an initial rec overy. Of 166 patients monitored for greater than or equal to 28 days, 35% had reappearance of vivax malaria II to 65 days later and 7% developed falc iparum malaria 5 to 21 days after the start of treatment, There were no sig nificant differences in the times taken for vivax malaria reappearance amon g the different groups except for those given mefloquine and chloroquine, i n which all vivax malaria reappearances developed >28 days after treatment, suggesting suppression of the first relapse by these slowly eliminated dru gs. There was no evidence of chloroquine resistance. The antimalarial drugs vary considerably in their intrinsic activities and stage specificities of action.