Chemosuppressive Field Trials in Thailand

Abstract

A chemosuppressive field trial in an area of Thailand with known chloroquineresistant falciparum malaria was undertaken to test the efficacy of the preparation sulfadoxine (S)-pyrimethamine (Py) in suppressing falciparum and vivax parasitemias. Seven hundred and forty-seven Thai villagers were randomly assigned to one of five study groups: sulfadoxine (1,000 mg)-pyrimethamine (50 mg) every 2 weeks [S-Py (high dose)]; sulfadoxine (500 mg)-pyrimethamine (25 mg) every 2 weeks [S-Py (low dose)]; diformyldapsone (400 mg)-pyrimethamine (25 mg) weekly [DFD-Py (high dose)]; diformyldapsone (200 mg)-pyrimethamine (12.5 mg) weekly [DFD-Py (low dose)]; and placebo. Six hundred and eight-eight study subjects (92%) completed the 26-week trial. Sulfadoxine (1,000 mg)-pyrimethamine (50 mg) given every 2 weeks was shown to be an effective chemosuppressive against both falciparum and vivax parasitemias, causing an eight-fold reduction in falciparum parasitemias, and an approximately three-fold reduction in vivax parasitemias. While the low dose S-Py group and the two DFD-Py groups were less effective than the high dose S-Py group in suppressing falciparum parasitemias, the high dose DFD-Py combination was as effective as the high dose S-Py combination in suppressing vivax parasitemias. There was no evidence of drug reactions. A discernible decrease in the leukocyte count was noted over a 6-month period in the high dose S-Py group.