Susceptibility of Plasmodium falciparum to pyrimethamine and sulfadoxine/pyrimethamine in Kisumu, Kenya.

Field studies were conducted in Kisumu, Kenya, to assess the susceptibility of local strains of Plasmodium falciparum to pyrimethamine alone (by a standard 7-day in-vivo test and a 48 h in-vitro field test) and to sulfadoxine-pyrimethamine (by a 7-day in-vivo test). Both in-vivo (10/11) and in-vitro (19/21) tests demonstrated that pyrimethamine resistance was very common. Parasite susceptibility to sulfadoxine-pyrimethamine was uniformly greater when 24 isolates were tested in vivo, thus indicating that this drug combination remains valuable despite the high frequency of resistance to pyrimethamine alone.