Drug Resistance in Plasmodium Falciparum from Thailand

SummaryA strain (JHK) of Plasmodium falciparum, apparently originating in Thailand, has been studied in seven patients for its response to various drugs.The parasites showed a poor or no response to the usual therapeutic doses of the following drugs: chloroquine, amopyroquine, pyrimethamine, proguanil, and a new hydroxynaphthalene derivative. The parasites responded rapidly to mepacrine but relapsed. Weekly suppressive doses of chloroquine failed to prevent the mosquito transmission to and the occurrence of the infections in the recipients. Pyrimethamine failed to exert sporontocidal effect. Pyrimethamine combined with either chloroquine or amodiaquine demonstrated no advantage over these drugs singly.The infections were cured by regimens of 8 g or more of quinine and appeared to be very sensitive to even small amounts of this drug.