Host failure in treatment of malaria with sulfalene and pyrimethamine.

An individual infected with a multidrug-resistant strain of Plasmodium falciparum failed to respond to treatment with sulfalene and pyrimethamine. Subinoculation studies showed that parasite resistance to the drug combination was not present. Plasma levels of sulfalene and pyrimethamine in this individual were similar to those of three individuals, subinoculated from him, who were cured by the drug combination. Erythrocyte levels of sulfalene in this individual were similar to those in an individual, subinoculated from him, who was cured by the drug combination. After treatment with the drug combination, in vitro tests showed similar antimalarial activity in the serum of this individual in comparison with the serum of this individual in comparison with the serum of an individual subinoculated from him. The failure of this individual to respond to treatment with sulfalene and pyrimethamine is attributed to an undefined host factor (or factors) that appear(s) to be present in his erythrocytes.