A comparison of the pyrimethamine and cycloguanil sensitivities of the pre-erythrocytic and erythrocytic stages of drug-sensitive and -resistant strains of Plasmodium yoelii.

The cycloguanil and pyrimethamine sensitivities of the pre-erythrocytic and erythrocytic stages of a drug-sensitive and drug-resistant strain of Plasmodium yoelii have been compared. With both compounds, and in both parasite strains, the pre-erythrocytic stages were more sensitive to inhibition than were the erythrocytic stages. In the resistant strain the increase in the level of drug tolerance in the erythrocytic stages was paralleled by a corresponding loss of sensitivity in the pre-erythrocytic stages.