FIG. 3.

Effect of adding increasing amounts of NP30 on degree of chloroquine resistance of P. falciparum. The degree of chloroquine resistance in isolate 2 is calculated as the IC₅₀ observed in the presence of various concentrations of NP30 divided by the control (no NPE added) chloroquine IC₅₀ (274 ± 56 nM). Values greater than 1 indicate that the NPE rendered the P. falciparum parasites less sensitive to chloroquine, while values less than 1 indicate that the NPE sensitized P. falciparum to chloroquine. Nonlinear analysis of the data points indicates that an NP30 concentration of approximately 1 μM (0.0002% on a weight/volume basis) results in a 50% decrease in the degree of chloroquine resistance of the parasites.