Figure 4

Synergistic antimalarial activity of GA and CQ. Erythrocytic P. falciparum 3D7 cultures at about 5% parasitemia were treated with combinatorial concentrations of GA and CQ, and the incorporation of ³H-hypoxanthine was measured as described in Material and Methods. The concentration of each drug was expressed as fraction of its IC₅₀ when used alone, and an isobologram was plotted essentially as described [37]. In such plots, a concave graph reflects synergism, a straight line reflects additive effect, and a convex graph reflects antagonism between two drugs [37]. A hypothetical straight line (broken) is drawn here for comparison, whereas the experimental graph, which is concave, reveals synergism between GA and CQ.