Isobole analysis of mitochondrial inhibitors on antimalarial activity. The fractional inhibitory concentrations of IC50 values for drugs in combination are shown for atovaquone versus proguanil (A), atovaquone versus DPI (B), atovaquone versus IDP (C), atovaquone versus rotenone (D), DPI versus pyridone (E), and DPI versus proguanil (F). Data are means of results from four independent experiments.