Concentration of anti-malarial drug in bloodstream during IPT. Drug concentration initially rises after administration of a therapeutic drug regimen. The concentration declines gradually as the drug is cleared from the bloodstream. Parasites with increasing sensitivity to the drug will be able to grow as the drug concentration declines. Parasites are divided roughly into three categories; fully sensitive, partially resistant and fully resistant. The interval between the time at which the concentration falls below the threshold for partially sensitive parasites and the time at which it falls below the threshold for sensitive parasites is a window of selection for resistant parasites. The dotted curve represents the target blood concentrations during chemoprophylaxis.