How antimalarial drug resistance affects post-treatment prophylaxis

In areas of intense malaria transmission reinfection following antimalarial treatment is inevitable. Antimalarial drug treatments with slowly eliminated drugs provide a variable period, after they have cleared the initial infection, during which subsequent reinfection is suppressed by residual levels of the antimalarial drug. This effect is called post-treatment prophylaxis or PTP [1,2]. PTP can range in duration from months, with very slowly eliminated compounds such as piperaquine and chloroquine, to none at all with rapidly eliminated drugs such as the artemisinin derivatives. PTP should provide additional benefit, above that conferred by effective cure of a symptomatic infection, by allowing a longer disease-free interval for clinical and haematological recovery. The benefits of preventing reinfection depend on the transmission intensity and thus the frequency of infection. It has been argued that preventing reinfection is as important as preventing recrudescence, although this remains to be proved, both at an individual and population level. The two are obviously linked as both are measures of antimalarial efficacy. This individual benefit of longer PTP is balanced against a potential societal harm; the increased propensity of slowly eliminated antimalarials to select for resistance [3-5]. PTP is an important component of intermittent preventive treatment, (also sometimes referred to as intermittent presumptive treatment) in pregnancy (IPTp) and is probably the most important effect of intermittent preventive treatment in infancy (IPTi), and in other high risk sub-groups [1,6,7]. The dose and the pharmacokinetic properties of the drug affect the duration of PTP. For the prevalent malaria parasites, antimalarial drug resistance reduces the duration of PTP.In practice, PTP is measured as the time from drug administration (either treatment of the first, usually symptomatic, infection or administration of IPT to an asymptomatic person) until the next infection is d