Key Points After being killed by artesunate, malaria parasites are expelled from red cells and then these pitted red cells reenter the circulation. When many pitted red cells are produced during therapy, their delayed clearance a few weeks later triggers hemolytic episodes.

Antimalarial immunity correlates with fast artemisinin-induced parasite clearance and low pitting rates. In nonimmune populations, artemisinin-induced P. falciparum clearance is related to pitting and starts after a 6-hour lag phase. In immune populations, passively and naturally acquired immune mechanisms operating faster than pitting may exist. This mechanism may mitigate the emergence of artemisinin-resistant P. falciparum in Africa.