Abstract: Using highly synchronous cultures of Plasmodium falciparum in vitro, the susceptibility of the different stages of the intraerythrocytic parasites to Qinghaosu (QHS) was assessed. The anti-parasitic effect of QHS was measured by comparing the changes of irradiation of 3 H-hypoxanthine incorporated into the nucleic acids of parasites exposed to various concentrations of QHS at different stages of growth. It was found that the trophozoite stage of the parasite was the most sensitive to QHS, whereas the early ring stage was the least sensitive, and the sensitivities of the late ring and schizont stages fell between those of the early ring and trophozoite stages. The results revealed the correlation of stage-dependent effects of QHS with the blockade of the protein metabolism of the parasite.

Key words: Qinghaosu (artemisinin), Antimalarial drug, Plasmodium falciparum, Malaria