Sensitivities of different stages of erythrocytic Plasmodium jalciparum to pyronaridine

FCC l/HN strain of Plasmodium falciparum sensitive to chloroquine was cultured and synchronous ring-forms were obtained with 5% mannitol. An infected blood suspension with 2.5% hematocrit and 0.5% ring-form parasites was divided into three parts to determine the sensitivity of the ring-forms, trophozoites and schizonts to pyronaridine separately. Each well on a 40-well plastic microculture plate was filled with 20μl drug solution and 180μl suspension of parasitized erythrocytes. The three synchronized erythrocytic stages of P. falciparum were exposed to pyronaridine or chloroquine for 8 h and then cultured in normal medium for 40 h. At the end of cultivation, the mean parasite rates and the parasite reduction rates were calculated. The ED50 for pyronaridine were 8.3 (95% confidence limits 8.1-8.4), 14.0 (13.4-14.7) and 11.6 (11.4-11.9) nmol/L at ring，trophozoite and schizont stages, respectively. The ED50 for chloroquine were 24.5 (95% CL 24.3- 24.8), 34.0 (32.4-35.6) and 64.9 (58.1- 72.4) nmol/L at ring, trophozoite and schizont stages, respectively. The results showed that the ring form parasite is most sensitive to both drugs. The efficacy of pyronaridine was greater than that of chloroquine.