Action of nitroquine on tissue schizonts of Plasmodium cynomolgi

Sporozoites of P. cynomolgi (Cambodian strain) were injected iv or ip into 29 monkeys. Four monkeys were treated with nitroquine acetate 2 mg/kg/d on d 4-11; 4 monkeys were untreated. Liver biopsies were performed on d 7 and d 9. Tissue schizonts were found in only 1 treated monkey, and the number of parasites was much less than that of the controls. The appearances of the tissue schizonts were characterized by the smaller size, lighter stained, and irregular size of nuclei. Thirteen monkeys were treated with nitroquine-DDS 5 mg/kg/d for 5 d or 8 d when parasitemia appeared, and 8 monkeys were treated with cholroquine base 20 mg/kg/d for 3 d as control. Parasitemia of all the 21 monkeys disappeared after the treatment. However, 5/8 relapsed 1 month later in chloroquine group and 5/13 relapsed in 1.5-2 months in nitroquine groups. The results suggest that the development of the tissue schizont can be suppressed by nitroquine on the nuclear division.