Objective: To study the antimalarial activity of naphthoquine phosphate combined with artemisinine against Plasmodium knowlesi in rhesus monkey.
Methods: Monkeys were randomly divided into 9 groups (3/group). The monkeys in groups A and B were treated i.g. once daily for 3 days with 6 or 10 mg/kg of naphthoquine phosphate respectively. Those in groups C and D were treated i.g. twice for the 1st day and once for the 2nd and 3rd day with 31.6 or 100 mg/kg of artemisinine respectively. In groups E, F and G, they were treated i.g. only once with the combination of naphthoquine phosphate 10 mg/kg and artemisinine 10, 20 or 25 mg/kg respectively. Groups H and I served as controls which were treated i.g. only once with 10 mg/kg of naphthoquine phosphate and 30 mg/kg of artemisinine respectively. Parasitemia was examined beginning 24 h after drug administration. The observation lasted 105 days when no more parasite was found.
Results: At 24 h after drug administration, the parasite reduction rate in all groups was higher than 90%. The parasite clearance time for groups E, F and G was (56.0 +/- 16.0), (53.3 +/- 4.6), and (56.0 +/- 8.0) h respectively, more rapid than that of Group H [(69.3 +/- 4.6) h]. There were 1, 3, 3, 2, 2, and 3 monkeys in groups A, B, D, E, F, and G respectively which were cured. No monkeys were cured in groups C, H and I.
Conclusion: The combination of naphthoquine phosphate and artemisinine is superior to the single component and the optimum proportion in the combination is 1 : 2.5 in treating P. knowlesi infection in monkeys.