Comparison of effects of pyronaridine, amodiaquine, mefloquine and qinghaosu on rodent malaria.

Blood schizontocidal effect of antimalarials were compared by 4-day suppressive test with an extended observation period of 31 days. On a drug-sensitive Plasmodium berghei ANKA strain, pyronaridine (PND) exhibited the best effect, followed by amodiaquine (ADQ), mefloquine (MFQ), and qinghaosu (QHS). On a moderately chloroquine-resistant P. berghei NS line, the order of effects was the same, PND greater than ADQ greater than MFQ greater than QHS. On a highly pyronaridine-resistant P. berghei RP line, ADQ, MFQ and QHS showed cross resistance with PND.

[The blood schizontocidal effects of pyronaridine, amodiaquine, mefloquine and qinghaosu on mice infected with Plasmodium berghei].

The asexual stages of P. berghei ANKA were completely eliminated as revealed in a "4-day suppressive test" with the daily dose of pyronaridine 12.5 mg base/kg or amodiaquine 25 mg base/kg. Mefloquine 25 mg base/kg and qinghaosu 100 mg/kg though exerted obvious suppressive effect, the cure rates were only 50% and 0%, respectively. In treating chloroquine-sensitive P. berghei ANKA strain pyronaridine exhibited the best therapeutic activity, which was followed by amodiaquine, mefloquine and quinghaosu. In treating moderately chloroquine-resistant P. berghei NS line the cure rate of pyronaridine 12.5 mg/kg.d x 4 was 70%, but none of the 10 infected mice from any group was cured by amodiaquine 100 mg/kg.d, mefloquine 100 mg/kg.d or qinghaosu 200 mg/kg.d. Though the latter 3 drugs showed prominent suppressive effects, parasitemia remained positive or recrudesced after dosing. We demonstrate that parasites resistant to chloroquine had cross resistance to amodiaquine, mefloquine and inghaosu at various degrees. Amodiaquine 100 mg/kg.d, mefloquine 100 mg/kg.d and qinghaosu 200 mg/kg.d exhibited no obvious suppressive activity on highly pyronaridine-resistant line of P. berghei, indicating the existence of cross resistance to pyronaridine.

A 5-year surveillance of sensitivity in vivo of Plasmodium falciparum to pyronaridine/sulfadoxine/pyrimethamine in Diaoluo area, Hainan Province.

The surveillance of sensitivity of P. falciparum to pyronaridine/sulfadoxine/pyrimethamine has been carried out in Diaoluo area in Hainan Province where chloroquine-resistant falciparum malaria is endemic, covering an area of 406 square kilometers, with a population of 3745 in 1986. From 1986 all outpatients diagnosed as falciparum malaria were administered with PND/S/P as the only antimalarial. In vivo sensitivity of P. falciparum was measured in some patients who were treated in hospital. It was demonstrated that P. falciparum in the Diaoluo area has retained its sensitivity to a single oral dose of PND/S/P of 500/1,000/50 mg with 100% cure rate for at least 5 years.

Tissue schizontocidal effect of trifluoroacetyl primaquine in Plasmodium yoelii infected mice and Plasmodium cynomolgi infected monkeys.

Trifluoroacetyl primaquine oxalate (M8506) was compared with primaquine phosphate for tissue schizontocidal action in rodent and simian malaria. In Plasmodium yoelii sporozoites infected mice, the causal prophylactic effects of M8506 at 5, 10 and 20 mg(base)/kg were 56.7%, 87.2% and 100%, respectively, comparable to those of primaquine (54.4%, 90.8% and 100%). In P. cynomolgi sporozoites infected rhesus monkeys 4 dosage regimens of the two agents were compared for radical curative effect. On the first day of treatment pyronaridine phosphate 10 mg(base)/kg twice a day were intramuscularly injected to eliminate erythrocytic stages of P. cynomolgi. At the dosage of 3.0 mg(base)/kg/day x 3, both M8506 and primaquine radically cured the monkeys. At 0.75 mg/kg/day x 3, 12 of 13 (92.3%) monkeys cured by M8506, 5 of 9 (55.6%) cured by primaquine. At 1.5 and 0.375 mg/kg/day x 3, the radical curative effects of M8506 were also better than those of primaquine. Since the toxicity of M8506 was significantly milder in mice, rats and dogs than that of primaquine, M8506 has potential as a tissue schizontocide.

Experimental studies on combinations of pyronaridine/primaquine versus chloroquine/primaquine.

The toxicity of combined use of blood schizontocide pyronaridine (PND) and primaquine (PQ) in mice and rats was significantly lower than that of chloroquine (CQ) plus primaquine (PQ). PND 1/2 LD50 (ca 600 mg/kg) in combination with PQ reduced the toxic action of PQ in mice, while CQ 1/2 LD50 (ca 300 mg/kg) plus PQ produced synergistic toxic effect. In animal models such as Plasmodium yoelii sporozoite infection in mice and P. cynomolgi sporozoite infection in rhesus monkeys, the tissue schizontocidal action of PQ was not affected by PND. Therefore, clinical evaluation of PND/PQ in comparison with CQ/PQ in treating vivax malaria is suggested.

[Tissue schizontocidal action and acute toxicity of trifluoroacetyl primaquine].

Trifluoroacetyl primaquine (M-8506), 6-methoxy-5-trifluoroacetyl-8-(4-methyl-butyl-amino)-aminoquinoline oxalate, synthesized by the Institute of Parasitic Diseases was compared with primaquine for tissue schizontocidal action and acute ig LD50. In P yoelii sporozoite infected mice, the protection rates with ig M-8506 5, 10 and 20 mg (base)/kg on the day of infection were 56.7, 87.2 and 100%, respectively. These were comparable to the protection rates with primaquine 5, 10 and 20 mg(base)/kg (54.4, 90.8 and 100%, respectively). The radical curative effect was conducted in P cynomolgi sporozoite infected Macaca mulatta. Since im pyronaridine 10 mg/kg b.i.d. (6 h apart) completely eliminated the parasites in monkeys infected with erythrocytic stages of P cynomolgi, the tissue schizontocidal activities of M-8506 and primaquine were observed by im administration of pyronaridine 10 mg/kg b.i.d. on d 1. M-8506 at 0.75, 1.5 and 3 mg/(kg.d) x 3d plus pyronaridine were given to 7, 4 and 2 infected monkeys with parasitemia respectively. All the monkeys, except one receiving 0.75 mg/(kg.d) x 3 d, were radically cured. Primaquine 0.75, 1.5 and 3 mg/(kg.d) x 3 d were administered to 3, 3 and 2 monkeys respectively. Two monkeys receiving primaquine 0.75 mg/(kg.d) x 3 d relapsed on d 42. The parasitemia reappeared earlier than that treated with M-8506 0.75 mg/(kg.d) x 3 d and relapsed on d 62. Because M-8506 is less toxic than primaquine in mice and more effective in radical treatment of simian malaria, further studies on trifluoroacetyl primaquine are worthy to be considered.

[Combined action of pyronaridine and sulfadoxine/pyrimethamine against Plasmodium berghei ANKA strain in mice].

Pyronaridine, a highly effective antimalarial drug, was synthesized and developed by this institute. In order to test whether the joint blood schizontocidal action of pyronaridine (PND) and 2:1 mixture of sulfadoxine/pyrimethamine (SP) resulted in a potentiation or an additive effect, groups of P berghei ANKA strain-infected mice were treated with various single oral doses of PND and SP. Thin blood smears were made after 72 h and the parasitemia-negative rates were calculated. The ED50 values obtained were plotted in isobolograms. An additive action of this triple combination was demonstrated. Mice were inoculated with P berghei ANKA strain-infected erythrocytes 3 and 2 d after the mice were given a single oral dose of PND 10 mg/kg alone, or combined with SP 3 mg/kg. Thin blood smears made on d 3, 5, 8 and 10 revealed that the parasitemia-positive rates and the duration of residual blood schizontocidal action of PND used alone was similar to that of PND used in combination (P greater than 0.05). Three groups of mice carrying P berghei ANKA strain gametocytes were administered orally with pyrimethamine 0.1 mg/kg, SP 0.3 mg/kg and SP 0.3 mg/kg plus PND 0.5 mg/kg, respectively. Anopheles stephensi were then fed on the mice 2 h after the medication. There resulted no significant differences of gametocytocidal and sporontocidal effects among the 3 groups, since the oocyst-positive rate and the glandpositive rate were similar in these groups.

Antimalarial and toxic effect of triple combination of pyronaridine, sulfadoxine and pyrimethamine.

The triple combination of pyronaridine, sulfadoxine and pyrimethamine which has been proven to be efficient in delaying emergence of drug resistance of rodent malarial parasites was further studied for potential application to malaria control. The antimalarial effect of the triple combination on Plasmodium berghei ANKA-infected mice and the toxic effects in mice and rats were additive. A single dose of pyronaridine 500 mg in combination with sulfadoxine, 1000 or 1500 mg, and pyrimethamine, 50 or 75 mg, given to 72 acute falciparum malaria patients resulted in a 100% cure rate with nil or mild side effects, and no recrudescence of asexual parasite over 4-week follow-up. Preliminary experiments on the drug effect on sporogony showed that the drug combination at the dose used could not completely interrupt the sporozoite formation although many retarded oocysts were found.