ABSTRACT
Malaria is one of the worldwide parasitic diseases which threaten the life of hundreds of millions of people at the malarious areas each year. The emergence of chloroquine-resistant strains of Plasmodium falciparum in most of the malarious areas has encountered the relevant countries with some difficulties about treating the acute cases of the disease particulary if the monotherapy regimen has been used. Because of many advantages for the combination therapy, the effectiveness of chloroquine [CQ] and Otostegia persica [OP], a medicinal plant in combination form, was tested against the chloroquine-sensitive and chloroquine-resistant strains of Plasmodium berghei in sourian mouse using in-vivo adapted fixed ratios method in this study. At the first step, ED[50]s [50% effective dose] of chloroquine and O. persica against both CQ-sensitive and CQ-resistant strains of P. berghei were calculated using in-vivo test in the mice. Ratios of 0, 10, 30, 50, 70, 90 and100% from each ED[50] were prepared and contrarily combined together to make the following fixed ratios of 0/100, 10/90, 30/70, 50/50, 70/30, 90/10, and 100/0 of CQ/OP and the parasites were exposed to the combined ratios. Determination of ED[50]s showed 1.1 mg/Kg and 2.4 mg/Kg of mouse body weight for chloroquine in CQ-sensitive and CQ-resistant strains respectively and 450 mg/Kg for O. persica in both strains. The results also showed that the combinations of "50% CQ + 50% OP", "30% CQ + 70% O.P" and "70% CQ + 30% OP" were more effective than other combinations against CQ-sensitive strain. The fixed ratio combinations of chloroquine and O. persica showed an additive in CQ-resistant strain. Toxicity consideration showed no toxic effect of the combinations on the mice. Otostegia persica potentiated the effectiveness of chloroquine against the chloroquine-sensitive strain of P. berghei but not on chloroquine-resistant P. berghei. Moreover, the greatly modified fixed ratios method in this study can be considered as useful methods for in-vivo combination tests in murine malaria parasites