Ivermectin: concentration-dependent effects on adenosine triphosphatases in adult worms of Onchocerca volvulus

The effect of increasing concentrations of ivermectin on adenosine triphosphatase (ATPase) activity was investigated in adult worms of Onchocerca volvulus. Mean Mg- and Na,K-ATPase activities decreased significantly (F ratio=29.82, P<0.01 and F ratio=28.54, P<0.01, respectively) with increasing concentrations of ivermectin (0–100 ng/ml) in the female worms. When male and female worms were mixed with equal amounts of proteins from each, only the Na,K-ATPase activity was significantly decreased (F ratio=56.61, P<0.01) over a similar range of ivermectin concentrations. Since ivermectin exhibits concentration-dependent effects on both ATPases in female adult worms, this might provide an insight into other effects of the drug. However, the adjustment of the dose of ivermectin to obtain a nodular concentration of at least 40 ng/ml is therefore recommended in the complete chemotherapy of onchocerciasis.