The entry of ivermectin and suramin into Onchocerca ochengi nodules.

No currently available drug, which is safe for mass treatment, effectively kills adults of Onchocerca volvulus, the causal agent of onchocerciasis in humans, or of O. ochengi, a cattle parasite used as a model of O. volvulus. Since adults of both of these filarial nematodes are found in well developed nodules, the lack of efficacy of these drugs may be a result of their poor penetration into the nodules. To check if this was the problem, the distributions of the microfilaricide, ivermectin, and the partial macrofilaricide, suramin, in plasma, skin, nodule capsules and nodule contents were determined in cattle naturally infected with O. ochengi in Cameroon. The cattle were treated with either a single, subcutaneous injection of 500 µg ivermectin/kg, or with intravenous injections of [14C]-labelled suramin, each of 10 mg/kg, given one a day for 6 days. Concentrations of ivermectin and suramin in various tissues were then assayed by high-pressure liquid chromatography and scintillation counting, respectively...