Studies on the activity of the Ciba Geigy compounds CGP 6140, 20376, 20309 and 21833 against third and fourth stage larvae of Onchocerca volvulus.

The effect of four new antifilarial compounds, (CGP 6140, 20376, 20309 and 21833, Ciba Geigy Ltd. Basle) on the viability of third and fourth stage larvae of Onchocerca volvulus was tested in vitro and in vivo. The motility of the larval stages and the moulting process from the third to the fourth stage were used as parameters for the drug activity in vitro. All four compounds showed good effects in vitro on the moulting rates compared to the controls after incubation at different concentrations in culture medium with serum. After an exposure for three hours to different concentrations of the compounds in medium without serum, only CGP 20376 had a clear inhibitory effect on the developing larvae. The moulting rate was reduced by this compound to 20% of the control values with 1 microgram/ml, a concentration that is comparable to plasma levels reported from chimpanzees. In both experimental situations, with serum and without serum, the motility of the developing larvae was only affected at very high concentrations of the compounds. The results obtained with fourth stage larvae were comparable. CGP 6140 and CGP 20376 were tested in vivo, using a diffusion chamber technique for the implantation of infective larvae into the peritoneum of Mastomys natalensis and assessing the survival of the implanted parasites. High doses of CGP 6140 had only unsatisfactory effects on the larvae in this model system whereas CGP 20376 had inhibited moulting and killed most larvae with a daily dose of 25 mg/kg for five consecutive days.