Background: At present, control of onchocerciasis depends almost entirely on yearly treatments with 150 microg/kg ivermectin. We aimed to compare the effect of higher doses, more frequent doses, or both with the standard regimen on adult Onchocerca volvulus.
Methods: We randomly allocated 657 patients who had onchocerciasis to 150 microg/kg ivermectin yearly (reference group), 150 microg/kg every 3 months, 400 then 800 microg/kg yearly, or 400 then 800 microg/kg every 3 months. We took skin snip samples from every patient before, and 3 years and 4 years after the first dose, and, at the same time excised one subcutaneous O volvulus nodule, which was examined histologically. The primary outcome was the vital status of the female worms. Analysis was done per protocol.
Findings: We obtained nodules from 511 patients. After 3 years of treatment, more female worms had died in the groups treated every 3 months than in the reference group (odds ratio=1.84 [95% CI 1.23-2.75], p=0.003 for 150 microg/kg; and 2.17 [1.42-3.31], p<0.001 for high doses). Female worms were also less fertile in these groups than in the reference group (0.24 [0.14-0.43], p<0.0001; and 0.14 [0.06-0.29], p<0.0001, respectively). No difference was recorded between groups treated yearly (p=0.83 for the proportion of dead females). Unexpected side-effects consisted of mild, temporary, subjective visual changes in patients on high-dose regimens.
Interpretation: Treatment with 3-monthly ivermectin could greatly reduce the number of female worms and acute itching and skin lesions; lower transmission of O volvulus; and change the duration of control programmes.