A Comparison of 6-, 12-, and 24-Monthly Dosing with Ivermectin for Treatment of Onchocerciasis

This study was designed to examine the optimal dose and interval of administration of ivermectin, the now-accepted drug of choice for onchocerciasis. Two hundred Liberians with Onchocerca volvulus infection received 100, 150, or 200 micrograms/kg ivermectin or placebo and were followed for 36 months. The reaction after the second dose of ivermectin was significantly less than after the initial dose, although it was still significant in the 200-micrograms/kg group. The skin microfilaria counts in the group treated 6-monthly with 150 micrograms/kg was significantly less than in the group treated yearly (12 and 24 months after initial therapy). Prevalence of microfilariae in the anterior chamber and punctate corneal opacities decreased progressively in all groups over 3 years. There appears to be a slight advantage, in terms of antiparasitic effect over the first 2 years, of therapy given 6-monthly compared with yearly.