A community trial of ivermectin for onchocerciasis in Sierra Leone: adverse reactions after the first five treatment rounds

Abstract

We have studied the adverse reactions reported after ivermectin in 1745 villagers in southern Sierra Leone, allocated at random to receive ivermectin or placebo and treated 'double-blind' with 4 doses at six-monthly intervals. Six months after the fourth dose all eligible villagers received ivermectin regardless of their previous treatment. At the first treatment round more adverse reactions were reported by villagers treated with ivermectin than by those who received placebo. Reactions occurred most often on the second day after treatment. There were significant correlations between an individual's skin microfilarial load and the risk of developing adverse reactions. On re-treatment there was no significant excess of reported adverse reactions in the ivermectin group compared to the placebo group. Unlike other adverse reactions, the risk of cutaneous reactions after the first dose of ivermectin was not correlated with skin microfilarial load. In addition, after re-treatment with ivermectin, cutaneous reactions were reported significantly more often than with placebo. We confirm that ivermectin is safe for mass distribution, but adverse reactions should be monitored and treated after the first dose. Throughout this study ivermectin was well tolerated, with significantly more villagers returning for re-treatment after ivermectin than placebo, and all adverse reactions were self-limiting or successfully managed with symptomatic treatment. We question whether strict clinical monitoring should be routine at re-treatment, when only cutaneous reactions were consistently reported. If clinical monitoring could be used more selectively, distribution campaigns might be easier to manage and more cost-effective.