Adverse reactions after large-scale treatment of onchocerciasis with ivermectin: combined results from eight community trials

Eight community trials were carried out by the Onchocerciasis Control Programme in West Africa to determine the safety of the new microfilaricide ivermectin during large-scale treatment of onchocerciasis. The trial areas were located in eight different countries and varied greatly in endemicity level; a total of 50,929 persons were treated and monitored for 72 hours. Overall treatment coverage was 60% of the census population, the main reasons for non-treatment being the exclusion criteria. Of those treated, 9% reported with adverse reactions, 2.4% with moderate reactions, and 0.24% with severe reactions. Most reactions were reported during the first day of follow-up, the most frequent severe reaction being severe symptomatic postural hypotension (in 49 cases). Three cases of severe dyspnoea were life-threatening but their relationship with ivermectin treatment is uncertain. The incidence of adverse reactions was directly related to skin microfilarial load and was highest in the foci with the highest endemicity levels. Treatment resulted in 98% reductions in mean microfilarial loads at all endemicity levels. The benefit of treatment largely compensated for the discomfort due to adverse reactions, which were all transient and managed successfully. Ivermectin thus appears to be sufficiently safe for large-scale treatment but monitoring by resident nurses for at least 36 hours is recommended.