Randomized, controlled, double-blind trial with ivermectin on Loa loa microfilaraemia: efficacy of a low dose (∼25 μg/kg) versus current standard dose (150 μg/kg)

Neurological serious adverse events (SAEs) following ivermectin treatment may occur in individuals harbouring high Loa loa microfilarial densities and are of major concern in the context of mass ivermectin distributions organized in Africa for onchocerciasis and lymphatic filariasis control. As those SAEs are induced by the rapid and massive microfilaricidal effect of a standard dose of ivermectin (150 μg/kg), we performed a randomized, controlled, double-blind trial to determine whether ivermectin given as: (a) a single low dose of 1.5 mg (i.e. 25 μg/kg for a 60 kg person); or (b) two doses of 1.5 mg given at a 2 week interval leads to a more progressive decrease in Loa microfilarial loads compared with the standard dosage. A low dose of ivermectin brought about a significantly smaller decrease in Loa microfilaraemia than the standard dose. However, this decrease was not sufficiently different from that obtained after the standard dose to be acceptable to public health programmes, which require a wide safety margin. A second low dose of ivermectin given 15 days after the first dose did not lead to a further decrease in Loa microfilaraemia. Lastly, the variability in the response observed in the group treated with 25 μg/kg suggests that even lower doses would have no effect on a significant number of patients. Ivermectin given at a low dose (≤25 μg/kg) is probably not adequate to prevent the occurrence of post-treatment neurological SAEs.