Ivermectin 400 μg/kg: long-term suppression of microfilariae in Bancroftian filariasis

Abstract Forty-three Wuchereria bancrofti carriers were given 4 successive semi-annual single doses of ivermectin 100 μg/kg ( iver 100). The geometric mean microfilaremia (mf) recurrence percentages, compared to the pre-initial treatment mf level, were 35%, 21%, 17% and 17% at 6, 12, 18 and 24 months respectively. However, the recurrence of mf 6 months after the fourth treatment remained high in 15 individuals, considered as ‘bad responders’. At month 24, the subjects were randomly allocated into 2 groups: the first group was treated with a fifth dose of iver 100 and the second with a first, single dose of 400 μg/kg of ivermectin ( iver 400). At month 30, the mf recurrence percentage was significantly higher in patients treated with iver 100 than in those receiving iver 400 (61% vs. 8%, P iver 100 group, 6 of the 8 ‘bad responders’ remained ‘bad responders’, whereas only 2 of 7 did so in the iver 400 group. Only 3 additional patients in the iver 100 group became consistently amicrofilaraemic, whereas 9 did so in the iver 400 group. Two ‘good responders’ in the iver 100 group became ‘bad responders’. A single dose of 400 μg/kg of ivermectin has been demonstrated to be efficient for the treatment of carriers refractory to repeated doses of 100 μg/kg and to result in better long-term mf suppression. These results suggest a possible effect of 400 μg/kg of ivermectin on macrofilaria.