Ivermectin has been shown in an open, in-hospital trial in South India to be effective in clearing microfilaremia in patients with bancroftian filariasis at dosages as low as 25-mcg/kg given once orally. A second, blinded, placebo-controlled trial of ivermectin and the currently used drug, diethylcarbamazine (DEC), has indicated that the efficacy of ivermectin and DEC were equivalent for 3 months, but by 6 months the ~30% microfilarial recurrence rate of the ivermectin-treated patients was significantly greater than the ~15% rate of the DEC group. Side effects were qualitatively and quantitatively identical for both groups. Thus, though ivermectin appeared somewhat less effective than DEC at 6 months, its single-oral-dose mode of administration with toxicity no greater than that of DEC means that this drug should engender greater patient compliance and, therefore, be much more effective in mass-treatment filariasis control programs than DEC. Observations on 200 Peace Corps volunteers going to Loa loa endemic areas of Africa have concluded after three years of a placebo- controlled chemoprophylaxis trial using weekly doses of DEC. In Gabon (where exposure to the parasite was heaviest) 30% of individuals in the placebo group developed overt clinical disease compared to none in the DEC-treated group (p<.02) and 50% became seropositive in the placebo group vs 13% in the DEC group (p<.02). No significant side effects were seen. These findings indicate that DEC given orally once-weekly can be an effective, acceptable chemoprophylactic for preventing loiasis.
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