Circulating filarial antigens for monitoring the efficacy of ivermectin in treatment of filariasis.

Seventy-three asymptomatic bancroftian filariasis patients with positive microfilaria in their blood films were included. The patients were randomly divided into 2 groups: ivermectin group (50 cases) given 2 doses each of 100 ug/kg body weight, 3 months apart, and 23 cases had 2 doses of placebo. The study was run blindly for one year. The initial mean microfilaria (MF) count was 111/ml. At 3 months after ivermectin therapy, mean MF became 7.8/ml and 24% of ivermectin treated cases had no detectable MF (P <0.05). At 6, 9 and 12 months, the mean MF count became 4.1, 6.5 and 11/ml with amicrofilaria in 54%, 42% and 40% of treated cases respectively (P <0.05). On the other hand, no statistically significant change in the mean MF count in placebo group was detected. The routine laboratory investigations were unchanged or slightly improved at 3 and 6 months. Side effects after the first dose of ivermectin were mild fever in 16% and weakness in 20%. None was recorded after the second dose. Circulating filarial antigens could be detected in 66% of cases before treatment, as all cases with high microfilaremia had positive antigenemia. The mean antigen level started to decline significantly after 9 months post treatment. At the end of the study (one-year), all negative microfilaremic cases had negative antigen levels, indicating that detection of antigen in-patients sera is a very good indicator of cure and efficacy of the drug.