Ivermectin and albendazole are broad‐spectrum anthelmintics that have been shown to decrease the prevalence and intensity of intestinal helminth infections in the setting of mass distribution programs for lymphatic filariasis, providing additional benefit to treated communities. In contrast, the effect of standard‐dose annual ivermectin and albendazole on M. perstans infection has been unimpressive. In the present study, median M. perstans microfilarial levels were unchanged from baseline in the standard annual dose group but decreased significantly in the high‐dose, twice‐yearly group at 12 and 18 months. Both groups demonstrated a significant decrease in median M. perstans microfilarial levels at 24 months, although the change was less remarkable in the standard‐dose annual therapy group. Clearance of M. perstans microfilariae was observed at 24 months in only 1 of 16 M. perstans–positive patients in the standard‐dose annual therapy group, compared with 4 of 17 in the high‐dose, twice‐yearly therapy group (P values were nonsignificant by Fisher’s exact test).
The major limitation of the present study was the lack of sufficient patients to enroll in the study groups receiving increased‐dose annual treatment or standard‐dose, twice‐yearly treatment, precluding independent analysis of the effects of dosage and frequency of dosing on reduction of microfilaremia. This distinction is particularly important from an economic standpoint, because albendazole and ivermectin are donated by Merck and GlaxoSmithKline, respectively, whereas the cost of drug distribution is borne by the lymphatic filariasis elimination programs themselves. Although the similarity between the microfilarial levels in the standard‐dose annual therapy group and the high‐dose, twice‐yearly therapy group at 6 months suggests that frequency of treatment may be the more important factor, additional studies are needed to resolve this question.
In summary, increased‐dose, twice‐yearly therapy with albendazole and ivermectin was more effective in reducing W. bancrofti microfilarial levels than was standard‐dose annual therapy in a region of high endemicity in Mali, West Africa, suggesting that more frequent and/or higher‐dose therapy might accelerate the interruption of transmission. Such a strategy could be particularly useful in regions where implementation of the control program has been delayed by economic or political factors. Additional studies are clearly necessary to confirm the findings in areas of differing endemicity and to determine the relative contributions of increased dosage and increased frequency to the observed effect.