Preliminary studies indicated that single-dose (500 mg)
mebendazole gave disappointing results in the treatment of
hookworm infections (Necator americanus) in Mali. A placebo-controlled, randomized trial conducted with the participation of 103 infected subjects (background hookworm prevalence > 50%) confirmed that
mebendazole (
Vermox) did not reduce parasite burdens significantly, as assessed through fecal egg counts. In contrast, a group of subjects treated with
pyrantel (
Combantrin) experienced a significant reduction in fecal worm egg counts (overall, both sexes combined showed a 75% reduction). Male subjects carried significantly more intense
infections compared with females, but there was no gender difference in response to treatment. A standard egg hatch assay showed that N. americanus from our subjects in Mali was more resistant to
benzimidazoles compared with a laboratory-maintained strain that had not been exposed to
anthelmintics in more than 100 generations (50% effective dose = 0.12 and 0.07 microg/ml of
thiabendazole, respectively), suggesting that, among other possibilities, the development of resistance to the
benzimidazoles by N. americanus may have contributed to the
drug failure. Whatever the underlying explanation, our results indicate that single-dose treatment with
mebendazole is an ineffective treatment for
hookworm infections and despite its relatively cheap cost and wide availability,
mebendazole should not be considered a
drug of choice in the mass treatment of
hookworm infections in this region of Mali.