Critical anthelmintic trials in ponies with four benzimidazoles: mebendazole, cambendazole, fenbendazole, and albendazole.

The comparative efficacy of four benzimidazoles against gastrointestinal parasites of ponies was evaluated by the critical test method. Mebendazole (8.8 mg/kg), cambendazole (20 mg/kg), fenbendazole (5 mg/kg), and albendazole (2.5 and 5 mg/kg) given in single oral doses were highly effective against adult large strongylids (Strongylus vulgaris, S. endentatus, S. equinus) and adult small strongylids (genera identified in order of frequency: Cylicostephanus, Cylicocyclus, Cyathostomum, Triodontophorus, Poteriostomum, Oesophagodontus, Cylicodontophorus, Gyalocephalus, and Craterostomum). Limited data indicated that all benzimidazoles were completely effective against adult Oxyuris equi and 95 to 100% effective against the 4th stage larvae. There was activity also against the large roundworm, Parascaris equorum, although the low levels of infection and skew distribution among the test animals did not permit a definitive determination of efficacy. Habronema muscae, Draschia megastoma, and Trichostrongylus axei were found in digests of the stomach but none were recovered in the feces after treatment; percent efficacy for these species was not calculated. None of the benzimidazoles showed activity against stomach bots, Gasterophilus spp., and tapeworms, Anoplocephala spp. nor against immature large and small strongylids outside the lumen of the digestive tract.