Efficacy of a single oral administration of milbemycin oxime against natural infections of Ancylostoma braziliense in dogs

The objective of this randomized, blinded, placebo controlled laboratory study was to confirm the efficacy of a single oral administration of two marketed formulations of milbemycin oxime (Interceptor® Flavor Tabs® and Sentinel® Flavor Tabs®) at a minimum dose of 0.5 mg/kg (0.23 mg/lb) against natural infections of Ancylostoma braziliense in dogs. Thirty-six hookworm infected dogs, a minimum of 10 weeks of age and of various breeds and genders were used. Fecal egg counts were done on three separate days prior to treatment for randomization purposes. Dogs were ranked by descending order of the fecal egg count arithmetic means and randomly assigned to either the two milbemycin treatment groups or the placebo control group in blocks of three dogs each, 12 dogs per group. Dogs were dosed according to the product label with blinding maintained by separation of function. Worm counts were done at necropsy 7 days after treatment. Reduction in A. braziliense worm counts in the milbemycin groups were compared to the placebo control group using analysis of variance of the A. braziliense logarithmic mean worm counts and percent efficacy was based on geometric means. Efficacy was defined as the ability of the test products to significantly (p ≤ 0.05) reduce parasite load by 90% or greater in treated dogs when compared to adequately infected placebo control dogs. The placebo control group had a geometric mean worm count of 19.2. The Interceptor treated group had a geometric mean worm count of 0.38 representing a 98% reduction in parasite load and the Sentinel treated group had a geometric mean worm count of 0.98 representing a 95% reduction in parasite load. Both reductions were highly significant (p < 0.0001). In this study, milbemycin oxime, when administered as two marketed formulations at a minimum dose of 0.5 mg/kg (0.23 mg/lb), was efficacious for removing adult A. braziliense in naturally infected dogs.