Efficacy of a new combination of fipronil and permethrin against Ctenocephalides felis flea infestation in dogs

BACKGROUND: Five studies were conducted to evaluate the effect of a new combination of fipronil and permethrin on cat fleas, Ctenocephalides felis, when applied to dogs, including dogs that underwent water exposure or shampooing. METHODS: In each study, 16 dogs were allocated to two groups. Each dog was infested with 100 unfed adult fleas on Days −1, 7, 14, 21 and 28. Eight dogs were treated with a new topical spot-on formulation containing 6.76% w/v fipronil + 50.48% w/v permethrinon Day 0; and eight dogs served as untreated controls. Twenty-four or 48 h after treatment or subsequent infestation, each dog was combed to remove and count live fleas. In addition, the dogs were subjected to different levels of water or shampoo exposure. In study 1, dogs were not subjected to any water exposure or shampooing; in study 2, dogs were water immersed twice during the month on Days 10 and 24; in study 3, dogs were water immersed three times on Days 10, 17 and 24; and in studies 4 and 5, dogs were shampooed once on Day 17. RESULTS: All groups of dogs administered a single topical treatment with a combination of fipronil and permethrin had significantly (p < 0.005) lower flea counts than untreated controls 24 h and 48 h post-treatment or post-infestation, regardless of whether they underwent water exposure/shampooing or not. The reductions in C. felis counts were between 98.4% and 100% at all time points in all studies. CONCLUSIONS: The new topical spot-on formulation of fipronil and permethrin maintains a high level of protection of dogs against C. felis flea infestations even when the dogs are exposed to environmental factors that are believed to adversely affect efficacy, such as water exposure or shampooing.