Comparative speed of kill of sarolaner (Simparica(™)) and spinosad plus milbemycin oxime (Trifexis(®)) against induced infestations of Ctenocephalides felis on dogs

BACKGROUND: Fleas are a ubiquitous ectoparasite infesting dogs and cause direct discomfort, allergic reactions and are responsible for the transmission of several pathogens. The rapid speed of kill of a parasiticide is important to alleviate the direct deleterious effects of fleas, reduce the impact of allergic responses, and break the flea life cycle. In this study, the speed of kill of a novel orally administered isoxazoline parasiticide, sarolaner (Simparica(™)) against fleas on dogs was evaluated and compared with spinosad in combination with milbemycin oxime (Trifexis(®)) for 5 weeks after a single oral dose. METHODS: Twenty-four dogs were randomly allocated to treatment with a single oral dose per product label of sarolaner (2 to 4 mg/kg), spinosad/milbemycin oxime (30 to 60 mg/kg / 0.2 to 0.4 mg/kg), or placebo based on pretreatment flea counts. Dogs were combed and live fleas counted at 8, 12, and 24 h after treatment and subsequent re-infestations on Days 7, 14, 21, 28, and 35. Efficacy (reduction in live flea counts) of each treatment was determined at each time point relative to counts for placebo dogs. RESULTS: There were no adverse reactions to treatment. A single oral dose of sarolaner provided ≥94.0 % efficacy (based on geometric means) within 8 h of treatment or subsequent weekly re-infestations of fleas to Day 35. By 12 h, fleas were eradicated from all dogs and they remained flea free at 24 h. Significantly greater numbers of live fleas were recovered from spinosad/milbemycin oxime-treated dogs at 8 h from Day 21 to Day 35 (P ≤ 0.0085), and at 12 and 24 h on Day 35 (P ≤ 0.0002). CONCLUSIONS: In this controlled laboratory evaluation, dogs treated with sarolaner had significantly fewer live fleas than spinosad/milbemycin oxime- treated dogs at 8 h after re-infestation from Day 21 after a single oral dose. The rapid and consistent kill of fleas after a single oral dose of sarolaner over 35 days indicates that this treatment should provide highly effective control of flea infestations, relief for dogs afflicted with flea allergy dermatitis, and also reduce the risk of transmission of flea-borne pathogens.