Field Comparison of Tolerance of A Collar Containing 10.0% Imidacloprid/4.5% Flumethrin (seresto) and A Placebo Collar Placed on Cats

Objectives A collar containing 10.0% imidacloprid/4.5% flumethrin (Seresto; Bayer Animal Health) controls flea and tick infestations for 8 months and is effective in preventing transmission of Bartonella henselae and Cytauxzoon felis among cats. The purpose of this study was to compare tolerance of client-owned cats for the 10.0% imidacloprid/4.5% flumethrin collar or a physically identical placebo collar.Methods A total of 96 client-owned cats were enrolled in the study. Cats that were systemically ill, of hairless breed or declawed in all four limbs were excluded. Cats were randomized by household to wear a placebo collar for 14 days followed by the 10.0% imidacloprid/4.5% flumethrin collar for 14 days or the 10.0% imidacloprid/4.5% flumethrin collar for 28 days. Examinations by a veterinarian were performed on days 0, 14 and 28. Owners recorded daily systemic and local health observations.Results All but two cats, including one that entrapped the mandible in the collar and one that developed local pyodermatitis (10.0% imidacloprid/4.5% flumethrin collar), completed the 28 day study. The majority of the local lesions or licking associated with the collars occurred in the first 14 days, and licking (but not skin lesions) was more common in cats wearing the 10.0% imidacloprid/4.5% flumethrin collars. No local lesions were reported for placebo cats after switching to the 10.0% imidacloprid/4.5% flumethrin collar, and only one cat wearing the 10.0% imidacloprid/4.5% flumethrin collar had reports of licking after day 14. Housing status, single or multiple cat household, and whether a collar had been worn previously were not associated with side effects.Conclusions and relevance Adverse events detected for cats wearing 10.0% imidacloprid/4.5% flumethrin collars were similar to those for cats wearing placebo collars and to cats wearing identification collars in a separate study. The data suggest that most cats originally intolerant of collars become receptive over time.