Comparative evaluation of the speed of flea kill of imidacloprid and selamectin on dogs.

Imidacloprid (Advantage, Bayer Corporation, Shawnee Mission, KS) and selamectin (Revolution [United States], Pfizer Animal Health, Exton, PA 19341; Stronghold [European Union], Pfizer Animal Health Ltd, Sandwich, Kent CT 13 9NJ, UK) were tested to assess the speed of flea kill achieved against existing flea infestations and subsequent reinfestations. Thirty-six dogs were infested with 100 unfed adult fleas on day-1. On day 0, 12 dogs (group 1) were treated with imidacloprid at the minimum label dose of 10 mg/kg body weight. Twelve dogs (group 2) were treated with selamectin at the minimum label dose of 6 mg/kg body weight. Twelve dogs (group 3) remained as untreated controls. Four sub-groups (A through D) of three dogs each were designated within each group. All dogs were subsequently reinfested with fleas on days 6, 13, 20, 27, 34, and 41. Live flea counts were performed for subgroups A through D at 6, 12, 24, and 36 hours after treatment/reinfestation. Imidacloprid provided significantly and consistently greater flea kill than selamectin at 6, 12, and 24 hours after treatment and at 6 and 12 hours after each reinfestation. Although both products are commercially labeled for monthly topical use, imidacloprid provided significantly greater 36-hour flea kill at 34 and 41 days after treatment.