Efficacy of selamectin against adult flea infestations (Ctenocephalides felis felis and Ctenocephalides canis) on dogs and cats.

Selamectin was evaluated in eight controlled studies (4 in dogs, 4 in cats) to determine the efficacy of a single topical unit dose providing the recommended minimum dosage of 6mgkg(-1) against Ctenocephalides felis felis and Ctenocephalides canis fleas on dogs and against C. felis on cats. In addition, the effect of bathing on the efficacy of selamectin against C. felis was evaluated. Identical studies were performed in Beagles and domestic shorthaired cats. For each study, animals were allocated randomly to treatments of 8-12 animals each. All studies (dog studies A, B, C, and D and cat studies A, B, C, and D) evaluated the efficacy of selamectin without bathing. In addition, study C in both dogs and cats evaluated efficacy with a shampoo bath at 24h after dosing, and study D evaluated the efficacy of selamectin with water soaking at 2h after dosing or with a shampoo bath at 2-6h after dosing. Dog study B evaluated efficacy against C. canis, whereas all other studies used C. felis. In each study, selamectin was administered on day 0 as a topical dose that was applied directly to the skin in a single spot at the base of the neck in front of the scapulae. Dogs and cats were infested with approximately 100 viable unfed C. felis or C. canis on days 4, 11, 18, and 27. On days 7, 14, 21, and 30, approximately 72h after infestation, a comb count of the number of viable fleas present on each animal was made. For C. felis and C. canis for dogs and cats, compared with controls, selamectin achieved significant reductions in geometric mean adult flea comb counts of > or =98.9% on days 7, 14, and 21 in all eight studies. On day 30, the reduction for C. felis remained at or above 98.0%. This included the dogs and cats that were soaked with water or bathed with shampoo at 2, 6, or 24h after treatment. There were no significant (P>0.05) differences between the flea counts from selamectin-treated animals in these studies, regardless of bathing status. On day 30, a significant reduction of 91.8% was achieved against C. canis on dogs. Thus, these studies demonstrated that a single topical unit dose of selamectin was highly effective against adult fleas on dogs and cats for at least 27 days.