Efficacy and speed of kill of a new spot-on formulation of selamectin plus sarolaner against flea infestations in cats

The efficacy of a new spot-on formulation of selamectin plus sarolaner against induced flea infestations in cats was confirmed in three placebo-controlled, blinded studies. Purpose-bred adult cats (n = 8/group) were blocked by pre-treatment flea counts and randomly allocated to treatment with either a placebo or with the spot-on formulation at the minimum dose of 6.0 mg selamectin and 1.0 mg sarolaner per kg bodyweight. Treatments were applied topically once on Day 0. All cats were infested with approximately 100 unfed, adult Ctenocephalides felis prior to treatment and at weekly intervals for 5 weeks. In Studies 1 and 2 comb counts were conducted to determine the numbers of viable fleas 24 h after treatment and subsequent weekly infestations. In Study 3, flea counts were conducted at 6, 12, 24 and 48 h after treatment and 3, 6, 12 and 24 h after subsequent weekly infestations to evaluate the speed of kill against fleas. Cats in the placebo-treated groups maintained flea infestations throughout all studies. In Study 1, no live fleas were found on any of the treated cats, resulting in 100% efficacy for 5 weeks after a single treatment (P ≤ 0.0001). In Study 2, selamectin/sarolaner reduced flea counts by 92.4% immediately after treatment and by 97.7%-100% after re-infestations for five weeks (P ≤ 0.0001). In the speed of kill study, selamectin/sarolaner started killing fleas within 12 h after treatment administration and within 6 h following re-infestation for at least 28 days. Efficacy was 98.1% by 24 h after treatment and 100% within 24 h after re-infestations for 5 weeks. A single topical administration of a new spot-on formulation of selamectin plus sarolaner at the minimum dose rapidly and consistently kills fleas on cats for at least 5 weeks.