Activyl® spot-on (Merck/MSD Animal Health) is a topical flea control product containing indoxacarb as the active ingredient. Two studies were conducted to evaluate the potential effects of water immersion, to simulate swimming, and shampooing on the efficacy of Activyl® against fleas on dogs. In the first study, 40 dogs were randomly assigned (10/group) to the following groups: A) placebo, B) indoxacarb, C) indoxacarb treatment followed by shampooing on Days 8 and 22, and D) indoxacarb treatment followed by water immersion on Days 8, 15, 22 and 29. Dogs were dosed exactly with the minimum recommended dose of 15 mg indoxacarb/kg body weight and all dogs were treated on Day 0. Therapeutic efficacy against an existing infestation was determined by counting live fleas 48 (±4) hours post treatment. Persistent efficacy was determined using weekly fleas infestations and counts conducted 24 (±4) hours post infestation. Therapeutic efficacy for groups B, C and D was 99%, 98% and 99%, respectively. Persistent efficacy was > 97% through Day 22 and 94% (Group B), 90% (Group C) and 92% (Group D) on Day 29.

The second study followed a similar design with the exceptions that dogs were treated with the commercially approved dose volumes (based on weight bands); all flea counts for persistent activity were done at 48 hours rather than 24 hours post infestation; and there were small differences in the days that immersion (Days 2, 9, 16, and 23), shampooing (Days 9 and 23) and flea counts (Days 2, 9, 16, 23, 30 and 37) were performed. Therapeutic efficacy on Day 2 ranged from 94.6 to 97.9% and persistent efficacy was > 99% on Day 37 for the three indoxacarb-treated groups.

In both studies, mean flea counts from the placebo group were higher (P≤ 0.05) than those from the three treated groups and the mean flea counts from the three treated groups did not differ from each other. Shampooing on Days 8 and 22 or on Days 9 and 23 and weekly water immersion (Days 8, 15, 22, and 29 or Days 2, 9, 16, and 23) did not significantly impact the persistent efficacy of indoxacarb spot-on against flea infestations.

Activyl® spot-on was highly efficacious for the control of flea infestations on dogs and was not affected by water immersion or shampooing.