Study: Selamectin >90% effective against fleas 30 days after treatment


Topical medication found to last longer than prescription oral preventives.

The topical medication selamectin (Revolution, Zoetis Inc.) remained more than 90 percent effective against fleas at day 30 after treatment, according to a new study published in the online journal Parasites and Vectors. The study was conducted at the Kansas State University College of Veterinary Medicine and sponsored by Zoetis, formerly the animal health business unit of Pfizer Inc.

Results of the study showed that selamectin administered topically at the label dose demonstrated activity that was more than 90 percent effective against Ctenocephalides felis in dogs within two days of treatment and lasted for up to 30 days after treatment. Oral medications spinosad-milbemycin oxime and spinosad administered at the label dose were more than 90 percent effective within one day after treatment, but only up to 23 days after treatment.

“Fleas are a major contributor to the production of allergic dermatitis in dogs,” says Michael W. Dryden, DVM, PhD, DACVM, of the Department of Diagnostic Medicine/Pathobiology at Kansas State University, the study’s lead author. “While initial speed of flea kill is important, the residual speed of kill of a product is critical to the success of a flea control product.”

Forty-eight dogs were selected for the study, and two batches of 24 were blocked and allocated randomly to treatment groups and flea count times. There were four treatment groups of 12 dogs each: negative control, topical selamectin, oral spinosad-milbemycin oxime and oral spinosad.

On day zero, dogs received a single treatment of the appropriate drug according to the approved commercial label. Each dog was infested with 100 fleas (C. felis KS1 strain) on days two, seven, 14, 21 and 28. Within each treatment group, six dogs were flea-counted at 24 hours and six at 48 hours after treatment or post-infection. Here are the findings:

> Efficacy of selamectin against an existing flea infestation was 60.4 percent at 24 hours after treatment and 91.4 percent at 48 hours, whereas spinosad-milbemycin oxime and spinosad were 100 percent at both time points.

> All products were more than 90 percent effective within 24 and 48 hours after subsequent infestations on Days 7, 14 and 21.

> After the day 28 flea infestation, selamectin was 93 percent at 24 hours and 95.7 percent effective at 48 hours. The efficacy of spinosad-milbemycin oxime after the day 28 infestation was 84.7 percent at 24 hours and 87.5 percent at 48 hours, and spinosad alone was 72.9 percent at 24 hours and 76.3 percent at 48 hours.

The complete study is available at

Besides flea control, Revolution (selamectin) is approved for the prevention of heartworm disease caused by Dirofilaria immitis and the treatment and control of ear mite (Otodectes cynotis) infestations. It is also indicated for the treatment and control of sarcoptic mange (Sarcoptes scabiei) and for the control of tick infestations due to Dermacentor variabilis.

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