Objective: To evaluate efficacy of a 9.1% (w/w) imidacloprid solution, applied topically, to remove fleas from dogs and the duration of residual flea control when dogs were exposed to continuing flea infestation.
Animals: 32 adult mixed-breed dogs.
Procedure: Dogs were allocated to 4 groups of 8 dogs each; dogs of 3 groups received a single dose of imidacloprid, and those of the fourth group received excipient. Each dog was infested with 100 adult fleas on study days -3, -1, 6, 13, 20, 27, and 33. Treatments were applied on day 0. Each dog was examined for live fleas on days -2, 1, 7, 14, 21, 28, and 34. Posttreatment efficacy was determined by comparing the mean number of live fleas remaining on the treated dogs with the mean number of live fleas remaining on the control dogs.
Results: All 3 imidacloprid dosages provided flea control > or = 96.9% one day after treatment. Maximal efficacy of all 3 dosages (99.1 to 100%) was observed at 7 days after treatment. Flea control with 3.75 mg of imidacloprid/kg of body weight ranged from 94.4 to 96.9% for days 14 to 28 and decreased to 91.6% by 34 days after treatment. Flea control with 7.5 and 10.0 mg of imidacloprid/kg was 97.8 to 100% through day 28. At day 34, dosages of 7.5 and 10.0 mg of imidacloprid/kg were 97.6 and 96.9% efficacious, respectively.
Conclusion: 7.5 or 10.0 mg of imidacloprid/kg are equivalent and superior to 3.75 mg/kg for flea control over the course of a 34 day posttreatment period.
Clinical relevance: Monthly imidacloprid application of 7.5 to 10 mg/kg will rapidly kill existing and reinfesting flea infestations on dogs and break the flea life cycle by killing adult fleas before egg production begins.