Efficacy of selamectin in the treatment and control of clinical signs of flea allergy dermatitis in dogs and cats experimentally infested with fleas.

Objective: To determine whether treatment with selamectin would reduce clinical signs of flea allergy dermatitis (FAD) in dogs and cats housed in flea-infested environments.

Design: Randomized controlled trial.

Animals: 22 dogs and 17 cats confirmed to have FAD.

Procedure: Animals were housed in carpeted pens capable of supporting the flea life cycle and infested with 100 fleas (Ctenocephalides felis) on days -13 and -2 and on alternate weeks with 10 to 20 fleas. On day 0, 11 dogs and 8 cats were treated with selamectin (6 mg/kg [2.7 mg/lb]). Dogs were retreated on day 30; cats were retreated on days 30 and 60. All animals were examined periodically for clinical signs of FAD. Flea counts were conducted at weekly intervals.

Results: Throughout the study, geometric mean flea counts exceeded 100 for control animals and were < or = 11 for selamectin-treated animals. Selamectin-treated cats had significant improvements in the severity of miliary lesions and scaling or crusting on days 42 and 84, compared with conditions on day -8, and in severity of excoriation on day 42. In contrast, control cats did not have any significant improvements in any of the clinical signs of FAD. Selamectin-treated dogs had significant improvements in all clinical signs on days 28 and 61, but in control dogs, severity of clinical signs of FAD was not significantly different from baseline severity at any time.

Conclusions And Clinical Relevance: Results suggest that topical administration of selamectin, even without the use of supplementary environmental control measures and with minimal therapeutic intervention, can reduce the severity of clinical signs of FAD in dogs and cats.