Comparative Efficacy of Two Fipronil Spot-on Formulations Against Experimen- tal Flea Infestations (Ctenocephalides felis) In Dogs

A new fipronil-based spot-on formulation applied once to dogs was evaluated against experimental flea infestations in a parallel group design, randomized, unicentre and blinded controlled study. Eight dogs served as negative controls (group 1), eight dogs were treated with a 10% w/v fipronil-based spot-on solution (Effipro® Spot-on, Virbac SA) at a dosage of 0.67 mL for a dog weighing from 2 to 10 kg and 1.34 mL for a dog weighing from 10.1 to 20 kg (group 2) and eight dogs served as positive controls (group 3) receiving the original fipronil spot-on (Frontline® Top spot, Merial) at a similar dosage. Each dog was infested with 100 unfed adult Ctenocephalides felis on days -6, -1, 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84 and 91. At 48 h after treatment or reinfestation, each dog was combed to remove and count live fleas. Geometric mean flea counts obtained were reduced by 99.7 and 100% in groups 2 and 3, respectively on day 2, compared to the negative control group. Dogs were protected from re-infestations with an efficacy >95 per cent for 93 days in group 2 and for 79 days in group 3. Both 10% w/v fipronil-based spot-ons, despite different vehicles, were equally able to eradicate flea infestation, to prevent new infestations and were well-tolerated.