The sustained speed of kill of ticks (Rhipicephalus sanguineus) and fleas (Ctenocephalides felis felis) on dogs by a spot-on combination of fipronil and permethrin (Effitix®) compared with oral afoxolaner (NexGard®).

The rapid speed of kill of a spot-on, combination of fipronil-permethrin (Effitix®, Virbac) was shown against infestations of Rhipicephalus sanguineus and Ctenocephalides felis on dogs. Efficacy was determined against new infestations at weekly intervals for one month after treatment. Dogs were allocated randomly to either an untreated control or to a single administration, given on Day 0, of either topical fipronil-permethrin (6.7-13.4mg/kg and 60-120mg/kg, respectively) or oral afoxolaner (2.72-6.8mg/kg), based on pre-treatment, host-suitability flea counts. Dogs were infested with 50, unfed, adult R. sanguineus on Days 7, 14, 21 and 28, and with 100C. felis on Days 8, 15, 22 and 29. Tick counts were performed 0.5, 2, 6, 12 and 24h, and flea counts were performed 0.5 and 24h after each infestation. No treatment-related adverse reactions occurred. Dogs in the untreated group maintained viable infestations throughout the study. Following infestation, live tick and flea counts for dogs treated with fipronil-permethrin compared with untreated dogs were rapidly and significantly reduced with efficacy apparent at 0.5h after infestation. Flea efficacies (arithmetic mean counts) at 0.5h after infestation on Day 7 (Day 28) were significantly greater for fipronil-permethrin, 70% (34%) compared with 8% (18%) for afoxolaner (P≤0.05). Tick efficacies at 2h on Day 7 (Day 28) were 74% (63%) for fipronil-permethrin compared with 10% (0%) for afoxolaner (P≤0.05). Efficacies for tick repellency as indicated by counts of ticks off the dogs at 2h on Day 7 (Day 28) were greater for fipronil-permethrin, 32% (22%) compared with afoxolaner, 0% (0%) (P≤0.05). Anti-attachment efficacies at 12h were greater for fipronil-permethrin compared with afoxolaner. Tick efficacies at 24h, based on arithmetic (geometric) means, were significantly greater on Day 28 for fipronil-permethrin compared with afoxolaner (P≤0.05), 74% (87%) and 45% (60%), respectively, and were similar (P >0.05) on Days 7, 14 and 21. Flea efficacies, 24h after infestation were >98% and similar for both treated groups on all infestation days (P >0.05). The topically applied fipronil-permethrin containing ectoparasiticide Effitix® offers rapid efficacy against R. sanguineus and C. felis which persists for one month after a single administration in dogs. Afoxolaner is also effective although speed of kill is slower. The rapid and sustained speed of kill of both parasites by fipronil-permethrin should contribute to effective management not only of these parasites and their direct adverse effects including irritancy and allergy, but also to reducing the risk of transmitting infections.