Three studies were conducted in client-owned dogs naturally infested with fleas and/or ticks, to confirm the efficacy of an indoxacarb plus permethrin spot-on (Activyl® Tick Plus, Merck/ MSD Animal Health), under field conditions.

In a multiregional field study, six veterinary clinics in France, Germany and Spain enrolled 194 dogs, randomly allocated to receive three applications of the test product (Activyl® Tick Plus) at 4 week intervals with the recommended dose (at least 15 mg indoxacarb/kg and 48 mg permethrin/kg) or a reference product (fipronil, Frontline®, Merial) at the manufacturer's recommended dose. Clinical examinations and baseline parasite counts were performed pre-treatment and at two-week intervals for twelve weeks. The most frequent tick species identified were Ixodes sp. (52.6%), Dermacentor reticulatus (32.5%) and Rhipicephalus sanguineus (14.6%).

In the indoxacarb plus permethrin group, percent reductions in parasite counts, based on arithmetic means (AM), were 98.5% for fleas and 98.6% for ticks on week 2, and 98.7% for fleas and 99.0% for ticks on week 12. In the fipronil group, percent reductions were 87.6% for fleas and 100% for ticks on week 2, and 73.5% for fleas and 99.3% for ticks on week 12. The mean flea and tick counts were not statistically different between the two groups. At the end of the evaluation period, the percentage of households with all dogs free of fleas and ticks were 88.9% and 92.0%, respectively, for the indoxacarb plus permethrin treated group and 66.6% and 92.0%, respectively, for the fipronil treated group.

Two field studies were conducted in Australia to confirm the efficacy of Activyl® Tick Plus under conditions where there were heavy natural flea infestations. Twenty-seven flea-infested dogs (AM 81.1 fleas per dog) were enrolled in Study 1 (Queensland) and 22 dogs (AM 88.7 fleas per dog) in Study 2 (New South Wales). Dogs were treated on weeks 0, 4 and 8 with the recommended dose. Visual thumb counts of fleas were conducted immediately pre-treatment and on weeks 4, 8 and 12. Efficacy, based on AM on weeks 4, 8 and 12, was 96.3%, 99.0% and 99.3% in Study 1 and 94.8%, 98.1% and 99.3% in Study 2. Twenty-three of the 26 dogs (Study 1) and 17 of the 21 dogs (Study 2) had 100% reduction in fleas.

Activyl® Tick Plus was very well tolerated in all three studies.