Efficacy of a new spot-on formulation of selamectin plus sarolaner against four common tick species infesting cats in Europe

A single application of a new spot-on formulation of selamectin plus sarolaner (Stronghold®Plus, Zoetis) was evaluated for efficacy against the most common tick species infesting cats in Europe. In each of the seven laboratory studies, 16 adult and purpose-bred cats were randomly allocated to one of two treatment groups based on pre-treatment tick counts. Weekly infestations with 50 unfed adult Ixodes ricinus (2 studies), Ixodes hexagonus (1 study), Dermacentor reticulatus (2 studies), or Rhipicephalus sanguineus (2 studies) were scheduled on Days −2, 5, 12, 19, 26 and 33. Cats were treated on Day 0 with the spot-on formulation at the minimum recommended label dose of 6.0 mg selamectin and 1.0 mg sarolaner per kg bodyweight or with a placebo. Ticks were counted 48 h after treatment and after each re-infestation. No treatment-related adverse reactions were recorded in any of the studies. Geometric mean live tick counts were significantly (P ≤ 0.0012) lower in the selamectin/sarolaner-treated group compared to the placebo-treated group at all time-points. Against I. ricinus and I. hexagonus, efficacy was ≥97.2% against existing infestations and ≥97.4% against weekly re-infestations for at least 5 weeks. Treatment was 100% effective against existing R. sanguineus infestations and was ≥95.8% for at least 4 weeks. Against D. reticulatus treatment resulted in ≥94.4% efficacy for at least 4 weeks. Thus, a single application of the new spot-on formulation of selamectin plus sarolaner at the minimum dose provides rapid treatment of existing infestations and is at least one month effective against re-infestation by all relevant European tick species in cats.