The speed of kill of a topical combination of selamectin plus sarolaner against induced infestations of Ixodes scapularis ticks on cats.

The speed of kill of a novel, topical product containing selamectin in combination with sarolaner (selamectin/sarolaner; Revolution® Plus/Stronghold® Plus) was evaluated against Ixodes scapularis ticks on cats. Sixteen cats were randomly allocated to a treatment group and treated topically on Day 0 with either placebo (vehicle control) or 6 mg/kg selamectin plus 1 mg/kg sarolaner. Cats were infested with approximately 50 unfed viable adult I. scapularis ticks on Days -2, 7, 14, 21, 28 and 35. Efficacy was assessed at 4, 8, 12, 24, 48 and 72 h after treatment on Day 0 and at 4, 8, 12 and 24 h after post-treatment re-infestations. There were no adverse reactions to the topical treatment with selamectin/sarolaner. Placebo-treated cats maintained tick infestations throughout the study. Treatment with selamectin/sarolaner significantly reduced tick counts within 12 h (P < 0.0001) and resulted in 100% efficacy by 24 h. For subsequent re-infestations, live tick counts were significantly reduced by 12 h after infestation on Day 7 (P = 0.0120) and by 24 h for Days 14-35 (P < 0.0001). At 24 h after the post-treatment re-infestations, efficacy based on geometric (arithmetic) means was ≥96.1% (94.5%) through Day 21, 75.3% (67.7%) on Day 28 and 66.4% (56.4%) on Day 35. Thus, a single topical dose of Revolution® Plus/Stronghold® Plus at the recommended minimum dose started killing ticks within 12-24 hours after treatment and re-infestations for up to 5 weeks. High acaricidal efficacy (≥90% reduction in tick burden) was achieved within 24 h after treatment and subsequent re-infestations for at least three weeks.