How fast Credelio, Simparica Trio, and NexGard kill ticks on dogs

Abstract

BACKGROUND: Canine acaricides with rapid onset and sustained activity can reduce pathogen transmission risk and enhance pet owner experience. This randomized, complete block design, investigator-masked study compared the speed of kill of Amblyomma americanum provided by three monthly-use isoxazoline-containing products. METHODS: Eight randomized beagles per group were treated (day 0), per label, with sarolaner (combined with moxidectin and pyrantel, Simparica Trio&#x2122;), afoxolaner (NexGard&#x2122;), or lotilaner (Credelio&#x2122;), or remained untreated. Infestations with 50 adult A. americanum were conducted on days -&#x2009;7, -&#x2009;2, 21, and 28, and tick counts were performed on day -&#x2009;5 (for blocking), and at 4, 8, 12, 24, 48, and 72&#xa0;h following treatment and subsequent infestations. Efficacy calculations were based on geometric mean live tick counts. A linear mixed model was used for between-group comparisons. RESULTS: On day 0, only lotilaner significantly reduced an A. americanum infestation by 12&#xa0;h (43.3%; P&#x2009;=&#x2009;0.002). Efficacy of lotilaner and afoxolaner at 24&#xa0;h post-treatment was 95.3% and 97.6%, respectively, both significantly different from sarolaner (74%) (P&#x2009;=&#x2009;0.002, P&#x2009;<&#x2009;0.001, respectively). On day 21, at 12&#xa0;h postinfestation, lotilaner efficacy (59.6%) was significantly different from sarolaner (0.0%) (P&#x2009;<&#x2009;0.001) and afoxolaner (6.3%) (P&#x2009;<&#x2009;0.001). At 24&#xa0;h, lotilaner efficacy (97.4%) was significantly different (P&#x2009;<&#x2009;0.001) from sarolaner and afoxolaner (13.6% and 14.9%, respectively). On day 28, at 12&#xa0;h postinfestation, lotilaner efficacy (47.8%) was significantly different from sarolaner (17.1%) (P&#x2009;=&#x2009;0.020) and afoxolaner (9.0%) (P&#x2009;=&#x2009;0.006). At 24&#xa0;h, lotilaner efficacy (92.3%) was significantly different from sarolaner 4.9% (P&#x2009;<&#x2009;0.001) and afoxolaner (0.0%) (P&#x2009;<&#x2009;0.001). Speed of kill for sarolaner and afoxolaner, but not lotilaner, significantly declined over the study period. Following reinfestation on day 28, neither sarolaner nor afoxolaner reached 90% efficacy by 48&#xa0;h. By 72&#xa0;h, sarolaner efficacy was 97.4% and afoxolaner efficacy was 86.3%. Only lotilaner achieved&#x2009;&#x2265;&#x2009;90% efficacy by 24&#xa0;h post-treatment and 24&#xa0;h postinfestation on days 21 and 28. Time to&#x2009;&#x2265;&#x2009;90% efficacy following new infestations consistently occurred 24-48&#xa0;h earlier for lotilaner compared with sarolaner or afoxolaner. CONCLUSIONS: Credelio (lotilaner) has a more rapid onset of acaricidal activity against A. americanum than Simparica Trio (sarolaner-moxidectin-pyrantel) and NexGard (afoxolaner). Only lotilaner's speed of tick kill is sustained throughout the dosing period.