Clinical efficacy and safety of a spray formulation containing carvacrol and eugenol against Rhipicephalus linnaei and Ctenocephalides felis felis in artificially infested dogs.

The control of ectoparasites in dogs is challenged by resistance and the environmental impacts of synthetic pesticides, driving the search for plant-based alternatives. This study evaluated the clinical efficacy and safety of a spray formulation containing carvacrol (10%) and eugenol (10%) against experimental infestations by the tick Rhipicephalus linnaei and the flea Ctenocephalides felis felis in dogs. Sixteen Beagles were randomly allocated to a treated group (TG, n = 8) and an untreated control group (CG, n = 8). The animals were artificially infested on days -2, + 5, and + 12, and parasite counts were performed on days + 2, + 7, and + 14. Efficacy was calculated as the percent reduction of arithmetic means relative to the CG. Safety was assessed through daily clinical examinations and hematological and biochemical analyses. The formulation achieved high initial therapeutic efficacy, with reductions of 96% for R. linnaei and 98% for C. felis felis on day + 2, meeting reference efficacy thresholds for ectoparasiticides. On days + 7 and + 14, reductions were lower (49-56% for fleas and 11-49% for ticks) and, despite remaining statistically significant compared to controls, did not reach the levels required to claim residual efficacy. No local or systemic adverse events were observed, and laboratory parameters remained within reference ranges for the respective species, with no significant differences between groups (p > 0.05). The results demonstrate that the carvacrol and eugenol spray formulation is effective for the therapeutic control of tick and flea infestations in dogs, representing a promising plant-based alternative.