Safety evaluation of orally administered afoxolaner and milbemycin oxime in eight-week-old dogs.

The safety profile of afoxolaner (an isoxazoline molecule) when combined with milbemycin oxime (a macrocyclic lactone) was evaluated according to the regulatory requirements when administered six times orally in a soft chewable formulation at a dose of at least 1×, 3×, or 5× the maximum exposure dose in 8-week-old Beagle dogs. Thirty-two healthy puppies (16 males and 16 females) were enrolled and allocated randomly to one of four treatment groups. Three doses were administered at 28-day intervals (Days 0, 28, and 56), followed by three additional doses administered with 14-day intervals (Days 84, 98, and 112). The study ended on Day 126. Treatment groups were as follows: Group 1: untreated, sham-dosed control; Group 2: afoxolaner/milbemycin oxime chews administered at a dose of at least 5 and 1 mg/kg, respectively (1×); Group 3: afoxolaner/milbemycin oxime chews administered at a dose of at least 15 and 3 mg/kg, respectively (3); and Group 4: afoxolaner/milbemycin oxime chews administered at a dose of at least 25 and 5 mg/kg, respectively (5×). All dogs were examined for general health twice a day beginning on Day -14. Physical examinations, and blood collections for clinical pathology analysis and afoxolaner and milbemycin oxime plasma concentrations, were performed throughout the study. No afoxolaner/milbemycin oxime treatment-related changes were observed in growth, physical variables, clinical pathology variables, or tissues examined histologically. No clinically relevant or statistically significant health abnormalities related to the administration of afoxolaner/milbemycin oxime were observed. No signs of macrocyclic lactone sensitivity were observed at any time during the study. Vomiting and diarrhea were observed sporadically across all groups including the controls. Based upon the results of this study, afoxolaner/milbemycin oxime soft chewables were shown to be safe when administered repeatedly at up to 5× the maximum exposure dose in dogs as young as 8 weeks of age.