Milbemycin oxime and lotilaner for heartworm prevention in dogs in Korea: a randomized controlled field trial.

IMPORTANCE: Heartworm disease can lead to chronic cardiopulmonary complications in dogs, and treatment is often prolonged and costly. In Korea, Dirofilaria immitis, the causative agent of canine heartworm disease, has been reported in both dogs and mosquitoes and is generally considered endemic. OBJECTIVE: This field study evaluated the effectiveness and safety of a combination of milbemycin oxime and lotilaner (Credelio Plus) for the prevention of heartworm disease in client-owned dogs in the Republic of Korea. DESIGN/SETTING/PATIENTS: This randomized, single-blind, controlled field trial was conducted between June 2023 and February 2024. Client-owned dogs that were at least 8 weeks old, weighed more than 2.0 kg, were walked more than 3 times per week, and tested negative for heartworm at baseline were enrolled. INTERVENTIONS: The dogs were allocated in a 1:1 ratio to receive either the investigational veterinary product (milbemycin oxime/lotilaner) or the control veterinary product (milbemycin oxime/afoxolaner) for six consecutive monthly treatments (days 0, 30, 60, 90, 120, and 150). MAIN OUTCOMES AND MEASURES: Prevention of D. immitis infection was assessed monthly from days 0 to 180 using a commercial antigen test kit and conventional polymerase chain reaction. Safety was evaluated using body weight, physical examination findings, hematology and serum chemistry analyses, and adverse event monitoring to assess general health status and identify potential treatment-related abnormalities during the study period. RESULTS: A total of 53 dogs were enrolled in the study, of which 52 were included in effectiveness and safety analyses. All dogs remained negative for D. immitis during the study period. In the safety evaluation, no statistically significant changes were observed in body weight, physical examination findings, or hematology and serum chemistry analyses following milbemycin oxime/lotilaner administration (p > 0.05). No adverse events were observed. CONCLUSIONS AND RELEVANCE: The results of this study support the use of milbemycin oxime/lotilaner combination as a safe and effective option for the prevention of canine heartworm infections under field conditions in Korea. These findings indicate that this combination product may be a useful option in veterinary parasite control. TRIAL REGISTRATION: Animal and Plant Quarantine Agency, Korea (clinical trial number: A221512).