Prophylactic Effect of Milbemycin Oxime against Dirofilaria immitis Infection in Dogs : Optimum Dose and Administration Time

To examine the prophylactic efficacy of milbemycin oxime against Dirofilaria immitis infection, 42 filaria-free beagles were inoculated with 100 ineffective larvae of the parasite. Milbemycin oxime was administered orally at doses of 0.05 to 1.0 mg/kg body weight one month after inoculation, and at a single dose of 0.25 mg/kg body weight on days 1 to 90 after inoculation. All dogs were euthanetized and autopsied to evaluate the prophylactic effect of the drug against D. immitis infection 6 months after inoculation. It was confirmed that a dose of 0.25 mg/kg of milbemycin oxime completely-protected the infection 15 to 60 days after infection.