Distribution of Milbemycin D in Plasma and Various Tissues in Dogs

Abstract

Dogs were administered orally with 1 mg/kg of milbemycin D (MD). The blood concentration of MD reached a peak 1 hour after administration, but became undetectable (less than 0.5 ng/ml) 120 hours after administration. The number of microfilariae of Dirofilaria immitis (mf) in the peripheral blood decreased, showing a good correlation with the blood concentration of MD. It was reduced remarkably, but failed to be zero even 120 hours after administration.
The following order of MD concentration was observed: blood plasma=brain<muscle<lung<kidney<lung<adipose tissue. This concentration was 1490.9 ng/g when it reached a peak in the adipose tissue. It ranged from 95.7 to 377.8 ng/g in the other tissues. It became undetectable (less than 5.0 ng/g) in the adipose tissue 240 hours after administration, showing that MD remained longer in this tissue than any other tissue, and that it had affinity to fat. MD concentration was 1.3 ng/ml at the highest in the cerebrospinal fluid.