Determination of milk/plasma ratio and milk and plasma pharmacokinetics of amoxicillin after intramuscular administration in lactating cows.

Abstract

This study was conducted to determine the passage ratio of amoxicillin into milk and its pharmacokinetics in milk and plasma after intramuscular administration. Five healthy dairy cows (Holstein, weighing 450-500kg, aged 2-4years) were used in this study. They received single intramuscular amoxicillin at a dose of 14mg/kg body weight. Blood and milk samples were collected prior to drug administration (0); after 15, 30, 45, 60, and 90min; and 2, 3, 4, 6, 8, 10, and 12hr after administration. The plasma and milk concentrations of amoxicillin were determined using high-performance liquid chromatography with ultraviolet detection. The passage ratio of amoxicillin into milk and plasma was determined using both AUC-based calculation and milk and plasma concentrations at sampling times; it was calculated 0.46 and 0.52, respectively. The terminal half-life and mean residence time of amoxicillin were 6.05 and 8.60hr in plasma and 2.62 and 5.35hr in milk, respectively. The Cmax2 levels of amoxicillin in plasma and milk were measured as 1,096 and 457ng/ml, respectively. It was observed that amoxicillin exhibited a secondary peak in plasma and milk. This study was the first to report on the passage ratio of amoxicillin into milk in lactating cows.