Determination of cloxacillin residues in dairy cows after intramammary administration.

Abstract

The aim of this study was to perform a comparative analysis of the characteristics of cloxacillin (CLO) (MRL of withdrawal in bovine milk is 30ng/g) after a single intramammary (IMM) dose in the dry period (DP) and lactation (LP), and to establish a high-performance liquid chromatography (HPLC) analytical method for CLO detection in milk. The research was conducted on a group of 10 cows in DP and 10 in LP. A single dose of 600mg of CLO was administrated by the IMM route for a single quarter in DP and 500mg for a single quarter in LP. CLO concentration was analyzed by HPLC. CLO was monitored at a wavelength of 206nm. Pharmacokinetic calculations were performed using Phoenix® WinNonlin® 6.4 software. The calibration curve was linear over the range of 13.03-28019.00ng/g with the coefficient of determination R2 >0.999. CLO withdrawal in both the LP and DP group had a biphasic nature. The total CLO elimination in the DP and LP group was reached after 36 and 6.5days, respectively. A quantitative and confirmatory method for the determination of CLO in fresh milk has been established. We have confirmed that the withdrawal of CLO in the DP group is not a linear process and has a stepwise character.