Pharmacokinetics of Enrofloxacin and Its Metabolite in Carp (Cyprinus carpio) After a Single Oral Administration in Medicated Feed

A precise and reliable analytical method of high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed to measure trace levels of enrofloxacin (ENR) and its major metabolite ciprofloxacin (CIP) in carp tissues. Optimized chromatographic separation was obtained on a Waters Xterra MS C18 reversed-phase column using gradient elution with methanol and 0.1% formic acid aqueous solution including 5 mmolL(-1) of ammonium acetate. The established method was applied to study the pharmacokinetics and distribution of ENR and CIP in tissues of carp following a single oral administration in feed at a dosage of 40 mg kg(-1) bw (body weight). Data were analyzed using DAS 2.0 dynamics software, and the experimental results suggest that ENR was rapidly absorbed and extensively distributed in carp tissues through systemic circulation, and the pharmacokinetic characteristics can be described with a two-compartment model. The elimination half-lives (t(1/2 beta)) from muscle, liver, gill, plasma and skin were 131, 160, 104, 132 and 310 h, respectively. The areas under the drug concentration-time curves (AUC) for these tissues were 491, 972, 750, 249 and 706 h mg kg(-1), respectively. The maximum concentration (C-max) values were 13, 29, 37, 9 and 5 mg kg(-1) with peak times (t(max)) of 8, 4, 4, 2 and 4 h, respectively. Ciprofloxacin, the active metabolite of ENR, was also detected in carp tissues, indicating that only 1.54% of de-ethylation of ENR occurs in carp. At a water temperature of 18 degrees C, the drug withdrawal time was determined to be no less than 24 d while the carp was fed at a single dosage of 40 mg kg(-1).