The disposition of enrofloxacin in seabream ( Sparus aurata L.) after single intravenous injection or from medicated feed administration

Abstract

Serum concentrations of enrofloxacin (EF) after intravenous (i.v.) or oral administration of single doses (2.5 and 10 mg/kg b.w., respectively) were investigated in seabream ( Sparus aurata L.) kept in seawater at 25–27 °C. The tissue disposition of the drug was studied after oral administration. At prefixed time points, from 1 h to 5 days after administration, blood and edible tissues (muscle plus adherent skin) from 10 individuals in each group were collected and stored at −20 °C. Each serum and tissue sample was essayed for EF by HPLC after liquid–liquid extraction. Serum was also checked for the presence of the metabolite ciprofloxacin (CF). The quantification limits for EF were 0.010 μg/ml in serum and 0.015 μg/g in tissues. Following intravenous administration, considerably high serum concentrations of EF (range 2.605–3.810 μg/ml) were detected during the first 4 h. The concentrations decreased subsequently, indicating a first rapid distribution, followed by a slow phase of elimination. At the last time point of the experiment (120 h), there were still detectable amounts of EF in serum samples (range 0.040–0.087 μg/ml). Enrofloxacin levels of 0.335–1.138 μg/ml were reached in serum within 1 h after in feed administration. The maximum values were measured at 8 h (1.709–2.846 μg/ml), then slowly declined and were measurable (0.048–0.149 μg/ml) for up to 120 h. Compared to serum, lower concentrations of EF were determined in muscle plus skin: 0.156–0.398 μg/g after 1 h, 0.102–2.002 μg/g at 8 h and 0.015–0.031 μg/g at the last sample point. No CF was found in serum.