Pharmacokinetics and Tissue Distribution of Enrofloxacin and Its Metabolite Ciprofloxacin After a Single Intraperitoneal Administration in Black Rockfish (Sebastes schlegelii) at Two Water Temperatures

Enrofloxacin (ENR) is a fluoroquinolone antimicrobial used to treat bacterial diseases in aquaculture and is metabolized into ciprofloxacin (CIP). This study investigated the serum pharmacokinetics and tissue distribution of ENR and CIP in black rockfish (Sebastes schlegelii) following a single intraperitoneal administration of ENR 10 mg/kg at 13 °C and 22 °C. Absorption, distribution, and elimination of ENR were accelerated at 22 °C compared with 13 °C, with the elimination half–life decreasing from 35.75 h at 13 °C to 21.11 h at 22 °C. Kidney levels indicated higher ENR values than serum, liver, and muscle levels at both temperatures. CIP was formed only at low levels (2.13–8.05%), with greater formation at 22 °C. The temperature–elimination relationship observed after intraperitoneal administration was opposite to that reported for oral administration under the same conditions, suggesting the occurrence of flip–flop kinetics at high water temperature following oral administration. These findings indicate that both water temperature and route of administration should be considered when evaluating the pharmacokinetics of ENR in fish.