Pharmacokinetics of florfenicol and behaviour of its metabolite florfenicol amine in orange-spotted grouper (Epinephelus coioides) after oral administration.

Pharmacokinetics and elimination of florfenicol and florfenicol amine in grouper held in sea water at 23.3 ± 0.8 °C were studied using HPLC method after they were given a single peroral dose of florfenicol at 24 mg kg(-1) body weight. Florfenicol was rapidly absorbed from intestine and distributed extensively to all the tissues examined. The maximum concentrations (Cmax , μg g(-1) or μg mL(-1) ) in plasma and tissues were observed at 2-6 h (the time to reach maximum concentration, Tmax ) except for bile (Tmax  = 24 h) and were in the order of intestine (52.02 ± 25.07) > bile (49.41 ± 28.16) > gill (45.12 ± 11.10) > plasma (28.28 ± 5.43) > liver (21.97 ± 12.08) > muscle (21.63 ± 6.12) > kidney (20.88 ± 11.28) > skin (19.10 ± 5.88). The drug distribution level was higher in plasma than in extravascular tissues except for bile, based on the ratios of the area under concentration-time curve between tissue and plasma (AUCtissue/plasma ). The elimination of florfenicol was rapid in fish, and the corresponding half-lives (T1/2β ) in the order of magnitude were bile (13.92 h) > muscle or liver (12.31 h) > skin (11.77 h) > plasma (11.57) > gill (11.04 h) > intestine (10.55 h) > kidney (10.05 h). The delayed Tmax , lower Cmax and longer T1/2β for florfenicol amine compared with florfenicol were measured in grouper.