We studied the metabolism and elimination of norfloxacin in rainbow trout (Oncorhynchus mykiss) following a single oral administration of 50 mg/kg at 15 ± 2°C. Norfloxacin was measured by high-performance liquid chromatography-tandem mass spectrometry in plasma, muscle, liver, kidney, skin and remainder tissues, and the concentrationtime curve was characterized by a double peak. The drug was absorbed rapidly; the first peak appeared within 4 h, and the second peak appeared within 24 h in all substrates tested. The maximal concentrations in plasma, muscle, liver and kidney were 0.468 mg/L, 14.146 mg/kg, 6.445 mg/kg and 0.977 mg/kg, respectively. The distribution half-life was 5.814, 9.026, 17.027 and 1.004 h, respectively. The elimination half-life was 41.205, 41.667, 44.896 and 54.908 h, respectively. Using the kidney as the reference tissue for norfloxacin monitoring in aquaculture and 2 μg/kg as a maximum residue limit standard, it takes 555 temperature-day (°C days) for norfloxacin to be completely eliminated from rainbow trout.
Keywords: elimination; norfloxacin; pharmacokinetics; rainbow trout; residues.
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