Effects of water temperature on tissue depletion of florfenicol and its metabolite florfenicol amine in crucian carp (Carassius auratus gibelio) following multiple oral doses

Tissue depletion of florfenicol (FF) and its metabolite florfenicol amine (FFA) was investigated in crucian carp (Carassius auratus gibelio) following administration of 10 mg/kg body weight (BW) daily for five consecutive days by oral gavage at water temperatures of 10 and 25 degrees C. Plasma and tissue samples, including muscle with skin in natural proportions, liver, and kidney, were collected from 10 fish per sampling point. The concentrations of FF and FFA in each sample were simultaneously determined using high performance liquid chromatography (HPLC) with fluorescence detection. Depletion profiles at different temperatures were estimated and withdrawal periods were calculated. FF was more rapidly eliminated at 25 degrees C, with apparent elimination half-life (t(1/2 lambda z)) values ranging from 8.1 h in skin-on muscle to 9.74 h in plasma, than at 10 degrees C. In contrast, water temperature did not affect FF withdrawal. At 10 degrees C, the withdrawal periods were calculated as 2.81 and 2.83 days based on the maximum residue limit (MRL) of FF plus FFA and the tolerance of FFA both at 1 mu g/g in skin-on muscle, respectively. At 25 degrees C, the corresponding withdrawal periods were calculated as 2.15 and 2.41 days, respectively. Each withdrawal period was rounded to the next day (3 days).