Pharmacokinetics and elimination regularity of florfenicol and florfenicol amine,in rice field eel(Monopterus albus)

The aim of this study was to evaluate the pharmacokinetics of florfenicol(FF) and its metabolite,florfenicol amine(FFA),after oral(p.o.) administration and investigate their depletion after multiple oral administrations for 3 consecutive days in rice field eel(Monopterus albus) at 25 ℃.After p.o.administration of 20 mg/kg,the peak concentration of FF(Cmax) and time to reach FF peak concentration(Tmax) in plasma,liver,kidney and muscle were 6.07 mg/L,7.57 mg/kg,9.34 mg/kg,5.87 μg/mg and 3.67 h,4.45 h,2.01 h,9.28 h,respectively.The order of t1/2β was kidney(29.26 h)liver(19.32 h)muscle(17.22 h)plasma(10.84 h).FFA was also found in all tissues with a lower concentration than FF after p.o.administrations throughout the study.The longest t1/2β of 45.93 h and the largest metabolic rate(MR) of 49.21% were observed in kidney.After multiple oral doses(20 mg/(kg·d) for 3 d),the highest residues was observed in kidney,next in liver and then in muscle.The residues was undetectable in all tissues after 10 d which was similar to the former 12 d withdrawal time to ensure that the residues of florfenicol are less than the maximal residue limit of tolerance established by Japan.