Florfenicol and its metabolite florfenicol amine residue depletion in Ictalurus punctatus

Florfenicol,a broad spectrum antibiotic,is a fluorinated derivative of thiamphenicol and is also similar in structure to chloramphenicol.Florfenicol has equal or superior antibacterial activity compared to thiamphenicol and chloramphenicol and does not cause human aplastic anemia.Florfenicol is used exclusively in controlling bacteria infectious diseases in cultultued fish.A residue depletion study was conducted of florfenicol(FF) and its metabolite forfenicol amine(FFA) in channel catfish(Ictalurus punctatus) at 18 ℃ and 28 ℃ water temperature.After repeated oral administration at a dosage of 10 mg/kg body weight for 3 consecutive days,channel catfish(Ictalurus punctatus) were killed and the musucle,skin,liver,kindey tissues were collected after oral gavage 1,2,3,5,7,9 d of oral gavage administration.Florfenicol(FF) and florfenicol amine(FFA) in tissues were determination by using reverse phase high performance liquid chromatography(RP-HPLC) with UV detection.The mobile phase was acetonitrile-sodium dihydrogen phosphate solution(0.01 mol/L,containing 0.005 mol/L SDS and 0.10% triethylamine)(2∶3,V∶V) and UV detection set at 225 nm.Analyte were extracted with acetone,Dichloromethane was added that made extracts demixed,Defatted with hexane and so on sample treating process.The standard curves were linear in the investigated ranges,0.05～10.0 μg/g of both florfenicol and florfenicol amine in tissues.The correlation coefficient for florfenicol and florfenicol amine were both r≥0.996 2.The recovery of florfenicol was from 75.14% to 92.65% and the recovery of florfenicol amine was from 76.00% to 91.50%.The within-day and day-to-day precision expressed by CV was less than 10% at two drug levels(0.1 and 1.0 μg/g).The detection limits for florfenicol and florfenicol amine in muscule,skin,liver,kindey were 20 and 15 μg/kg,50 and 50 μg/kg,50 and 50 μg/kg,50 and 50 μg/kg respectively.The results showed that the elimination rate was markedly different in different water temperature and the same tissues or different water temperature and the same tissues.The sum of FF and FFA is taken marker residue.The depletion of the marker residue in channel catfish,Ictalurus punctatus is faster at higher water temperature.To compare with other tissues,the elimination of the marker residue in kindey was slowest,Kindey was the main reservoir of the marker residue in channel catfish(Ictalurus punctatus).It is proposed that withdrawl time were 234 ℃·d and 224 ℃·d respectively at 18 ℃ and 28 ℃,According to the maximum residue limit(MRL) of the marker residue of 300 μg/kg in kindey.The reliable theory basis to make dosage regimen and withdrawl time at different water temperature based on the study.