Pharmacokinetics And Residues Of Marbofloxacin In Crucian Carp (Carassius Auratus) At Different Temperatures

Pharmacokinetics and residue elimination of marbofloxacin(MBF) were studied in crucian carp(Carassius auratus) kept at two water temperatures of 15 and 25℃.MBF concentrations in plasma and tissues were analyzed by means of reversed-phase high-performance liquid chromatography(RP-HPLC) after liquid-liquid extraction.The correlation of calibration curves were all good,which correlation coeffcients(r) were more than 0.9990.The average extraction recoveries were more than 90%from plasma, more than 80%from muscle,liver and kidney,and more than 73%from skin.The method was accurate and the relative recoveries were in the range of 85%-115%in all tissues.The intra-day and inter-day coefficients of variation were less than 10%and 15%, respectively.This indicated that the method had a good precision.The limits of detection (LOD) were 0.02μg/mL,0.02μg/g,0.025μg/g,0.02μg/g and 0.025μg/g in plasma,muscle, skin,liver and kidney,respectively.The limits of quantitation(LOQ) were 0.05μg/mL, 0.05μg/g,0.0625μg/g,0.05μg/g and 0.0625μg/g in the corresponding tissues, respectively.Fish were administered orally with a single dosage of 10mg/kg body weight in the pharmacokinetics group.The results revealed that the pharmacokinetic characteristics of MBF in crucian carp manifested rapid absorption,wide distribution and slow elimination. Water temperature played an important role in the kinesics process.The plasma concentration-time data conformed to two-compartment open models at both temperatures.The absorption half-lives(t_1/2ka) of MBF were found to be 0.36 and 0.23h at 15 and 25℃,respectively,and the distribution half-lives(t_1/2α) were 4.48h at 15℃and 0.87h at 25℃.The maximum plasma concentration(C_max) and the time-point of maximum plasma concentration(T_max) were calculated as 6.43μg/mL and 1.74h at 15℃and 8.36μg/mL and 0.78h at 25℃.The elimination half-lives(t_1/2β) were 50.75 and 25.05h at 15 and 25℃,respectively.The distribution volumes(V_d/F) of MBF were estimated to be 1.36L/kg at 15℃and 0.87L/kg at 25℃.The total clearances of MBF (CL_b) were computed as 0.03 and 0.05L/(h·kg) at 15 and 25℃,respectively.The areas under the concentration-time curve(AUC) were 301.80μg·h/mL at 15℃and 182.80μg·h/mL at 25℃. After repeated oral administration with a dosage of 10mg/kg body weight per day for 3 days,fish were sacrificed at 3,10,24,48,72,96,144,192,240 and 312h after the last administration and samples of muscle,skin,liver and kidney were collected to determine MBF concentrations.The results showed that the elimination half-lives(t_1/2ke) of MBF from all tissues at 15℃were longer than those at 25℃.The drug could still be detected at 13d time-point after the last administration at both temperatures,and the concentrations of MBF were highest in skin at this time-point.Comparing with the other tissues,the elimination of MBF in skin was slowest,which behaved as a reservoir in crucian carp.The pharmacokinetics study revealed that a repeated oral dosage of 5.46mg/kg body weight every two days at 15℃and a repeated oral dosage of 4.41mg/kg body weight every day at 25℃might be efficacious against bacteria in crucian carp.Based on the results of the residue study,the withdrawal periods should not be less than 68d at 15℃and 30d at 25℃in order to make the tissues safe for consumption.