Pharmacokinetics And Residue Elimination Of Oxytetracycline In Hybrid Tilapia, Oreochromis Aureus×O. Niloticus

Oxytetracycline has been widely used in aquaculture industry due to its low cost and strong anti-bacterial activity.There is an urgent need to carry out studies on pharmacokinetics and residue depletion to establish reasonable dosage time,dosage quantity and withdrawal period prior to harvesting as well as to minimize the impact of irrational drug use.In this study,oxytetracycline is orally administered to hybrid tilapia,Oreochromis aureus×O. niloticus in either aqueous solution or medicated feed in a single dose of 50mg/kg body weight for pharmacokinetics studies of oxytatracycline,and in medicated feed for 5 days at a dose of 50mg/kg body weight to study residue elimination of oxytetracycline.The concentration of hybrid tilapia was determined by high performance liquid chromatography.The results are as follows:Pharmacokinetic data of the hybrid tilapia plasma conformed to a two-compartment model with first-order absorption in either aqueous solution or medicated feed administration,viz., Ct=0.23e^{-0.028(t-0.010)}+0.353e^{-0.011(t-0.010)}-0.584e^{-0.468(t-0.010)} for aqueous solution,and Ct=0.839e^{-0057(t-0.459)}+0.442e^{-0.013(t-0.459)}-1.281e^{-0.282(t-0.459)} for medicated feed.The main pharmacokinetic parameters of aqueous solution and medicated feed administration were respectively as follows:absorption half-life(t_1/2ka)=1.481h,2.458h,distribution half-life (t_1/2α)=24.834h,12.193h,elimination half-life(t_1/2β)=60.312h,51.533h,T_max=7.230h,8.221h, C_max=0.494μg/ml,0.796μg/ml,AUC=37.744h,43.075h.The parameters show that the hybrid tilapia absorbs the drug quicker via orally aqueous solution administration than via medicated feed,but the oxytetracycline distributes and eliminates slower through aqueous solution administration than via medicated feed.The concentration of oxytetracycline was highest in the kidney and lowest in the muscle.The highest concentrations of tissues and organs appeared on day 5,and were 23.537 mg/kg (kidney),14.437 mg/kg(liver),3.166 mg/kg(blood),2.342 mg/kg(muscle),respectively. The oxytetracycline residues in the muscle and liver of the hybrid tilapia fell below the maximum residue limit on the 22nd and 26^th day post dosing at 21℃.The results suggest that a withdrawal time should be at least 26 days before the use of dosed fish as human food.