Pharmacokinetics, bioavailability and withdrawal period of antibiotic oxytetracycline in catfish Pangasianodon hypophthalmus

Abstract

The antibiotic oxytetracycline (OTC) has been widely used for therapeutic and preventive management of bacterial diseases in finfish and shellfish. In the present study the bioavailability, pharmacokinetics, and withdrawal period of the OTC have been determined following in-feed administration in intensively cultured catfish Pangasianodon hypophthalmus. Furthermore, the pharmacokinetic parameters of oral route were also compared with parenteral route. Drug concentrations were measured in various tissues at different time intervals by LC-MS/MS. The study revealed the drug kinetics best followed the enterohepatic circulation model with very poor bioavailability and low blood concentration after oral administration. In the withdrawal study, after 10-days of in-feed administration at the therapeutic dose the drug reached very high concentrations in the liver and kidneys but did not attain minimum inhibitory concentrations (MICs) in blood or flesh. OTC concentration also did not exceed the recommended MRL value in flesh; however, considering high amounts of the chemical in the liver and kidneys a withdrawal period of 4 days (at 28 ? 1.5oC) is recommended for consumer safety. Poor bioavailability and non-attainment of minimum therapeutic concentration in blood and flesh do not warrant in-feed administration of OTC for control of bacterial diseases in P. hypophthalmus.