Pharmacokinetics of doxycycline in tilapia (Oreochromis aureus x Oreochromis niloticus) after intravenous and oral administration

The pharmacokinetics of doxycycline was studied in plasma after a single dose (20 mg/kg) of intravenous or oral administration to tilapia (Oreochromis aureus 9 Oreochromis niloticus) reared in fresh water at 24 degrees C. Plasma samples were collected from six fish per sampling point. Doxycycline concentrations were determined by high-performance liquid chromatography with a 0.005 mu g/mL limit of detection, then were subjected to noncompartmental analysis. Following oral administration, the double-peak phenomenon was observed, and the first (C-max1) and second (C-max2) peaks were 1.99 +/- 0.43 mu g/mL at 2.0 h and 2.27 +/- 0.38 mu g/mL at 24.0 h, respectively. After the intravenous injection, a C-max2 (12.12 +/- 1.97 mu g/mL) was also observed, and initial concentration of 45.76 mu g/mL, apparent elimination rate constant (lambda(z)) of 0.018 per h, apparent elimination half-life (t(1/2 lambda z)) of 39.0 h, systemic total body clearance (Cl) of 41.28 mL/h/kg, volume of distribution (Vz) of 2323.21 mL/kg, and volume of distribution at steady-state (Vss) of 1356.69 mL/kg were determined, respectively. While after oral administration, the lambda(z), t(1/2 lambda z), and bioavailability of doxycycline were 0.009 per h, 77.2 h, and 23.41%, respectively. It was shown that doxycycline was relatively slowly and incompletely absorbed, extensively distributed, and slowly eliminated in tilapia, in addition, doxycycline might undergo enterohepatic recycling in tilapia.