Pharmacokinetics of oxolinic acid in sea-bass, Dicentrarchus labrax (L., 1758), after a single rapid intravascular injection

The pharmacokinetics of oxolinic acid was studied in sea-bass ( Dicentrarchus labrax ). The fish were kept in seawater at 15.2°C with a 12 h/12 h photoperiod. Oxolinic acid was injected in the caudal vein of anaesthetized sea-bass in a single rapid intravascular administration at a dose of 10 mg/kg of body weight. Plasma concentrations of oxolinic acid were determined using two analytical methods, a classic plate diffusion bioassay using Escherichia coli and a high performance liquid chromatography (HPLC) using solid phase extraction with an internal standard and a U.V. detection. The mean recoveries were 99.6% and 110.8% and determination limits were 0.04 μg/mL and 0.02 μg/mL, for the bioassay and the HPLC respectively. Compared to other fish species, the oxolinic acid was rapidly (absorption half life, t_a1/2= 0.69 h) distributed to body tissues outside the blood volume (volume of central compartment, V_c= 0.4 L/kg) and presented a large volume of distribution (V_dss= 2.55 L/kg). Considering its disappearance from the central compartment (rate constant: central-eliminated, k ₁₀= 0.16 h^–1) and its total body clearance ( Cl _t= 0.066 L/kg.h), the elimination phase of the oxolinic acid in sea-bass was shorter than in trout kept in freshwater, and longer than in salmon in seawater. Consequently, the area under the concentration–time curve ( AUC = 157 μg.h/mL) and the mean residence time ( MRT = 42 h) were relatively low and short, respectively.