In this study, the pharmacokinetic profile of enrofloxacin (EF) and its major metabolite, ciprofloxacin (CF), were investigated in brown trout (Salmo trutta fario) (n = 150) after intravenous (i.v.) and oral (p.o.) administrations of a single dose of 10 mg kg(-1) body weight (b.w.) at 10 degrees C. The plasma concentrations of the drugs were determined by high-performance liquid chromatography (HPLC-UV) from 0.08 to 120 h. Pharmacokinetic parameters were described by the two-compartment open model for intravenous and oral administrations, respectively. After intravenous administration, the elimination half-life (t(1/2 beta)), apparent volume of distribution at steady-state (V(ss)) and total body clearance (Cl(tot)) of enrofloxacin were 19.14 +/- 1.51 h, 3.40 +/- 0.18 L kg(-1) and 0.14 +/- 0.01 L kg h(-1), respectively. After oral administration, the maximum plasma concentration (C(max)), time of maximum concentration (t(max)) and bioavailability (F%) were 2.30 +/- 0.08 mu g mL(-1), 8 h and 78 +/- 4%, respectively. Ciprofloxacin was not detected in the present study. The elimination half-life for enrofloxacin following oral administration was longer than values calculated for other animals. After oral administration, the mean plasma concentration was well above the minimum inhibitory concentrations (MICs)-that is, >0.5 mu g mL(-1) at 36 h-for most gram-negative fish pathogens. It is possible and practical to obtain therapeutic blood concentrations of enrofloxacin in brown trout (S. trutta fario) using oral administration of 10 mg kg(-1) body weight; therefore, it may be effective in the therapy for brown trout diseases. (C) 2009 Elsevier B.V. All rights reserved.