Comparative pharmacokinetics of gentamicin in laying hens.

The aim of this study was to compare pharmacokinetics of gentamicin sulphate (5 mg/kg body weight) after single intravenous, intramuscular and subcutaneous administration in laying hens. Blood samples were collected at time 0 (pretreatment), and at 0.083, 0.166, 0.25, 0.5, 0.75, 1, 2, 4, 8, 12, 24, 36 and 48 h after drug administration in 24 laying hens. Gentamicin concentrations were determined using the HPLC method recommended by the European Union by some modifications. The total concentration of the gentamicin (C1, C2 and C1a) was calculated. The lowest detection limit was 0.01 μg/ml. Noncompartmental pharmacokinetic analyses were performed using Excel add-in program, PK solver. Following IV administration the area under the plasma time-concentration curve from time zero to infinity (AUC0-∞), first-order elimination rate constant (λz), terminal half-life (t1/2λz) and mean residence time (MRT) were 224.46 μg/mL h, 0.06 h-1, 11.52 h and 9.50 h, respectively. After i.m. and s.c. dosing, the mean maximum plasma concentrations (Cmax) were 26.64 and 36.92 μg/mL, achieved at a same post-injection times (Tmax) of 0.75 h, respectively. The t1/2λz was 8.35 and 8.24 h, the MRT was 11.05 and 9.79 h, respectively, after IM and SC administration. There are no significant between IM and SC administration excluding the Cmax values and between i.v. and other administration excluding the t1/2λz values.