The pharmacokinetics of amikacin were studied in healthy mature female chickens (n = 6). Single doses of amikacin were injected as an i.v. bolus (10 mg/kg) and i.m. (20 mg/kg) into the same birds with a 30-day rest period between treatments. Amikacin was determined by the fluorescence polarization immunoassay method. The i.v. pharmacokinetics could be described by a two-compartment model with a t1/2 alpha of 0.150 +/- 0.064 h and a t1/2 beta of 1.44 +/- 0.34 h. The total body clearance was 0.109 +/- 0.017 1/h/kg and the volume of distribution at steady-state was 0.193 +/- 0.060 l/kg. Following a single i.m. injection, the peak plasma concentration (Cmax) was 50.79 +/- 4.05 micrograms/ml and occurred at 0.50 +/- 0.26 h. The i.m. extent of absorption was 91.2 +/- 17.6%. Simultaneous modeling of i.v. and i.m. results provided estimates of an absorption half-life of 0.480 +/- 0.158 h. The i.m. pharmacokinetics after repeated administration were studied following the tenth dose (20 mg/kg, every 8 h). The Cssmax was 38.58 +/- 6.96 micrograms/ml and occurred at 0.79 +/- 0.37 h, and the biological half-life of amikacin was 1.86 +/- 0.47 h. The multiple dosing yielded peak concentrations of 39 micrograms/ml and trough concentrations of 3.26 micrograms/ml. Based on these data, the recommended amikacin dosage in chickens is 20 mg/kg body weight every 8 h.

SUMMARY Healthy mature roosters (n = 10) were given gentamicin (5 mg/kg of body weight, IV) and, 30 days later, another dose im Serum concentrations of gentamicin were determined over 60 hours after each drug dosing, using a radioimmunoassay. Using nonlinear least-square regression methods, the combined data of IV and im treatments were best fitted by a 2-compartment open model. The mean distribution phase half-life was 0.203 ± 0.075 hours (mean ± SD) and the terminal half-life was 3.38 ± 0.62 hours. The volume of the central compartment was 0.0993 ± 0.0097 L/kg, volume of distribution at steady state was 0.209 ± 0.013 L/kg, and the total body clearance was 46.5 ± 7.9 ml/h/kg. Intramuscular absorption was rapid, with a half-life for absorption of 0.281 ± 0.081 hours. The extent of im absorption was 95 ± 18%. Maximal serum concentration of 20.68 ± 2.10 μg/ml was detected at 0.62 ± 0.18 hours after the dose. Kinetic calculations predicted that IM injection of gentamicin at a dosage of 4 mg/kg, q 12 h, and 1.5 mg/kg, q 8 h, would provide average steady-state serum concentrations of 6.82 and 3.83 μg/ml, with minimal steady-state serum concentrations of 1.54 and 1.50 μg/ml and maximal steady-state serum concentrations of 18.34 and 7.70 μg/ml, respectively.

The disposition and absorption kinetics of gentamicin were studied in healthy, mature male and female turkeys (n = 10). Single doses of gentamicin (5 mg/kg) were injected either i.v. or i.m. with a 30-day rest period between each treatment. Baseline and serial venous blood samples (n = 17) were collected from each turkey. Serum concentrations of gentamicin were determined in duplicate for 24 h after each treatment, using radio-immunoassay. Using nonlinear least-square regression methods, the combined data of the i.v. and i.m. treatments were best described by a two-compartment open model. Kinetic analysis of the data after a single i.v. dose provided the following mean values: t1/2 alpha = 0.170 +/- 0.093 h, t1/2 beta = 2.57 +/- 0.79 h, MRT = 3.62 +/- 0.96 h, Vc = 0.090 +/- 0.017 l/kg, Vd(ss) = 0.172 +/- 0.024 l/kg, Vd(area) = 0.190 +/- 0.030 l/kg, and Clt = 49.8 +/- 9.8 ml/h/kg. After a single i.m. dose, the following mean values were determined: MRT = 5.10 +/- 1.73 h, t1/2abs = 0.74 +/- 0.66 h, tlag = 0.07 +/- 0.19 h, Clt/F = 50.7 +/- 12.5 ml/h/kg, Vd(area)/F = 0.193 +/- 0.044 l/kg, and F = 102 +/- 21%. Kinetic calculations made with the single i.m. data predicted that an i.m. injection of gentamicin at the dosage rate of 3 mg/kg q. every 12 h would provide average steady state serum concentrations of 4.93 micrograms/ml.