Pedersoli, W.M., Ravis, W.R., Jackson, J., Shaikh, B. Disposition and bioavailability of neomycin in Holstein calves.J. vet. Pharmacol. Therap.17, 5–11.The disposition and absorption kinetics of neomycin were studied in healthy ruminating dairy calves (n‐6), approximately 3‐months‐old. The calves were treated with single intravenous (i.v.) (12 mg/kg), intramuscular (i.m.) (24mg/kg), oral (p.o.) (96 mg/kg) and repeated p.o. (96 mg/kg, b.i.d., 15½ days) doses of neomycin. A 3‐week rest period was allowed between treatments A and B and B and C Baseline and serial venous blood samples were collected from each calf plasma concentrations of neomycin were determined by a high performance liquid chromatography procedure. The resulting data were evaluated by using compartmental pharmacokinetic models and nonlinear least squares regression analysis. The mean of some selected parameters weret½λ3 7.48 ± 2.02 h, Clt= 0.25 ± 0.04 L/h/kg,Vd(ss)= 1.17 ± 0.23 L/kg, andMRT =4.63 ± 0.87 h for the i.v. data andt½= 11.5 ± 3.8 h,MRTabs= 0.960 ± 1.001 h, F = 127 ± 35.2%, andClt/F= 0.199 ± 0.047 L/h/kg for the i.m. data, respectively. Only one calf absorbed neomycin to any significant degree (F = 0.0042) after a single p.o. dose. Selected mean parameters determined after repeated oral dosing were: F = 0.45 ± 0.45%, Cmax= 0.26 ± 0.37m̈g/ml, and tmax= 2.6 ± 2.9 h. Terminal half‐lives determined for the i.v. and i.m. treatments were considerably longer than those reported p