Comparative pharmacokinetics of an injectable cephalexin suspension in beef cattle

This study describes and compares the pharmacokinetics of a single 7.5 mg/kg dose of cephalexin monohydrate oil-based 20% suspension after its administrations to six cows by the intramuscular (i.m.) and subcutaneous (s.c.) routes, and to five calves by the i.m. route. Significantly (P < 0.05) higher peak plasma concentrations (5.6 ± 0.79 μg/ml versus 3.93 ± 1.24 μg/ml) and lower half-life (1.81 ± 0.56 h versus 4.21 ± 0.82 h) and mean residence time (4.12 ± 1.07 h versus 6.63 ± 0.85 h) were obtained after i.m. administration when compared to the s.c. administration to cows. No differences were found between pharmacokinetic parameters calculated for cows and calves. Cephalexin plasma concentrations remained above 0.5–0.75 μg/ml for 11–14 h and 8–9 h after the s.c. and i.m. administrations, respectively. Thus, route of administration may be an important issue to be considered when calculating dosage schedules for successful treatments and safe withdrawal times for veterinary medicines.