The pharmacokinetics of ceftazidime (CAZ) were studied in lactating (LTG) and non-lactating (NLTG) cows. Two groups (LTG and NLTG) of 5 healthy dairy cows were given ceftazidime (10 mg/ kg body weight) intravenously (i.v.) and intramuscularly (i.m.). Serum and milk (LTG) and serum samples (NLTG) were collected over a 24-h period post-administration. CAZ concentrations in serum and milk were determined by high-performance liquid chromatography, and an interactive and weighted-non-linear least-squares regression analysis was used to perform the pharmacokinetic analysis. The pharmacokinetic profiles in LTG and NLTG cows which had received CAZ i.v. fitted a three-compartment model and a two-compartment model, respectively. The CAZ concentration-time curves in serum and the area under the curve were greater and more sustained (p < 0.05) in the LTG cows by both routes, while the serum clearance (Cls = 72.5 +/- 18.1 ml/h per kg) was lower (p < 0.05) than that in the NLTG cows (Cls = 185.9 +/- 44.2 ml/h per kg). CAZ given i.v. exhibited a relatively long half-life of elimination (t1/2 beta (LTG) = 1.1 +/- 0.2 h; t1/2 beta (NLTG) = 1.4 +/- 0.3 h). Compared with other cephalosporins, CAZ had good penetration into the mammary gland (47.7 +/- 38.2% for CAZ i.v.; 51.1 +/- 39.0% for CAZ i.m.). Finally, the bioavailability of CAZ (F(LTG) = 98.9 +/- 36.8%; F(NLTG) = 77.1 +/- 25.3%) was suitable for its used by the i.m. route in lactating and non-lactating cows.

CEFOTAXIME and ceftazidime are third-generation cephalosporins that are stable to 3-lactamases and have a wide antibacterial spectrum and low toxicity (O'

Concentrations of cefotaxime in serum and tissue fluid were studied in the bovine after intravenous and intramuscular administration at a dosage of 10 mg • kg^-1 body weight. Steers implanted subcutaneously with tissue cages were used. After intravenous bolus administration, profiles of mean concentrations in serum over time were described by a two-compartment open model. The rate constant of elimination was 1.4 ± 0.3 h^-1 and the half-life 0.6 ± 0.1 h. The rate constant of distribution was 11.5 ± 1.9 h^-1, and the half-life was 0.06 ± 0.01 h. The volume of distribution at steady state was 250.6 ± 37.3 ml • kg^-1. The area under the curve was 31.8 ± 7.4 μg • ml^-1 • h. The penetration ratio into tissue fluid was 36.5 ± 15.4%. After intramuscular injection, the half-life was 1.1 ± 0.3 h, the area under the curve was 27.5 ± 6.8 μg • ml^-1 • h, and the penetration ratio into tissue fluid was 47.1 ± 15.8%. The concentrations in tissue fluid after intravenous and intramuscular administration of cefotaxime were elevated during a 6-hour period after administration.

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