THE PHARMACOKINETICS OF CEFTAZIDIME IN LACTATING AND NONLACTATING COWS

The pharmacokinetics of ceftazidime (CAZ) were studied in lactating (L TG) and non-lactating (NLTG) cows. Two groups (LTG and NLTG) of 5 heal thy dairy cows were given ceftazidime (10 mg/kg body weight) intraveno usly (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-performan ce liquid chromatography, and an interactive and weighted-non-linear l east-squares regression analysis was used to perform the pharmacokinet ic analysis. The pharmacokinetic profiles in LTG and NLTG cows which h ad received CAZ i.v. fitted a three-compartment model and a two-compar tment 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 (Cl-s=72.5/-18.1 ml/h per kg) was lower (p <0.05) than that in the NLTG cows (Cl -s=185.9+/-44.2 ml/h per kg). CAZ given i.v. exhibited a relatively lo ng half-life of elimination (t(1/2 beta) (LTG)=1.1+/-0.2 h; t(1/2 beta ) (NLTG)=1.4+/-0.3 h). Compared with other on cephalosporins, CAZ had good penetration into the mammary gland (47.7+/-38.2% for CAZ i.v.; 51 .1+/-1+/-39.0% for CAZ i.m.). Finally, the bioavailability of CAZ (F(L TG)=98.9+/-36.8%;F(NLTG)=77.1+/-25.3%) was suitable for its use by the i.m. route in lactating and non-lactating cows.