PLASMA AND URINE DISPOSITION AND DOSE PROPORTIONALITY OF CEFTIOFUR AND METABOLITES IN DOGS AFTER SUBCUTANEOUS ADMINISTRATION OF CEFTIOFUR SODIUM

Nine male dogs (10.3-13.5 kg body weight) were randomly assigned to th ree groups of three dogs each and administered ceftiofur sodium subcut aneously as a single dose of 0.22, 2.2, or 4.4 mg ceftiofur free acid equivalents/kg body weight. Plasma and urine samples were collected se rially for 72 h and assayed for ceftiofur and metabolites (derivatized to desfuroylceftiofur acedtamide) using high-performance liquid chrom atography. Urine concentrations remained above the MIC(90) for Escheri chia coli (4.0 mu g/mL) and Proteus mirabilis (1.0 mu g/mL) for over 2 4 h after doses of 2.2 mg/kg (8.1 mu g/mL) and 4.4 mg/kg (29.6 mu g/mL ), the interval between treatments for ceftiofur sodium in dogs, where as urine concentrations 24 h after dosing at 0.22 mg/kg (0.1 mg/Ib) we re below the MIC(90) for E. coli and P. mirabilis (0.6 mu g/mL). Plasm a concentrations were dose-proportional, with peak concentrations of 1 .66 +/- 0.0990 mu g/mL, 8.91 +/- 6.42 mu g/mL, and 26.7 +/- 1.07 mu g/ mL after doses of 0.22, 2.2, and 4.4 mg/kg, respectively. The area und er the plasma concentration versus time curve, when normalized to dose , was similar across all dosage groups.