[C-14] CEFTIOFUR SODIUM-ABSORPTION, DISTRIBUTION, METABOLISM, AND EXCRETION IN SHEEP FOLLOWING INTRAMUSCULAR INJECTIONS

Six Columbia and mixed-breed sheep (three rams and three females, 33-4 4 kg) were euthanatized 12 h after the last of 5 intramuscular doses a t 2.2 mg of [C-14]ceftiofur sodium/kg of body weight. Total dose accou ntability was 103.5 +/- 4.5%: 92.55 +/- 4.10% in urine, 6.53 +/- 0.85% in feces, 2.40 +/- 0.14% in the carcass, and 0.69 +/- 0.32% in the in testinal tract. Kidneys were the tissues with highest residue concentr ation (9.016 +/- 1.153 mu g/g, 0.29% of the dose). Most residues found in kidney and liver were associated with macromolecules (95.7% and 90 .5%, respectively). Of the free residues, all corresponded to polar me tabolites devoid of the beta-lactam ring necessary for biological acti vity. Desfuroylceftiofur (DFC)-dimer was the most abundant metabolite (47.58%) found in urine. Polar metabolites devoid of a beta-lactam rin g comprised 38.5% of the total residues. In plasma, DFC was conjugated to albumin. Free residues containing an intact beta-lactam ring were not found. [C-14]- Ceftiofur itself was never found in the excreta or plasma or as a tissue residue.