METABOLISM OF [C-14] CEFTIOFUR HYDROCHLORIDE IN SWINE AFTER INTRAMUSCULAR INJECTIONS

Twelve mix-breed swine (26.5-42.5 kg) received three intramuscular dos es of [C-14]ceftiofur hydrochloride at 24 h intervals. Three males and three females received 6.76 +/- 0.83 mg of [C-14]ceftiofur free acid equivalents (CE)/kg body weight (bw)/day, while three males and three females received 4.41 +/- 0.97 mg of CE/kg bw/day. All swine were euth anatized 12 h after the last dose. Most of the C-14-residues (> 80%) i n tissues were associated with macromolecules. The rest of the C-14-ac tivity corresponded to desfuroylceftiofur (DFC)-cysteine. The type and percentages of metabolites present in the urine of swine were similar to those previously observed for ceftiofur sodium (Gilbertson et al., J. Agric. Food Chem. 1995, 43, 229-234), with DFC-cysteine and DFC-di mer being the major ones. In plasma, the major portion of the C-14-act ivity ( > 85%) was associated with macromolecules. DFC-cysteine was th e only detectable C-14-component of the macromolecule free plasma frac tion. This study indicated that ceftiofur hydrochloride was absorbed i n the same ionic form as ceftiofur sodium, acceding to the same primar y metabolite DFC. The type of metabolites present in swine after intra muscular injection were the same, regardless of the salt administered.