DETERMINATION OF FREE METABOLITES OF CEFTIOFUR IN ANIMAL-TISSUES WITHAN AUTOMATED LIQUID-CHROMATOGRAPHIC CLEANUP

Ceftiofur, a recently introduced antibiotic of the beta-lactam group, is rapidly converted to both free and protein-bound metabolites when a dministered by the prescribed procedure, intramuscular injection. Free metabolites retain antimicrobial activity and may be detected by anti biotic-screening tests based on antimicrobial activity. It is thus des irable to distinguish ceftiofur metabolites from other antibiotics. A multiresidue procedure for p-lactams in milk was adapted for determina tion of free ceftiofur metabolites by collecting appropriate liquid ch romatographic fractions during cleanup. analysis of tissues from treat ed animals showed that the principal free metabolite was the desfuroyl ceftiofurcysteine conjugate.