Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 13, 1998
Publication Date: N/A
Interpretive Summary: Ceftiofur is a new drug of the B-lactam group intended for veterinary use. It is considered to have low toxicity and no holding time is required following treatment. Ceftiofur is converted to a variety of metabolites in animal tissues; some of which are inhibitory to bacteria. These metabolites may therefore be detected by tests for antibiotics based on inhibition of bacterial growth. It would therefore be useful to be able to distinguish these metabolites from other possible veterinary drug residues. This paper describes a method for determining the principal-free metabolite of ceftiofur, the conjugate with the amino acid cysteine. The cleanup approach used, which involves HPLC fractionation of sample extracts, can be used for simultaneous determination of a variety of antibiotic residues in a single procedure.
Ceftiofur, a recently introduced antibiotic of the B-lactam group, is rapidly converted to metabolites, both free and protein bound, when administered by the prescribed procedure, intramuscular injection. The free metabolites retain antimicrobial activity and may be detected by antibiotic screening tests based on antimicrobial activity. It is thus desirable to distinguish ceftiofur metabolites from other antibiotics. A multiresidue procedure for B-lactams in milk was adapted for the determination of free ceftiofur metabolites by collecting appropriate HPLC fractions during cleanup. Analysis of tissues from treated animals showed that the principal-free metabolite was the desfuroylceftiofurcysteine conjugate.