title: Identification of cephapirin metabolites and degradants in bovine milk by electrospray ionization--ion trap tandem mass spectrometry.
abstract: Liquid chromatography-ion trap tandem mass spectrometry (LC-MS/MS) with electrospray ionization was used to identify cephapirin metabolites and degradants in milk from cows dosed with cephapirin. The milk was extracted according to a previously published procedure. Structures for various components were tentatively identified by their molecular weight, product ion mass spectra, and/or correspondence to standard mass spectra. These components may have occurred as metabolites or as degradants that occurred on storage or during extraction. Compounds identified in the milk included cephapirin, desacetylcephapirin, cephapirin lactone, hydrolyzed cephapirin, and a reduced cephapirin lactone that has not previously been reported. Methylcephapirin was also identified, possibly as a trace contaminant in the formulation. Analysis of incurred milk extracts showed that cephapirin and desacetylcephapirin are the major residues in milk. Desacetylcephapirin residues persisted about as long as the parent drug. The detection limit for both residues by LC-MS/MS was approximately 1 ng/mL in milk. These results have implications for microbiological methods or rapid test kits, if such methods or kits respond to cephapirin metabolites and degradants present in the milk.
authors.affiliation: Center for Veterinary Medicine, U.S. Food and Drug Administration, 8401 Muirkirk Road, Laurel, Maryland 20708, USA. dheller@cvm.fda.gov
authors.forename: D N
authors.initials: DN
authors.lastname: Heller
authors.forename: D A
authors.initials: DA
authors.lastname: Kaplan
authors.forename: N G
authors.initials: NG
authors.lastname: Rummel
authors.forename: J
authors.initials: J
authors.lastname: von Bredow
mesh_terms: D000818:Animals; D002417:Cattle; D002514:Cephapirin / Q000031:analogs & derivatives / Q000032:analysis* / Q000378:metabolism; D002853:Chromatography, Liquid / Q000379:methods*; D005260:Female; D013058:Mass Spectrometry / Q000379:methods*; D008892:Milk / Q000737:chemistry*
chemical_list: D002514:Cephapirin