Depletion of residues from milk and blood of cows dosed orally and intravenously with sulfamethazine
Paulson, G.D.; Feil, V.J.; Zaylskie, R.G.; Giddings, J.M.; Slanger, W.D.
Journal - Association of Official Analytical Chemists 77(4): 895-900
1994
ISSN/ISBN: 0004-5756 PMID: 8069119 Document Number: 425551
Cows were dosed orally (n = 4) or intravenously (n = 4) with sulfamethazine (sulmet; 4-amino-N-(4,6-dimethyl-2-pyrimidinyl)benzenesulfonamide) for 5 consecutive days (220 mg/kg of body weight on day 1 and 110 mg/kg on days 2-5). The concentrations of sulmet, N-4-acetylsulfamethazine (Ac-sulmet), and the N-4-lactose conjugate of sulfamethazine (lac-sulmet) were measured in milk and blood collected at 24 h intervals after the last doses of sulmet were given. The method of analysis included (1) spiking of samples with known amounts of 13C-6-labeled reference compounds, (2) resolution of the 3 compounds by reversed-phase chromatography, (3) hydrolysis of lacsulmet, (4) treatment with diazomethane to yield N-1-methyl derivatives, and (5) gas chromatography/mass spectrometry. The ratios of intensities of selected mass spectral ions containing 12C-6 and the corresponding ions containing 13C-6 were used for residue quantitation. Sulmet, which was always the most abundant residue in the blood, decreased to less than 100 ppb 4 days after the last doses were given and to less than 10 ppb 7 days after the last doses. The concentrations of sulmet in milk were approximately one fifth the concentrations of sulmet in blood. The concentrations of lac-sulmet and Ac-sulmet in milk were lower than the concentrations of sulmet in milk.