Toward a regulatory method: comparison and validation of multiresidue procedures for determination of beta-lactam antibiotics in milk
1996
Carson, M.C. | Chu, P.S. | Von Bredow, J.
Intramammary infusion of beta-lactam antibiotics is often used to treat mastitis in lactating dairy cattle. Failure to follow label guidelines for dosage or milk discard time may result in residues of these drugs (amoxicillin, ampicillin, cloxacillin, cephapirin and penicillin G) entering the raw milk bulk tank. Under the U.S. Pasteurized Milk Ordinance, industry must now monitor each milk tanker for the presence of beta-lactams prior to accepting the milk for processing. Several screening tests are currently accepted by the Food and Drug Administration (FDA) for use in this program. Screening tests are designed to pass safe milk; a negative result indicates that the milk contains no unsafe residues of the drugs the test detects. By themselves, screening tests generally do not meet FDA criteria for a regulatory method. Use of a regulatory determinative procedure adds certainty that milk testing positive by a screening test contains violative drug residues. We conducted a laboratory evaluation of several determinative procedures developed by other laboratories for their suitability as part of a regulatory method. The criteria the procedures were evaluated against include: 1) number of residues detected at their tolerance/safe levels; 2) accuracy; 3) precision; 4) ruggedness; and 5) practicability. The procedures studied include: 1) a 2-dimensional liquid chromatographic (LC) assay developed by W.A. Moats, 2) a liquid-liquid extraction procedure employing diazomethane derivatization followed by capillary gas chromatography developed in the lab of M. Petz; 3) a "receptorgram" assay developed by Charm Sciences, Inc.; and 4) an LC procedure using pre-column derivatization with triazole/HgCl2 developed by J. Boison. A comparison of these procedures and our validation results will be presented.
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