Project Number: 5442-32000-014-14
Start Date: Jun 01, 2014
End Date: May 31, 2015
Under an Interagency agreement from FDA-CFSAN, scientists at USDA-ARS-NPA will experimentally determine the drug residue partitioning characteristics of a list of pre-determined drugs added to pasteurized milk evaluated through pre-determined milk partitioning procedures. During the performance period of this Interagency agreement, USDA-ARS will: 1. In consultation with FDA, identify and obtain at least 8 veterinary drugs with radio-isotope-labeling for the partitioning study. Depending on the pilot study results, and, if time allows, additional drugs could be added to the list of potential drugs. The list of potential drugs has been provided to USDA-ARS in order of preference, although this prioritized list may change, based on new information obtained on available drugs, and based on the pilot test results. 2. The main focus of the study will be on the extent of binding of drug to fat and protein within dairy milk products. Approach will be to assay radioactivity in milk fractions after (a) skimming of cream, (b) curding, and (c) isolation of whey protein. Triplicates will be used, along with blanks and controls at three environmentally relevant drug concentrations. 3. The work will be divided into three experimental phases. a) Distribution of fortified, radiolabeled, target drugs into the aqueous (skim milk) and cream (fat) phases. This will be accomplished by centrifugation. Radiochemical will be quantitated in both compartments by liquid scintillation counting and combustion analysis, respectively. Aliquots of skim milk and cream extracts will by assessed qualitatively and quantitatively for metabolites/degradates by thin layer chromatography-radioactivity monitoring. b) Partitioning of fortified, radiolabeled, target drugs in skim milk into the curd (insoluble protein) fraction and the whey (water soluble protein) fraction during cheese making. Curding (protein hydrolysis) will be achieved with rennet incubation, followed by physical removal of the curd layer from the whey fraction. Aliquots of whey and curd extracts will by assessed qualitatively and quantitatively for metabolites/degradates by thin layer chromatography-radioactivity monitoring. c) Determine the extent of binding of fortified, radiolabeled, target drugs to whey fraction proteins. This will be accomplished by separation of the whey proteins(>10 kiloDaltons; retentate) from the small molecule/water-soluble fraction (permeate) via ultrafiltration. Aliquots of retentate and/or its extracts as well as permeate will by assessed qualitatively and quantitatively for metabolites/degradates by thin layer chromatography-radioactivity monitoring. 4. USDA-ARS will provide a detailed report of the results and methodology to FDA. 5. Provide the resulting data to FDA in a format mutually agreed upon.