Stability study of selected veterinary drug residues spiked into extracts from different food commodities

Authors: Lehotay, Steven; LE FLOCH, MAIWENN - French Agency For Food, Environmental And Occupational Health & Safety (ANSES); Lightfield, Alan; COUËDOR, PIERRICK - French Agency For Food, Environmental And Occupational Health & Safety (ANSES); HURTAUD-PESSEL, DOMINIQUE - French Agency For Food, Environmental And Occupational Health & Safety (ANSES); MICHLIG, NICOLAS - Oak Ridge Institute For Science And Education (ORISE); VERDON, ERIC - French Agency For Food, Environmental And Occupational Health & Safety (ANSES)

Submitted to: Food Additives & Contaminants. Part A: Chemistry, Analysis, Control, Exposure & Risk Assessment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2023
Publication Date: 8/15/2023
Citation: Lehotay, S.J., Le Floch, M., Lightfield, A.R., Couëdor, P., Hurtaud-Pessel, D., Michlig, N., Verdon, E. 2023. Stability study of selected veterinary drug residues spiked into extracts from different food commodities. Food Additives & Contaminants. Part A: Chemistry, Analysis, Control, Exposure & Risk Assessment. 40:1198-1217. https://doi.org/10.1080/19440049.2023.2240444.
DOI: https://doi.org/10.1080/19440049.2023.2240444

Interpretive Summary: Veterinary drug residues in food animal tissues are monitored worldwide to ensure compliance with domestic and international regulations, and analyses must meet regulatory needs. The results must be demonstrated to be accurate for a wide array of drugs, which includes guidelines for proving stability of the drug analytes in the final extracts in case of re-analysis. In this study, 31 common veterinary drugs were tested for rates of degradation at regulatory levels of interest in extracts of eggs, milk, meat, kidney, and liver at different storage temperatures over the course of a month. Results from two different laboratories and methods were compared to show differences and similarities in how long the veterinary drug solutions could be stored to still achieve acceptable results, which is useful information for regulatory chemists worldwide.

Technical Abstract: Analyte stability is more commonly a confounding factor in analytical chemistry than many analysts recognize. Most guides to analytical method validation call for a stability assessment of the analytes in reference solutions, samples, and extracts, but reports of such stability studies are rare in the scientific literature. In this study, we assessed the stability of 31 common veterinary drugs in water and final extracts of bovine (milk and kidney/liver) and chicken (muscle and egg) matrices. Two different sample preparation methods were evaluated for one month storage of the final extracts at typical room, refrigerator, and freezer temperatures. Liquid chromatography – mass spectrometry (LC-MS) by triple quadrupole and high-resolution techniques was used for analysis of the extracts spiked at different relevant concentrations for general regulatory purposes (10-1000 ng/g sample equivalent). Comparison of results between two labs demonstrated that stable drugs (=20% loss) at all tested conditions consisted of danofloxacin, enrofloxacin, florfenicol, flubendazole, hydroxy-flubendazole, flumequine, flunixin, 5-hydroxy-flunixin, lincomycin, and meloxicam. The tested drugs found to be the most unstable consisted of the ß-lactams (ampicillin, cefalexin, cloxacillin, and penicillin G). Curiously, the following antibiotics (mostly macrolides) were apparently more stable in sample extracts than water: emamectin, erythromycin, ivermectin, lasalocid, monensin, tilmicosin, tulathromycin, and tylosin. Those and the other drug analytes (ciprofloxacin, doxycycline, florfenicol amine, 2-amino-flubendazole, oxytetracycline, sulfadiazine, sulfadimethoxine, sulfamethazine, and trimethoprim) were mostly stable for a month in refrigerated extracts, especially at higher concentrations, but not in all cases. In practice, freezer storage of extract solutions was found to be acceptable for at least a month, with a few exceptions.