Animal drug residue methods

The process of development and validation of animal drug residue methods for US Food and Drug Administration regulatory use... 

Any effort to develop performance criteria for screening test for animal drug residues must have the twin goals of providing for good method performance and of not unnecessarily restricting the development and maturation of an analytical technology that has potential benefits for human food safety and public health. 

R. J. Heitzman, Veterinary Drug Residues. Residues in Food Producing Animals and their Products Reference Materials and Methods, Final Report EUR 14126EN, Office for Official Publications of the European Communities Luxembourg, 1992. 

The US Food and Drug Administration (FDA) evaluates methods to be used in government regulatory laboratories for the determination and confirmation of drug residues in food derived from animal products. The FDA Center for Veterinary Medicine (CVM) oversees the validation (i.e., demonstration that the method is suitable for use) via a protocol known as a method trial. CVM ensures that the appropriate government laboratories have the tools needed to monitor the Nation s food supply. 

The FDA requires [FDC Act, Section 512 (b)(1)(G)] that methods used for the detection and confirmation of drug residues in animal products be practicable. Overseeing the reliability of these methods is the responsibility of the FDA CVM. The methods are corroborated using an interlaboratory evaluation of the method known as a method trial. The method trial is used to demonstrate that the method is suitable for use to detect and confirm drug residues and can be performed by a trained analytical chemist. 

The final difference is that the FDA analyst alone makes the recommendation based on the data for the acceptance of the confirmatory procedure. The conclusion of the analyst stating the suitability of the procedure for confirming the presence of the marker residue is sent directly to the CVM method trial coordinator in the Office of New Animal Drug Evaluation (ONADE) and not back to the sponsor as with the determinative procedure. 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

N. Haagsma and C. van der Water, Immunochemical methods in the analysis of veterinary drug residues, in Analysis of Antibiotic Drug Residues in Food Products of Animal Origin, ed. V. K. Agarwal, Plenum Press, New York, pp. 81-97 (1992). 

A variety of methods were developed for the identification and determination of the antimicrobial nitrofurans. They include LC, colorimetric and polarographic methods. Nitrofurans could be determined in animal tissues by extraction with acetonitrile, SPE and LC-UVD533. An LC-UVD method was statistically validated for the determination of nitrofuran drug residues in poultry534. 

There has been an increasing worldwide public outcry to know what residues and contaminants are in the food supply, and a demand that food be free of residues that could have an impact on the public health. A simplistic but often voiced concept is that edible animal products should be only consumed when all administered drugs and drug-related residues have been totally eliminated. For some time in the past, this concept seemed to guarantee the highest degree of food safety as animal products destined for human consumption were found to be free of drug residues by the analytical methods applied at that time. 

---