Drug residue methods

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

Quality criteria for quantitative analytical methods, in general, have been proposed or arc lo be proposed by several international organizations including the Association of Official Analytical Chemists, the Food and Drug Administration, the Codex Committee for Residues of Veterinary Drugs in Food, the International Dairy Federation, and the European Union. The European Union, in particular, has laid down minimum quality criteria for quantitative drug residue methods,... 

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. 

A method should be able both to quantify the amount of marker drug residue present in the sample and to identify the compound unambiguously. Historically, this required two distinct procedures a determinative procedure used to quantify the analyte, and a confirmatory procedure used to unequivocally identify the analyte. The need for two procedures was driven by the limitations of available technology. Most determinative methods over the last two decades have been based on liquid chromatography, usually with ultraviolet (UV)/visible or fluorescence defection. Limitations of cost. 

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). 

Ryan, J.J. and H.A. McLeod. 1979. Chemical methods for the analysis of veterinary drug residues in foods. Part I. Residue Rev. 71 1-82. 

Detection of drug residues that contaminate surfaces and vapors seeping from caches requires that the sensitivity of such methods is generally in the sub-microgram range. Individuals who have handled drugs may have residues on their hands in the range of 1-10 pg [2], which can... 

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. 

Researchers at Sunesis pharmaceuticals have developed a fragment-based drug discovery method termed tethering [25]. The approach, which is illustrated in Scheme 2.6, shares a number of features with DCC. Whereas protein-directed DCLs equilibrate small molecules via disulfide formation, say, in the presence of a protein that acts as a thermodynamic trap, tethering uses a cysteine residue on the protein surface to reversibly capture small-molecule thiol fragments from solution. Tethering is designed... 

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