The Food and Drug Administration in December published a final rule revising the definition of "no residue" in the new animal drug regulations to mean that no residue is detected with an approved regulatory method. This means that any residue in the target tissue must be undetectable or below the limit of detection (LOD) of the approved regulatory method.

The agency has defined the limit of detection of an analytic method as the lowest concentration of analyte—the chemical that is detected and measured by the analytic method—that can be confirmed by the approved regulatory method.

This final rule became effective Jan. 22, 2003. Additional information on the final rule may be found in the Dec. 23, 2002, Federal Register (www.fda.gov/OHRMS/DOCKETS/98fr/02-32216.htm) and from Dr. Steven D. Brynes, Center for Veterinary Medicine (HFV-151), Division of Food Safety, Food and Drug Administration, 7500 Standish Place, Rockville, MD 20855, (301) 827-6975.

The FDA revised the original residue definition promulgated in 1987, "Regulation of Carcinogenic Compounds Used in Food-Producing Animals," in response to a 1995 legal opinion by the Department of Justice, which concluded that the operational definition of "no residue" was not legally supportable. The department did state the FDA might use the "no significant risk" level as a benchmark for rejecting analytic methods, however.

The FDA will use submitted data on the method to determine the LOD. The data necessary to meet the requirements of the new rule are identical, or nearly identical, to those previously delineated. Moreover, the revision of the definition of "no residue" preserves the public health to the same degree.