Scientific Publications by FDA Staff

Int J Toxicol 1996 Oct;15(5):436-44

A Case Study: Harmonization of Veterinary Drug Maximum Residue Levels Between the U.S. and Canada

Brynes SD, Teske RH

The Free Trade Agreement between the United States and Canada (FTA) went into effect January 1, 1989. To implement certain provisions of the agreement on technical regulations and standards, the United States Center for Veterinary Medicine, the Canadian Bureau of Veterinary Drugs, and Agriculture Canada established the Working Group on Veterinary Drug Tolerances. The primary charges to the Working Group on Veterinary Drug Tolerances were (1) to harmonize the procedures used for evaluating new animal drugs, performing risk assessments and calculating tolerances, and (2) to harmonize the tolerances (or maximum residue levels, MRLs) for approved drugs, with the goal of having the same tolerances in each country. The first of these charges was met early in the negotiations. Both the US and Canada will use a 6-step evaluation procedure for the human food safety evaluation of new animal drugs. On September 29, 1990, Canada published a list of MRLs for 38 drugs that had been harmonized through the FTA. The progress of the working group and its continuing efforts to harmonize tolerances for approximately 15 other veterinary drugs will be discussed. This paper proposes use of the toxicologically determined acceptable daily intake (ADI) for the drug as the safety standard for reaching conclusions on the acceptability of residues in meat for human consumption. Specifically, the `equivalence¿ of different MRLs for the same veterinary drug would be determined by considering whether they are likely to result in dietary residues that exceed the other country's ADI for the drug. Estimates are made for the veterinary drugs lasalocid and halofuginone hydrobromide. Based on these estimates, the US and Canadian MRLs for each drug would be considered `equivalent¿ for trade purposes.