Dietary intake estimates as a means to the harmonization of maximum residue levels for veterinary drugs. II. Proposed application to the Free Trade Agreement between the United States and Canada.

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 Food and Drug Administration's Center for Veterinary Medicine, Health and Welfare Canada's Bureau of Veterinary Drugs, and Agriculture Canada established the Working Group on Veterinary Drug Tolerances. The progress of the working group and its continuing efforts to harmonize tolerances for approximately 15 veterinary drugs are 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, fenbendazole, morantel tartrate, halofuginone, and tilmicosin. Based on these estimates, the U.S. and Canadian MRLs for each drug would be considered equivalent for trade purposes.