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The harmonization of standards and procedures for establishing tolerances or maximum residue levels (MRLs) for veterinary drug residues in edible animal products is a major goal of the international veterinary drug community. Such harmonization would contribute to easing trade barriers. 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 another country's ADI for the drug. Two methods of estimating dietary intake are described, and estimates are made for the veterinary drugs albendazole and ivermectin. Based on these estimates, the US and JECFA MRLs for each drug would be considered 'equivalent' for trade purposes.

Aquaculture has become a highly technical industry. There is a great need for the producers, scientists, government agencies, and drug manufacturers to become more involved in the drug development process so that the industry continues its growth. I believe that this should be the major goal of this conference. I urge all of the attendees to participate intensely in our round tables to make this goal a reality in future years.

The United States Food and Drug Administration's assessment strategy for the determination of the carcinogenic potential of drug residues in food-producing animals is embodied in its Human Food Safety Policy. This policy calls for the utilization of a threshold-assessment procedure to determine whether a veterinary drug possesses carcinogenic potential. Chronic lifetime studies in rodents must be performed if it is deemed that the agent may possess carcinogenic properties. A virtually safe level (VSL) of exposure for man is established by applying a modified statistical linear-extrapolation model to the carcinogenic dose-response relationship seen in the test-animal studies. Identification of the major metabolites in the total drug residue in the target animals is required, and the same process applied to the parent drug may be applied to the metabolites. If a carcinogenic metabolite is found in the edible tissue which is significantly more potent and/or more persistent than the parent drug, the VSL is established for the metabolite rather than for the parent compound. A rigorous identification of metabolites is required, which is followed by the development of analytical methodology to ensure that carcinogenic residues in tissue are below the VSL.