Bound residues of veterinary drugs: bioavailability and toxicological implications.

Basic considerations dealing with the biological significance of drug residues and safety evaluation are studied. The specific problem of covalently bound residues is considered from three different points of view. (1) Analytical characteristics clearly distinguish between soluble residues, which deplete relatively fast, and bound material which is slowly eliminated from edible tissues of target animals. (2) These two residual fractions have not the same bioavailability. (3) Finally, toxicity assessment of bound residues is considered.