To estimate human dietary exposure to veterinary drug residues and establish maximum residue limits (MRLs), derivation of median residue concentration and upper tolerance limit (UTL) is necessary. The first value represents a typical residue concentration for the entire dataset of concentrations measured in samples (e.g. tissue, milk, eggs) from individual animals over a range of time periods. UTL values are calculated to consider those samples in which marker residues are present at concentrations higher than average levels, potentially posing a higher risk to consumers.

Consult the guidance document on median and tolerance limit values for marker residues to:

• plot the residue concentrations graphically and determine the median residue concentrations in edible tissues at any time point after drug administration, using the hypothetical data set provided;
• learn about the concept of UTL residues (95/95 UTL, the upper limit of the one-sided 95% confidence interval over the 95th percentile of marker residue concentrations); and
• see how the design of the marker residue depletion study influences the resulting 95/95 UTL, with subsequent impacts on the derivation of maximum residue levels.