Importance of pharmacokinetics in the determination of withdrawal times

Models for the statistical determination of withdrawal times have been compared using computer-generated kinetic residue data. Estimates of withdrawal times obtained by direct evaluation of the 'known' frequency distributions of residue contents of very large samples have been compared to results obtained by regression analysis of the data on very small samples of the same populations. In this context, the hypothesis was tested that the natural logarithms of the residue contents were normally distributed and that the decrease of the natural logarithms was linear with time. Withdrawal times were then determined as the times when the upper limit of the (statistical) tolerance interval in a given percentile was below the acceptable daily intake. From the results obtained with computer-generated small data bases, it was concluded that adequate, but not necessarily precise, withdrawal times could be determined on a limited base of suitable kinetic residue data.