THE WITHDRAWAL TIME-ESTIMATION OF VETERINARY DRUGS REVISITED

The aim of this article is to review current issues concerning the sta tistical determination of a withdrawal time for a veterinary drug, Spe cial attention has been paid to the Food and Drug Administration (FDA) approach which consists of using a regression method to estimate a 99 th percentile of the population with a 95% confidence level, The diffe rent assumptions of the simple regression techniques are reviewed. It is shown, both on theoretical grounds and using Monte Carlo simulation s, that the main assumptions for the correct use of linear regression do not hold when a tissue depletion curve is under investigation, Fina lly, it is suggested that methods other than the regression technique must be evaluated, especially a revised version of the so-called simpl er approach, which consists of using a non-parametric strategy to esti mate a withdrawal time.