Primer on estimating withdrawal times after extralabel drug use.

1:)8ssage of AMDUCA and its implementation by the r FDA-Center for Veterinary Medicine has allowed food animal veterinarians to use drugs legally in an exttalabel manner as long as an appropriately extended withdrawal time (WDT) is followed. Providing these extended WDT for specific drug classes has been the main focus for the FARAD Digest series in the ]AVMA.1 But, what is the basis of these extrapolations and how can veterinarians be reasonably assured that a WDT selected for a specific exttalabel indication is appropriately extended? The purpose of this article is to address these pivotal questions and to illustrate the scientific basis involved in deriving extended WDT.