According to federal regulations enacted through the Animal Medicinal Drug Use Clarification Act (AMDUCA), extralabel drug use (ELDU) means "actual use or intended use of a drug in an animal in a manner that is not in accordance with the approved labeling. This includes, but is not limited to, use in species not listed in the labeling, use for indications (disease or other conditions) not listed in the labeling, use at dosage levels, frequencies, or routes of administration other than those stated in the labeling, and deviation from the labeled withdrawal time based on these different uses."
According to AMDUCA, veterinarians who treat food animals with drugs in an extralabel manner must use evidence "...derived from food safety data or other scientific information..." in order to determine an appropriate withdrawal interval (WDI) that allows for a conservative estimate of drug residue level in edible animal tissues. Based on published scientific reports and population-based pharmacokinetic modeling, FARAD has developed a WDI Lookup Tool that provides recommended WDI values for a limited number of approved food animal drugs used in an extralabel manner.
The withdrawal interval (WDI) is a scientifically-derived recommended withholding time for a drug following its extralabel use in a food animal. The WDI is distinct from the official withdrawal time (WDT) for a drug. WDTs are established by the FDA for all approved (labeled) uses of food animal drugs and can be located in VetGRAM or at the FDA Center for Veterinary Medicine.