Phibro Animal Health Corp.; Carbadox in Medicated Swine Feed; Revocation of Approved Method

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The Food and Drug Administration (FDA) is issuing a final order to revoke the approved method for detecting residues of carbadox, a carcinogenic new animal drug used in swine feed. An approved method is required by the Federal Food, Drug, and Cosmetic Act (FD&C Act), as implemented by regulation, to show that no residue of carcinogenic concern from a new animal drug persists in any edible tissue or in any food derived from treated animals. The approved method measures quinoxaline-2-carboxylic acid (QCA) as a marker residue to detect the presence of any residue of carcinogenic concern. QCA is a metabolite of carbadox that FDA has judged does not present a carcinogenic risk. FDA is revoking the approved method for carbadox based on its determination that the method is inadequate to monitor the residue of carcinogenic concern in compliance with FDA's operational definition of no residue because there is no established relationship between the concentration of QCA residues as measured by the approved method and the concentration of the residue of carcinogenic concern.