The U.S. Food and Drug Administration is extending the public comment period for the Part 15 public hearing on "Scientific Data and Information Related to the Residue of Carcinogenic Concern for the New Animal Drug Carbadox." The agency is taking this action in response to a request for an extension to allow interested persons additional time to submit comments. The FDA is extending the comment period by 60 days, until June 10.

The FDA is seeking input on the benefits of carbadox, as well as scientific data and information on its safety and possible carcinogenic residues of it in swine tissue.

There are three approved New Animal Drug Applications for animal drug products containing carbadox, all held by Phibro Animal Health:

The FDA's Center for Veterinary Medicine says it reviewed data available at the time it approved the 1998 supplemental applications for carbadox and made several conclusions about carbadox tissue residues based on that information. However, subsequent human food safety information demonstrates that carcinogenic carbadox residues persist longer than previously known. Because there is no established relationship between the noncarcinogenic residue quinoxaline-2-carboxylic acid measured by the approved method and the residue of carcinogenic concern, they concluded that the approved method measuring the concentration of QCA in animal tissue does not allow CVM to conclusively determine whether the residue of carcinogenic concern remains in the tissue.

The National Pork Producers Council in September 2020 submitted comments to FDA urging the agency to develop a new residue test for carbadox rather than pull it from the market, noting that the animal drug "has been effectively used by most pork producers for decades to support animal health." Producers adhere to FDA's 42-day withdrawal period for carbadox, says NPPC, which also pointed out that since the drug mainly is used in nursery pigs, the withdrawal period is likely 60 days or more.