A coalition of 20 consumer protection, public health, and animal welfare organizations have sent a letter to U.S. Food and Drug Administration (FDA) Commissioner Marty Makary, M.D., urging the agency to immediately withdraw its approval of Carbadox, a carcinogenic swine feed additive.

In 2023, FDA published a final order revoking the regulatory method (i.e., the residue detection method) for Carbadox and proposed to withdraw its approval for the drug. Despite this, two years have passed without the withdrawal of the approval for Carbadox being finalized and put into effect. During this time, there has not been an approved method to test that the drug is being used safely by pork producers, although the existing tolerances still stand.

Carbadox has been shown to be carcinogenic in laboratory animals. FDA cited the Delaney Clause as the basis for its 2023 proposal to withdraw approvals for Carbadox. Under the Delaney Clause, FDA shall not approve a new animal drug application if “such drug induces cancer when ingested by man or animal or, after tests which are appropriate for the evaluation of the safety of such drug, induces cancer in man or animal.”

Carbadox is known to break down into carcinogenic residues, such as desoxycarbadox, which can be present in the edible tissues of swine and result in an elevated cancer risk in consumers. This was known in 1998, when the residue detection method for Carbadox was established, but in 2003, new evidence was brought to light showing that the residue detection method may not be able to determine whether the carcinogenic residues can be found in the meat of, or food derived from, swine. Another study was submitted to FDA reaffirming this finding in 2016, at which time FDA publicly stated concerns about the now-revoked residue detection method.

In 2005, FDA notified the sponsor of Carbadox, Phibro, that additional data is needed to meet statutory requirements for the detection method, providing Phibro time to carry out the necessary studies. To date, however, FDA has not received data demonstrating that the approved method is adequate to measure the residue of carcinogenic concern in compliance with FDA regulations or that an alternative analytical method would meet such requirements—leading to the method’s withdrawal in 2023.

FDA says that, although Carbadox currently remains available for use by the swine industry, if approvals of the applications for Carbadox are ultimately withdrawn, then Carbadox will no longer be available for industry use.

Calling Carbadox “low-hanging fruit,” as its health risks are evident and FDA has already put in place the necessary framework to remove it from the market, the letter calls on Dr. Makary to immediately finalize the withdrawal of the agency’s approval of Carbadox for use in swine.

Withdrawing approvals for Carbadox in swine would bring the U.S. into regulatory alignment with the EU, UK, Canada, China, Australia, Brazil, and Japan. 

The letter was signed by the Antibiotic Resistance Action Center at George Washington University, Consumer Federation of America, Consumer Reports, the Environmental Working Group, the Institute for Agriculture and Trade Policy, Northeast Organic Dairy Producers Alliance, and other groups.