Phibro makes case for carbadox

by Erica Shaffer
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TEANECK, NJ – Phibro Animal Health Corp. requested a hearing with the US Food and Drug Administration citing new data that refutes the FDA’s claim that carbadox, the active ingredient in the Phibro’s Mecadox swine drug, is carcinogenic.

In April, the Center for Veterinary Medicine (CVM) of the FDA announced the agency would rescind approval of carbadox to treat swine diseases on concerns the drug may leave trace amounts of cancer-causing residues. At the time, Michael R. Taylor, FDA deputy commissioner for foods and veterinary medicine, said Phibro had failed to provide sufficient scientific data to prove the safety of carbadox. Now, Phibro claims to have the evidence it needs to keep carbadox on the market.

“…new studies conducted by Phibro confirm the safety of carbadox, and therefore refute CVM’s proposal to withdraw approval for the use of carbadox in medicated swine feed,” Phibro wrote in an executive summary of the company’s findings. “At a minimum, these new data and the related discussion in Phibro’s response to the [Notice of Opportunity for a Hearing] raise genuine and substantial issues of fact that require a hearing pursuant to the regulations.”

FDA’s demands for new evidence surprised the company, Phibro said. “It was not clear when FDA made its request that it was even possible to do what FDA demanded. Moreover, the need to do such studies was not clear, as molecules that are so tightly bound to tissues that they effectively cannot be cleaved and extracted without taking extraordinary measures are also not digestible when the tissue is ingested.”

However, scientists from Charles River Laboratories in Wilmington, Massachusetts, and the Univ. of Edinburgh successfully used radioactive residue technology and extraction techniques “to extract and characterize all carbadox bound residues.” Charles River Laboratories specializes in laboratory services for the pharmaceutical, medical device and biotechnology industries.

After successfully extracting 100 percent of the residues present at the end of the 42-day FDA-mandated withdrawal period, scientists determined that no harmful residues were president. Further, the studies confirmed that carbadox residues present at the end of the withdrawal period were comprised of tissue-bound QCA — “a harmless non-carcinogenic metabolite of carbadox.”

Phibro went on to say that carbadox is not used in human medicine, and the drug is not medically important for humans which make carbadox-based drugs desirable for swine producers. Removing the drug from the market would likely push swine producers to use medically important antibiotics, “and increase the likelihood of difficult-to-control antimicrobial resistance in important bacterial pathogens.”

Additionally, Phibro warned, removal of carbadox from the market would result in higher costs for the swine industry. The company estimated that the total cost to the US swine industry as high as $200 million in the first year carbadox is removed from the market driven by increased incidents of enteric diseases such as Salmonella, swine dysentery and E coli. “It is anticipated that annual costs will continue to grow to approximately $345 million per year,” Phibro said.

FDA first approved carbadox in the early 1970s to control swine dysentery and bacterial swine enteritis. The drug also has been used as a growth and feed efficiency-promoting drug in swine feed. But the Codex Alimentarius Commission determined in 2014 there are no safe level of residues of carbadox or its metabolites in food.

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