Roxarsone is going off the market, at least temporarily, after being used for more than 60 years to control coccidia in poutlry as a result of an agreement between the U.S. Food & Drug Administration (FDA) and Alpharma LLC, a subsidiary of pharmaceutical giant Pfizer.

FDA said new research found traces of inorganic (trivalent) arsenic in the livers of chickens whose feed included 3-Nitro, whose active ingredient, roxarsone, includes organic (pentavalent) arsenic.

“Pfizer views its decision to suspend sales as prudent in light of the agency’s request that Pfizer assist in removing an avoidable exposure to very low levels of inorganic arsenic from eating liver from chickens treated with 3-Nitro,” the company said in a statement. Dr. William Flynn, a FDA Center for Veterinary Medicine (CVM) official, said the government would not allow Pfizer to return 3-Nitro to the market “until the agency’s concerns are met.”  Roxarsone was first approved in 1944 for control of coccidiosis.

FDA said it conducted an experiment with 50 broiler chickens fed 3-Nitro compared with a control group of 50, using newly developed methods that allowed agency scientists to detect very low levels of inorganic arsenic in the livers. The agency said the levels of inorganic arsenic, which is considered to be carcinogenic, were higher in the livers of the experimental group than in the control group, suggesting that some organic arsenic converts to the inorganic form in the chicken.

“We would like to stress that the levels of inorganic arsenic were very low, representing a very low health risk to people who eat chicken,” said Dr. Bernadette Dunham, director of CVM, in a conference call with the media. The levels in livers were in low numbers of parts per billion, she said, and the study focused on arsenic levels in liver and did not report any findings for levels in muscle tissue.  However, the agency would expect those levels to be “40 times less” than in livers, Dunham stated.

The National Chicken Council released a statement saying “chicken is safe to eat” and emphasizing that FDA expressed no concern about consumption of chicken. NCC said the product is used in many flocks, but not all.

“Chicken companies will continue to safeguard chicken flocks because healthy flocks are needed to produce healthful food for people,” NCC’s statement said. “Consumers can continue to buy and eat chicken as they always have.”

Alpharma will continue to sell limited quantities of 3-Nitro until one month after Wednesday’s announcement. The suspension affects sales of all products containing roxarsone. Alpharma owns all FDA approvals for use of roxarsone in the United States. While 3-Nitro is approved for use in turkey and swine as well as chickens, FDA said broilers account for the great majority of usage.

FDA’s study is available at http://tinyurl.com/3-Nitro.