WASHINGTON – The Food and Drug Administration revoked approval for four arsenic-based animal drugs at the request of the drug manufacturers, according to a New York Timesreport.

Roxarsone, carbasone and arsanilic acid have been used as feed supplements for pigs and poultry to promote growth and prevent disease, among other uses. The Center for Food Safety and the Institute for Agriculture and Trade Policy had petitioned the FDA to revoke the approvals of those drugs and another arsenic-based drug called nitarsone. The petition was rendered moot after the FDA revoked its approval of three of the drugs.

Zoetis and Fleming Labs already had removed Roxarsone, carbasone and arsanilic acid from the market after tests of chickens showed levels of arsenic that exceeded amounts that would occur naturally.

“The only arsenical used as a feed additive in broiler production in the last ten years, Roxarsone, was suspended in 2011 and the product is no longer manufactured or used,” said Ashley Petersen Ph.D., and the National Chicken Council’s vice president of scientific and regulatory affairs. “No other feed additives containing arsenic are currently used in broiler meat production in the United States.”

Nitarsone is the only remaining approved arsenic-based animal drug, and it is not used in broiler production, according to the NCC. FDA denied the petition against nitarsone because the agency is in the process of evaluating potential concerns related to the drug's safety, NCC added.

In June 2011, Alpharma, a subsidiary of Pfizer Inc., voluntarily suspended US sales of 3-Nitro (Roxarsone), which was used by poultry producers since the 1940s. The suspension came after an FDA study of 100 broiler chickens found inorganic arsenic, a known carcinogen, at higher levels in the livers of chickens treated with 3-Nitro compared with untreated chickens. At the time, FDA officials said the levels of inorganic arsenic detected were very low and did not pose a health risk.