WEDNESDAY, June 8 (HealthDay News) -- A drug maker has agreed to suspend the sale of its animal drug 3-Nitro from the market because it contains organic arsenic that can be transformed into inorganic arsenic, a known carcinogen, the U.S. Food and Drug Administration (FDA) said Wednesday.

The drug, also known as Roxarsone, was approved by the FDA in 1944 and has been used in broiler chickens to control coccidiosis -- a disease that affects the intestinal tracts of animals -- and to speed weight gain, feed efficiency and improve color of the meat.

"The levels of inorganic arsenic found in chicken livers are very low and represent a very low health risk to people who eat chicken," Dr. Bernadette Dunham, director of FDA's Center for Veterinary Medicine, said during an afternoon press conference.

"Consumers can continue to eat chicken as 3-Nitro is suspended from the market," she said. "Furthermore, FDA does not believe there is a need to recall chicken already in commerce."

The Alpharma division of Pfizer Inc. voluntarily suspended 3-Nitro after testing of 100 chickens found higher levels of arsenic in chickens given 3-Nitro than in birds that did not receive the drug.

The FDA pointed out that organic arsenic occurs naturally in the environment and is commonly found in water, air, soil and food.

However, over the last eight years, studies have found that the less toxic form of arsenic -- organic arsenic, which is commonly found in 3-Nitro -- can become the more toxic inorganic arsenic, the FDA said. And it is this form of arsenic that researchers found in the livers of chickens treated with 3-Nitro.

Although 3-Nitro was approved in 1944, over the years there have been several other FDA reviews and approvals of the drug. The latest was in 2009, according to the agency.

At the time 3-Nitro was approved it was assumed that the organic arsenic in 3-Nitro would be excreted as organic arsenic, which is not known to cause cancer.

"Until recently, scientific evidence indicated that animals exposed to organic arsenic rapidly excrete the compound in its original form -- as organic arsenic. FDA approved the product at doses and withdrawal times that, based on this available information, allowed for the safe and effective use of the product when used according to the label directions," the agency said.

According to the FDA, Alpharma will continue selling 3-Nitro for the next month, which the company says will allow time for chicken farmers to find alternate ways of protecting their animals from coccidiosis.

With the suspension of 3-Nitro only one approved animal drug containing arsenic remains on the market, called Nitarsone, also made by Alpharma. This drug is also used in chickens and turkeys. The FDA has little information on this drug, but is now looking into it, Dr. Bill Flynn, deputy director for science policy at FDA's Center for Veterinary Medicine, said during the press conference.

More information

For more information on 3-Nitro, visit the U.S. Food and Drug Administration.