Posted July 13, 2011
A pharmaceutical company planned to halt sales of a drug used to treat a parasitic disease and increase growth in chickens after it was found that use of the drug could cause detectable concentrations of inorganic arsenic in the livers of treated birds.
The drug, known as Roxarsone or 3-Nitro, had been used in broiler chickens since the 1940s and used less often in turkeys and swine, according to the Food and Drug Administration. The FDA announced that a study of 100 chickens showed that inorganic arsenic was detected at higher concentrations in the livers of birds treated with the drug than in the livers of control birds. Pfizer subsidiary Alpharma planned to halt sales of the drug by July 8, which gave producers 30 days to seek alternative treatment options.
(Courtesy of USDA)
Agency officials said the liver arsenic concentrations and the public health risks were low, however, and the company was working with the FDA to examine data on use of the drug in animals.
"FDA does not believe there is a need to recall chicken already in commerce," Dr. Bernadette M. Dunham, director of the FDA Center for Veterinary Medicine, said in a conference call with news media. "FDA's findings demonstrate a very low but avoidable public exposure to inorganic arsenic, a carcinogen."
The FDA also planned to notify partners in other countries about the findings.
Roxarsone had been used to promote growth in broiler chickens, improve pigmentation, and, in combination with other drugs, combat coccidiosis. Signs of coccidiosis in chickens include enteritis, emaciation, decreased appetite, and diarrhea.
The FDA initiated its study after published reports over the past eight years indicated organic arsenic, which is present in Roxarsone, could transform into the more dangerous inorganic arsenic in the environment, Dr. Dunham said. The agency developed an assay able to detect low concentrations of inorganic arsenic in edible tissues, and the amount of inorganic arsenic in the livers of tested chickens was found to be high, relative to amounts in control chickens, she said.
An FDA report of the study indicates that the livers of chickens euthanized five days after treatment was stopped had a mean inorganic arsenic concentration of 1.4 ppb. Those euthanized three days after treatment was stopped had a mean concentration of 1.7 ppb, and those euthanized the same day treatment was stopped had a mean concentration of 7.8 ppb. Concentrations in control birds were below the limit of quantification.
David Goldman, MD, assistant administrator of the Office of Public Health Science in the Department of Agriculture's Food Safety and Inspection Service, indicated his agency also was not substantially concerned about continued consumption of chicken while Roxarsone was being withdrawn.
"FSIS has concluded that the risk to consumers posed by eating chicken is very low and does not believe that there is a significant increased risk associated with continuing to eat chicken while Roxarsone is being phased out," Dr. Goldman said.
"FDA does not believe there is a need to recall chicken already in commerce. FDA's findings demonstrate a very low but avoidable public exposure to inorganic arsenic, a carcinogen."
Dr. Hector Cervantes, chair of the Drugs and Therapeutics Committee of the American Association of Avian Pathologists, said the FDA and Pfizer may have been able to avoid suspending the sale of Roxarsone by expanding the FDA's testing to include withdrawal periods such as 7, 10, or 14 days, which he said would be more representative of withdrawal periods commonly used in the broiler industry. Although some of the treated birds in the FDA study were euthanized following the required minimum five-day withdrawal period, he said that broiler chickens slaughtered at 56 days of age would typically not have received the drug in their feed after 32 days of age.
However, Laura Alvey, an FDA spokeswoman, indicated that it was incorrect that extending the withdrawal period for the chickens tested by the agency would have prevented suspension of sales of the drug. She said the FDA needs to focus on conditions of use established in conjunction with approval of the product and assume that the minimum withdrawal period will be used.
The loss of Roxarsone will sharply increase demand for other anticoccidial drugs, particularly those used to control Eimeria tenella, Dr. Cervantes said. Loss of the drug is also likely to increase production costs for broiler producers, he said.
"Personally, I'm not aware of any alternatives to this feed additive that could do the same thing," Dr. Cervantes said.
Dr. William T. Flynn, deputy director for science policy in the FDA CVM, said about 90 percent of Roxarsone use involved chickens, but data on the prevalence of use in chickens was not immediately available. He was aware of one other arsenic-based pharmaceutical, nitarsone, that is marketed in the U.S., and the FDA and Pfizer had been in talks regarding that product. FDA information indicates that nitarsone is approved for use to prevent blackhead in chickens and turkeys and to increase growth in turkeys.