The U.S. Food & Drug Administration announced April 1 that it has received a letter of commitment from Zoetis that, by the fall of 2015, the company will suspend sale of Histostat (nitarsone) and formally request that FDA withdraw the approval for the drug by the end of 2015.

Nitarsone is the only arsenic-based animal drug that is currently approved for use in food animals. Nitarsone is approved for the prevention of blackhead disease (histomoniasis) in turkeys and chickens, but is predominantly used in turkeys.

Arsenic is in the environment as a naturally occurring substance or as a contaminant and is found in water, air, soil and food. FDA pointed out that published scientific reports have indicated that organic arsenic, the less toxic form of arsenic present in the arsenic-based animal drugs, could transform into inorganic arsenic, a known carcinogen.

In 2011, Alpharma, then the sponsor of 3-Nitro (roxarsone), suspended marketing of that drug after an FDA study measured higher levels of inorganic arsenic were present in the livers of chickens fed roxarsone, compared to those of untreated control chickens.

FDA formally withdrew the approvals for three other arsenic-based animal drugs — roxarsone, arsanilic acid and carbasone — in February 2014. FDA has since completed additional studies that affirm the findings of its 2011 roxarsone study.

Ownership of the roxarsone application subsequently changed to Zoetis, which continued the suspension from sale of 3-Nitro, and ultimately, withdrew the new animal drug application for that drug. On the same day, Zoetis and Huvepharma AD voluntarily withdrew all new animal drug approvals and supplements for 3-Nitro, as well as two other arsenical new animal drugs, arsanilic acid and carbasone.

Zoetis holds three approved animal drug applications for nitarsone: Histostat-50 (approved for use in chickens and turkeys for prevention of blackhead); and two combination use approvals, BMD/Histostat and Albac/Histostat (approved for use in turkeys for prevention of blackhead). All three uses would cease to be marketed upon withdrawal of the nitarsone approval.

Blackhead is a disease that occurs seasonally in certain parts of the country and is a cause of significant mortality in turkeys. Currently, nitarsone is the only animal drug approved for managing this disease in turkeys. Under the phase-out plan being announced, nitarsone will continue to be available for the 2015 season. This strategy allows affected producers the opportunity to consider alternatives for managing this disease in the future, FDA said.