In resolving a longstanding dispute, the Food and Drug Administration has announced that it will rescind approval for three of the four arsenic drugs that had been used in animal feeds at the request of the companies that market them.

The companies, Zoetis and Fleming Labs, already had largely withdrawn the three drugs from the market after recent studies showed levels of arsenic in chicken that exceeded amounts that occur naturally.

The compounds — roxarsone, carbarsone and arsanilic acid — have been used in 101 drugs added to feed for chickens, turkeys and pigs to prevent disease, increase feed efficiency and promote growth, according to the Center for Food Safety, which together with several other advocacy groups filed a petition almost four years ago seeking to ban the drugs in animal feeds.

“Zoetis withdrew roxarsone from the market voluntarily two years ago, and the companies have moved to withdraw the other two,” said Richard Sellers, vice president for feed regulation and nutrition at the American Feed Industry Association. “Now the F.D.A. is legally withdrawing their ability to market those drugs.”