WASHINGTON (AP) -- The Food and Drug Administration on Friday approved the first drug to treat an unusual condition that causes painful, curved erections in men.

The agency said it approved the biotech drug Xiaflex to treat Peyronie's disease, which causes an abnormal bend in the penis during erection. The disease is caused by scar tissue and can lead to pain and other difficulties during sex.

FDA says the injectable drug is the first non-surgical treatment for the disease.

Drugmaker Auxilium Pharmaceuticals estimates 5 percent of U.S. men are affected.

Xiaflex was previously approved in 2010 to treat a hand disease that interferes with patients' ability to straighten their fingers. The FDA said in its release that Xiaflex is believed to treat Peyronie's disease by breaking down collagen plaque that builds up in the penis and causes the deformity.

The FDA said it is limiting distribution of the drug to certified physicians and health care centers due to serious potential side effects, including injury of the penis. Health care professionals must enroll and complete a training program before prescribing the drug.

The FDA approved Xiaflex for its new use based on two studies of 832 men with Peyronie's disease. Patients received up to eight injections of the drug and were then followed for a year to see if their condition improved. Patients who received the drug reported significantly fewer problems than those who received a dummy injection.

The drug was developed by BioSpecifics Technologies Corp. of Lynbrook, N.Y., and submitted to the FDA by Chesterbrook, Pa.-based Auxilium Pharmaceuticals Inc.

Shares of Auxilium rose $1.80, or 9.3 percent, to $21.13 in afternoon trading.