Just days after the Food and Drug Administration ordered Merck & Co. to revise the labeling on Propecia to reflect mounting evidence that its baldness drug can cause continued sexual dysfunction long after patients have stopped taking it, the agency promised to maintain its scrunity of the pharmaceutical giant as new victims emerge.

“The FDA will continue to vigilantly evaluate and analyze all reports that are available on finasteride and take regulatory actions as warranted,” an official at the FDA’s Center for Drug Evaluation and Research wrote in a letter, dated April 20, to an American doctor who has interviewed hundreds of men afflicted by Post-Finasteride Syndrome (so called for Propecia’s generic name, finasteride).

That document, obtained by The Examiner, also reveals the FDA’s drive to gather data from victims who have suffered side effects that have yet to be acknowledged by Merck in its labeling for Propecia and its other finasteride drug, Proscar, which treats symptoms of enlarged prostate.

“The FDA wants to know about all adverse reactions potentially caused by finasteride,” said the official. “This includes cases of patients who developed Peyronie’s [disease], anxiety, panic attacks, cognitive dysfunction, chronic insomnia, muscle wasting and the other persistent side effects.”

Among those other persistent side effects that have gone unlisted in Merck’s Propecia labeling, the American doctor wrote in a related correspondence, are “reduced exercise tolerance, weight gain with increased fat deposition and muscle and joint aches.”

Affecting up to 10 percent of adult males, Peyronie’s disease is a painful disorder characterized by the growth of fibrous scar tissue inside the penis, which often causes curvature of the erect organ.  In severe cases, Peyronie’s can make sexual intercourse impossible.

To gather data on finasteride’s possible role in causing Peyronie’s disease, penis shrinkage and other persistent side effects, the FDA encourages victims to document their adverse reactions through its MedWatch program.

Once again, Merck did not reply to the Examiner’s request for comment on this evolving story. With annual sales of more than $400 million, Propecia was approved by the FDA in 1997 to treat male pattern baldness.