Prescribing labels for Merck & Co's drugs for baldness and enlarged prostate will add reports of sexual side effects that continued after use of the medicines was stopped, U.S. health regulators said.
Labels will be revised for Proscar, which treats symptoms of enlarged prostate, and hair-loss treatment Propecia, the Food and Drug Administration said. The active ingredient in both drugs is finasteride.
The Propecia label will now include notification of problems with libido, ejaculation and orgasms that continued after use of the drug was ended. Proscar's label will include notification of decreased libido.
The labels of both drugs will also include a description of reports of male infertility and poor semen quality that normalized or improved after use of the drugs was stopped.
In announcing the label changes, FDA cited events reported to the agency.
"The cases suggest a broader range of adverse effects than previously reported in patients taking these drugs," FDA said in a notification posted on its website. But it also said no clear causal links between finasteride and sexual adverse events had been established.
FDA said sexual side effects were included in the labels of both drugs when they were approved in the 1990s. But in subsequent clinical trials, the side effects were resolved in patients who stopped using the drugs as well as in most patients who continued therapy, the agency said.
Last year, the labels of both drugs were revised to include erectile dysfunction that continued after patients stopped using the drugs, the FDA said.
Only a small percentage of men who use the drugs have experienced sexual side effects, the agency added. For example, it said, an analysis of clinical trials showed 3.8 percent of men taking Propecia reported one or more of the sexual side effects, compared with 2.1 percent of those who received a placebo.
FDA said it believes that finasteride remains safe and effective for its approved uses and that patients on Proscar and Propecia should contact their doctors if they have concerns.
In a statement, Merck said it believes both drugs are generally well tolerated and effective for their intended uses and that it supports efforts to ensure patient safety through monitoring of reported side effects.
The drugs are relatively modest-sized products for the U.S. drugmaker. Merck reported $447 million in Propecia sales last year, and $223 million for Proscar.
Merck shares were down 0.5 percent to $38.27 in afternoon trading on the New York Stock Exchange.
(Reporting By Lewis Krauskopf; editing by John Wallace)