Oct. 7 (Bloomberg) -- Merck & Co.'s Proscar, which helps to shrink enlarged prostates, doesn't increase a man's risk of hip fractures and may actually help prevent them, research found.

In a study of men 45 and older, those who took Proscar had a 23 percent reduced risk of hip fractures versus those who didn't, said the study's lead author, Steven Jacobsen of Kaiser Permanente in Pasadena, California. The research, published in tomorrow's Journal of the American Medical Association, was done because the drug slows problematic prostate growth by interfering with hormones that are key to strong bones.

About half of U.S. men in their sixties and as many as 90 percent of men in their seventies and eighties have symptoms of an enlarged prostate, also known as benign prostatic hyperplasia or BPH, according to the National Institutes of Health. Men with the condition are sometimes treated with medicines like Proscar and GlaxoSmithKline Plc's Avodart, though doctors were unsure of their effect on bone health, Jacobsen said.

``We undertook this study to see if they posed a greater risk of hip fracture,'' said Jacobsen, director of research at Kaiser Permanente Southern California, in an Oct. 3 telephone interview. ``We found the opposite.''

Researchers in the study used data from Kaiser Permanente Southern California, which is a managed care organization with more than three million members. They included 7,076 men who had a hip fracture between 1997 and 2006. Those men were compared with 7,076 men without a hip fracture during the same period.

Fewer Fractures Seen

The researchers then looked at which men took Proscar, known generically as finasteride, from 1991 to 2006. Proscar was the only 5-alpha reductase inhibitor given to patients in the study. Glaxo's Avodart, which is from the same class of medicines as Proscar, wasn't included in this trial.

The researchers found that 109 men who took Proscar had a hip fracture compared with 141 men who didn't have a fracture and took the drug.

``We have not had time to review the study but it appears interesting,'' said Ian McConnell, a spokesman for Whitehouse Station, New Jersey-based Merck. ``We look forward to analyzing it in further detail.''

The prostate, which is a walnut-sized gland that forms part of the male reproductive system, is located just below the bladder, where urine is stored, and surrounds the urethra, where urine passes from the body. During puberty, a man's prostate doubles in size. The gland starts to grow again at around age 25, and years later the gradual growth can lead to BPH, according to the National Institutes of Health.

Proscar Affects Testosterone

As the prostate gets bigger, it is stopped from expanding by a layer of tissue. That causes the gland to press against the urethra leading to more frequent urination and limiting the bladder's ability to empty all of the urine. Doctors are unsure what causes this, the U.S. agency said.

Proscar works by stopping the male hormone testosterone from converting into a more potent form, slowing the growth of the prostate and even causing it to shrink, Jacobsen said. Doctors were unsure whether interfering with these hormones would increase a man's risk of osteoporosis. Both male and female hormones are important to bone health, he said.

``It really wasn't clear how this might work,'' he said. Future studies are needed to look into why Proscar may be protective to bones, Jacobsen said.

Other Drugs Studied

The researchers also found in a secondary analysis of the data that the more commonly prescribed alpha blockers, which work through the nervous system to relax muscles in the prostate and the surrounding tissue, may increase the risk of fractures. In the study, 2,250, or 32 percent, of the men who took an alpha blocker had hip fractures, compared with 2,139, or 30 percent, of those on the drug who didn't have hip fractures.

Alpha blockers include the generic doxazosin, also sold by Pfizer Inc. as Cardura, and Flomax, by Boehringer Ingelheim GmbH of Germany.

More hip fractures may occur in those taking alpha blockers because the drugs help lower blood pressure by relaxing blood vessels, Jacobsen said. This may cause someone who stands up quickly to become dizzy, especially in those just starting out taking the drugs. Doctors should monitor patients who are just starting out with these medicines, he said.

The study was funded by the Kaiser Foundation Community Benefit fund and the Southern California Permanente Medical Group. Jacobsen reported receiving research funding from and serving as an unpaid consultant for Merck Research Laboratories.

To contact the reporter on this story: Nicole Ostrow in New York at nostrow1@bloomberg.net.

Last Updated: October 7, 2008 16:02 EDT