Merck drug increases bone density at two years

Merck & Co's experimental osteoporosis drug significantly increased bone mineral density after 24 months in a mid-stage clinical trial, improving on results seen at 12 months, researchers said on Tuesday.

The 50 milligram, once a week, dose of Merck's odanacatib resulted in an average bone mineral density (BMD) increase of 5.48 percent in the lumbar spine at 24 months compared to a slight decrease for those on a placebo. At 12 months, odanacatib had boosted BMD by 3.42 percent.

"This study provides strong evidence that the drug should be an effective treatment for osteoporosis," said Michael McClung, director of the Oregon Osteoporosis Center in Portland who presented the data at the American Society for Bone and Mineral Research meeting in Montreal.

Odanacatib belongs to a new class of drugs for the bone-weakening disease and has been one of the experimental products Merck has touted to investors, although it is probably at least four years away from being submitted to regulators for approval.

The Phase 2b study tested the once weekly drug at four doses -- 3 mg, 10 mg, 25 mg, and 50 mg -- in 399 women with low levels of bone mineral density, considered an indicator for determining a patient's fracture risk.

The highest 50 mg dose showed the most promise, and that will be tested in a 17,000-patient, late-stage study for which Merck is currently enrolling patients.

While BMD changes in the lumbar spine was the study's primary goal, odanacatib also demonstrated BMD increases in the hip and neck regions, secondary areas of study in the trial, which Merck funded.

Odanacatib blocks an enzyme known as cathepsin K, which is believed to play a central role in bone loss. Merck said odanacatib is the most advanced such drug in development.

Bisphosphonates, including Merck's Fosamax, have been the dominant class of drugs for osteoporosis, which affects about 10 million Americans, mostly women. Sales of Fosamax have plunged this year due to new competition from cheaper generic versions in the United States.

Although widely used, bisphosphonates can be tough to tolerate. They must be taken on empty stomachs and can cause heartburn, while odanacatib was taken without regard to timing of meals. Also, U.S. regulators earlier this year warned that patients on bisphosphonates may develop severe pain in muscles, joints and bones.

"We have a menu of treatment options for osteoporosis already, but the major problem in our field is that many patients won't or can't take the current drugs," McClung said.

"To have effective treatment options that are safe and have a different tolerability profile would be very helpful."

More patients on the 50 mg dose dropped out of the trial due to drug-related issues than those on placebo -- 13 compared to 11. But that difference was not statistically significant.

The number of patients with side effects were similar between the drug group and the placebo group. The most common side effects in the 50 mg group were nausea, headache, rash and muscle spasms.

The progressive increases in bone density seen with odanacatib may mean it can cut fracture risk more than bisphosphonates, which reduce the risk by about 50 percent, said Arthur Santora, Merck's executive director of clinical research.

"We haven't shown that odanacatib is better, but the preliminary data are very encouraging," Santora said.

"With long-term therapy, there's the potential for greater fracture risk reduction than seen with earlier drugs that will have to be proven in clinical studies."

(Editing by Dave Zimmerman) Keywords: MERCK/OSTEOPOROSIS

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