The new drug, expected to win approval from federal regulators, would offer another much-needed treatment for some of the 10 million Americans, 80 percent of them women, who have a disease that weakens bones and often leads to years of pain, disability and early death.

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A large clinical trial of a new osteoporosis drug found that it stimulates bone growth and prevents fractures at least as well as the only other such drug on the market. The new drug, expected to win approval from federal regulators, would offer another much-needed treatment for some of the 10 million Americans, 80 percent of them women, who have a disease that weakens bones and often leads to years of pain, disability and early death.

Doctors who care for people with osteoporosis said they hoped the new drug would also spur price competition in an arena that has had none. The new drug would compete with a medicine made by Eli Lilly, called Forteo, that costs $2,550 for a four-week supply. A spokeswoman for Radius, the maker of the new drug, said it was the company’s policy not to discuss price.

Experts agree that new drugs are urgently needed for this debilitating disease. People with osteoporosis have bones that are fragile and break easily. Bone is naturally lost with age. But osteoporosis is an extreme, abnormal bone loss that can cause devastating fractures, particularly of the spine and hip.

Yet most patients, even those at highest risk, are not getting any treatment, according to the National Osteoporosis Foundation. The first treatment option, a class of drugs called bisphosphonates, which includes Fosamax, slows the loss of existing bone but does not build bone. Those drugs can cost just pennies a day but can have very rare side effects — a sudden shattering of the thighbone or an erosion of the jawbone — which have discouraged people from using them. The only other option is Forteo. But its price is so high that insurers have required, for example, that patients try a bisphosphonate first.

The new drug is almost guaranteed to cost much more than most bisphosphonates. The clinical trial was conducted by Radius, and the results were published Tuesday in The Journal of the American Medical Association. The trial compared the new drug, abaloparatide, with a placebo and with Lilly’s drug, Forteo.

Like Forteo, the new drug must be injected daily, but it is a derivative of a different hormone — one that stimulates only bone growth. Lilly’s drug stimulates both bone growth and bone loss, though the net effect is a gain in bone.

With the Radius drug, holes in osteoporotic bone appeared to fill faster than with the Lilly drug. But the study was not large enough to determine whether that translated to fewer fractures. Both drugs were far better than a placebo. After 18 months, four women of the 824 taking the Radius drug had a new spine fracture, compared with six of the 818 taking Lilly’s drug and 30 of the 821 taking a placebo.

Radius has filed an application with the Food and Drug Administration to market the drug.

Osteoporosis is not one disease, and no one treatment will work for everyone, said Dr. Steven Teitelbaum, an osteoporosis expert at the Washington University School of Medicine in St. Louis. At Washington University and other leading medical centers with a major focus on osteoporosis, doctors perform bone biopsies to decide which drug is best for a high-risk patient. Some patients have osteoporosis because they lose bone too quickly. For them, a bisphosphonate or a similar injected drug, Prolia, made by Amgen, is preferred. Those who make new bone too slowly need a drug that builds it. Until now the only such drug has been Forteo.

Patients can generally take Forteo for only two years because it has been found to increase the incidence of bone cancer in rats. So far this effect has not been seen in people, said Dr. Henry Kronenberg, chief of the endocrine unit at Massachusetts General Hospital. But the FDA requires the drug to carry a warning on its label about the rat data, and insurance policies generally pay for only two years of treatment. After patients stop taking Forteo, they are usually prescribed a bisphosphonate to help them keep the new bone they gained.

The new drug’s development grew out of cancer research. Two endocrinologists, Dr. Andrew Stewart, now the director of the diabetes, obesity and metabolism institute at the Icahn School of Medicine at Mount Sinai, and his mentor, Dr. Arthur Broadus at Yale University, tried to figure out why some cancer patients had excessive amounts of calcium in their blood. It is a dangerous condition, leading to lassitude and even coma. When the doctors studied tumors that had made patients’ skeletons release calcium, they discovered the cancer was secreting a hormone no one had ever heard of that regulated calcium levels in the blood.

But how could a hormone cause high levels of calcium in the blood by removing calcium from bones and also cause bone growth?

“It seems counterintuitive,” Stewart said. “But the magic depends entirely on how you give it.” He explained that a continuous flow of the hormone leaches calcium from bone, but that a single spike of the hormone builds bone.

The Lilly drug relies on another hormone that also makes calcium leach from bones when given continuously. But if it is given once a day, it both builds and tears down bone. The hormone Stewart and Broadus discovered became the basis for the new drug made by Radius.

Osteoporosis experts expect that if the Radius drug is approved, it is likely to be reserved for patients at highest risk. It is almost guaranteed to cost much more than most bisphosphonates, and it will not have the same decades of use to show its long-term safety. Those qualifying patients would include people older than 50 who have broken a bone, especially one in the wrist, spine, or hip, in the absence of trauma, said Dr. Paul Miller, lead author of the new clinical trial and the medical director of the Colorado Center for Bone Research, a private practice in Lakewood, Colo. They would also include those who took a bisphosphonate and had one of the rare, atypical fractures, he said.

The big question — other than price — is which bone-building drug is better for preventing fractures.

That, unfortunately, may never be known. In their paper, Miller and his colleagues note that it would take a study of 44,000 patients to see a meaningful difference. The FDA requires only that the new drug be shown to be at least as good as the existing one, which is what the new study found.

“It’s an imperfect world for osteoporosis,” Kronenberg said.