Study: New Osteoporosis Drug Replaces Bone

B O S T O N, May 9, 2001 -- The first osteoporosis drug to replace lost bone instead of merely stopping additional bone loss could be available by the end of this year, says the drug's manufacturer, Eli Lilly.

The new drug — to be called Fortéo — is a daily injection of human parathyroid hormone (PTH) produced by genetically engineered bacteria.

PTH normally is secreted by the parathyroid glands in human beings. The hormone controls bone formation and the excretion of calcium and phosphorus.

Researchers say the drug version of PTH stimulated new bone growth, reducing the risk of repeat backbone fractures in women with osteoporosis by 65 percent to 69 percent, depending on the dose. Risk of fracture elsewhere in the body was reduced by approximately 50 percent.

The study appears in this week's New England Journal of Medicine and was sponsored by manufacturer Eli Lilly. A New Drug Application has been filed with the FDA and awaits approval. Lilly has also formed partnerships with two other companies to develop inhaler and pill forms of the drug.

Drug Has Bone-Growth Potential

Experts interviewed by ABCNEWS.com expressed excitement about the bone-building potential of PTH.

"This is the first bone active agent that works on bone formation and not just slowing bone breakdown — so it has a totally different mechanism of action from the other approved drugs for osteoporosis," says Joan McGowan, director of the musculo-skeletal diseases branch at the National Institutes of Health.

Bone mineral density in the spine increased by 9 percent for the 20 microgram dose and 13 percent for the 40 microgram dose.

Dr. Hunter Heath, medical director, of the U.S. endocrinology division at Eli Lilly, said the best candidates for parathyroid hormone would be like the women in the study, who were around age 70, and had at least one previous osteoporosis-related fracture. "This wouldn't be for prevention," he says.

However, once a convenient pill or inhaler is developed, people will be more willing to use PTH and it could be used as prevention, says Dr. John Potts, director of research at Massachusetts General Hospital, an independent researcher commenting on the study.

Some Problems With Drug, Too

"The tolerability [of the drug] was really quite good," said Heath. The most common side effects were nausea (18 percent) and headache (13 percent) in the 40 microgram-dose group and dizziness (6 percent) and leg cramps (3 percent) in those taking 20 micrograms.

The PTH study was halted for review in 1998 due to some rats showing excessive bone growth and developing bone cancer. Heath says a review by experts concluded these risks would not pose a threat in humans.

First, "the rats were given [the hormone] throughout their lifetimes. This is equivalent to giving [it to] babies through 75 years," says Heath. "There are major differences between human and rat skeletal systems. The rat skeleton never stops growing."

Researchers also looked at people with primary hyperthyroidism — a disease that causes elevated levels of PTH — and found they were not at higher risk for bone tumors.

Osteoporosis Increases as Population Ages

Heath says he cannot speculate on the effectiveness of PTH beyond the 21-month length of the study. Many currently available drugs have been found to be less effective after three to four years than they were at the start of treatment. He says men with osteoporosis have been involved in small numbers in PTH studies and it "appears to be effective" for them as well.

Osteoporosis affects approximately 8 million women over age 50 and by 2015, an estimated 12 million will be affected.