"It's a very effective drug," says Sundeep Khosla, MD, of the Endocrine Research Unit of the Mayo Clinic's College of Medicine in Rochester, Minn. "In terms of getting a drug that shuts down bone resorption, we may be close to the best we can do."

Dr. Khosla wrote an editorial on denosumab published in the August 20, 2009 New England Journal of Medicine, and he reported no financial interest in the sales of this drug.

The bottom line, Dr. Khosla says, is that denosumab will be good for patients who need a different option to stem bone loss, but "it's not going to blow everything else we have out of the water, I don't think."

According to the FDA, the most commonly reported side effects associated with the drug include pain in the back, arms and legs, muscle and bone pain, high cholesterol levels, and urinary tract infections.

Serious adverse events were rare but included infections that required hospitalization, low blood calcium, and skin reactions including cellulitis, rashes and eczema.

Denosumab (Prolia) is not cleared by the kidneys, which may make it a safer option for people who have renal disease. 

Dr. Khosla says denosumab, which clears the body more quickly than bisphosphonates, may also be good for women of childbearing age who don't want to risk exposing a developing fetus to the lingering effects of a those drugs. 

In a press release, Amgen, the company that developed denosumab (Prolia), said it would charge a wholesale price of $825 per injection for the drug, or $1,650 per year. By comparison, the wholesale price of the infused form of the drug ibandronate (Boniva) is around $2,000 per year, while the generic drug alendronate (Fosamax) can cost as little as $100 annually.