"You're going to have blowback by insurers" over how much they will pay, he said, but Amgen might try to charge more than $10,000 per year.
Dr. Lenore Buckley, a professor at Virginia Commonwealth University, said all these drugs carry some risks. The studies found denosumab caused eczema in some patients, and a dozen of the women got a serious skin infection, cellulitis, that sometimes required hospitalization for intravenous antibiotics.
"Because this drug affects the immune system, the long-term effects on cancer risk or immune function is still unknown," she warned, saying she expects FDA will require Amgen to track risks over time if the drug is approved.
The effectiveness of denosumab and existing drugs appears to plateau after two or three years, she added.
The two studies were released Tuesday by the New England Journal of Medicine.
Amgen, of Thousand Oaks, California, paid for both. Nearly all the researchers receive consulting, advisory and other fees from the company and competitors, or are Amgen employees. The biotech company designed the studies, handled data collection and analysis, and helped write the journal reports.
One study included 7,868 women, aged 60 to 90, with moderate to severe osteoporosis. Half got denosumab injections every six months for three years. They had 68 percent fewer spine fractures and 40 percent fewer hip fractures than the study participants who got dummy shots.
The second study included 1,468 men with prostate cancer at increased fracture risk due to cancer hormone therapy, although 556 dropped out for reasons from side effects and cancer progression to the study being extended from two to three years. Denosumab cut the risk of spine fractures 62 percent over three years compared to dummy shots. Spine bone density loss was far smaller for those given the drug.
Until recently, studies of osteoporosis drugs just measured changes in bone density, assumed to equate with lower fracture risk. Newer studies also measure fracture rates, but there are no head-to-head studies on that.
However, based on some prior studies, independent experts say denosumab appears more effective at preventing spine fractures than three older pills -- Fosamax, Actonel and Boniva -- and calcitonin nasal sprays, which all use various pathways to slow down cells called osteoclasts that break down bone. Experts think denosumab prevents spine fractures about as well as Reclast, an intravenously injected drug that slows bone breakdown, and daily just below the skin injections of Forteo, the only drug that stimulates bone-building cells called osteoblasts. And denosumab appears to prevent fractures of the hip, forearm and ankle about the same as all those drugs.
Dr. Jacob Warman, an osteoporosis expert at Brooklyn Hospital Center, said denosumab might have potential as an add-on to existing drugs to boost results. He expects that would be covered by insurers, who pay for multiple medicines for other conditions.
Amgen spokeswoman Kerry Beth Daly said the company has not yet set a price for the drug, but will try to keep it affordable. She said pricing also will reflect denosumab's twice-a-year dosing.
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