SAN FRANCISCO – The pivotal clinical trial of denosumab showed a 20% decrease in nonvertebral fractures compared with placebo treatment, but a new subgroup analysis shows the protective effect is significantly higher in patients with femoral neck osteoporosis.
The preplanned subgroup analysis of data from the FREEDOM (Fracture Reduction Evaluation of Denosumab in Osteoporosis Every 6 Months) trial found that denosumab decreased nonvertebral fractures by 35% in patients with a femoral neck bone mineral density T score of −2.5 or lower and by only 3% in patients with higher femoral neck T scores, compared with patients in those subgroups who received placebo, Dr. Steven R. Cummings said.
The report of a 20% reduction in nonvertebral fractures in the overall trial for denosumab “underestimates its efficacy for those patients that we're most interested in treating with this drug – those with osteoporosis,” he said at a conference on osteoporosis sponsored by the University of California, San Francisco.
The findings have been submitted for publication. The analysis is one of several preplanned subgroup analyses being conducted, though this one is “the most interesting result for clinical care,” said Dr. Cummings, emeritus professor of medicine, epidemiology and biostatistics at the university.
The original FREEDOM study enrolled 7,808 postmenopausal women aged 60-80 years with osteoporosis to receive every 6 months either a subcutaneous injection of denosumab (60 mg) or placebo along with daily calcium and vitamin D supplements. All of the subjects had bone mineral density T scores that were less than −2.5 but not less than −4.0 at the lumbar spine or total hip. At 36 months, denosumab was associated with reductions of 68% in vertebral fracture and 40% in hip fracture (N. Engl. J. Med. 2009;361:756–65).
The FREEDOM results were the basis of the Food and Drug Administration's approval of denosumab in June 2010.
Data for 2,343 patients who continued denosumab for another 2 years and 2,207 patients who switched from placebo to denosumab in an ongoing extension of the trial suggest that the incidence of nonvertebral fractures continues to decline in the first 5 years of denosumab use. The 5-year results have been submitted for publication, he said.
For nonvertebral fractures, the incidence decreased from 2.6% in the denosumab group in the first year of the FREEDOM trial to 2.1% in year 2 and 2.2% in year 3. Nonvertebral fractures were seen in 1.4% of patients in year 4 and 1.1% of patients in year 5, extension study data show. Similar rates were seen for vertebral fractures.
The extension study did not include a placebo comparison, so “we did a pretty rigorous estimate of what the rates would be if the placebo group had continued out to 5 years,” Dr. Cummings said. They estimated that nonvertebral or vertebral fracture rates would be 2.6% in the placebo group in years 4 and 5, more than twice that of patients on denosumab in the extension study.
A separate study highlighted another advantage of denosumab that it shares with zoledronic acid – greater adherence rates compared with oral therapies, he added. An open-label study of 250 women with untreated osteoporosis found an 87% adherence rate in the first year in patients randomized to get a denosumab injection every 6 months, compared with a 77% adherence rate for patients randomized to weekly oral alendronate therapy. Alendronate use was monitored by electronic bottle caps (Osteoporos. Int. 2011;22:1725–35).
The study's 2-year results, which have not yet been published, show that the difference in adherence rates between groups continues to widen, Dr. Cummings said.
Dr. Cummings has been a consultant to Amgen Pharmaceuticals, which markets denosumab; to Merck, which markets alendronate; and to Eli Lilly & Co.