Shieh A, et al. Vitamin D insufficiency is associated with decreased bisphosphonate response. The Endocrine Society (ENDO) 2011; Abstract P1-228.
ENDO: Vitamin D Ups Bisphosphonate Response
http://www.medpagetoday.com/MeetingCoverage/ENDO/27006
By Kristina Fiore, Staff Writer, MedPage Today
June 10, 2011
Action Points
• Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
• Note that in this study, the quality of the clinical response to bisphosphonates was a function of 25(OH)D levels with the majority of nonresponders having vitamin D insufficiency.
Review
BOSTON -- Vitamin D insufficiency may be one factor in the diminished response to bisphosphonates seen in clinical practice, researchers said here.
Women who had blood levels of 25(OH)D above 33 ng/mL -- lower levels were defined as vitamin D insufficiency -- were seven times more likely to respond to osteoporosis therapy than those with lower levels (OR 7.24, 95% CI 3.44 to 14.82, P<0.0001), according to Richard Bockman, MD, PhD, of Weill Cornell Medical College in New York City.
"As vitamin D levels increase, the more likely a patient is to have a positive response to bisphosphonates," Bockman said during a press briefing at the Endocrine Society meeting here.
Although randomized controlled trials have shown that bisphosphonates increase bone mineral density and prevent fractures, clinician experience in the real world has told a different story, as patients don't seem to respond to bisphosphonates at comparable rates to those seen in trials, Bockman said.
He estimated that about 30% of patients in an osteoporosis specialty clinic who are prescribed the drugs are typically nonresponders.
Since vitamin D plays a key role in bone health, Bockman and his team sought to assess the relationship between serum levels of 25(OH)D and patient response to bisphosphonates.
They conducted a retrospective chart review of 160 postmenopausal patients at their center who were taking a bisphosphonate -- either alendronate (Fosamax), risedronate (Actonel), ibandronate (Boniva), or zoledronate (Zometa) -- for at least 18 months.
Women were excluded if they had chronic steroid use, metabolic bone disease, chronic kidney disease, or issues with adherence.
The researchers classified them as responders or nonresponders. Women fell into the latter group if, after starting therapy, they had any new fractures, had a greater than 3% drop in bone mineral density, or had persistently low scores on dual x-ray absorptiometry (DEXA) scanning.
Ultimately, 89 patients were determined to be responders and 71 were nonresponders.
Bockman and colleagues found that 16.8% of responders had insufficient levels of 25(OH)D compared with 54.9% of nonresponders (P<0.0001).
The proportion of nonresponders increased with decreasing 25(OH)D concentrations:
• Under 20 ng/mL: 83.3% were nonresponders
• 20 to 30 ng/mL: 77.8% were nonresponders
• 30 to 40 ng/mL: 42.3% were nonresponders
• Greater than 40 ng/mL: 24.6% were nonresponders
"Serum levels of 33 ng/mL was definitely the breaking point," Bockman said during the briefing. "At that point, you see a sharp drop-off in patients not responding."
He said that clinicians should seek to optimize vitamin D status in order to achieve the maximal benefits from bisphosphonate therapy.
"It's clear that vitamin D status is a modifiable factor that should be checked and optimized in patients who are going to be treated for low bone mineral density and osteoporosis on agents such as bisphosphonates," he said.
The researchers reported no conflicts of interest.
Primary source: The Endocrine Society
Source reference:
Shieh A, et al "Vitamin D insufficiency is associated with decreased bisphosphonate response" ENDO 2011; Abstract P1-228.
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