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Electronic letters published:
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In response
Relative Effectiveness of Osteoporosis Drugs for Preventing Nonvertebral Fracture
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Suzanne M. Cadarette, PhD Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, Jeffrey N. Katz, MD, MS; and Daniel H. Solomon, MD, MPH
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s.cadarette{at}utoronto.ca Suzanne M. Cadarette, et al.
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We agree with and appreciate the comments raised by Drs. Beri and Khattri. In their letter, Drs. Beri and Khattri highlight our finding that calcitonin recipients under study were sicker than alendronate recipients based on measured variables (1). They also point out that bisphosphonate dosing instructions are complex, and thus frail patients may have been preferentially treated with calcitonin, administered by daily nasal spray. We agree that residual confounding could explain part of our findings, and discussed limitations of administrative claims data in our manuscript. Results from our theoretical sensitivity analysis identified that it is unlikely that the higher fracture risk observed among calcitonin recipients compared with alendronate recipients is due to unmeasured confounding. However as this analysis was based on the assumption of a single unmeasured confounder (2), it is possible that multiple unmeasured confounding factors collectively introduced bias into the results. Nonetheless, we did adjust for many factors associated with frailty, such as age, history of falls, vertebral fractures, Parkinson’s disease, dementia, comorbidity score and medication use. We also completed seven different subgroup analyses, all with results similar to our main findings: no large difference in nonvertebral fracture rates between risedronate or raloxifene and alendronate, and higher nonvertebral fracture risk among calcitonin recipients compared with alendronate recipients. Of interest, however, we did document more fractures among raloxifene recipients compared with alendronate recipients in the subgroup with previous fracture. We therefore emphasize caution in interpreting findings comparing calcitonin and alendronate, as well as results comparing raloxifene and alendronate, as raloxifene recipients were apparently healthier based on measured variables. Our results comparing bisphophonates are more compelling because risedronate and alendronate recipients were similar based on measured risk factors for fracture, however, we cannot rule out potential differences in unmeasured factors. 1. Cadarette SM, Katz JN, Brookhart MA, Stürmer T, Stedman MR, Solomon DH. Relative effectiveness of osteoporosis drugs for preventing nonvertebral fracture. Ann Intern Med. 2008;148:637-46. 2. Schneeweiss S. Sensitivity analysis and external adjustment for unmeasured confounders in epidemiologic database studies of therapeutics. Pharmacoepidemiol Drug Saf. 2006;15:291-303. Conflict of Interest:Dr. Solomon has received salary support from Merck through a research grant to the Brigham and Women’s Hospital for unrelated work. There was no pharmaceutical industry support for this study. |
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Abhimanyu Beri, M.D. Michigan State University, Saakshi Khattri
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abhiberi{at}gmail.com Abhimanyu Beri, et al.
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We read with great interest the article by Cadarette et al (1). Osteoporosis and fracture risk in the elderly, especially post-menopausal women is a growing problem in the population. A few things came to our mind while reading this article. First, the authors do not mention or control regarding patients’ dietary calcium intake and physical activity, two factors that are the first recommendations for prevention of osteoporosis. Secondly, there is also no estimation of prescription and over the counter calcium and vitamin D supplementation in the patients (2,3). This may be lower in poorer patients who might have been preferentially included in this study. Thirdly, the subset that was prescribed calcitonin was a less healthy group, as evident by their age, higher co-morbidity score the fact that they had more prescription drugs per patient and had a much higher incidence of co-morbidities. We would specifically like to point out a history of falls, vertebral fractures, Parkinson’s and dementia that was almost 50% more than the other drug groups. A basic requirement for prescription of bisphosphonates is the ability to sit upright or stand for 30 minutess after swallowing these drugs orally (4). As patients with the above co-morbidities are less likely to have this ability, we feel that a bias during prescription may have been present and that the less healthy patients were prescribed calcitonin. And as we do not know the T-scores for these patients, we cannot estimate the true degree of osteoporosis in them. References: 1.Cadarette SM, Katz JN, Brookhart MA, Stürmer T, Stedman MR, Solomon DH. Relative Effectiveness of Osteoporosis Drugs for Preventing Nonvertebral Fracture. Ann Intern Med 2008; 148: 637-646 2.Papadimitropoulos E, Wells G, Shea B, et al. Meta-analyses of therapies for postmenopausal osteoporosis. VIII: Meta-analysis of the efficiency of vitamin D treatment in preventing osteoporosis in postmenopausal women. Endocrin Rev. 2002; 23: 560-569. 3.Positive effects of exercise on falls and fracture risk in osteopenic women. Hourigan SR, Nitz JC, Brauer SG, O'Neill S, Wong J, Richardson CA. Osteoporos Int. 2008 Jan 11 [Epub ahead of print] 4.http://www.merck.com/product/usa/pi_circulars/f/fosamax/fosamax_pi.pdf (Accessed on May 6, 2008) Conflict of Interest:None declared |
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