Antiresorptive Treatment of Postmenopausal Osteoporosis: Comparison of Study Designs and Outcomes in Large Clinical Trials with Fracture as an Endpoint
Robert Marcus,
Mayme Wong,
Hunter Heath, III and
John L. Stock
Department of Medicine, Stanford University School of Medicine, and the Musculoskeletal Research Laboratory, Geriatric Research, Education, and Clinical Center, Veterans Affairs Medical Center (R.M.), Palo Alto, California 94304; and Lilly Research Laboratories, Eli Lilly and Company (M.W., H.H.III, J.L.S.), Indianapolis, Indiana 46285
Correspondence: Address all correspondence and requests for reprints to: Robert Marcus, M.D., Professor of Medicine, Stanford University, Geriatric Research, Education, and Clinical Center 182-B, Veterans Affairs Medical Center, 3801 Miranda Avenue, Palo Alto, California 94304. E-mail: marcuse{at}Stanford.edu
Antiresorptive treatments for postmenopausal osteoporosis havebeen studied extensively, but due to the volume of publisheddata and lack of head-to-head trials, it is difficult to evaluateand compare their fracture reduction efficacy. The objectiveof this review is to summarize the results from clinical trialsthat have fracture as an endpoint and to discuss the factorsin study design and populations that can affect the interpretationof the results. Although there are numerous observational studiessuggesting that estrogen and hormone replacement therapies mayreduce the risk of vertebral and nonvertebral fractures, thereis no large, prospective, randomized, placebo-controlled, double-blindclinical trial demonstrating fracture efficacy. The effectsof raloxifene, alendronate, risedronate, and salmon calcitoninon increasing bone mineral density (BMD) and decreasing fracturerisk have been shown in randomized, placebo-controlled, double-blindclinical trials of postmenopausal women with osteoporosis. Althoughthe increases in lumbar spine BMD vary greatly in these trials,the decrease in relative risk of vertebral fractures is similaramong therapies. However, nonvertebral fracture efficacy hasnot been consistently demonstrated. Combined administrationof two antiresorptive therapies results in greater BMD increases,but the effects on fracture risk are unknown. Direct comparisonsof clinical trial results should be considered carefully, giventhe differences in study design and populations. Differencesin study design that may influence the efficacy of fracturerisk reduction include calcium and vitamin D supplementation,primary fracture endpoints, definition of vertebral deformityor fracture, discontinuation rates, and statistical power. Factorsin the study population that may influence fracture efficacyinclude the age of the population and the proportion of subjectswith prevalent fractures. The use of surrogate endpoints suchas BMD to predict fracture risk should be approached with caution,as the relationship between BMD changes and fracture risk reductionwith antiresorptive therapies is uncertain. Consideration ofthese results from clinical trials can contribute to clinicaljudgment in selecting the best treatment option for postmenopausalosteoporosis.
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