Antiresorptive Treatment of Postmenopausal Osteoporosis: Comparison of Study Designs and Outcomes in Large Clinical Trials with Fracture as an Endpoint

Antiresorptive treatments for postmenopausal osteoporosis have been studied extensively, but due to the volume of published data and lack of head-to-head trials, it is difficult to evaluate and compare their fracture reduction efficacy. The objective of this review is to summarize the results from clinical trials that have fracture as an endpoint and to discuss the factors in study design and populations that can affect the interpretation of the results. Although there are numerous observational studies suggesting that estrogen and hormone replacement therapies may reduce the risk of vertebral and nonvertebral fractures, there is no large, prospective, randomized, placebo-controlled, double-blind clinical trial demonstrating fracture efficacy. The effects of raloxifene, alendronate, risedronate, and salmon calcitonin on increasing bone mineral density (BMD) and decreasing fracture risk have been shown in randomized, placebo-controlled, double-blind clinical trials of postmenopausal women with osteoporosis. Although the increases in lumbar spine BMD vary greatly in these trials, the decrease in relative risk of vertebral fractures is similar among therapies. However, nonvertebral fracture efficacy has not been consistently demonstrated. Combined administration of two antiresorptive therapies results in greater BMD increases, but the effects on fracture risk are unknown. Direct comparisons of clinical trial results should be considered carefully, given the differences in study design and populations. Differences in study design that may influence the efficacy of fracture risk reduction include calcium and vitamin D supplementation, primary fracture endpoints, definition of vertebral deformity or fracture, discontinuation rates, and statistical power. Factors in the study population that may influence fracture efficacy include the age of the population and the proportion of subjects with prevalent fractures. The use of surrogate endpoints such as BMD to predict fracture risk should be approached with caution, as the relationship between BMD changes and fracture risk reduction with antiresorptive therapies is uncertain. Consideration of these results from clinical trials can contribute to clinical judgment in selecting the best treatment option for postmenopausal osteoporosis.