Increases in hip and spine bone mineral density are predictive for vertebral antifracture efficacy with ibandronate

The relationship between bisphosphonate-induced bone mineral density (BMD) gains and antifracture efficacy remains to be fully elucidated. Data from two antifracture studies were analyzed. Postmenopausal osteoporotic women received oral (2.5 mg daily, 20 mg intermittent) or intravenous (0.5 mg, 1 mg quarterly) ibandronate. Outcome measures included moving averages plots and logistic regression analyses of the relationship between BMD change and vertebral fracture rate. In moving averages plots, ibandronate-induced BMD gains were consistently associated with decreased fracture rates. In the oral study, total-hip BMD increases at years 2 and 3 and lumbar spine BMD increases at year 3 were associated with 3-year vertebral fracture rate (relative risk reduction [RRR] at year 3 for 1% change from baseline: hip, 7.9% [95% CI 2.1-13.5%, P = 0.0084]; lumbar spine, 4.7% [-0.1% to 9.3%, P = 0.0565]). In the intravenous study, total-hip BMD increases at years 1, 2, and 3 and lumbar spine BMD increases at years 2 and 3 were significantly associated with vertebral fracture rate (RRR at year 3 for 1% change from baseline: hip, 11.6% [7.0-16.0%, P <0.0001]; lumbar spine, 6.9% [2.9-10.6%, P = 0.0008]). In a pooled analysis, changes in total-hip and lumbar spine BMD were associated with 3-year vertebral fracture risk reduction and explained a substantial proportion of the antifracture effect (23-37% at 2 and 3 years). This analysis suggests that ibandronate-induced BMD gain in postmenopausal osteoporotic women is associated with vertebral fracture risk reduction.