Anti-fracture efficacy of zoledronate in subgroups of osteopenic postmenopausal women: secondary analysis of a randomized controlled trial

Background We recently reported that the administration of zoledronate every 18 months to osteopenic older women reduces the incidence of fractures. Objective Here, we present a more detailed analysis of that trial to determine whether baseline clinical characteristics impact on the anti-fracture efficacy of this intervention. Methods This is a prospective, randomized, placebo-controlled, double-blind trial in osteopenic postmenopausal women aged >= 65 years, to determine the anti-fracture efficacy of zoledronate. 2000 women were recruited using electoral rolls and randomized to receive 4 infusions of either zoledronate 5 mg or normal saline, at 18-month intervals. Each participant was followed for 6 years. Calcium supplements were not supplied. Results Fragility fractures (either vertebral or nonvertebral) occurred in 190 women in the placebo group (227 fractures) and in 122 women in the zoledronate group (131 fractures), odds ratio (OR) 0.59 (95%CI 0.46, 0.76; P < 0.0001). There were no significant interactions between baseline variables (age, anthropometry, BMI, dietary calcium intake, baseline fracture status, recent falls history, bone mineral density, calculated fracture risk) and the treatment effect. In particular, the reduction in fractures appeared to be independent of baseline fracture risk, and numbers needed to treat (NNT) to prevent one woman fracturing were not significantly different across baseline fracture risk tertiles. Conclusions The present analyses indicate that the decrease in fracture numbers is broadly consistent across this cohort. The lack of relationship between NNTs and baseline fracture risk calls into question the need for BMD measurement and precise fracture risk assessment before initiating treatment in older postmenopausal women.