Changes in bone mineral density, bone turnover markers, and vertebral fracture risk reduction with once weekly teriparatide

Objective: We aimed to evaluate the surrogacy of bone mineral density and bone turnover markers for incident vertebral fracture using data from 237 patients treated with once weekly 56.5 mu g teriparatide or placebo. Methods: This analysis was conducted using data from the Teriparatide Once-Weekly Efficacy Research trial, a randomized, double-blind, placebo-controlled trial for patients with severe osteoporosis in Japan. A total of 237 subjects (placebo group, n = 130; teriparatide group, n = 107) were assessed at baseline and at 72 weeks. Main outcome measures included estimation of the treatment effects of once weekly teriparatide on vertebral fracture risk reduction using percentage changes in lumbar bone mineral density and bone turnover markers. Results: The percentage change in lumbar bone mineral density was 6.69% in the teriparatide group compared with 0.28% in the placebo group (p<0.01). One incident vertebral fracture occurred in the teriparatide group compared with 16 in the placebo group. The unadjusted and adjusted hazard ratios of the teriparatide group compared with the placebo group were 0.07 (95% confidence interval: 0.01 to 0.56) and 0.64 (95% confidence interval: 0.06 to 6.36), respectively. The proportion of treatment effect explained by changes in lumbar bone mineral density was 83% (Freedman's method) and 66% (Chen's method). There were no notable changes in hazard ratios if we adjusted for bone turnover markers. Conclusions: Most of the vertebral fracture risk reduction with once weekly 56.5 mg teriparatide is explained by changes in lumbar bone mineral density rather than changes in bone turnover markers.