Serum 25-hydroxy-vitamin D and the risk of fractures in the teriparatide versus risedronate VERO clinical trial

PurposeUsing data from the 2-year, randomized, double-dummy VERO trial, we examined the changes in 25-hydroxy-vitamin D (25[OH]D) concentrations over time, and whether the fracture risk reduction of teriparatide versus risedronate varies by baseline 25(OH)D sufficiency category.MethodsPostmenopausal women with established osteoporosis received subcutaneous daily teriparatide 20g or oral weekly risedronate 35mg, with concomitant 500-1000mg of elemental calcium and 400-800IU/day of vitamin D supplements. Fracture endpoints were analyzed by predefined subgroups of 25(OH)D insufficient and sufficient patients. Heterogeneity of the treatment effect on fractures was investigated by logistic and Cox proportional hazards regression models.ResultsAt baseline, mean serum 25(OH)D was 31.9ng/mL in the teriparatide group and 31.5ng/mL in the risedronate group, and 16.8% and 17.9% of patients, respectively, were 25(OH)D insufficient. At month 6, the mean serum 25(OH)D concentration decreased in teriparatide-treated patients to 24.5ng/mL (by approximately 23%) but remained relatively constant in risedronate-treated patients (32.2ng/mL) (p0.1) treatment-by-25(OH)D interactions in all fracture analyses.ConclusionsSerum 25(OH)D concentration decreases during teriparatide treatment. Fracture risk reduction with teriparatide versus risedronate did not significantly differ between the two groups of patients defined by baseline 25(OH)D.Trial registrationClinicalTrials.gov Identifier: NCT01709110EudraCT Number: 2012-000123-41