Effects of Intravenous Zoledronic Acid Once Yearly on Bone Remodeling and Bone Structure

ABSTRACT: In a substudy of the HORIZON pivotal fracture trial, in which yearly intravenous zoledronic acid 5 mg was found to significantly reduce risk of various fracture types in patients with postmenopausal osteoporosis, 152 patients underwent bone biopsy. Zoledronic acid reduced bone turnover by 63% and preserved bone structure and volume, with evidence of ongoing bone remodeling in 99% of biopsies obtained. Introduction: In the HORIZON pivotal fracture trial (PFT), enrolling 7736 women with postmenopausal osteoporosis, three annual intravenous infusions of the bisphosphonate zoledronic acid (5 mg) significantly reduced morphometric vertebral, clinical vertebral, hip, and nonvertebral fractures by 70%, 77%, 41%, and 25%, respectively. Whereas 79% of patients received zoledronic acid/placebo only (stratum I, n6113), 21% received concomitant treatment with other antiresorptive drugs, excluding other bisphosphonates, PTH, and strontium (stratum II, n  1652). Materials and Methods: To determine effects on bone remodeling and bone architecture, iliac crest bone biopsies were obtained in 152 patients on active treatment or placebo at 3 yr after double tetracycline labeling. In five patients, only qualitative histology was performed, leaving 147 biopsy cores (79 on active treatment and 68 on placebo) for CT analysis and histomorphometry. Results: Analysis of bone structure by CT revealed higher trabecular bone volume (BV/TV) in the zoledronic acid group (median, 16.6% versus 12.8%; p0.020). In addition, patients treated with zoledronic acid exhibited higher trabecular numbers (p  0.008), decreased trabecular separation (p  0.011), and a trend toward improvement in connectivity density (p  0.062), all indicating better preservation of trabecular structure after treatment with zoledronic acid. Qualitative analysis revealed presence of tetracycline label in 81 of 82 biopsies from patients on zoledronic acid and all 70 biopsies from placebo patients, indicative of continued bone remodeling. No bone pathology was observed. Zoledronic acid induced a 63% median (71% mean) reduction of the activation frequency (Ac.f; p < 0.0001) and reduced mineralizing surface (MS/BS; p < 0.0001) and volume referent bone formation rate (BFR/BV) versus placebo, indicating reduced bone turnover.