Denosumab or Zoledronic Acid in Postmenopausal Women With Osteoporosis Previously Treated With Oral Bisphosphonates

CONTEXT: Denosumab and zoledronic acid (ZOL) are parenteral treatments for patients with osteoporosis. OBJECTIVE: The objective of the study was to compare the effect of transitioning from oral bisphosphonates to denosumab or ZOL on bone mineral density (BMD) and bone turnover. DESIGN AND SETTING: This was an international, multicenter, randomized, double-blind trial. PARTICIPANTS: A total of 643 postmenopausal women with osteoporosis previously treated with oral bisphosphonates participated in the study. INTERVENTIONS: Subjects were randomized 1:1 to sc denosumab 60 mg every 6 months plus iv placebo once or ZOL 5 mg iv once plus sc placebo every 6 months for 12 months. MAIN OUTCOME MEASURES: Changes in BMD and bone turnover markers were measured. RESULTS: BMD change from baseline at month 12 was significantly greater with denosumab compared with ZOL at the lumbar spine (primary end point; 3.2% vs 1.1%; P < .0001), total hip (1.9% vs 0.6%; P < .0001), femoral neck (1.2% vs −0.1%; P < .0001), and one-third radius (0.6% vs 0.0%; P < .05). The median decrease from baseline was greater with denosumab than ZOL for serum C-telopeptide of type 1 collagen at all time points after day 10 and for serum procollagen type 1 N-terminal propeptide at month 1 and at all time points after month 3 (all P < .05). Median percentage changes from baseline in serum intact PTH were significantly greater at months 3 and 9 with denosumab compared with ZOL (all P < .05). Adverse events were similar between groups. Three events consistent with the definition of atypical femoral fracture were observed (two denosumab and one ZOL). CONCLUSIONS: In postmenopausal women with osteoporosis previously treated with oral bisphosphonates, denosumab was associated with greater BMD increases at all measured skeletal sites and greater inhibition of bone remodeling compared with ZOL.