Department of Orthopedics, National Taiwan University Hospital

Denosumab is a monoclonal antibody directed against the protein RANK-L, the principal regulator of osteoclast development. Thus, it acts as a potent anti-resorptive agent and is now widely used in the treatment of osteoporosis. Because it's easily to be used with very low risk of complications, patient has better compliance and persistence of denosumab than bisphosphonates. It's market share increasing very rapidly in Taiwan.

Although denosumab has excellent effect to increase bone mass and prevent fracture in FREEDOM study with very low complications, even up to ten years, it's effect is reversible. After holding the drug, circulating denosumab levels fall rapidly, and bone resorption reaching twice baseline levels for about 6 months. Over the first 12 months off therapy, all the bone density gained on treatment is lost4. According to previous meta-analysis study, although the persistence of denosumab therapy is better than bisphosphonates, only 62% patients keep the treatment after two years. We could image how low the persistence is after five-year or ten-year treatment in the real world.

How to prevent bone loss after denosumab therapy is an important issue, especially when considering the compliance, persistence, or other comorbidities of the patient. There is only one randomized controlled trial dealing with this problem, although the primary goal of the study is designed to compare the compliance and persistence1. After switching from denosumab to alendronate for one year, bone mineral density does not decrease rapidly, although there is mild elevation of bone turn over marker.

We want to verify if zoledronic acid could be used as a sequential therapy after denosumab to prevent rapid bone loss by randomized clinical trial.