This study is to investigate whether the alternating use of Prolia (Denosumab) and Aclasta (Zoledronic acid) can continue to increase bone density.

This study intends to use a randomized trial to test whether the long-term treatment of Denosumab and Zoledronic acid can achieve sustained bone density progress and avoid the risk of rapid bone loss after the withdrawal of Denosumab.

Inclusion Criteria:

1. Postmenopausal women or men over 50 years old with osteoporosis or osteopenia leading to fractures.
2. Denosumab treatment for at least two years and less than three years (up to maximum of five doses).

Exclusion Criteria:

1. Secondary osteoporosis.
2. Metabolic bone diseases.
3. Malignancy.
4. Continuous steroid treatment, hormone therapy or other medical treatment affecting bone metabolism.
5. Patients had ever used antiosteoporosis medications other than Dmab
6. Estimated glomerular filtration rate < 35 mL/min.
7. Allergy to Zoledronate.
8. Any other contraindications to Zoledronate use.
9. History of diagnosed hypocalcemia.
10. Age greater than 80 years.

After application