Single or Repeat Zoledronate Versus Alendronate Following Denosumab (EUROpean Denosumab Effects Consolidation Study)

125 postmenopausal women treated with Dmab for 3 or more years who will reach osteopenia with denosumab will be randomized into three groups: i) zoledronate infusion (5mg) at 6 months after last Dmab dose (single Zol group) ii) zoledronate infusion (5mg) at 6 and 12 months after last Dmab dose (double Zol group) iii) alendronate 70mg orally weekly for 12 months (ALN group) All women will receive no further treatment during the 2nd year of the study. Participating centers: ECTS affiliated bone centers Endpoints: Primary: BMD changes at the lumbar spine at 12 months. Secondary: i) BMD changes at the lumbar spine at 24 months; ii) BMD changes at the non-dominant femoral neck and total hip at 12 and 24 months; iii) changes at levels of bone turnover markers throughout the study; iv) incident fractures: vertebral (clinical and morphometric identified on VFA scans) and non-vertebral; v) clinical parameters: height change, VAS for back pain, and use of analgesics