Bisphosphonates for Prevention of Post-Denosumab Bone Loss

Osteoporosis in premenopausal women with normal menstrual function and no specific cause is termed idiopathic osteoporosis (IOP). IOP is a rare disease with an estimated prevalence of \<200,000 affected premenopausal women in the United States.

Women with IOP completing at least one year and up to three years of denosumab (Protocol AAAN0161) will be offered participation in this open-label study in which they would choose whether to take oral alendronate 70 mg weekly for 12 months or a single intravenous dose of zoledronic acid 5 mg. Subjects and study personnel will be blinded to BMD outcomes until 12 months.

Discontinuation of denosumab is followed by substantial increases in bone turnover markers to well above baseline, 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 lost. Studies done at the institution has demonstrated the occurrence of multiple vertebral fractures in some patients who have stopped denosumab. Based upon these new fracture data, the Prolia label is currently recommending that consideration should be given to transition to another antiresorptive drug in patients stopping denosumab. The main goals of this extension study are to determine rates of bone loss and incidence of radiographic vertebral fractures during one year of bisphosphonate therapy (oral alendronate or intravenous zoledronic acid) initiated after completing denosumab.