Comparison of the Effect of an Ongoing Treatment With Alendronate or a Drug Holiday on the Fracture Risk in Osteoporotic Patients With Bisphosphonate Long Term Therapy

Inclusion Criteria: * Postmenopausal women or men \> 60 years * DXA T-Score at lumbar spine, total hip or femur neck \<-2,0 before the start of the bisphosphonate therapy or at baseline or at least one low trauma vertebral fracture grade 2-3 or multiple low trauma vertebral fractures independent of bone mineral densitiy * Pretreatment with bisphosphonates for at least four years * Risk for hip and vertebral fractures min. 30% according to DVO-guideline for osteoporosis 2009 * Signed informed consent Exclusion Criteria: * Other pharmacological treatment of osteoporosis during the last 48 months * Other bone diseases * Malabsorption syndromes * Renal insufficiency with a calculated creatinine clearance \< 35 ml/min * Diseases of the esophagus, delayed esophageal clearance * UUnability to realise the intake instructions * Hypocalcemia