MAGnesium Effect With ANtiosteoporotic Drugs

Inclusion Criteria: * Women aged 50 years or older, with postmenopausal osteoporosis, fractured or not, requiring initiation of injectable bisphosphonate therapy as part of their care. * Able to give informed consent to participate in the research. * Affiliation to a Social Security system. Exclusion Criteria: * Initial densitometry more than one year old. * Patient receiving a treatment or food supplement containing magnesium (Mg). * Contra-indication to the administration of Mg: hypersensitivity to magnesium carbonate or to one of the excipients. * Patients with a magnesium level \> 1.07 mmol/l. * Patient with chronic renal failure, defined as creatinine clearance \< 35 mL/min estimated by Cockcroft-Gault or glomerular filtration rate \< 30 mL.min-1 estimated by CKD-EPI and taking into account which is more pejorative. * Patient with a medical and/or surgical history deemed by the investigator or his representative to be incompatible with the trial. * Patient under legal protection or deprived of liberty. * Refusal to participate.