Pain and Magnesium

Inclusion Criteria: * \- Age ≥ 18 years, * Patient with breast cancer who has a scheduled total mastectomy with or without treatment two weeks after inclusion with or without preoperative chemotherapy, * Patient free from any new treatment or diet at the time of the inclusion, * Cooperation and understanding sufficient to comply with the requirements of the study, * Patients affiliated to the French Social Security, * Patients with free and informed consent has been obtained Exclusion Criteria: * Hypersensitivity to the active substance or to any of the excipients * Patient with magnesemia \>1,05 mmol/l * Patient with severe renal insufficiency with creatinine clearance \<30 ml min, * Patient with an addiction to alcohol, as determined by the investigator, * Diabetes (type I and II), * Medical and surgical history incompatible with the study, * Patient receiving treatment with Quinidine, L-Dopa, * Childbearing age, no use of effective contraceptive method, pregnancy or lactation * Patient exclusion period, or the total allowable compensation exceeded * Patients undergoing a measure of legal protection (guardianship, supervision ...)