The Effect of Metformin on Reducing Lupus Flares

Inclusion Criteria: * Willingness of the subject to participate in the study, proven by signing the informed consent; * Systemic lupus erythematosus (SLE), as defined by meeting at least 4 of 11 classification criteria of American College of Rheumatology for the classification of systemic lupus erythematosus, either sequentially or coincidentally. The 4 criteria doesn't need to be present at the time of study enrollment; * The course of SLE longer than1 year; and there is a clear record of disease flares in the past 1 year with prednisone more than 20mg/day; * Patients with mild/moderate disease activity (score≤ 6 at screening on SLEDAI); no British Isles Lupus Assessment Group (BILAG) A or no more than one B; * A stable treatment regimen with fixed doses of prednisone (≤ 20mg/day), antimalarial, or immunosuppressive drugs (azathioprine/ mycophenolate mofetil/ methotrexate/ ciclosporin/ leflunomide/ thalidomide) for at least 30 days. Exclusion Criteria: * Patients who are unwilling to sign the inform consent; * Alanine aminotransferase (ALT)/ aspartate aminotransferase (AST) \> 2 times upper normal limits; creatinine clearance rate \< 60ml/min; * Patients who used cyclophosphamide 6-months before screening; used biological agents 12-months before screening; * Previous exposure of metformin within 30 days before screening; or previous history of intolerant to metformin; * Patients who diagnosed of diabetes mellitus; * Pregnancy or lactation.