Prophylactic Trimethoprim/Sulfamethoxazole to Prevent Severe Infections in Patients With Lupus Erythematous

Inclusion Criteria: * Systemic Lupus Erythematosus according to the American College of Rheumatology Criteria * On a daily dose of prednisone of ≥ 15 mg/d or equivalent, and that are expected to remain on the this dose for at least 1 month. * Have signed an informed consent Exclusion Criteria: * Absolute contraindication to receive TMP-SMX (known allergy to TMP-SMX or sulfa drugs; TMP-SMX induced thrombocytopenia) * Received TMP-SMX treatment in the previous month * Creatinine clearance \<30ml/min/m2 * Chronic viral infection (Hepatitis C virus, Hepatitis B virus, Human immunodeficiency virus) * Malignant neoplasm, except for skin neoplasm * Primary immune deficiencies * Solid organ or hematopoietic stem cell transplant recipients * Pregnancy or Breastfeeding * Current active infection, except mild active infections that to the judgement of the primary investigator do not jeopardize the study outcomes (e.g. tinea). * Uncontrolled chronic infection (e.g. tuberculosis- intensive phase treatment), except mild active chronic infections that to the judgement of the primary investigator do not jeopardize the study outcomes (e.g. onychomycosis). * Controlled chronic infection, that needs to be treated or prevented with TMP-SMX. * Absolute Neutrophil Count \< 750/mm3, platelets \<30x10\^9/L, o hemoglobin \<7 g/dL * Patients receiving Methotrexate * Patients participating in another research study that to the judgement of the principal investigator could jeopardize the safety or efficacy of the study drug.