Bosentan Use in Patients With Diabetic Nephropathy

Inclusion Criteria: * Men or women ≥ 18 years of age with a body weight of ≥ 40 kg; * For female patients, only non-pregnant women who are surgically sterile, postmenopausal or have documented infertility (over 50 years of age and amenorrheic for at least 1 year), or those of childbearing potential using intrauterine devices (IUDs); * Patients diagnosed Type 2 diabetes with overt nephropathy (urinary albumin excretion ≥ 300mg/24h); * Patients on current treatment with angiotensin II receptor blockers for ≥ 3 months; * Patients stable for at least 3 months prior to screening (no change in medications for diabetic nephropathy); * Provide written informed consent; Exclusion Criteria: * Patients with a history of pulmonary chronic obstructive disease, cardiac failure or coronary artery disease; * Patients with documented cancers, acute infections or chronic inflammatory diseases; * Patients who are pregnant or breast-feeding; * Patients with known hepatic disorders or AST and ∕or ALT upper than normal limit; * Patients with hemoglobin or hematocrit that is ≥ 30% below the normal range (patients with secondary polycythemia are permitted); * Patients with systolic blood pressure \< 110mm Hg; * Patients with plasmatic albumin level \< 30g/L; * Patients with a documented creatinine clearance ≤ 60ml/min; * Patients on anticoagulants or anti-inflammatory drugs, including cyclooxygenase inhibitors, AINS, prednisone and immunosuppressive drugs, platelet aggregation inhibitors, except low dose aspirin, ACE inhibitors, antidiabetic agents (rosiglitazone, pioglitazone) and antioxidants (vitamin E)(except statins or low-dose aspirin ≤ 80mg/day); * Patients on treatment or planned treatment with another investigational drug; * Patients who are receiving an endothelin receptor antagonist, phosphodiesterase type 5 inhibitor, or with a prostanoid (excluding acute administration during a catheterization procedure to test vascular reactivity) within 2 months of inclusion; * Patients who are receiving calcineurin-inhibitors (i.e., cyclosporine A and tacrolimus), fluconazole, glibenclamide (glyburide) at inclusion or are expected to receive any of these drugs during the study; * Patients with a known hypersensitivity to bosentan or any of the excipients;