Endothelin-1 Receptor Blockade in Resistant Hypertension

This study tests bosentan, a drug that blocks a blood vessel-constricting chemical called endothelin-1, to see if it can lower blood pressure in people with resistant hypertension — meaning their blood pressure remains high even when they are already taking three or more blood pressure medications. **You may be eligible if...** - You are between 30 and 80 years old - Your blood pressure remains at or above 140/90 mmHg despite taking three or more blood pressure medications (including at least one diuretic/water pill) at full doses - Your high blood pressure is confirmed by home monitoring or a 24-hour blood pressure monitor - Your hemoglobin level is 12 g/dL or above - Women of childbearing potential must use reliable contraception (not just hormonal methods alone during bosentan treatment) **You may NOT be eligible if...** - Your hypertension is caused by a secondary condition (other than sleep apnea or mild to moderate chronic kidney disease) - Your blood pressure is extremely high (180/110 mmHg or above) - You have severe chronic kidney disease (stage 4-5) or are on dialysis - You have had a kidney transplant - You have orthostatic hypotension (blood pressure drops significantly when you stand) - You are taking medications that interact with bosentan (such as certain antifungals, cyclosporine, or antiretroviral drugs) - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.