Sildenafil (Viagra) has shown promise in treating patients with Primary Pulmonary Hypertension which is caused by a narrowing of the blood vessels in the lungs, leading to high blood pressure in the pulmonary system and heart failure. Therefore treatments for PPH are designed to relax and widen the damaged blood vessels making it easier for the heart to pump blood through the lungs. Nitric oxide treatment discussed elsewhere on this web site involves the continuous inhalation of nitric oxide to widen blood vessels in the lungs. An inhaled mist form of epoprostenol called iloprost is also being used experimentally in the same manner and with the same goal. The advantage of these inhaled treatments is that they are "selective treatments" meaning they only affect the blood vessels in the pulmonary system. This reduces side effects experienced by patients taking more "systematic treatments".
Recently, researchers learned that a drug widely used for impotence, sildenafil (sold as Viagra), may also be effective as a selective vasodilator of the pulmonary system. Sildenafil is an inhibitor of PDE 5, a hormone produced by the body that causes blood vessel to constrict. Researchers believe that because of the high concentrations of PDE 5 in the lungs, sildenafil may function in a similar manner to nitric oxide or iloprost.
To test this theory doctors recently conducted a clinical trial in which 30 patients with severe pulmonary hypertension; 11 of whom had previously been treated with iloprost, received sildenafil treatment. The patients were randomly divided into four groups: 1) patients who had been treated with low-dose sildenafil, 2) patients who had been treated with low-dose sildenafil followed by inhaled iloprost, 3) patients who had been treated with high-dose sildenafil, and 4) patients who had been treated with high-dose sildenafil followed by inhaled iloprost. The results of the trial revealed two things: 1) those who were treated previously with iloprost showed more improvement than those who hadn't been and 2) that those who were treated with high-dose sildenafil showed more improvement than those who had been treated with low-dose sildenafil.
Another study contrasting the effects of inhaled iloprost to oral sildenafil in pulmonary hypertension found that while iloprost caused a greater reduction in pulmonary artery pressure, sildenafil was effective for a longer period of time. Than combining the two drugs, researches saw further reduction in pulmonary artery pressure and an increase in heart efficacy without affecting overall (systemic) blood pressure significantly.
Case reports of patients with primary pulmonary hypertension treated with sildenafil have also yielded encouraging results. For instance, two siblings with a similar medical history, severe symptoms and elevated levels of pulmonary artery pressures were diagnosed with PPH. Both were treated with combination therapies that included sildenafil. While one had no improvement during the treatment and died several weeks after being discharged from the hospital, the other patient improved dramatically. At a three-month follow-up, her pulmonary status had greatly improved. In another instance, a 21 year-old man with primary pulmonary hypertension was treated with Sildenafil at a daily dose of 500mgs and improved significantly.
These early findings demonstrate some promise and larger clinical trials using sildenafil as a treatment of pulmonary hypertension are being developed.
