Phosphodiesterase 5 inhibitors What are phosphodiesterase 5 inhibitors? Phosphodiesterase 5 (PDE 5) inhibitors are a type of targeted therapy used to treat people with pulmonary hypertension (PH). Targeted therapies slow the progression of PH and may even reverse some of the damage to the heart and lungs. There are two types of PDE 5 inhibitor currently used to treat PH: sildenafil (Viagra, Revatio and now “generic” i.e. not branded) tadalafil (Adcirca and now “generic” i.e. not branded). PDE 5 inhibitors are also used to treat erectile dysfunction. This is because the body has the same type of cells in the blood vessels of the lungs as the blood vessels of the penis. Viagra (sildenafil) has been used to treat erectile problems since 1998. PDE 5 inhibitors are taken as nearly always tablets. An injection of sildenafil is available for short-term use when patients aren’t able to eat or drink, for example when having an operation. How do phosphodiesterase 5 inhibitors work? PDE 5 inhibitors stop a particular enzyme (phosphodiesterase type 5 [PDE5]), found in blood vessel walls, from working properly. PDE5 helps control blood flow to the pulmonary arteries. By stopping PDE5 from working, PDE 5 inhibitors (ie sildenafil and tadalafil) cause the blood vessels to relax. This increases blood flow to the lungs and lowers blood pressure. How do sildenafil and tadalafil work? Risks associated with taking phosphodiesterase 5 inhibitors Like all medicines, PDE 5 inhibitors are associated with some risks. However, problems are usually temporary, and wear off quickly once your body gets used to the new medicine. These may be headache, flushing and lightheadedness due to low blood pressure. For this reason, most people are given their first dose at the hospital so these side effects can be monitored and managed accordingly. PDE 5 inhibitors are known to interact with certain types of medicine. Your PH specialist will discuss the types of drugs you should avoid if you are taking PDE 5 inhibitors. Your PH team will discuss all the risks associated with taking PDE 5 inhibitors with you.