The patent was published in and expired in These medicines are called PDE5 inhibitors. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors. It was initially studied for use in hypertension high blood pressure and angina pectoris a symptom of ischaemic heart disease. If you are a Mayo Clinic patient, this could include protected health information.Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects . Viagra comes as an oral tablet that contains the active drug sildenafil. Sildenafil is also available in generic form. Viagra is classified as a phosphodiesterase type 5 (PDE5) . Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in .