PDE5 inhibitors

A phosphodiesterase type 5 inhibitor (PDE5 inhibitor) is a drug used to block the degradative action of cGMP-specific phosphodiesterase type 5 (PDE5) on cyclic GMP in the smooth muscle cells lining the blood vessels supplying the corpus cavernosum of the penis. These drugs are used in the treatment of erectile dysfunction and were the first effective oral treatment available for the condition. Because PDE5 is also present in the arterial wall smooth muscle within the lungs, PDE5 inhibitors have also been explored for the treatment of pulmonary hypertension, a disease in which blood vessels in the lungs become overloaded with fluid, usually as a result of failure of the left ventricle of the heart.

PDE5 inhibitors such as sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra) are clinically indicated for the treatment of erectile dysfunction. Sildenafil and tadalafil are also indicated for the treatment of pulmonary hypertension.

Sildenafil, the prototypical PDE5 inhibitor, was originally discovered during the search of a novel treatment for angina. Studies in 2002 explored its potential for increasing neurogenesis after stroke.

PDE5 inhibitors are contraindicated in those taking nitrate medications, such as isosorbide mononitrate or isosorbide dinitrate. Concurrent use of these medications can lead to life-threatening low blood pressure or heart attack. They are also contraindicated in men for whom sexual intercourse is inadvisable due to cardiovascular risk factors.

The occurrence of adverse drug reactions (ADRs) with PDE5 inhibitors appears to be dose-related. Headache is a very common ADR, occurring in >10% of patients. Other common ADRs include: dizziness, flushing, dyspepsia, nasal congestion or rhinitis.

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