Sildenafil citrate

Sildenafil citrate, commonly known by its brand name Viagra, is a medication used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). It is classified under the group of drugs known as phosphodiesterase type 5 (PDE5) inhibitors. Sildenafil works by increasing blood flow to the penis during sexual stimulation, which helps to achieve and maintain an erection. For the treatment of PAH, it functions by relaxing the blood vessels in the lungs to allow blood to flow more easily.

Medical Uses

Sildenafil citrate is primarily used for the treatment of two conditions:

• Erectile Dysfunction: It is the most common use of sildenafil, where it helps men achieve and maintain an erection sufficient for sexual activity.
• Pulmonary Arterial Hypertension: Sildenafil is also prescribed to manage PAH, a condition characterized by high blood pressure in the arteries that supply the lungs.

Mechanism of Action

Sildenafil citrate works by inhibiting an enzyme called phosphodiesterase type 5 (PDE5). By blocking PDE5, sildenafil increases the levels of cyclic guanosine monophosphate (cGMP) in the blood vessels, leading to relaxation of the smooth muscle cells and vasodilation. In the context of erectile dysfunction, this mechanism facilitates the flow of blood into the corpus cavernosum of the penis, thereby aiding in erection. In pulmonary arterial hypertension, vasodilation of the pulmonary artery reduces the pulmonary blood pressure.

Side Effects

Common side effects of sildenafil include headaches, heartburn, flushed skin, and nausea. Rare but more serious side effects can occur, such as sudden hearing loss or priapism, a painful erection lasting more than four hours, which requires immediate medical attention. Patients are advised to consult their healthcare provider if they experience any adverse effects.

Contraindications

Sildenafil should not be used in conjunction with nitrate medications due to the risk of significant hypotension. It is also contraindicated in patients with certain cardiovascular conditions, severe liver impairment, or a history of stroke.

Pharmacokinetics

Sildenafil is absorbed rapidly in the body, with maximum plasma concentrations reached within an hour of oral administration. Its metabolism occurs primarily in the liver through the action of cytochrome P450 enzymes. The drug is excreted as metabolites predominantly in the feces.

History

Sildenafil was originally developed by scientists in the United Kingdom and was brought to market by Pfizer Inc. It became available in the United States as the first oral treatment for erectile dysfunction in 1998.

Society and Culture

The introduction of sildenafil has had a significant impact on society, particularly in terms of discussing sexual health issues more openly. It has also been involved in numerous legal and ethical debates regarding direct-to-consumer advertising and its use beyond the approved medical indications.

See Also

• Phosphodiesterase inhibitor
• Sexual dysfunction
• Vasodilation