Viagra®

Viagra® or Sildenafil citrate is a drug used to treat male erectile dysfunction and pulmonary arterial hypertension.
Viagra® pills are blue and diamond-shaped with the words "Pfizer" on one side.

Mechanism of action

A substance called nitric oxide binds to the receptors of the enzyme guanylate cyclase which results in increased levels of cyclic guanosine monophosphate, leading to smooth muscle relaxation in the corpus cavernous. This is resulting in increased inflow of blood in the penis  and an erection.

Similar to Cialis® and Levitra®, Viagra® is a potent and selective inhibitor of cGMP specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernous. This is resulting in better erections. Sildenafil is metabolized by hepatic enzymes and excreted by both the liver and kidneys.  

Contraindications and side effects

Contraindications include:

• When taking nitric oxide donors, organic nitrites and nitrates, such as glyceryl trinitrate, and other similar medications   
• In men for whom sexual intercourse is inadvisable due to cardiovascular risk factors
• Severe liver damage
• Severe impairment in renal function
• Low blood pressure
• Recent stroke or heart attack
• Hereditary degenerative retinal disorders

Common side effects include sneezing, headache, flushing, dyspepsia, prolonged erections, palpitations and photophobia.

Viagra® and Pulmonary hypertension

Viagra is also effective in a rare disease called pulmonary arterial hypertension. Several researches have proven that this medication relaxes the arterial wall, decreasing pulmonary arterial resistance and pressure, and reduces the strain on the right side of the heart thus improving symptoms of right-sided heart failure. 

Viagra® and Raynaud's phenomenon

Several experts in this field have recently reported that Viagra cuts the frequency of Raynaud's phenomenon attacks. Viagra reduced their duration by roughly one half, and more than quadrupled the mean capillary blood velocity.  This attacks are related to oversensitivity to cold.

Viagra® and cognitive enhancement

Several recent studies showed that Viagra® may help reduce and relieve cognitive deficits associated with aging. Although mechanism of this still isn't known, scientists found that in rats, administration of Viagra partially reversed the memory impairment.

Viagra® and Analgestic properties

Several studies have determined that Viagra demonstrates anti-nociceptive or pain-relieving properties in rodents. Current evidence seems to suggest that the cGMP that accumulates as a result of Phosphodiesterase 5 inhibition interacts with the cholinergic system to mediate this pain-reducing effect.