Why is Viagra used for Pulmonary Hypertension?

Viagra is the brand name for sildenafil, which is a common medicine to treat erectile dysfunction (ED). Pfizer markets sildenafil as Viagra to treat ED and in June 2005 FDA (Food and Drug Administration) also approved the marketing of sildenafil as Revatio for pulmonary hypertension. Revatio is marketed in the 20 mg dose as a white colored pill against Viagra that is marketed in 25 mg, 50 mg and 100 mg doses as a diamond blue colored pill. In addition to Viagra other common drugs marketed for ED are Cialis and Levitra.

Mechanism of Action of Sildenafil

Sildenafil works by relaxing muscles of blood vessel walls, which increases blood flow to the area by augmenting NO (nitrous oxide) and cGMP (cyclic guanosine monophosphate). Sildenafil acts upon phosphodiesterase type 5 (PDE5) enzyme that is specifically found in tissues of penis, lungs, eyes etc. Sildenafil works by binding to the active site of PDE5, thus prevents it from the breakdown of cGMP making vascular smooth muscles more sensitive to NO and cGMP, thus relaxes the blood vessels. This leads to erection in ED patients and improves exercise capacity in men and women in pulmonary hypertension cases. Pulmonary hypertension is improved with pulmonary arterial walls relaxation; therefore, it is used for its treatment.

What Is Pulmonary Hypertension?

Pulmonary hypertension (PH) involves elevated pressure in the vessels of the lungs. It is estimated to affect about 1 lakh people worldwide. Pulmonary hypertension is usually idiopathic; however, it is mostly associated with some underlying chronic lung disease or chronic heart disease. It is associated with the symptoms of exertional shortness of breath, fatigue and dizziness. It is noted that the prognosis of patients with pulmonary hypertension is very poor without any treatment; patients live for only less than three years.

Why is Viagra used for Pulmonary Hypertension?

Why is Viagra used for Pulmonary Hypertension?

Revatio (sildenafil) was approved by FDA for the treatment of pulmonary hypertension after a 12 week study based on 277 patients suffering with pulmonary hypertension were tested with 20 mg, 40 mg and 80 mg sildenafil three times daily. After the end of 12 weeks, all the groups treated for different doses of sildenafil showed significant improvements against the control group. In addition, to the improved lung pressure and heart function 94% patients on sildenafil were still alive in a one-year long trial.

Thus, FDA approved the lowest dose of sildenafil 20 mg three times daily as no particular dose had an advantage over one another. Pfizer launched sildenafil 20 mg in the brand name of Revatio in 2005. Revatio is the first oral drug that has been approved for the early intervention of pulmonary hypertension. Tracleer, is another drug that is used to treat this condition, but the effectiveness of Revatio has not been evaluated in patients who are on Tracleer.

Along with the medications, it is advised to seek medical help in emergency cases of pulmonary hypertension. It is also advised for patients of pulmonary hypertension to stay active by walking, following a healthy diet, stress reduction, smoking cessation, and resting.

Side Effects of Revatio

The side effects of Revatio are similar to Viagra that are usually mild. The side effects include headache, facial flushing, rash, and diarrhea, increased susceptibility to urinary tract infections, nasal congestion, insomnia, and nose bleeding. The side effects involving vision includes blurred vision, sensitivity to light and/or tinge of bluish-greenish vision known as cyanopsia and in extremely rare cases vision loss.

Revatio should be avoided in patients who are allergic to it and those who are already taking other medicines (riociguat) for pulmonary hypertension. It is also contraindicated in people who are already on nitrates (nitroglycerin, isosorbide dinitrate, isosorbide mononitrate) for heart problems. When sildenafil is combined with a nitrate, it can cause severe lowering of blood pressure. It is also not combined with other drugs of erectile dysfunction such as Cialis or Levitra. Sildenafil should always be taken as prescribed drug and from a pharmacy as many counterfeit drugs are also available in the market.

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