Sildenafil Citrate, marketed under the trade names Viagra® and Revatio®, is a powerful vasodilator. It works by relaxing smooth muscle in blood vessels throughout the body which results in an increase in blood flow. Pfizer initially targeted the drug to treat male erectile dysfunction, but some PAH specialists prescribed the drug for off-label use to their patients. Anecdotal evidence was positive for many patients, prompting Pfizer to organize a number of clinical trials which would expand the use of and increase the demand for it's product.

June 03, 2005

Revatio is prescribed to treat pulmonary arterial hypertension (WHO Group I) to improve exercise ability and help lessen symptoms and slow down worsening changes in your physical condition. Revatio has not been studied in patients taking bosentan.

The differences between Viagra and Revatio are mostly superficial. Viagra is a blue and diamond-shaped tablet. Revatio is round and white. The dosing is different, but chemically they are the same. Both are oral medications. For treatment of PAH, this drug - in whatever form your doctor prescribes it - must be taken three or more times per day at equal intervals. It is important to take this drug as directed by your physician. You will probably begin at a low dose and be asked to build up to a target maintenance level.

In November 2009, the FDA also approved a liquid form of Revatio for injection:

"The FDA has approved Revatio (sildenafil, from Pfizer) injection, an intravenous phosphodiesterase-5 (PDE-5) inhibitor, for the treatment of adults with pulmonary arterial hypertension (PAH) (WHO Group I) to improve exercise ability and delay clinical worsening. Revatio injection is for the continued treatment of patients with PAH who are currently prescribed Revatio tablets but who are temporarily unable to take oral medication."

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When you are being evaluated as a candidate for this medication, your doctor may have you come into his office or clinic so that your blood pressure can be monitored. Revatio may cause a drop in your systemic blood pressure so care will be taken to ensure your blood pressure does not drop to an unsafe level. If you feel dizzy at any time while you are taking this medication, you should notify your doctor.  If you become dizzy or nauseated, or have pain, numbness, or tingling in your chest, arms, neck, or jaw while taking this medication,  call your doctor right away. You could be having a serious side effect of Revatio.

The most common adverse reactions include epistaxis, headache, dyspepsia, flushing, insomnia, erythema, dyspnea, and rhinitis.

Revatio should never be taken in combination with organic nitrates

Some PAH patients demonstrate through six-minute walk tests and echo results, an increase in exercise tolerance and a reduction in pulmonary artery pressures due to the increase in blood flow throughout the body, including the lungs.

Sildenafil is an inhibitor of cGMP specific phosphodiesterase type-5 (PDE5) in the smooth muscle of the pulmonary vasculature, where PDE5 is responsible for degradation of cGMP. Sildenafil, therefore, increases cGMP within pulmonary vascular smooth muscle cells resulting in relaxation. In patients with pulmonary hypertension, this can lead to vasodilation of the pulmonary vascular bed and, to a lesser degree, vasodilatation in the systemic circulation.

Studies in vitro have shown that sildenafil is selective for PDE5. Its effect is more potent on PDE5 than on other known phosphodiesterases (10-fold for PDE6, > 80-fold for PDE1, > 700-fold for PDE2, PDE3, PDE4, PDE7, PDE8, PDE9, PDE10, and PDE11). The approximately 4,000-fold selectivity for PDE5 versus PDE3 is important because PDE3 is involved in control of cardiac contractility. Sildenafil is only about 10-fold as potent for PDE5 compared to PDE6, an enzyme found in the retina and involved in the phototransduction pathway of the retina. This lower selectivity is thought to be the basis for abnormalities related to color vision observed with higher doses or plasma levels.

In addition to pulmonary vascular smooth muscle and the corpus cavernosum, PDE5 is also found in other tissues including vascular and visceral smooth muscle and in platelets. The inhibition of PDE5 in these tissues by sildenafil may be the basis for the enhanced platelet anti-aggregatory activity of nitric oxide observed in vitro, and the mild peripheral arterial-venous dilatation in vivo.

The cost of Revatio is about $10,000 per year.

Now that sildenafil citrate has been approved to treat PAH, your insurance company should cover the cost of your medication. For those of you with no drug coverage or a high co-payment, you may want to ask your physician if he or she can prescribe Viagra as the price of Viagra has dropped due to competition in the marketplace.

Pfizer Labs

Sildenafil Citrate (Revatio®) is one of a handful but ever growing list of oral medications available that is FDA approved to treat PAH. It is often prescribed in combination with another class of medication such as Tracleer or Sitaxsentan which are endothelin receptor antagonist.

Full Prescribing Information