Popular erectile dysfunction treatment relieves lung disease symptoms: ScienceAlert

You may be surprised to learn that the drug sildenafil, better known by its brand name Viagra, has other medical purposes besides treating male erectile dysfunction. It can also be used to treat lung diseases that often have a poor prognosis.

Sildenafil works by inhibiting an enzyme called phosphodiesterase.

Through a complex pathway involving other molecules, sildenafil ultimately helps to relax smooth muscles and dilate blood vessels. This last effect is known as vasodilatation.

Vasodilation causes more blood flow to the organs, whether that organ is the penis or the lungs.

Lung diseases

Vasodilation caused by sildenafil may be beneficial in lung diseases such as pulmonary arterial hypertension (PAH) or idiopathic pulmonary fibrosis (IPF).

People living with PAH and IPF experience progressive shortness of breath and chronic cough. In addition to the lungs, PAH and IPF can affect many other organ systems.

PAH is a disease that causes breathing difficulties and heart strain due to high pressure in the arteries of the lung, which were designed for much lower pressures. Fortunately, it is a rare disease that affects one or two individuals per 1,000,000 people each year.

IPF is the most common lung disease with between two and 29 people per 100,000 developing the disease per year. It occurs due to repeated and chronic thickening, hardening and scarring (fibrosis) of the lungs.

Both diseases often do not have a clear etiology, meaning that doctors and researchers do not fully understand why these diseases begin and progress.

Both diseases are incurable and often get worse over time despite our best treatment options. There are currently few effective treatments, and there is always interest in finding more.

Evidence of sildenafil in PAH

The use of sildenafil in PAH is already well established, effective and approved in Canada. There are several high-quality randomized controlled trials that have demonstrated efficacy in improving exercise capacity and symptom burden.

Sildenafil is usually branded as Revatio in PAH (rather than Viagra for erectile dysfunction), although there is little difference between Viagra and Revatio, except that patients usually take Revatio three times a day in smaller doses.

Our recent publication synthesized the evidence for multiple treatments for PAH. We looked at combinations of sildenafil or another drug in the same class, such as tadalafil (brand name Cialis) or vardenafil (brand name Levitra), with another commonly used PAH drug.

The results showed that the number of clinical worsening events such as disease progression or hospitalization was reduced by 12.7 percent compared to placebo. Markers of exercise capacity, measured using a six-minute walk test, also improved by nearly 50 meters.

Evidence for sildenafil in IPF

The use of sildenafil in IPF is much less safe as there have been few randomized controlled trials, which are considered the gold standard of evidence.

Only four trials have investigated its use in IPF. A meta-analysis of this small number approached statistical significance, suggesting that benefits would become apparent if more trials were completed.

The most recent European Respiratory Society / American Thoracic Society guidelines addressing the question recommended against the use of sildenafil in IPF due to lack of data.

However, recently a drug (treprostinil) that acts similarly to sildenafil showed promise in patients with combined interstitial lung disease (an umbrella term for lung diseases that includes IPF) and pulmonary hypertension. The largest effect was seen in patients with diagnosed interstitial lung disease.

This further demonstrates the potential promise of drugs such as sildenafil or similar vasodilation mechanisms in the management of IPF.

Why does this matter?

For conditions like PAH or IPF that are incurable, reusing drugs like sildenafil has merit.

On the one hand, it is very expensive to develop new drugs. On the other hand, there are more safety concerns with new drugs; Because Viagra is widely used, the side effect profile is well known in the medical community.

For example, sildenafil is known to cause low blood pressure and should be avoided in people with conditions that make them susceptible to hypotension or taking specific high blood pressure medications. Other common side effects include flushing, headaches, and vision changes, among others.

While sildenafil may not be the magic pill for all lung diseases, it is clear that it has promising uses that go beyond erectile dysfunction.

Tyler Pitre, MD (internal medicine physician), McMaster University; Dena Zeraatkar, Assistant Professor, Evidence and Impact and Anesthesiology of Health Research Methods, McMaster University, and Jasmine Mah, MD (Internal Medicine Resident) and PhD Candidate (Focus on Geriatrics), Dalhousie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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