The popular treatment for erectile dysfunction relieves the symptoms of lung diseases

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

Sildenafil works by blocking an enzyme called phosphodiesterase.

Through a complex pathway involving other molecules, sildenafil ultimately helps relax smooth muscle and dilate blood vessels. The latter effect is known as vasodilation.

Vasodilation leads to more blood flow to the organs – whether that organ is the penis or the lungs.

lung disease

The 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 suffer from progressive shortness of breath and a chronic cough. PAH and IPF can affect many other organ systems besides the lungs.

PAH is a disease that causes breathing difficulties and heart strain due to increased pressure in the pulmonary arteries, which were designed to handle much lower pressures. Luckily, it’s a rare disease, affecting one or two people in every 1,000,000 people each year.

IPF is a more common lung disease, with between two and 29 people in every 100,000 developing the condition each year. It results from repeated and chronic thickening, stiffening, and scarring (fibrosis) of the lungs.

Both diseases often don’t have a clear etiology, meaning doctors and researchers don’t fully understand why these diseases start and progress.

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

Evidence for 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 its effectiveness in improving exercise capacity and symptom burden.

Sildenafil is usually referred to as Revatio for PAH (instead of 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 has synthesized the evidence for several PAH treatments. 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 worsening clinical events, such as disease progression or hospitalizations, was reduced by 12.7 percent compared to placebo. Physical capacity markers, measured by a six-minute walk test, were also improved by nearly 50 meters.

Evidence for sildenafil in IPF

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

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

The latest European Respiratory Society/American Thoracic Society guidelines addressing the issue advise against the use of sildenafil in IPF due to a lack of data.

Recently, however, a drug (treprostinil) that works similarly to sildenafil has emerged in patients with combined interstitial lung disease (an umbrella term for lung disease that includes IPF) and pulmonary hypertension. The greatest effect was seen in patients diagnosed with interstitial lung disease.

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

Why this matters

For conditions like PAH or IPF that are incurable, reusing drugs like Sildenafil makes sense.

For one, it is very expensive to develop new drugs. Second, there are more concerns about the safety of new drugs; Since Viagra is widely used, its 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 medical conditions that predispose them to hypotension or taking certain high blood pressure medications. Other common side effects include flushing, headache, and blurred vision.

While Sildenafil may not be the magic bullet for all lung conditions, it is clear that it has promising uses beyond erectile dysfunction.

Tyler Pitre, MD (internal medicine physician), McMaster University; Dena Zeraatkar, Assistant Professor, Health Research Methods Evidence and Impact and Anesthesiology, McMaster University, and Jasmine Mah, MD (internal medicine resident) and PhD student (majoring in geriatrics), Dalhousie University

This article was republished by The Conversation under a Creative Commons license. Read the original article.