Sildenafil is a phosphodiesterase 5 inhibitor. Phosphodiesterase, an enzyme produced in the lungs and other parts of the body, breaks down a substance called cyclic guanosine monophosphate. Cyclic guanosine monophosphate relaxes and widens arteries.

Sildenafil decreases the enzyme’s activity so more cGMP is available to relax or widen the arteries. When the arteries are widened, it’s easier for the heart to pump blood through the lungs, reducing blood pressure in the lungs. As the heart’s ability to pump blood through the lungs increases, it improves a person’s ability to exercise.

Revatio is a round, white 20 mg pill, which distinguishes it from Viagra, a blue diamond-shaped pill.

The recommended, FDA-approved dose for Revatio is 20 mg three times a day. Patients have received up to 80 mg three times a day in trials and clinical practice.

Take each dose four to six hours apart, with or without food.

The injected form of Revatio generally is available only in hospitals. It’s administered three times a day, through single-use 10 mg (125 mL) doses.

Doctors must prescribe sildenafil, and you likely will need approval from your insurance company before starting therapy. Depending on your insurance plan, you might fill your prescription at a retail pharmacy or through specialty pharmacies such as Accredo, Aetna, Alliance Rx Walgreens Prime, Axium, BriovaRx, Cigna, CVS specialty, Humana and Kaiser Permanente.

Sildenafil is generally well tolerated. The most common side effects are:

• Nose bleeds
• Upset stomach and heartburn
• Difficulty sleeping
• Skin reddening
• Worsening shortness of breath
• Nasal congestion

Other side effects include fluid retention, nausea and diarrhea, arm or leg pain, temporary muscle aches, fever and numbness.

More serious side effects include:

Low blood pressure: Blood pressure throughout the body can decrease because sildenafil relaxes arteries throughout the body. People with low blood pressure (less than 90/50 mmHg) should use sildenafil with caution.

Prolonged erection: Prolonged erection (greater than four hours) is rare but serious. If you experience prolonged erection, go to an emergency room or contact your doctor immediately.

Vision loss: Sudden loss of vision in one or both eyes has occurred in people taking phosphodiesterase 5 inhibitors, including sildenafil. Sudden vision loss can indicate serious dysfunction of the optic nerve and needs immediate medical attention.

This type of blindness, called non-arteritic anterior ischemic optic neuropathy, can be permanent. It isn’t clear whether the blindness is related to the drug or underlying cardiovascular diseases that increase the risk for this type of blindness, even without sildenafil use.

No research exists to determine whether sildenafil is beneficial or safe for people with retinitis pigmentosa. Sildenafil isn’t recommended for people with that condition.

Seek immediate medical attention if you suddenly lose your vision.

Hearing loss: If you have sudden hearing loss accompanied by dizziness and/or ear ringing occurs, seek prompt medical attention.

Allergic reaction: Although allergies to sildenafil are possible, they aren’t likely. Any medication can cause side effects or sensitivities. Check with your doctor if you develop a rash or throat tightening.

Monitoring for side effects

No regular bloodwork for side effects is required. Your doctor might ask you to monitor your blood pressure regularly, particularly during your first few days taking the drug or when your dose increases. Blood pressure monitoring isn’t necessary for most patients.

Note: If you experience any symptoms/side effects mentioned above, promptly notify your physician.

Certain patient populations must take precautions while taking sildenafil, while others should avoid it. Learn about who can and who shouldn’t take this medication:

Pregnant and breastfeeding patients: Sildenafil hasn’t caused harm to fetuses in animal studies. However, birth effects haven’t been studied in pregnant or nursing women. There are no adequate and well-controlled human studies.

In clinical practice, sildenafil is commonly used for pregnant and lactating women with severe PAH, as the risk of untreated or undertreated PAH is higher than the risk of adverse effects from sildenafil.

Children and teens: Clinical trials of sildenafil for pediatric PAH patients have been small and part of studies with a wide range of ages and diseases. Generally, sildenafil seems safe and effective for pediatric patients. The treatment algorithm from the sixth World Symposium on Pulmonary Hypertension recommended PDE5 inhibitors for pediatric patients.

People with liver disease: People with mild to moderate liver disease don’t need to adjust their sildenafil doses. Severe liver disease hasn’t been studied.

People with kidney disease: People with kidney disease don’t have to adjust their dosage.

People with sickle cell disease: People with PH related to sickle cell disease can develop a serious condition known as vaso-occlusive crisis. Sildenafil’s effectiveness for PH related to sickle cell anemia hasn’t been established.

People with HIV/AIDS: If you have human immunodeficiency virus (HIV/AIDS), consult you pharmacist. Phosphodiesterase inhibitors such as sildenafil can significantly impede the efficacy of some antiretroviral medications.

Other conditions: People with dehydration, left-heart diseases and certain abnormalities of the body’s nervous system function should use sildenafil with caution.

Sildenafil isn’t recommended for people with pulmonary veno-occlusive disease and pulmonary capillary hemangiomatosis.

Don’t take sildenafil with nitrates or nitric oxide donors because your systemic blood pressure could drop to unsafe levels.

Use caution when drinking alcoholic beverages or taking anti-hypertension or blood pressure-lowering medications.

Sildenafil is broken down predominantly by an enzyme called CYP3A in the liver. Significant interactions can occur with medications that affect this enzyme pathway.

Simultaneous use of bosentan and sildenafil can increase bosentan in blood and decrease sildenafil levels. It’s not known whether those changes are clinically significant.

Using sildenafil with epoprostenol can reduce sildenafil levels in the blood.

Using sildenafil with beta blockers (a heart or blood pressure medicine) can increase sildenafil levels.