How does this medication work? What will it do for me?

Sildenafil belongs to the family of medications known as phosphodiesterase type 5 inhibitors. It is used to treat pulmonary hypertension (high blood pressure in the blood vessels between the heart and lungs) when people have not responded to conventional treatment.

It helps reduce pulmonary blood pressure by widening blood vessels.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

What form(s) does this medication come in?

20 mg
Each white-to-off-white, round biconvex, film-coated tablet engraved "SIL" over "20" on one side and "APO" on the other side, contains sildenafil 20 mg as sildenafil citrate. Nonmedicinal ingredients: colloidal silicon dioxide, croscarmellose sodium, magnesium stearate and microcrystalline cellulose; film coating: hydroxyl propyl methyl cellulose, hydroxyl propyl cellulose, polyethylene glycol, and titanium dioxide.

How should I use this medication?

The recommended adult dose of sildenafil for pulmonary hypertension is 20 mg 3 times daily. Doses should be taken approximately 6 to 8 hours apart.

Sildenafil may be taken with or without food.

The solution for injection is used to continue treatment with sildenafil when a person with pulmonary hypertension is temporarily unable to take sildenafil by mouth. The maximum dose of this form of sildenafil is 10 mg given by intravenous (into a vein) injection 3 times a day. This dose of sildenafil is approximately equal in activity to 20 mg of sildenafil taken by mouth.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important that this medication be taken exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not take sildenafil if you:

  • are allergic to sildenafil or any ingredients of the medication
  • are taking nitroglycerin (sprays, ointments, skin patches or pastes, tablets) or other nitrate medications (e.g., isosorbide dinitrate or isosorbide mononitrate) due to the risk of developing dangerously low blood pressure
  • have pulmonary hypertension caused by sickle cell anemia (a red blood cell abnormality)
  • have a history of vision problems related to nerve damage to the retina caused by decreased blood flow
  • are taking the medications ketoconazole, itraconazole, ritonavir or riociguat

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • back pain
  • cough
  • diarrhea
  • difficulty sleeping
  • fever
  • flu-like symptoms (sudden lack of energy, fever, cough, sore throat)
  • flushing
  • headache
  • indigestion
  • muscle aches
  • nausea
  • nosebleeds
  • pain in the extremities

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • blurred vision
  • shortness of breath
  • sudden decrease or loss of hearing
  • temporary memory loss

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • chest pain
  • seizure
  • symptoms of a serious allergic reaction (such as swelling of the face, lips, tongue, or throat; skin rash; hives; or difficulty breathing)
  • signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort
  • sudden decrease or loss of vision or other vision changes
Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Bleeding problems: Sildenafil may cause your body to take longer to stop bleeding. If you have bleeding problems or a bleeding disorder, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Blood pressure: Sildenafil can cause a rapid decrease in blood pressure that may add to the blood pressure-lowering effect of other medications. Tell your doctor if you are taking medications to treat high blood pressure. If you are taking medication for high blood pressure, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Grapefruit juice: Grapefruit juice can increase the amount of sildenafil in your blood. Do not drink grapefruit juice while taking this medication.

Heart or blood vessel problems: Sildenafil can make heart or blood vessel problems worse. If you have had a heart attack, stroke, or life-threatening abnormal heart rhythm within the last 6 months, or have angina, chest pain, an irregular heartbeat, or high or low blood pressure, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Lung problems: Sildenafil is not recommended for people with a form of high blood pressure in the lungs called pulmonary veno-occlusive disease. If you have pulmonary veno-occlusive disease or experience sudden cough, shortness of breath, chest pain, or rapid breathing, talk to your doctor before taking this medication.

Nitrate-containing medications: Sildenafil should never be taken with any medications that contain nitrates. Blood pressure may suddenly drop to life-threatening levels if sildenafil is taken with any nitrate-containing medication (e.g., nitroglycerin tablets, spray, or patches) or any other nitrates (e.g., isosorbide dinitrate or amyl nitrite "poppers"). Dizziness, fainting spells, heart attack, or stroke may be experienced.

Penis deformation: Men with an anatomical deformation of the penis such as angulation, cavernosal fibrosis, or Peyronie's disease should be closely monitored by their doctor while taking this medication.

Prolonged erection: Tell your doctor if you have ever had an erection that lasted longer than 4 hours, or have sickle cell anemia or leukemia, before taking this medication.

Prostate problems: Tell your doctor if you are taking medications to treat prostate problems, such as alpha-blockers (e.g., doxazosin), as sildenafil combined with these medications may cause dangerously low blood pressure.

Vision problems: If you have or have had a temporary decrease or permanent loss of vision in one or both eyes, including a condition called non-arteritic anterior ischemic optic neuropathy (NAION), or if you have retinitis pigmentosa, tell your doctor before taking this medication.

This medication can cause partial or complete vision loss that may be temporary or permanent. If you experience a sudden loss of vision in one or both eyes or other vision-related problems, contact your doctor immediately. If you do experience vision changes, do not drive or operate machinery until your vision returns to normal.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if sildenafil passes into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of this medication have not been established for children with pulmonary hypertension.

What other drugs could interact with this medication?

There may be an interaction between sildenafil and any of the following:

  • alcohol
  • alpha agonists (e.g., clonidine, methyldopa)
  • alpha-blockers (e.g., alfuzosin, doxazosin, prazosin)
  • alprostadil
  • amiodarone
  • angiotensin converting enzyme inhibitors (ACEIs; captopril, enalapril, ramipril)
  • angiotensin receptor blockers (ARBs; e.g., candasartan, irbesartan, losartan)
  • aprepitant
  • "azole" antifungals (e.g., ketoconazole, itraconazole, voriconazole)
  • barbiturates (e.g., pentobarbital, phenobarbital)
  • beta-adrenergic blockers (e.g., atenolol, propranolol, sotalol)
  • boceprevir
  • bosentan
  • calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
  • carbamazepine
  • cimetidine
  • clonidine
  • cobicistat
  • conivaptan
  • cyclosporine
  • dasatinib
  • deferasirox
  • desipramine
  • dexamethasone
  • diuretics (water pills; e.g., furosemide, hydrochlorothiazide, triamterene)
  • enzalutamide
  • fusidic acid
  • grapefruit juice
  • haloperidol
  • HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., delaviridine, efavirenz, etravirine, nevirapine)
  • HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
  • hydralazine
  • macrolide antibiotics (e.g., clarithromycin, erythromycin)
  • metronidazole
  • mifepristone
  • mitotane
  • nefazodone
  • nitrates (e.g., nitroglycerin, isosorbide mononitrate, isosorbide dinitrate, or amyl nitrite "poppers")
  • norfloxacin
  • oxcarbazepine
  • peginterferon Alfa-2b
  • phenytoin
  • other phosphodiesterase inhibitors (e.g., tadalafil, vardenafil)
  • pimozide
  • primidone
  • quinidine
  • rifabutin
  • rifampin
  • riociguat
  • St. John's wort
  • sertraline
  • simeprevir
  • "statin" anticholesterol medications (e.g., atorvastatin, lovastatin, simvastatin)
  • telaprevir
  • tetracycline
  • tocilizumab
  • tyrosine kinase inhibitors (e.g., dasatinib, imatinib, nilotinib, sunitinib)

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.