Sildenafil citrate dosage, forms, and strengths

Sildenafil is a generic prescription drug that widens arteries. People know it far better as brand-name Viagra, a treatment for erectile dysfunction. This is what it’s popularly known for. However, sildenafil is also used to treat high blood pressure in the lung’s arteries, a condition called pulmonary hypertension. For erectile dysfunction, men should only take doses as needed before sexual activity. For pulmonary hypertension, doses are taken three times daily for as long as necessary.

Sildenafil forms and strengths

Sildenafil comes in three dosage forms. Sildenafil tablets are the most commonly used. Low-dose tablets (20 mg) are for pulmonary hypertension. Higher-dose tablets are appropriate for erectile dysfunction. Patients with pulmonary hypertension can also take a liquid sildenafil or be given an intravenous injection.

• Tablets: 20 mg (pulmonary hypertension), 25 mg, 50 mg, 100 mg

• Oral suspension: 10 mg/mL (pulmonary hypertension)

• Injection: 10 mg/12.5 mL (pulmonary hypertension)

Sildenafil dosage for adults

Sildenafil is FDA-approved for erectile dysfunction and pulmonary hypertension. Healthcare professionals may use the drug off-label for other conditions, such as Raynaud’s syndrome or altitude sickness, but these are not approved uses. For pulmonary hypertension, low-dose sildenafil is administered daily for as long as necessary. For erectile dysfunction, men take a pill when needed, but no more than one dose per day. 

No one who has had an allergic reaction to sildenafil will be prescribed this medicine.

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Sildenafil dosage for erectile dysfunction

Popularly known as brand-name Viagra, sildenafil is widely used to treat erectile dysfunction (ED). Defined as an inability to achieve or maintain an erection, clinical erectile dysfunction affects more than thirty million men in the United States.

Sildenafil is a phosphodiesterase-5 inhibitor (PDE-5 inhibitor). Phosphodiesterase-5 breaks down the enzyme cGMP. This enzyme cGMP is needed because it causes smooth muscle relaxation and increased blood flow to the penis. By blocking PDE-5, cGMP increases, and erections can occur. 

Tablets are taken at least one hour before anticipated sexual activity, but men could take their dose a half hour to four hours before sexual activity. However, a dose starts to lose its potency about two hours after a dose is taken. Sexual stimulation is required for the drug to work. 

Men will start on a 50 mg dose which can rise to 100 mg if necessary. The maximum dose is one tablet per day.

• Standard sildenafil dosage for erectile dysfunction: 25–100 mg tablet taken only once daily at least one hour before sexual activity

• Maximum sildenafil dosage for erectile dysfunction: 100 mg daily

Sildenafil dosage for pulmonary hypertension

Pulmonary hypertension is when the blood pressure in the arteries of the lungs is higher than normal. This makes the heart work harder to pump blood through the lungs. This can lead to heart damage and cause symptoms such as shortness of breath, chest pain, and lightheadedness. Pulmonary hypertension affects about 1% of the population.

Pulmonary hypertension has many potential causes, including heart disease, lung disease, medications, and other health conditions. Physicians will focus on treating those problems, but they will also use drugs like sildenafil to lower blood pressure. 

Sildenafil is taken orally three times daily and can range from 60 mg to 240 mg. Sildenafil injections are limited to 30 mg per day. For pulmonary hypertension, people may be prescribed generic sildenafil or a brand-name version called Revatio.

• Standard sildenafil dosage for pulmonary hypertension: 20–80 mg taken orally three times daily OR 10 mg intravenous injection three times daily

• Maximum sildenafil dosage for pulmonary hypertension: 240 mg taken orally OR 30 mg daily administered as intravenous injections 

Sildenafil dosage for children

Healthcare professionals use sildenafil to treat pulmonary hypertension in children as young as 1 year old. Children can take tablets or an oral suspension. Healthcare professionals do not use sildenafil injections in pediatric patients.

Sildenafil dosage restrictions

When sildenafil is used for pulmonary hypertension, no dosage reductions are required for people with kidney disease or liver problems. However, men using higher-dose sildenafil for erectile dysfunction will be started on the lowest possible dose if they have severe kidney or liver impairment, or are over the age of 65. Although the starting dose is lower than normal, the dose can eventually be increased to the maximum dosage if there are no issues with side effects.

• Patients with renal impairment (creatinine clearance <30 mL/min): Starting dose reduced to 25 mg per day for erectile dysfunction treatment

• Patients with hepatic impairment: Starting dose reduced to 25 mg per day for erectile dysfunction treatment (no dosage adjustment for pulmonary hypertension)

• Patients over 65 years of age: Starting dose reduced to 25mg per day for erectile dysfunction treatment

Sildenafil dosage for pets 

Veterinarians use sildenafil to reduce blood pressure in dogs and cats diagnosed with pulmonary hypertension. They’re more likely to use it when pets are showing symptoms like fainting and other signs of heart failure. Some veterinarians may use it if a pet also has heart disease, heart failure, or lung disease. Dosage guidelines vary, ranging between doses of 0.5 mg to 3 mg/kg given anywhere from once per day to three times per day.

How to take sildenafil

Although sildenafil has three dosage forms, erectile dysfunction is treated only with sildenafil tablets. For pulmonary hypertension, pediatric patients and adults who can’t swallow a tablet may be prescribed sildenafil oral suspension. Sildenafil injections are administered by a healthcare provider only.

• Your healthcare provider will tell you how much sildenafil to take and how often it can be taken. Do not use more than directed.

• Sildenafil can be taken with or without food.

• Please read the Patient Information sheet that comes with this medicine.

• For erectile dysfunction:

  • Take the prescribed dose about one hour before you have sex. 

  • The dose can be taken one-half hour to four hours before sexual activity.

  • Do not take more than one dose a day. Allow at least 24 hours between doses.

  • Store sildenafil tablets at room temperature.

• For pulmonary arterial hypertension: 

  • Take or administer the prescribed dose three times a day, four to six hours apart.

• How to take sildenafil oral suspension for pulmonary hypertension:

  • Please read and follow the Instructions for Use.

  • Do not use the medicine if it’s still in powder form, doesn’t have a bottle adapter, or is missing an oral syringe. The pharmacist can provide a bottle adapter or oral syringe.

  • Shake the bottle well for at least 10 seconds. 

  • Always measure the dose with the oral syringe provided in the package.

  • Do not mix the dose with other liquids or flavorings.

  • The person getting the medicine should be upright.

  • Place the syringe in the mouth against the cheek. Push the plunger completely down.

  • Wash the syringe with water and allow it to dry after each use.

  • Store sildenafil oral suspension in the refrigerator. Do not freeze.

  • Throw away any unused medicine 60 days after receiving it from the pharmacist or on the expiration date written on the bottle’s label.

Sildenafil dosage FAQs

How long does it take sildenafil to work?

In clinical trials, sildenafil showed significant effects on erectile response 60 minutes after the dose was taken, though the effects may be evident within 30 minutes. For pulmonary hypertension, sildenafil lowers blood pressure about one to two hours after a dose is taken.

How long does sildenafil stay in your system?

With a half-life of four hours, sildenafil and its active metabolite are completely cleared from the system in about 20 hours, though the effects fade before then. For erectile dysfunction, sildenafil produces its maximum effects for about two hours and can still produce an erectile response four hours after a dose is taken. For pulmonary hypertension, sildenafil’s benefits in lowering blood pressure were the same as a placebo (inert pill) after eight hours. 

What happens if I miss a dose of sildenafil?

For treatment of erectile dysfunction, take only one dose per day. If a dose has been forgotten, take it when remembered but wait at least 30 minutes before attempting sexual activity.

For pulmonary hypertension, take a missed dose as soon as you remember it. If it’s almost time for the next dose, skip the missed dose and take the next dose as scheduled.

Can you overdose on sildenafil?

If too much sildenafil is taken, get immediate medical attention. Side effects of sildenafil, such as headache, flushing, stomach upset, nasal congestion, back pain, low blood pressure, or painful erections (priapism), are more likely and could be worse than normal. Serious side effects are also possible such as heart rate problems, chest pain (angina), and heart attack.

What interacts with sildenafil?

Do not take sildenafil if you are using medications called nitrates, such as nitroglycerin, or over-the-counter nitrites (“poppers”), such as amyl nitrite. Sildenafil should also never be combined with heart failure drugs called guanylate cyclase stimulators (riociguat or vericiguat). 

Make sure the prescriber knows about all drugs and substances you use, including vitamins, supplements, and illicit substances. To avoid more serious drug interactions, the prescriber will need to know about:

• Other ED drugs or supplements, particularly Cialis (tadalafil) or vardenafil

• Alpha blockers

• Blood pressure medications

• HIV/AIDS drugs called protease inhibitors, especially ritonavir

• Antibiotics

• Oral antifungal drugs such as ketoconazole or itraconazole

To reduce the risk of side effects, avoid drinking grapefruit juice when taking sildenafil.

Is it safe to take sildenafil during pregnancy?

Although there isn’t much information about the safety of sildenafil during pregnancy, animal studies have shown no adverse effects on a fetus. Pregnant women or women who are breastfeeding should ask for medical advice before taking sildenafil.

Sources

• Plumb’s Veterinary Drug Manual, 7 edition

• Pulmonary hypertension, StatPearls

• Revatio prescribing information, DailyMed (NIH National Library of Medicine)

• Sildenafil citrate powder for oral suspension prescribing information, DailyMed (NIH National Library of Medicine)

• Systemic and pulmonary hypertension in dogs and cats, Merck Veterinary Manual

• Viagra drug summary, Prescriber’s Digital Reference (PDR)

• Viagra sildenafil citrate tablet prescribing information, DailyMed (NIH National Library of Medicine)