Sildenafil

What is Sildenafil?

Sildenafil is a prescription medication that belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. It is primarily used to treat erectile dysfunction in men and pulmonary arterial hypertension, a condition involving high blood pressure in the arteries that supply the lungs. The medication works by relaxing blood vessels and improving blood flow to specific areas of the body.

Uses

Sildenafil has several FDA-approved medical uses:

Erectile dysfunction: The most common use, helping men achieve and maintain erections sufficient for sexual activity by increasing blood flow to the penis.

Pulmonary arterial hypertension (PAH): Used to treat high blood pressure in the pulmonary arteries, improving exercise capacity and slowing disease progression.

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Altitude sickness prevention: Sometimes prescribed off-label to prevent high-altitude pulmonary edema in people traveling to high elevations.

Raynaud’s phenomenon: Occasionally used off-label to improve blood circulation in fingers and toes affected by this condition.

Female sexual dysfunction: Limited off-label use for certain cases of female sexual arousal disorder, though evidence is mixed.

How it works

Sildenafil works by blocking the enzyme phosphodiesterase type 5 (PDE5), which normally breaks down a substance called cyclic guanosine monophosphate (cGMP). When PDE5 is inhibited, cGMP levels increase, causing smooth muscle relaxation and blood vessel dilation. This mechanism improves blood flow to targeted areas, whether the penis during sexual arousal or the pulmonary arteries in cases of PAH.

Side effects

Common side effects:

• Headache
• Facial flushing
• Nasal congestion
• Indigestion or stomach upset
• Dizziness
• Back pain
• Muscle aches
• Vision changes (blue-tinted vision or increased light sensitivity)

Serious side effects requiring immediate medical attention:

• Sudden vision loss in one or both eyes
• Sudden hearing loss or ringing in ears
• Chest pain or irregular heartbeat
• Erection lasting more than 4 hours (priapism)
• Severe drop in blood pressure causing fainting

Warnings and precautions

Patients with cardiovascular disease should use sildenafil with extreme caution, as sexual activity and the medication itself can strain the heart. Those with severe liver or kidney disease may need dose adjustments or should avoid the medication entirely, as these organs are responsible for processing and eliminating the drug.

Sildenafil can cause dangerous drops in blood pressure, particularly in patients already taking blood pressure medications or those with underlying heart conditions. Men with anatomical penile abnormalities or conditions predisposing to priapism should discuss risks with their healthcare provider.

The medication is not approved for use in women for erectile dysfunction treatment, and its safety during pregnancy has not been established for most uses. Patients over 65 may be more sensitive to side effects and typically require lower starting doses.

Interactions

Nitrates (nitroglycerin, isosorbide): Can cause life-threatening blood pressure drops and is absolutely contraindicated.

Alpha-blockers (doxazosin, tamsulosin): May cause excessive blood pressure reduction, requiring careful dose timing and monitoring.

Riociguat: Another pulmonary hypertension medication that can cause dangerous hypotension when combined with sildenafil.

CYP3A4 inhibitors (ketoconazole, ritonavir, erythromycin): Increase sildenafil levels in the blood, requiring dose reductions.

Blood pressure medications: May enhance hypotensive effects, requiring monitoring and possible dose adjustments.

Grapefruit juice: Can increase sildenafil levels and side effects by inhibiting drug metabolism.

St. John’s wort: May reduce sildenafil effectiveness by increasing drug breakdown in the liver.

Poppers (amyl nitrite): Recreational drugs that can cause dangerous blood pressure drops similar to medical nitrates.

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Dosage

For erectile dysfunction, the typical starting dose is 50mg taken approximately one hour before sexual activity, with doses ranging from 25mg to 100mg based on effectiveness and tolerance. The medication should not be taken more than once daily.

For pulmonary arterial hypertension, the usual dose is 20mg three times daily, taken approximately 4-6 hours apart. Patients with liver or kidney problems may require lower doses.

Dosage should always be determined and monitored by a healthcare provider, who will consider individual patient factors, other medications, and underlying health conditions when prescribing sildenafil.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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