Sildenafil 

1. Introduction

Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor primarily used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). It works by relaxing blood vessels, enhancing blood flow to specific areas of the body, such as the penis or lungs.

2. Indications

  • Erectile Dysfunction (ED): Improves the ability to achieve and maintain an erection during sexual stimulation.
  • Pulmonary Arterial Hypertension (PAH): Lowers pulmonary blood pressure to improve exercise capacity and delay disease progression.

3. Dosage

Adults (Erectile Dysfunction):

  • Starting dose: 50 mg orally, taken approximately 1 hour before sexual activity.
  • Adjust dose: Based on efficacy and tolerability, may increase to 100 mg or reduce to 25 mg.
  • Maximum dose: 100 mg per day.

Adults (Pulmonary Arterial Hypertension):

  • Standard dose: 20 mg orally three times daily, taken 4–6 hours apart.

Elderly:

  • Start with the lowest effective dose (e.g., 25 mg for ED), as elderly patients may have reduced drug clearance.

Children:

  • Approved for PAH in children aged ≥1 year: 10 mg (≤20 kg) or 20 mg (>20 kg) three times daily.

Patients with Renal Impairment:

  • Mild to moderate impairment: No dose adjustment needed.
  • Severe impairment: Start with 25 mg for ED; use cautiously for PAH.

Patients with Hepatic Impairment:

  • Start with 25 mg for ED; use cautiously for PAH.

4. Administration

  • Take orally with or without food.
  • For ED, avoid high-fat meals as they may delay the onset of action.
  • Do not take more than one dose per day.

5. Forms Available

  • Tablets: 25 mg, 50 mg, 100 mg
  • Oral suspension (for PAH): 10 mg/mL

6. Side Effects

6.1 Common Side Effects:

  • Headache
  • Flushing
  • Dyspepsia (indigestion)
  • Nasal congestion
  • Dizziness

6.2 Less Common Side Effects:

  • Visual disturbances (e.g., blurred vision, blue-tinted vision)
  • Back pain or muscle aches
  • Nausea

6.3 Rare but Serious Side Effects:

  • Priapism (prolonged erection lasting >4 hours; medical emergency)
  • Sudden hearing loss
  • Non-arteritic anterior ischaemic optic neuropathy (NAION)
  • Severe hypotension, particularly when combined with nitrates
  • Severe allergic reactions (e.g., rash, angioedema)

7. Warnings

  • Cardiovascular Risk: Avoid use in patients with significant cardiovascular conditions (e.g., recent heart attack, unstable angina).
  • Hypotension: May cause a significant drop in blood pressure, particularly when taken with nitrates or alpha-blockers.
  • Vision Loss: Rare risk of NAION, particularly in patients with existing eye conditions or cardiovascular risk factors.
  • Hearing Loss: Sudden, unexplained hearing loss may occur; discontinue use if symptoms appear.
  • Priapism: Seek immediate medical attention if an erection persists for >4 hours.

8. Precautions

  • Avoid use in patients with severe hepatic or renal impairment without specialist advice.
  • Use cautiously in patients with anatomical deformation of the penis or predisposition to priapism (e.g., sickle cell anaemia, leukaemia).
  • Avoid combining with other PDE5 inhibitors or pulmonary vasodilators without medical supervision.

9. Interactions

  • Nitrates (e.g., nitroglycerin, isosorbide): Contraindicated due to the risk of severe hypotension.
  • Alpha-blockers (e.g., tamsulosin, doxazosin): May cause additive blood pressure-lowering effects; start with a low sildenafil dose.
  • CYP3A4 inhibitors (e.g., ketoconazole, ritonavir): May increase sildenafil levels; consider starting with a lower dose (e.g., 25 mg).
  • CYP3A4 inducers (e.g., rifampin): May reduce sildenafil efficacy.
  • Alcohol: May enhance hypotensive effects; limit alcohol intake.

10. Monitoring Parameters

  • Monitor for efficacy in improving ED or PAH symptoms.
  • Watch for adverse effects, particularly priapism, vision/hearing changes, or hypotension.
  • Assess cardiovascular status before initiation in patients with underlying heart conditions.

11. Use in Children

  • Approved for PAH in children aged ≥1 year, but not for ED.
  • Use only under specialist supervision in paediatric PAH.

12. Use in Pregnancy

  • Category B (for PAH): Animal studies show no harm, but limited human data is available. Not used for ED in women.

13. Use in Elderly

  • Start with the lowest effective dose (e.g., 25 mg for ED) due to reduced clearance and higher susceptibility to side effects like hypotension.

14. Use in Kidney Disease

  • Dose adjustment required in severe renal impairment for ED.
  • Use cautiously in PAH; regular monitoring is essential.

15. Use in Liver Disease

  • Dose adjustment required in severe hepatic impairment for ED.
  • Use cautiously in PAH; avoid in severe hepatic dysfunction.

16. Patient Counselling Points

  • For ED, take sildenafil about 30–60 minutes before sexual activity, but it may work as early as 15 minutes or as late as 4 hours.
  • Do not use sildenafil if you are taking nitrates, as it may cause a dangerous drop in blood pressure.
  • Inform your doctor if you experience chest pain, vision changes, hearing loss, or a prolonged erection.
  • Avoid excessive alcohol consumption, as it can reduce the effectiveness of sildenafil.
  • Store sildenafil tablets in a cool, dry place away from sunlight.

17. Table of Brand Names, Manufacturer, and Prices in USD

Brand NameManufacturerStrength/Dosage FormPrice (USD)
ViagraPfizer50 mg Tablet$70 (1 tablet)
RevatioPfizer20 mg Tablet (for PAH)$50 (1 tablet)
Generic SildenafilVarious50 mg Tablet$10 (1 tablet)

18. 15 FAQs (Frequently Asked Questions)

1. What is Sildenafil used for?
Sildenafil is used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH).

2. How does Sildenafil work?
It inhibits PDE5, enhancing blood flow to specific areas by relaxing blood vessels.

3. How quickly does Sildenafil work?
For ED, it works within 30–60 minutes. For PAH, effects build over regular use.

4. Can Sildenafil be taken with food?
Yes, but avoid high-fat meals, as they may delay its effect.

5. How long does Sildenafil last?
Its effects typically last 4–6 hours for ED.

6. Can Sildenafil cause vision changes?
Yes, temporary vision changes, including blue-tinted vision, may occur.

7. Is Sildenafil safe for everyone?
No, it is contraindicated in patients taking nitrates, those with severe cardiovascular conditions, or those with certain eye disorders.

8. Can women take Sildenafil?
It is not approved for sexual dysfunction in women but may be used for PAH.

9. Can Sildenafil cause low blood pressure?
Yes, especially when combined with nitrates or alpha-blockers.

10. Can Sildenafil be used daily?
For PAH, it is taken daily. For ED, it is used as needed, not exceeding one dose daily.

11. Can alcohol be consumed with Sildenafil?
Limit alcohol intake, as it can reduce effectiveness and increase the risk of hypotension.

12. What happens if Sildenafil doesn’t work?
Consult your doctor; dose adjustments or alternative treatments may be necessary.

13. Can Sildenafil cause priapism?
Yes, prolonged erections lasting >4 hours require immediate medical attention.

14. Does Sildenafil interact with other medications?
Yes, it interacts with nitrates, alpha-blockers, and CYP3A4 inhibitors/inducers.

15. How should Sildenafil be stored?
Store at room temperature, away from moisture and heat.