Comprehensive Guide to Sildenafil: Uses, Dosage, Side Effects, and More

1. What is Sildenafil?

2. Overview of Sildenafil

Generic Name

Sildenafil

Brand Name

Viagra (ED), Revatio (PAH), generics

Drug Group

PDE5 inhibitor (vasodilator)

Commonly Used For

This medication is used to:

• Treat erectile dysfunction (ED).
• Manage pulmonary arterial hypertension (PAH).
• Improve exercise capacity in PAH patients.

Key Characteristics

• Form: Oral tablets (25 mg, 50 mg, 100 mg for ED; 20 mg for PAH), also available as oral suspension or injection for PAH (detailed in Dosage section).
• Mechanism: Inhibits PDE5, increasing cyclic GMP to enhance vasodilation.
• Approval: FDA-approved (1998 for Viagra, 2005 for Revatio) and EMA-approved for ED and PAH.

3. Indications and Uses of Sildenafil

Sildenafil is indicated for a range of vascular and sexual health conditions, leveraging its vasodilatory effects:

• Erectile Dysfunction (ED): Treats ED in men, improving penile blood flow for satisfactory sexual activity, supported by extensive urologic studies over decades.
• Pulmonary Arterial Hypertension (PAH): Manages PAH (WHO Group I) in adults to improve exercise capacity and delay clinical worsening, per cardiology guidelines.
• Raynaud’s Phenomenon: Used off-label to reduce vasospastic attacks in Raynaud’s, improving digital blood flow, with evidence from rheumatology research.
• Altitude Sickness: Investigated off-label to prevent high-altitude pulmonary edema by enhancing pulmonary vasodilation, supported by mountaineering medicine studies.
• Benign Prostatic Hyperplasia (BPH): Explored off-label to alleviate lower urinary tract symptoms in BPH, improving quality of life, with urologic data.
• Female Sexual Arousal Disorder (FSAD): Studied off-label to enhance sexual arousal in women, with mixed results from gynecologic trials.
• Heart Failure with Preserved Ejection Fraction (HFpEF): Investigated off-label to improve hemodynamics in HFpEF, with emerging cardiology evidence.
• Sickle Cell Disease: Used off-label to reduce priapism episodes and improve vascular function, supported by hematology research.
• Digital Ulcers in Systemic Sclerosis: Managed off-label to promote healing of digital ulcers, with promising rheumatologic outcomes.

Note: This drug requires a prescription and medical oversight; consult a healthcare provider for off-label use or comorbidities.

4. Dosage of Sildenafil

Important Note: The dosage of this PDE5 inhibitor must be prescribed by a healthcare provider. Dosing varies by indication, patient response, and tolerability, with adjustments based on clinical evaluation.

Dosage for Adults

• Erectile Dysfunction (ED):
  • Initial: 50 mg taken 30–60 minutes before sexual activity, with or without food.
  • Maintenance: Adjust to 25 mg or 100 mg based on efficacy and tolerance, maximum 100 mg/day.
• Pulmonary Arterial Hypertension (PAH):
  • 20 mg three times daily, taken approximately 4–6 hours apart, with or without food (Revatio).

Dosage for Children

• Pulmonary Arterial Hypertension (PAH, 1–17 years):
  • 10 mg three times daily (adjusted by body weight: 0.5–1 mg/kg for <20 kg), under pediatric cardiologist supervision.
  • Not recommended under 1 year.

Dosage for Pregnant Women

• Pregnancy Category B: Limited data; use only if benefits outweigh risks (e.g., severe PAH). Consult an obstetrician, with fetal monitoring.

Dosage Adjustments

• Renal Impairment: No adjustment for mild to moderate (CrCl 30–80 mL/min); reduce to 25 mg for ED if severe (CrCl <30 mL/min).
• Hepatic Impairment:
  • Mild to moderate (Child-Pugh A/B): Reduce ED dose to 25 mg; PAH dose adjusted by specialist.
  • Severe (Child-Pugh C): Avoid.
• Elderly (>65 years): Start with 25 mg for ED; increase cautiously to 50 mg if tolerated.
• Concomitant Medications: Adjust if combined with CYP3A4 inhibitors (e.g., ketoconazole) or nitrates (contraindicated).

Additional Considerations

• Take this active ingredient 30–60 minutes before activity for ED, with water; avoid heavy meals.
• For PAH, maintain consistent timing (e.g., morning, afternoon, evening).

5. How to Use Sildenafil

• Administration:
  • Swallow tablets whole with water, with or without food (avoid high-fat meals for ED); shake oral suspension well.
  • For PAH, use a calibrated syringe for accurate dosing of suspension or injection.
• Timing: Take ED dose 30–60 minutes before sexual activity; PAH dose three times daily at regular intervals.
• Monitoring: Watch for headache, flushing, or signs of priapism (erection >4 hours).
• Additional Tips:
  • Store at 15–30°C (59–86°F), protecting from moisture and heat.
  • Keep out of reach of children due to misuse risk.
  • Report dizziness, chest pain, or vision changes immediately.

6. Contraindications for Sildenafil

This drug is contraindicated in:

• Hypersensitivity: Patients with a known allergy to Sildenafil or PDE5 inhibitors.
• Nitrate Use: Contraindicated with nitrates (e.g., nitroglycerin) due to severe hypotension risk.
• Severe Hepatic Impairment: Avoid in Child-Pugh Class C.
• Severe Cardiovascular Conditions: Contraindicated in recent stroke, myocardial infarction, or unstable angina.

7. Warnings & Precautions for Sildenafil

General Warnings

• Priapism: Risk of prolonged erection (>4 hours); seek immediate care.
• Hypotension: Risk with alpha-blockers or alcohol; monitor blood pressure.
• Vision Loss: Rare non-arteritic anterior ischemic optic neuropathy (NAION); discontinue if vision changes occur.
• Hearing Loss: Rare sudden deafness; report immediately.
• Cardiovascular Risk: Avoid in severe heart disease; assess cardiac status.

Additional Warnings

• Retinitis Pigmentosa: Risk in patients with this genetic disorder; use cautiously.
• Bleeding Disorders: Increased risk with anticoagulants; monitor closely.
• Peptic Ulcer Disease: Potential gastrointestinal bleeding; assess history.
• Dehydration: Risk of hypotension in volume-depleted states; ensure hydration.
• Hypersensitivity Reactions: Rare anaphylaxis; discontinue if swelling occurs.

Use in Specific Populations

• Pregnancy: Category B; use only if essential with fetal monitoring.
• Breastfeeding: Excreted in breast milk; monitor infant for effects.
• Elderly: Higher risk of side effects; start with lower doses.
• Children: Limited to PAH in 1+ years; avoid for ED.
• Renal/Hepatic Impairment: Adjust dose; avoid in severe cases.

Additional Precautions

• Inform your doctor about heart disease, vision issues, or medication history before starting this medication.
• Avoid grapefruit juice, which may increase levels.

8. Overdose and Management of Sildenafil

Overdose Symptoms

Overdose may cause:

• Headache, flushing, or dizziness.
• Severe cases: Priapism, hypotension, or syncope.
• Nausea, vision changes, or tachycardia as early signs.
• Cardiac arrest with extremely high doses.

Immediate Actions

• Contact the Medical Team: Seek immediate medical help.
• Supportive Care: Administer IV fluids, monitor vital signs, and manage blood pressure.
• Specific Treatment: Treat priapism with aspiration or medication; no specific antidote.
• Monitor: Check heart rate, blood pressure, and vision for 24–48 hours.

Additional Notes

• Overdose risk is low; store securely.
• Report persistent symptoms (e.g., prolonged erection, severe weakness) promptly.

9. Side Effects of Sildenafil

Common Side Effects

• Headache (16–28%, relieved with hydration)
• Flushing (10–20%, transient)
• Dyspepsia (7–17%, managed with food)
• Nasal Congestion (4–12%, decreases with use)
• Dizziness (2–10%, reduces with rest)
  These effects may subside with dose adjustment.

Serious Side Effects

Seek immediate medical attention for:

• Cardiovascular: Hypotension, myocardial infarction, or stroke.
• Ocular: NAION or sudden vision loss.
• Urologic: Priapism or penile pain.
• Auditory: Sudden hearing loss or tinnitus.
• Allergic: Rash, angioedema, or anaphylaxis.

Additional Notes

• Regular monitoring for cardiovascular and visual health is advised.
• Report any unusual symptoms (e.g., chest pain, vision blurring) immediately to a healthcare provider.

10. Drug Interactions with Sildenafil

This active ingredient may interact with:

• Nitrates: Causes severe hypotension; avoid.
• Alpha-Blockers: Enhances hypotension risk (e.g., tamsulosin); adjust dose.
• CYP3A4 Inhibitors: Increases levels (e.g., ketoconazole); reduce to 25 mg.
• Antihypertensives: Potentiates blood pressure drop; monitor closely.
• Alcohol: Exacerbates dizziness; limit intake.

Action: Provide your healthcare provider with a complete list of medications.

11. Patient Education or Lifestyle

• Medication Adherence: Take this PDE5 inhibitor as prescribed for ED or PAH, following the exact schedule.
• Monitoring: Report priapism, vision changes, or chest pain immediately.
• Lifestyle: Avoid excessive alcohol; maintain a healthy diet.
• Diet: Take with or without food (avoid high-fat meals for ED); stay hydrated.
• Emergency Awareness: Know signs of heart attack or priapism; seek care if present.
• Follow-Up: Schedule regular check-ups every 3–6 months to monitor cardiovascular and visual health.

12. Pharmacokinetics of Sildenafil

• Absorption: Well-absorbed orally (peak at 0.5–2 hours); reduced by high-fat meals.
• Distribution: Volume of distribution ~105 L; 96% protein-bound.
• Metabolism: Hepatic via CYP3A4 and CYP2C9 to an active metabolite (N-desmethyl).
• Excretion: Primarily fecal (80%) as metabolites; renal (13%); half-life 4 hours.
• Half-Life: 4 hours, with effects lasting 4–6 hours for ED.

13. Pharmacodynamics of Sildenafil

This drug exerts its effects by:

• Inhibiting PDE5 in penile and pulmonary vascular smooth muscle, increasing cGMP.
• Enhancing nitric oxide-mediated vasodilation for ED and PAH.
• Demonstrating dose-dependent cardiovascular and visual side effects.
• Exhibiting synergy with sexual stimulation for ED efficacy.

14. Storage of Sildenafil

• Temperature: Store at 15–30°C (59–86°F); protect from moisture.
• Protection: Keep in original container, away from light.
• Safety: Store in a locked container out of reach of children due to misuse risk.
• Disposal: Dispose of unused tablets per local regulations or consult a pharmacist.

15. Frequently Asked Questions (FAQs) About Sildenafil

Q: What does Sildenafil treat?
A: This medication treats erectile dysfunction and pulmonary hypertension.

Q: Can this active ingredient cause headache?
A: Yes, headache may occur; use hydration or pain relief.

Q: Is Sildenafil safe for children?
A: Yes, for PAH in 1+ years with a doctor’s guidance.

Q: How is this drug taken?
A: Orally as tablets, as directed before activity or regularly for PAH.

Q: How long is Sildenafil treatment?
A: As needed for ED; long-term for PAH with monitoring.

Q: Can I use Sildenafil if pregnant?
A: Yes, with caution for PAH; consult a doctor.

16. Regulatory Information for Sildenafil

This medication is approved by:

• U.S. Food and Drug Administration (FDA): Approved in 1998 (Viagra) for ED, 2005 (Revatio) for PAH.
• European Medicines Agency (EMA): Approved for ED and PAH.
• Other Agencies: Approved globally for these indications; consult local guidelines.

17. References

1. U.S. Food and Drug Administration (FDA). (2023). Viagra (Sildenafil) Prescribing Information.
   • Official FDA documentation detailing the drug’s approved uses, dosage, and safety for ED.
2. U.S. Food and Drug Administration (FDA). (2023). Revatio (Sildenafil) Prescribing Information.
   • Official FDA documentation for PAH indications.
3. European Medicines Agency (EMA). (2023). Sildenafil Summary of Product Characteristics.
   • EMA’s comprehensive information on the medication’s indications and precautions in Europe.
4. National Institutes of Health (NIH). (2023). Sildenafil: MedlinePlus Drug Information.
   • NIH resource providing detailed information on the drug’s uses, side effects, and precautions.
5. Journal of Sexual Medicine. (2023). Sildenafil in Erectile Dysfunction.
   • Peer-reviewed article on Sildenafil efficacy (note: access may require a subscription).