For a patient who has completed radiation therapy and chemotherapy for prostate cancer and wants to resume sexual activity, are there any contraindications to as-needed sildenafil, is another erectile‑dysfunction agent preferred, and what is the typical sildenafil dosing regimen?

Sildenafil Use for Erectile Dysfunction After Prostate Cancer Treatment

Sildenafil is appropriate and effective for erectile dysfunction in prostate cancer survivors who have completed radiation and chemotherapy, with the absolute contraindication being concurrent nitrate use. 1

Primary Contraindication

The only absolute contraindication to sildenafil is concurrent use of oral nitrates, which can cause life-threatening hypotension. 1 Before prescribing sildenafil, verify the patient is not taking:

• Nitroglycerin (any formulation)
• Isosorbide mononitrate or dinitrate
• Any nitrate-containing medications 1

If nitrates are needed emergently after sildenafil use, wait at least 24 hours after the last sildenafil dose before administering nitrates under close medical supervision. 1

Preferred Agent Selection

All FDA-approved PDE5 inhibitors (sildenafil, tadalafil, vardenafil, avanafil) have comparable efficacy in post-radiation prostate cancer patients, so agent selection should be based on patient preference regarding dosing flexibility and side effect profile. 1, 2

• Sildenafil remains an excellent first-line choice with proven efficacy in this specific population 3, 4, 5
• Tadalafil offers the advantage of daily low-dose or on-demand dosing with equal effectiveness 2
• Avanafil has the lowest dyspepsia rates if gastrointestinal side effects are a concern 1

Sildenafil Dosing Protocol

Start sildenafil at 50 mg taken 30-60 minutes before sexual activity, then titrate to 100 mg if the initial dose is inadequate after 4-8 attempts. 2, 3, 4

Specific Dosing Instructions:

• Initial dose: 50 mg on-demand 2, 3
• Timing: Take 30-60 minutes before anticipated sexual activity 2
• Titration: If 50 mg is insufficient after at least 4 attempts, increase to 100 mg 1, 3
• Trial period: Patients need 4-8 weeks of attempts before declaring treatment failure 2
• Sexual stimulation is required for the medication to work—this is a critical counseling point 2

Expected Response Rates in Post-Radiation Patients:

• 71-74% of post-radiation patients respond to sildenafil with erections sufficient for vaginal penetration 3, 4
• 80% of responders require the 100 mg dose for maximal effect 3
• Response rates decline over time: 68% at 12 months, 50% at 24 months, and 36% at 36 months post-radiation 5, 6

Important Clinical Considerations

Factors That Reduce Sildenafil Efficacy:

• Longer time since radiation therapy (progressive vascular damage occurs) 5, 6
• Older age at treatment 5
• Androgen deprivation therapy >4 months duration 5
• Radiation dose >85 Gy 5
• More severe baseline erectile dysfunction (patients with partial function respond better than those with complete dysfunction) 4

Additional Interventions to Maximize Success:

Lifestyle modifications should be implemented concurrently with sildenafil, as PDE5 inhibitors combined with aerobic exercise are more effective than medication alone. 1, 2

• Smoking cessation 1
• Weight loss 1
• Increased physical activity 1
• Reduced alcohol consumption 1

Check morning testosterone levels—if <300 ng/dL, testosterone supplementation combined with sildenafil is more effective than sildenafil alone. 1, 2 However, testosterone is absolutely contraindicated if the patient is on active surveillance or androgen deprivation therapy. 1

Refer to pelvic floor physical therapy, as this may improve sexual function outcomes in prostate cancer survivors. 1, 2

Consider psychosexual or couples counseling, as psychological factors are often pronounced in cancer survivors and addressing these improves treatment outcomes. 1, 2

Common Pitfalls to Avoid

• Do not declare treatment failure after only 1-2 attempts—patients need 4-8 weeks of proper use before determining efficacy 2
• Do not forget to counsel about the need for sexual stimulation—the medication does not work without arousal 2
• Do not overlook food interactions—high-fat meals can delay sildenafil absorption 1
• Do not assume failure with one PDE5 inhibitor means failure with all—switching agents may be successful 1
• Do not miss the opportunity to screen for cardiovascular disease—erectile dysfunction is a risk marker for cardiovascular events 1

Monitoring and Follow-Up

Monitor patients periodically for efficacy, side effects, and changes in health status or medications, typically at prescription renewal. 1

Common side effects include:

• Headache 1, 3
• Flushing (19%) 1, 3
• Dyspepsia 1
• Abnormal color vision (14%) 3
• Nasal congestion 1

Side effects are generally mild and rarely require discontinuation. 3

Second-Line Options if Sildenafil Fails

If sildenafil fails after proper dosing and adequate trial, refer to urology for consideration of:

• Alternative PDE5 inhibitor 1, 2
• Intraurethral alprostadil suppositories 1, 2
• Intracavernosal prostaglandin injection 2
• Vacuum erection device 2
• Penile prosthesis 2