For a prostate‑cancer survivor resuming sexual activity, how many sildenafil (Viagra) tablets per month should be prescribed for on‑demand use?

Sildenafil Prescription Quantity for Prostate Cancer Survivors

For prostate cancer survivors resuming sexual activity with on-demand sildenafil, prescribe 8 tablets per month initially, allowing for approximately 2 attempts per week, which aligns with the minimum adequate trial requirement of at least 5 separate attempts before assessing treatment response. 1

Initial Prescription Strategy

• Start with 8 tablets monthly to provide sufficient opportunity for an adequate trial while avoiding excessive unused medication, as many men will need dose titration or may not use the medication weekly 1
• The NCCN guidelines emphasize that at least 5 separate attempts at the prescribed dose are required before determining efficacy, making 8 tablets appropriate for initial assessment over 4-6 weeks 2
• Post-radiotherapy prostate cancer survivors have response rates of 71-77% with sildenafil, but many require dose escalation to 100 mg for maximal effect 3, 4

Rationale for 8 Tablets Monthly

• Most couples do not attempt intercourse more than twice weekly, particularly in the survivorship population where sexual function is being re-established 3, 4
• This quantity allows for proper dose titration assessment: patients should complete at least 5 attempts at their current dose with adequate sexual stimulation, proper timing, and limited alcohol before declaring treatment failure or escalating dose 1
• Approximately 24% of post-radiotherapy patients continue using sildenafil long-term, suggesting many will discontinue or require alternative therapy after initial trial 3

Critical Prescribing Requirements Before Dispensing

Absolute Contraindication Screening

• Verify no nitrate use in any form (sublingual nitroglycerin, long-acting nitrates, recreational "poppers") as concurrent use causes potentially fatal hypotension 1
• Assess cardiovascular fitness: patient should be able to walk 1 mile in 20 minutes or climb 2 flights of stairs without symptoms; refer to cardiology if unable 1

Modifiable Factors That Reduce Efficacy

• Screen for heavy alcohol consumption, which impairs erectile function independent of medication and accounts for many apparent treatment failures 1
• Evaluate for testosterone deficiency: post-radiotherapy patients often develop hypogonadism, and combining testosterone therapy with sildenafil may be more effective than sildenafil alone 2, 1
• Identify medications that worsen erectile dysfunction (antihypertensives, antidepressants, opioids) 1

Dosing Instructions to Provide

• Start with 50 mg taken 1 hour before anticipated sexual activity, with option to increase to 100 mg if response is inadequate after at least 5 attempts 5, 3, 4
• Avoid taking with large or fatty meals, as this reduces absorption and efficacy 1
• Sexual stimulation is required for the medication to work; sildenafil enhances but does not replace natural arousal 1
• Maximum frequency is once daily; do not take more than one dose in 24 hours 5

When to Increase Monthly Quantity

After establishing efficacy and tolerability, consider increasing to 12-16 tablets monthly for patients who:

• Successfully respond to treatment and desire more frequent sexual activity (3-4 times weekly) 1
• Have completed adequate trial (minimum 5 attempts) demonstrating consistent benefit 1
• Have stable cardiovascular status and no new contraindications 1

Special Considerations for Post-Radiotherapy Patients

• Post-radiotherapy erectile dysfunction may be delayed in onset and progressive, unlike post-surgical ED which is immediately evident 2
• Response rates are lower than general ED population: 71-77% achieve erections sufficient for penetration versus 80-85% in non-cancer populations 3, 4
• Most responders require 100 mg dosing: 80% of successful post-radiotherapy patients needed dose escalation from 50 mg to 100 mg 4
• Mean intercourse duration is approximately 12-13 minutes in responders, with 71% spousal satisfaction rate 4

Common Pitfalls to Avoid

• Do not prescribe 30 tablets monthly initially: this creates excessive unused medication when many patients will require dose adjustment, alternative therapy, or discontinue use 3
• Do not declare treatment failure without adequate trial: ensure patient has completed at least 5 attempts at maximum tolerated dose with proper technique before switching agents 1
• Do not overlook testosterone screening: hypogonadism is common after radiation therapy and significantly reduces PDE5 inhibitor response 2, 1
• Do not forget to counsel about timing: sildenafil should be taken 1 hour before sexual activity, and incorrect timing accounts for many apparent failures 1, 5

Follow-Up and Reassessment

• Schedule follow-up at 4-6 weeks to assess efficacy after adequate trial, evaluate side effects, and determine if dose escalation or quantity adjustment is needed 1
• Verify cardiovascular health hasn't changed and review any new medications that might interact or contraindicate continued use 1
• If treatment fails after adequate trial at maximum dose (100 mg), consider switching to alternative PDE5 inhibitor (tadalafil or vardenafil) or second-line therapies 1