In a hypertensive male with controlled blood pressure and no nitrate use who experienced a priapism lasting >4 hours while on a phosphodiesterase‑5 inhibitor, does sildenafil or tadalafil carry a higher risk of priapism?

Priapism Risk: Sildenafil vs. Tadalafil

Neither sildenafil nor tadalafil demonstrates a clinically significant difference in priapism risk based on available evidence, as both agents carry extremely low rates of this adverse event (<2%) with no statistical difference between them. 1

Evidence Quality and Limitations

The 2009 American College of Physicians guideline explicitly states that clinical trials evaluated for erectile dysfunction treatment "did not report priapism," and notes that "prolonged erection and priapism were reported infrequently during postmarketing surveillance" for PDE5 inhibitors as a class. 1 This means:

• No head-to-head trial data exists comparing priapism rates between sildenafil and tadalafil
• Postmarketing surveillance shows infrequent occurrence for both agents, without distinguishing between specific PDE5 inhibitors 1
• Very-low-quality evidence shows adverse events do not statistically differ among sildenafil, tadalafil, and vardenafil 1

Real-World Evidence from Combination Therapy

The most relevant recent data comes from a 2023 study examining 476 post-prostatectomy patients using PDE5 inhibitors combined with intracavernosal injections—a scenario that dramatically amplifies priapism risk: 2

• Tadalafil users (n=112): 1.7% experienced priapism
• Sildenafil users (n=364): 1.4% experienced priapism
• No statistical difference (P = 0.47) 2

This combination therapy context represents a "stress test" for priapism risk, as combining PDE5 inhibitors with erectogenic injections theoretically maximizes the likelihood of this complication. The fact that rates remained equivalent suggests no meaningful difference in monotherapy either.

Prolonged Erections (≥2 hours, <4 hours)

The same 2023 study found tadalafil users had higher rates of prolonged erections (6.3% vs. 3.3%, P<0.01), though these did not meet the definition of priapism (≥4 hours). 2 Importantly:

• 53% occurred within the first 6 injections during dose titration 2
• This suggests a dose-finding phenomenon rather than an inherent drug property
• In your patient's context (controlled hypertension, no injections), this distinction is less relevant

Clinical Decision-Making for Your Patient

For a hypertensive male with controlled blood pressure who experienced priapism >4 hours on a PDE5 inhibitor:

If the goal is to avoid future priapism:

1. Neither agent offers a safety advantage based on available evidence 1, 2
2. Switching from one PDE5 inhibitor to another does not reduce priapism risk in subsequent use
3. Consider discontinuing PDE5 inhibitors entirely and proceeding to alternative therapies (vacuum erection devices, intraurethral alprostadil, or intracavernosal injections with careful dose titration) 3

If continuing PDE5 inhibitor therapy despite prior priapism:

• Sildenafil may be preferred due to its shorter half-life (4 hours vs. 17.5 hours for tadalafil), allowing faster resolution if priapism recurs 4
• Tadalafil's 36-hour duration of action means prolonged exposure if priapism develops, as documented in a 2005 case report of 36-hour tadalafil-associated priapism requiring surgical shunting 5
• Start at the lowest effective dose and educate the patient to seek emergency care immediately if erection persists >2 hours

Critical Safety Considerations

• Verify no nitrate use before prescribing any PDE5 inhibitor (absolute contraindication) 3, 6
• Assess cardiovascular fitness (ability to walk 1 mile in 20 minutes or climb 2 flights of stairs) 3, 6
• Counsel on emergency management: If erection persists >4 hours, immediate urologic evaluation is required to prevent permanent erectile tissue damage 3

Common Pitfall

The most critical error is assuming one PDE5 inhibitor is "safer" than another for priapism prevention. The evidence does not support this distinction. 1, 2 If your patient has already experienced priapism on one agent, the risk-benefit calculation should favor discontinuing the entire drug class rather than switching to an alternative PDE5 inhibitor.