Is it safe to use Viagra (sildenafil) in patients with a history of nonarteritic ischemic optic neuropathy (NAION)?

Sildenafil Use in Patients with History of Nonarteritic Ischemic Optic Neuropathy

Sildenafil (Viagra) is contraindicated in patients with a history of nonarteritic ischemic optic neuropathy (NAION) due to increased risk of recurrence in the contralateral eye. 1, 2

Risk Assessment and Evidence

• Very-low-quality evidence exists regarding the association between PDE-5 inhibitors and NAION, making it difficult to establish a definitive causal relationship 3
• A study of 4 million veterans aged 50 years or older showed PDE-5 inhibitors were not significantly associated with confirmed NAION (relative risk 1.02 [95% CI, 0.92 to 1.12]) 3
• However, PDE-5 inhibitors were associated with an increased risk for "possible NAION" (relative risk 1.34 [CI, 1.17 to 1.55]) 3
• Case reports document sequential NAION affecting the contralateral eye in patients who continued PDE-5 inhibitor use after an initial NAION episode 1

FDA Labeling and Warnings

• The FDA label for sildenafil explicitly warns about NAION risk, stating: "When used to treat erectile dysfunction, non-arteritic anterior ischemic optic neuropathy (NAION), a cause of decreased vision including permanent loss of vision, has been reported postmarketing in temporal association with the use of phosphodiesterase type 5 (PDE-5) inhibitors, including sildenafil" 4
• The FDA recommends physicians "discuss the increased risk of NAION with patients who have already experienced NAION in one eye, including whether such individuals could be adversely affected by use of vasodilators, such as PDE-5 inhibitors" 4
• Patients should be advised to seek immediate medical attention for sudden vision loss while taking PDE-5 inhibitors 4

Risk Factors and Mechanism

• Most patients who developed NAION while using PDE-5 inhibitors had underlying anatomic or vascular risk factors, including: 4
  • Low cup-to-disc ratio ("crowded disc")
  • Age over 50
  • Diabetes
  • Hypertension
  • Coronary artery disease
  • Hyperlipidemia
  • Smoking
• The vasodilatory properties of sildenafil may potentially affect ocular blood flow in susceptible individuals 4, 5

Clinical Decision Algorithm

1. For patients with prior history of NAION:

   • Avoid sildenafil and all PDE-5 inhibitors 1, 2
   • Consider alternative treatments for erectile dysfunction

2. For patients without prior NAION but with multiple risk factors:

   • Discuss potential risks versus benefits 4
   • Consider lower starting doses if benefits outweigh risks 5
   • Educate about warning signs requiring immediate attention 4

3. For all patients prescribed sildenafil:

   • Instruct to immediately discontinue use and seek medical attention if experiencing any visual changes 4, 5
   • Document discussion of potential risks in medical record 4

Common Pitfalls and Caveats

• Failure to recognize that NAION can occur even 36 hours after sildenafil intake when blood levels are minimal 6
• Not inquiring about PDE-5 inhibitor use when evaluating patients with sudden vision loss 2
• Overlooking that patients with a history of NAION in one eye are at particularly high risk for involvement of the fellow eye if PDE-5 inhibitor use continues 1, 2
• Not recognizing that the absence of immediate visual symptoms after initial use does not guarantee safety with continued use 7