What is the use of nitroglycerin (glyceryl trinitrate) ointment in treating anal fissures?

Nitroglycerin Ointment for Anal Fissure Treatment

Nitroglycerin (glyceryl trinitrate) ointment is used for anal fissures as a topical therapy to reversibly decrease resting anal pressure, allowing fissure healing without permanent sphincter damage. 1

Mechanism of Action

Nitroglycerin works as a nitric oxide donor that:

• Reduces the increased anal canal pressure caused by a hypertonic internal anal sphincter
• Improves anodermal blood flow
• Promotes relaxation of the internal anal sphincter 2
• Creates a "chemical sphincterotomy" effect 1

Clinical Use and Efficacy

Dosing and Administration

• Standard concentration: 0.2-0.4% nitroglycerin ointment
• Typical application: 375 mg of 0.4% ointment (delivering 1.5 mg nitroglycerin) twice daily 2
• Route: Intra-anal application
• Duration: Treatment for at least 6 weeks is suggested, with pain relief typically occurring after 14 days 1

Efficacy

• Healing rates vary considerably:
  • Early studies reported 70-80% healing rates
  • More recent studies show more modest results of 25-50% healing 1
  • One study demonstrated significant reduction in maximum anal resting pressure from 122.1 to 72.5 cm of water within 20 minutes of application 3

Treatment Algorithm

1. First-line approach: Conservative management with fiber supplementation, adequate fluid intake, sitz baths, and topical analgesics 1
2. Second-line approach: Topical nitroglycerin for patients who don't respond to conservative measures
3. Third-line approach: Consider surgical options (lateral internal sphincterotomy) for patients who fail medical therapy

Side Effects and Limitations

Common Side Effects

• Headache is the most common adverse effect, occurring in most patients
  • Can be severe in 20-25% of patients
  • Usually transient but may lead to treatment discontinuation in some cases 2
• Local burning sensation may occur 4

Comparative Effectiveness

• Lateral internal sphincterotomy provides faster pain relief (70% vs 40% at 2 weeks) and earlier healing compared to nitroglycerin 4
• After 6 weeks of treatment, healing rates between nitroglycerin and sphincterotomy become more comparable 4
• Calcium channel blockers (diltiazem or nifedipine) appear to be more effective than glyceryl trinitrate with less risk of headache and hypotension 1

Important Considerations

Patient Selection

• Best suited for patients with:
  • Acute anal fissures
  • Chronic fissures with tolerable pain
  • Patients who wish to avoid surgery
  • Patients with compromised sphincter function 1

Pitfalls to Avoid

1. Don't use as monotherapy: Always combine with conservative measures (fiber, fluids, sitz baths)
2. Don't discontinue too early: Complete treatment course of at least 6 weeks is recommended
3. Be aware of recurrence: Fissures may recur after treatment is stopped (reported in some patients) 3
4. Monitor for headaches: May require dose adjustment or discontinuation if severe
5. Consider alternatives: If nitroglycerin fails, calcium channel blockers or surgical options should be considered 1

Special Considerations

• Availability may be limited: Appropriately diluted GTN preparations may not be commercially available in some regions 1
• Patients should be counseled about potential headaches before starting treatment
• Regular follow-up at 2-week intervals is recommended to assess healing and symptom relief 4