What are the contraindications for Nitroglycerin (NTG)?

Contraindications for Nitroglycerin (NTG)

Nitroglycerin is absolutely contraindicated in patients who have recently used phosphodiesterase-5 inhibitors (sildenafil within 24 hours, vardenafil within 24 hours, tadalafil within 48 hours, avanafil within 12 hours), have hypotension (SBP <90 mmHg), or are taking the soluble guanylate cyclase stimulator riociguat. 1, 2, 3

Absolute Contraindications

• Phosphodiesterase-5 inhibitor use:
  • Sildenafil or vardenafil within 24 hours
  • Tadalafil within 48 hours
  • Avanafil within 12 hours 1
• Hypotension (systolic BP <90 mmHg or ≥30 mmHg below baseline) 1
• Soluble guanylate cyclase stimulator (riociguat) use 2
• Known hypersensitivity or allergy to nitroglycerin 2
• Early myocardial infarction (specifically with right ventricular involvement) 2, 1
• Severe anemia 2
• Increased intracranial pressure 2

Relative Contraindications

• Right ventricular infarction - can cause severe hypotension due to preload dependency 1
• Extreme bradycardia (<50 bpm) 1
• Tachycardia in the absence of heart failure (>100 bpm) 1
• Severe aortic stenosis - can worsen hemodynamics 4
• Hypertrophic obstructive cardiomyopathy - can worsen outflow obstruction 3
• Severe hypertension (≥200/110 mmHg) - may cause unpredictable blood pressure response 3

Hemodynamic Considerations

Nitroglycerin works primarily through venodilation at lower doses and arterial dilation at higher doses, which can lead to:

1. Decreased preload - particularly problematic in:

   • Right ventricular infarction - these patients are preload dependent 1
   • Hypovolemic patients 1

2. Decreased blood pressure - particularly concerning in:

   • Patients with baseline hypotension 3
   • Patients taking other vasodilators 1
   • Patients under anesthesia 1

Monitoring Requirements

When administering nitroglycerin:

• Monitor blood pressure after each dose
• Discontinue if systolic BP drops below 90 mmHg or 30 mmHg below baseline
• Have patient seated to prevent falls from orthostatic hypotension
• Be vigilant for development of tolerance with prolonged use 1

Special Considerations

1. Inferior STEMI: While traditionally considered a relative contraindication due to possible right ventricular involvement, recent evidence suggests that computer-interpreted inferior STEMI alone may not predict higher rates of hypotension following NTG administration 5. However, caution is still warranted, and clinical assessment for RV involvement is important.

2. Combination with other medications: Use caution when combining with:

   • Anesthetic agents
   • Calcium channel blockers (especially nicardipine)
   • Other vasodilators 1

3. Tolerance development: Continuous administration leads to tolerance, potentially limiting efficacy and requiring dose adjustments 6

By understanding these contraindications and taking appropriate precautions, clinicians can safely administer nitroglycerin while minimizing adverse events and optimizing patient outcomes.