What are the contraindications for isosorbide mononitrate?

Isosorbide Mononitrate Contraindications

Isosorbide mononitrate is contraindicated in patients with hypersensitivity or idiosyncratic reactions to nitrates or nitrites, and in patients taking phosphodiesterase inhibitors such as sildenafil, tadalafil, or vardenafil due to risk of severe hypotension. 1

Primary Contraindications

• Hypersensitivity to nitrates or nitrites: Patients who have shown allergic reactions to any nitrate compounds should not receive isosorbide mononitrate 1

• Concurrent use of phosphodiesterase inhibitors:

  • Sildenafil (within previous 24 hours)
  • Tadalafil (within previous 48 hours)
  • Vardenafil (timing less established, but approximately 24 hours)

  This combination can cause profound, potentially fatal hypotension 2

• Severe hypotension: Patients with systolic blood pressure <90 mmHg or >30 mmHg below baseline 2

Relative Contraindications/Use with Caution

• Right ventricular infarction: Patients with inferior wall MI with right ventricular involvement are especially dependent on adequate right ventricular preload and can experience profound hypotension with nitrate administration 2

• Severe aortic stenosis: These patients may be dependent on adequate preload to maintain cardiac output

• Hypertrophic cardiomyopathy: May worsen outflow tract obstruction

• Severe anemia: May worsen oxygen delivery

• Increased intracranial pressure: Nitrates can potentially increase cerebral blood flow

• Cirrhosis with ascites: Can cause hypotension and sodium retention in these patients 3

Special Considerations

Hemodynamic Effects

Isosorbide mononitrate causes venodilation and arterial vasodilation, which can lead to:

• Decreased preload
• Decreased afterload
• Reduced myocardial oxygen demand
• Potential hypotension, especially in volume-depleted patients 2

Dosing Considerations

To avoid nitrate tolerance:

• Implement a daily nitrate-free interval of at least 10-12 hours
• Consider once-daily dosing of sustained-release formulations 4
• Avoid continuous 24-hour exposure 2

Monitoring Requirements

When administering isosorbide mononitrate, monitor:

• Blood pressure (avoid titrating systolic BP below 110 mmHg in normotensive patients)
• Heart rate (watch for reflex tachycardia)
• Signs of hypoperfusion 2

Management of Nitrate-Induced Hypotension

If severe hypotension occurs:

• Place patient in Trendelenburg position (leg elevation)
• Administer IV fluids
• Consider atropine if bradycardia is present
• Discontinue nitrate therapy 2

Clinical Pearls

• Isosorbide mononitrate is 100% bioavailable after oral dosing and does not undergo first-pass hepatic metabolism, unlike isosorbide dinitrate 2
• The half-life of isosorbide mononitrate is 4-5 hours 2
• Headache is a common side effect that often diminishes with continued use
• Patients may develop tolerance with continuous administration; a nitrate-free interval helps prevent this phenomenon 2, 4

Remember that while isosorbide mononitrate can be beneficial in many cardiovascular conditions, its use must be carefully considered in light of these contraindications to minimize risks and optimize patient outcomes.