Can Imdur (isosorbide mononitrate) cause bradycardia?

Isosorbide Mononitrate (Imdur) and Bradycardia

Yes, isosorbide mononitrate (Imdur) can cause bradycardia, specifically paradoxical bradycardia, as stated in the FDA drug label. 1

Mechanism and Risk

Isosorbide mononitrate, like other organic nitrates, works primarily through vasodilation. This vasodilatory effect can lead to several hemodynamic changes that may result in bradycardia:

1. Paradoxical bradycardia: The FDA drug label explicitly states that "hypotension induced by isosorbide mononitrate may be accompanied by paradoxical bradycardia and increased angina pectoris." 1

2. Hemodynamic effects: The vasodilation caused by isosorbide mononitrate leads to:

   • Venous pooling
   • Reduced cardiac output
   • Hypotension
   • Reflex parasympathetic stimulation

Clinical Considerations

When prescribing isosorbide mononitrate, be aware of these important clinical considerations:

• Volume status: Use with caution in patients who may be volume depleted or already hypotensive, as this increases the risk of bradycardia. 1

• Drug interactions: The vasodilating effects may be additive with other vasodilators. Particular caution is needed when combining with:

  • Calcium channel blockers (marked symptomatic orthostatic hypotension has been reported) 1
  • Beta-blockers (may enhance bradycardic effects)
  • Other negative chronotropic agents

• Overdose risk: In overdose situations, heart block and bradycardia are recognized complications. 1

Management of Bradycardia Associated with Isosorbide Mononitrate

If bradycardia occurs:

1. Assess severity: Determine if the bradycardia is symptomatic or asymptomatic.

2. Position change: Have the patient lie down and elevate their legs to improve venous return.

3. Volume expansion: If hypotension accompanies bradycardia, intravenous fluid administration may help (unless contraindicated by heart failure or renal disease). 1

4. Medication adjustment: Consider dose reduction or discontinuation if bradycardia is significant.

5. Atropine: For symptomatic bradycardia unresponsive to other measures, atropine may be considered as per bradycardia management guidelines. 2

Prevention

To minimize the risk of bradycardia:

• Start with lower doses in susceptible patients
• Monitor heart rate and blood pressure, especially when initiating therapy
• Avoid concomitant use with other medications that can cause bradycardia when possible
• Ensure patients are adequately hydrated
• Instruct patients to sit or lie down if they experience lightheadedness

Special Populations

Exercise additional caution in:

• Elderly patients
• Patients with baseline bradycardia
• Patients taking multiple cardiac medications
• Patients with conduction system disease

Remember that while bradycardia is a potential side effect, many patients tolerate isosorbide mononitrate well. In a large clinical trial with over 8,700 patients, significant bradycardia was not reported as a common side effect, with headache being the primary adverse effect in about 20% of patients. 3