What are the contraindications for Imdur (isosorbide mononitrate) in patients with hypersensitivity, severe hypotension, anemia, increased intracranial pressure, head trauma, cerebral hemorrhage, or impaired renal or hepatic function, especially in the elderly?

Contraindications of Imdur (Isosorbide Mononitrate)

Imdur is absolutely contraindicated in patients with hypersensitivity to nitrates or nitrites, and should be avoided in those with severe hypotension, severe anemia, increased intracranial pressure, concurrent phosphodiesterase inhibitor use, and right ventricular infarction. 1

Absolute Contraindications

Hypersensitivity

• Patients who have demonstrated hypersensitivity or idiosyncratic reactions to other nitrates or nitrites must not receive isosorbide mononitrate. 1

Hemodynamic Contraindications

• Hypotension is a critical contraindication - nitrates should not be used in patients with hypotension or bradycardia 2
• Severe anemia represents a contraindication as nitrates can worsen tissue oxygen delivery 2

Neurological Contraindications

• Increased intracranial pressure is an absolute contraindication - nitrates can further elevate intracranial pressure and are contraindicated in patients at risk for this condition 2
• Head trauma and cerebral hemorrhage are contraindications due to the risk of worsening intracranial pressure 2

Drug Interactions - Absolute Contraindications

• Concurrent use of phosphodiesterase inhibitors (sildenafil, tadalafil, vardenafil) is absolutely contraindicated - this combination can cause severe, potentially fatal hypotension 2
  • Must avoid nitrates within 24 hours of sildenafil or vardenafil use 2
  • Must avoid nitrates within 48 hours of tadalafil use 2

Relative Contraindications and High-Risk Situations

Cardiac Conditions

• Right ventricular infarction requires extreme caution - nitrates can precipitate severe hypotension in right-sided ischemia by reducing preload 2
• Advanced aortic stenosis is a relative contraindication due to fixed cardiac output 2

Renal and Hepatic Impairment

• While not absolute contraindications, impaired renal or hepatic function requires dose adjustment and careful monitoring, particularly in elderly patients 2
• No specific dose adjustment is mandated by guidelines for elderly patients without organ dysfunction 2

Critical Clinical Pearls

Tolerance Development

• Continuous nitrate exposure leads to tolerance - this is why once-daily Imdur dosing is designed to provide a nitrate-free interval during nighttime hours to prevent tolerance development 3, 4
• The plasma nitrate profile with once-daily Imdur 60 mg is high enough for daytime protection but low enough during the latter dosage interval to avoid tolerance 3

Withdrawal Considerations

• Abrupt discontinuation can cause rebound angina - nitrates should be tapered gradually rather than stopped suddenly 4
• There is no evidence of rebound ischemia 24 hours after Imdur administration when used as prescribed 4

Special Population Concerns

• In elderly patients with cardiovascular disease, nitrates carry increased risk of orthostatic hypotension leading to falls 2
• Headache is the most common adverse effect but typically resolves within 5-6 days of continued therapy 5

Volume Status

• Volume-depleted patients should not receive nitrates - use only in patients with adequate preload, particularly those with acute coronary syndrome and/or acute pulmonary edema 2

Monitoring Requirements

• Blood pressure monitoring is essential, particularly when initiating therapy 2
• Use the smallest effective dose for symptom relief 2