What is Imdur (isosorbide mononitrate)?

Imdur (Isosorbide Mononitrate): A Vasodilator for Cardiovascular Conditions

Imdur (isosorbide mononitrate) is an oral vasodilator medication that primarily acts by dilating blood vessels, particularly veins, to reduce cardiac workload and improve blood flow to the heart in patients with angina and heart failure.

Mechanism of Action

• Isosorbide mononitrate is the major active metabolite of isosorbide dinitrate
• Acts through release of nitric oxide, which:
  • Relaxes vascular smooth muscle
  • Dilates peripheral arteries and veins (predominantly venous)
  • Reduces preload (decreases venous return to heart)
  • Reduces afterload (decreases systemic vascular resistance)
  • May dilate coronary arteries 1

Clinical Uses

• Primary indication: Treatment of chronic stable angina pectoris
• May be used in heart failure patients with persistent symptoms despite optimization of other therapies 2
• Can improve exercise tolerance and decrease symptoms of dyspnea at night and during exercise 2
• May attenuate ventricular remodeling in heart failure 2

Formulation and Dosing

• Available as extended-release tablets (30mg, 60mg, 120mg)
• Typical dosing: 60mg once daily in the morning
• Duration of action: Effective for approximately 12 hours after administration 3
• Bioavailability: Approximately 100% 1
• Half-life: Approximately 5 hours 1
• Metabolism: Primarily hepatic, not subject to first-pass metabolism 1

Clinical Efficacy

• Provides effective antianginal prophylaxis for up to 12 hours 3
• Once-daily dosing in the morning provides symptom control throughout the day 3
• Comparable efficacy to:
  • Isosorbide dinitrate 20-30mg three times daily
  • Diltiazem 60mg three times daily 3, 4
• Improvements from baseline are generally maintained during long-term treatment 3

Nitrate Tolerance Management

• A critical consideration with all nitrates is the development of tolerance
• A "nitrate-free interval" of at least 10 hours is essential to maintain efficacy 2, 5
• Once-daily morning dosing of Imdur creates a plasma nitrate profile that:
  • Is high enough during daytime for antianginal protection
  • Low enough during nighttime to avoid tolerance development 4
• Higher doses (120mg or 240mg daily) may maintain efficacy better over longer periods 3

Side Effects and Precautions

• Most common side effect: Headache (usually mild to moderate, improves with continued therapy) 3
• Other potential side effects:
  • Hypotension
  • Dizziness
  • Flushing
• Contraindications:
  • Systolic blood pressure <90 mmHg
  • Severe bradycardia (<50 bpm)
  • Concomitant use with phosphodiesterase-5 inhibitors (sildenafil, tadalafil, vardenafil) 2, 5

Important Clinical Considerations

• Abrupt discontinuation after long-term treatment may exacerbate anginal symptoms in some patients 3, 6
• No evidence of rebound worsening of ischemia 24 hours after administration 3
• Patient compliance is better with once-daily administration compared to multiple daily dosing regimens 3
• For patients with persistent symptoms despite Imdur, combination with beta-blockers may provide superior antianginal protection 4

Practical Administration Tips

• Take in the morning to ensure a nitrate-free interval overnight
• Swallow tablets whole; do not crush or chew extended-release formulations
• Monitor for hypotension, especially when initiating therapy
• May be used as part of combination therapy with beta-blockers or calcium channel blockers for enhanced effect 5

Imdur offers the convenience of once-daily dosing while providing effective symptom control for patients with chronic stable angina, with the added benefit of potentially reducing nitrate tolerance through its extended-release formulation.