What is the recommended dosage and management of Imdur (isosorbide mononitrate) for angina pectoris?

Dosage and Management of Imdur (Isosorbide Mononitrate) for Angina Pectoris

For patients with angina pectoris, the recommended starting dose of Imdur (isosorbide mononitrate extended-release) is 30-60 mg once daily in the morning, which may be increased to 120 mg once daily after several days if needed for symptom control. 1

Dosing Regimen

Initial Dosing

• Start with 30 mg (given as a single 30 mg tablet or half of a 60 mg tablet) or 60 mg (given as a single tablet) once daily 1
• Administer in the morning upon arising
• Tablets should be swallowed whole with half a glass of fluid, not chewed or crushed 1

Dose Titration

• After several days, the dosage may be increased to 120 mg once daily if needed 1
• Rarely, doses up to 240 mg may be required 1
• Dose adjustments should be based on clinical response and tolerability

Administration Considerations

Timing and Nitrate-Free Interval

• Once-daily morning administration provides effective prophylaxis of symptoms throughout the day (approximately 12-24 hours) 2
• Morning administration creates a natural nitrate-free interval during sleep, which helps prevent tolerance 2, 3
• This dosing schedule maintains antianginal efficacy during long-term treatment 3

Special Populations

• No significant differences in pharmacokinetics between elderly (≥65 years) and younger individuals (45-64 years) at the 60 mg dose 1
• Elderly patients (65-74 years) showed 30% lower clearance at the 120 mg dose compared to younger patients, but this difference was not statistically significant 1
• No dose adjustment required for patients with renal insufficiency, liver cirrhosis, or cardiac dysfunction 1

Clinical Efficacy and Monitoring

Efficacy Measures

• Antianginal effects typically observed 1-12 hours after administration 2
• Efficacy demonstrated by:
  • Reduction in angina attack frequency
  • Decreased need for sublingual nitroglycerin
  • Improved exercise tolerance 2, 3

Tolerance Management

• Once-daily dosing with a nitrate-free interval helps prevent tolerance development 3
• Studies show maintenance of antianginal effects during long-term treatment with proper dosing 2, 4
• Higher doses (120-240 mg) may maintain efficacy over longer periods compared to lower doses (30-60 mg) 1, 2

Side Effects and Contraindications

Common Side Effects

• Headache (most common) - usually mild to moderate, improves with continued therapy 2, 5
• Hypotension
• Dizziness

Contraindications

• Concomitant use with phosphodiesterase inhibitors:
  • Sildenafil (within previous 24 hours)
  • Tadalafil (within previous 48 hours)
  • Vardenafil (timing not definitively established) 6
• Initial systolic blood pressure less than 90 mmHg or 30 mmHg below baseline 6
• Marked bradycardia or tachycardia 6
• Hypertrophic cardiomyopathy 6

Practical Management Tips

Discontinuation

• Abrupt discontinuation during long-term treatment may exacerbate anginal symptoms 2
• When discontinuing, gradually taper the dose

Combination Therapy

• Can be used in combination with beta-blockers for enhanced antianginal effects 3
• When used with other antianginal drugs, optimize dosing of one drug before adding another 6
• Consider switching drug combinations before attempting a three-drug regimen 6

Treatment Monitoring

• Monitor for symptom relief (reduction in angina attacks)
• Track sublingual nitroglycerin consumption
• Assess exercise tolerance
• Monitor for side effects, particularly headache and hypotension

Common Pitfalls to Avoid

1. Inappropriate timing: Administering twice daily instead of once daily can lead to tolerance development
2. Inadequate nitrate-free interval: Continuous 24-hour nitrate exposure leads to tolerance
3. Concomitant use with phosphodiesterase inhibitors: Can cause profound hypotension, MI, and even death 6
4. Abrupt discontinuation: May cause rebound angina; taper gradually
5. Crushing or chewing extended-release tablets: Disrupts controlled release mechanism and alters drug delivery

By following these dosing and management guidelines, Imdur can provide effective prophylaxis against angina symptoms while minimizing the development of tolerance and adverse effects.