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 tablets) is 30-60 mg once daily in the morning, which can be titrated to 120 mg once daily after several days if needed, with a maximum dose of 240 mg daily in rare cases. 1
Initial Dosing and Administration
- Starting dose: 30 mg (given as a single 30 mg tablet or as 1/2 of a 60 mg tablet) or 60 mg (given as a single tablet) once daily 1
- Administration time: Take in the morning upon arising 1
- Administration method: Swallow whole with half a glass of fluid; do not chew or crush 1
- Dose titration: After several days, may increase to 120 mg once daily if needed 1
- Maximum dose: Rarely, 240 mg may be required 1
Mechanism of Action and Pharmacokinetics
Isosorbide mononitrate works through:
- Venous dilation (decreases preload)
- Arterial dilation (decreases afterload)
- Coronary artery dilation (improves myocardial perfusion)
The extended-release formulation provides:
- Peak plasma concentrations in 3-4.5 hours 1
- Duration of effect: 12-24 hours 2
- Half-life: 6.2-6.6 hours 1
Preventing Nitrate Tolerance
Nitrate tolerance is a significant concern with long-term nitrate therapy and typically develops after 24 hours of continuous therapy 2. To prevent tolerance:
- Administer once daily in the morning 1
- Ensure a daily nitrate-free interval (typically overnight) 2
- Do not use continuous 24-hour dosing regimens 2
Clinical Efficacy
- Provides antianginal protection for up to 12 hours after morning administration 3
- Maintains effectiveness during long-term treatment when properly dosed 3, 4
- Studies show significant reduction in anginal attacks and nitroglycerin consumption 5, 4
- No evidence of rebound worsening of ischemia 24 hours after administration 3
Combination Therapy
- May be used as monotherapy or in combination with beta-blockers 6
- When used with beta-blockers, the 60 mg once-daily regimen is more effective than twice-daily dosing (which may lead to tolerance) 6
- First-line treatment for angina typically includes beta-blockers and/or calcium channel blockers, with nitrates as add-on therapy 2
Contraindications and Precautions
- Avoid in patients with hypotension (systolic BP <90 mmHg) 2
- Contraindicated with phosphodiesterase inhibitors (sildenafil, tadalafil, vardenafil) due to risk of severe hypotension 2
- Not recommended in patients with hypertrophic obstructive cardiomyopathy 2
- Use with caution in patients with marked bradycardia or tachycardia 2
Adverse Effects and Management
- Headache is the most common side effect (usually mild to moderate) 3, 5
- Headache typically improves with continued therapy and rarely leads to treatment discontinuation 3
- Hypotension may occur; monitor blood pressure 2
- Abrupt discontinuation may exacerbate anginal symptoms; taper if discontinuing 3
Special Populations
- No significant differences in pharmacokinetics between elderly (≥65 years) and younger individuals (45-64 years) for the 60 mg dose 1
- Older patients (65-74 years) may show 30% lower clearance with higher doses (120 mg) 1
- No dose adjustment needed for mild to moderate renal insufficiency 1
Monitoring
- Review patient's response to therapy after 2-4 weeks of treatment 2
- Monitor for symptom relief and reduction in nitroglycerin consumption 4
- Assess for side effects, particularly headache and hypotension 2
Common Pitfalls to Avoid
- Administering nitrates without a nitrate-free interval, leading to tolerance
- Co-administration with phosphodiesterase inhibitors (can cause severe hypotension)
- Abrupt discontinuation (may worsen angina)
- Failure to swallow extended-release tablets whole (crushing or chewing alters release profile)
- Inadequate patient education about potential headaches, which typically improve with continued use
By following these recommendations, Imdur can be effectively used to manage angina pectoris while minimizing the development of tolerance and adverse effects.