Conversion from Imdur 15mg to Nitroglycerin Patch
When converting from Imdur (isosorbide mononitrate) 15mg daily to a nitroglycerin patch, the equivalent starting dose is a 0.2-0.4 mg/hour (5-10 mg/24h) transdermal nitroglycerin patch applied in the morning with removal after 12-14 hours to prevent tolerance development. 1
Dosing Recommendation
The conversion from oral isosorbide mononitrate to transdermal nitroglycerin should follow these guidelines:
- Starting dose: For patients on low-dose Imdur (15mg), begin with a nitroglycerin patch delivering 0.2-0.4 mg/hour (5-10 mg/24h) 1
- Application schedule: Apply the patch in the morning and remove after 12-14 hours to ensure a nitrate-free interval 1, 2
- Nitrate-free interval: A daily nitrate-free period of 10-12 hours is essential to prevent tolerance development 3
Application Instructions
- Discontinue Imdur 15mg
- Apply the nitroglycerin patch (0.2-0.4 mg/hour) the following morning
- Remove the patch in the evening (after 12-14 hours)
- Apply a new patch the next morning
Dose Titration
- If angina is inadequately controlled after initial conversion, increase the dose to 0.4-0.6 mg/hour (10-15 mg/24h) 1
- Maximum recommended dose is 0.8 mg/hour (20 mg/24h) 1
- Titrate based on symptom control rather than blood pressure response 1, 2
Rationale for Intermittent Dosing
Continuous 24-hour nitrate therapy leads to rapid development of tolerance within 24-48 hours, resulting in loss of anti-anginal efficacy 2, 4, 5. Multiple studies have demonstrated that:
- Continuous nitrate patch therapy produces complete loss of efficacy within 1 week 5
- A daily nitrate-free interval of 10-12 hours prevents tolerance development 3
- Intermittent therapy maintains anti-anginal protection during daytime hours when most patients experience angina 4
Important Precautions
- Contraindications: Do not use nitroglycerin within 24 hours of sildenafil use, 48 hours of tadalafil use, or in patients with hypotension 2
- Blood pressure monitoring: Avoid use in patients with systolic BP <90 mmHg or >30 mmHg below baseline 2
- Side effects: Headache is commonly reported with nitrates and typically resolves with continued use 2
- Special populations: Use with extreme caution in patients with aortic stenosis as they may develop marked hypotension 2
Management of Nocturnal Angina
If the patient experiences nocturnal angina during the nitrate-free interval, consider:
- Adjusting the timing of the nitrate-free interval 1
- Adding a beta-blocker for coverage during the nitrate-free period 1
This conversion approach ensures continued anti-anginal efficacy while minimizing the risk of tolerance development, which is the primary limitation of continuous nitrate therapy.