What are the recommendations for switching from Imdur (isosorbide mononitrate) 15mg daily to an NTG (nitroglycerin) patch?

Switching from Imdur 15mg Daily to NTG Patch

When switching from Imdur (isosorbide mononitrate) 15mg daily to a nitroglycerin (NTG) patch, use a transdermal NTG patch at 0.2-0.4 mg/h (5-10 mg/24h) initially, applied in the morning with a 10-12 hour nitrate-free interval to prevent tolerance development. 1

Rationale for Switching

Switching between nitrate formulations may be necessary for several reasons:

• Improved patient compliance with once-daily patch application
• Better management of angina symptoms throughout the day
• Need for a nitrate-free interval to prevent tolerance

Conversion Protocol

1. Timing of switch:

   • Apply the first NTG patch in the morning after discontinuing Imdur
   • Remove the patch after 12-14 hours to provide a nitrate-free interval 1

2. Initial dosing:

   • For patients on low-dose Imdur (15mg), start with NTG patch 0.2-0.4 mg/h (5-10 mg/24h) 1
   • This provides comparable nitrate effects while minimizing risk of hypotension

3. Application schedule:

   • Apply patch in the morning (e.g., 8 AM)
   • Remove in the evening (e.g., 8-10 PM)
   • This creates the necessary nitrate-free interval to prevent tolerance 2

Monitoring and Dose Adjustment

1. Initial monitoring (first 24-48 hours):

   • Monitor for headache, dizziness, and hypotension
   • Assess for symptom control during the day
   • Check for rebound angina during nitrate-free period

2. Dose titration:

   • If angina is inadequately controlled, increase to 0.4-0.6 mg/h (10-15 mg/24h)
   • Maximum recommended dose is 0.8 mg/h (20 mg/24h) 1
   • Titrate based on symptom control rather than blood pressure response 1

Important Considerations

Preventing Nitrate Tolerance

Nitrate tolerance develops rapidly with continuous therapy and becomes significant after 24 hours of continuous exposure 1:

• Intermittent patch therapy (10-12 hour application) is superior to continuous therapy for maintaining efficacy 2
• Even with proper dosing, some attenuation of effect may occur over time
• Doses of 0.6-0.8 mg/h (15-20 mg/24h) are usually optimal for most patients 2

Avoiding Rebound Phenomena

• Some patients may experience rebound angina during the nitrate-free interval
• If nocturnal angina occurs, consider:
  • Adjusting the timing of the nitrate-free interval
  • Adding a beta-blocker for the nitrate-free period 1

Contraindications and Precautions

• NTG is contraindicated within 24 hours after sildenafil use, 48 hours after tadalafil, or with hypotension 1
• Avoid in patients with systolic BP <90 mmHg or >30 mmHg below baseline 1
• Use caution in patients with marked bradycardia or tachycardia 1

Special Situations

1. Patients with frequent or nocturnal angina:

   • May benefit from a different nitrate-free interval schedule
   • Consider alternative nitrate formulations if patch therapy is inadequate

2. Patients with poor response:

   • If minimal response to NTG patch, consider returning to oral nitrates or exploring alternative antianginal therapies
   • Patients with large first-dose nitrate responses tend to be less susceptible to tolerance development 2

By following this protocol, you can effectively transition patients from Imdur 15mg daily to an appropriate NTG patch regimen while maintaining efficacy and minimizing adverse effects.