Isordil (Isosorbide Dinitrate) Dosage for Angina
Start with 5-20 mg two to three times daily, then titrate to a maintenance dose of 10-40 mg two to three times daily, ensuring at least a 14-hour nitrate-free interval each day to prevent tolerance. 1
Initial Dosing Strategy
- Begin therapy with 5-20 mg of isosorbide dinitrate administered two or three times daily 1
- The FDA label emphasizes using the minimum effective dose that produces desired clinical effect 1
- Some patients may require higher doses during titration 1
Maintenance Therapy
- The standard maintenance regimen is 10-40 mg administered two or three times daily 1
- An asymmetric three-times-daily schedule (such as 7 AM, 1 PM, and 6 PM) provides approximately 6 hours of antianginal prophylaxis per day while minimizing tolerance 2, 3
- Research demonstrates that doses of 15-30 mg produce near-maximal improvement in exercise tolerance, with higher doses (60-120 mg) offering no additional benefit 4
Critical Tolerance Management
You must provide at least a 14-hour daily nitrate-free interval to prevent refractory tolerance 1
- Continuous 24-hour plasma levels result in rapid tolerance development, making the medication ineffective 1
- No dosing regimen should be expected to provide more than 12 hours of continuous anti-anginal efficacy per day 1
- The optimal nitrate-free interval varies by patient but must be at least 14 hours 1
- Tolerance develops rapidly with higher doses (50 mg three times daily) and more frequent dosing schedules 5, 4
Practical Dosing Schedules
- Three times daily regimen: Administer at 8 AM, 1 PM, and 6 PM to provide daytime coverage with overnight nitrate-free interval 2
- This asymmetric schedule allows the 14-hour nitrate-free period from 6 PM to 8 AM 2
- After the first morning dose, antianginal effects peak at 1 hour but may return to baseline by 3 hours, necessitating the midday dose 2
Important Safety Contraindications
- Do not use within 24 hours of sildenafil or 48 hours of tadalafil due to risk of life-threatening hypotension 6
- Avoid in systolic blood pressure <90 mmHg or >30 mmHg below baseline 7
- Use extreme caution in right ventricular infarction, as these patients depend critically on preload 6
- Contraindicated with marked bradycardia or tachycardia 7
Common Pitfall to Avoid
The most critical error is prescribing four-times-daily or continuous dosing without adequate nitrate-free intervals 4, 3. Studies consistently show that symmetric dosing (every 6 hours) or four-times-daily regimens produce marked tolerance, reducing both the magnitude and duration of antianginal effects compared to the initial dose 4, 3. This renders the medication essentially ineffective for long-term management.