Converting Cardizem IR to Cardizem ER
When converting from immediate-release (IR) to extended-release (ER) diltiazem formulations, use the same total daily dose administered once daily with the ER formulation. 1
Conversion Strategy
The conversion is straightforward: calculate the total daily dose of IR diltiazem and administer that same total dose once daily as the ER formulation. 1 For example:
- If a patient takes diltiazem IR 60 mg four times daily (240 mg total daily), convert to diltiazem ER 240 mg once daily 1
- If a patient takes diltiazem IR 90 mg three times daily (270 mg total daily), convert to diltiazem ER 240-300 mg once daily 1
The American College of Cardiology confirms that diltiazem ER formulations are designed for once-daily dosing with a range of 120-360 mg daily, though doses up to 540 mg have been studied safely for hypertension. 1, 2
Key Pharmacokinetic Considerations
Extended-release formulations (CD, ER, SR) provide controlled delivery over 24 hours, maintaining consistent blood levels throughout the day. 1 Research demonstrates that once-daily diltiazem CD is as effective as twice-daily diltiazem SR in lowering blood pressure over 24 hours, with the advantage of improved compliance. 3, 4
The ER formulations maintain normal circadian blood pressure patterns and significantly decrease the slope of early morning blood pressure rise. 4
Dosing Range and Titration
The therapeutic range for diltiazem ER extends from 120-360 mg daily, with 120 mg representing the minimum effective starting dose. 1 However, hypertension typically requires higher doses (up to 360 mg daily) compared to angina (typically 240 mg daily). 1, 2
A critical pitfall is underdosing diltiazem for hypertension. Analysis of FDA data shows a clear linear dose-response relationship through the 480-540 mg/day range, with 90-120 mg/day representing a "no-effect dose." 2 Despite this, over 70% of diltiazem prescriptions for hypertension use 180-240 mg doses, which may be suboptimal. 2
Monitoring After Conversion
After converting to ER formulation, the American College of Cardiology recommends: 1
- Reassess patients in 1 month after conversion
- Monitor blood pressure and heart rate regularly
- Watch for return of symptoms (elevated blood pressure, angina, rapid heart rate)
- Monitor for common adverse effects including hypotension, bradycardia, peripheral edema, and constipation
Peripheral edema is dose-related and more common in women; consider adding diuretics if this occurs. 1
Critical Contraindications to Remember
Before and after conversion, ensure diltiazem remains appropriate. The American Heart Association and American College of Cardiology identify absolute contraindications: 5, 1
- Second or third-degree AV block without a functioning pacemaker
- Sick sinus syndrome without a pacemaker
- Decompensated systolic heart failure or severe LV dysfunction
- Hypotension (systolic BP <90 mmHg)
- Wolff-Parkinson-White syndrome with atrial fibrillation/flutter
Exercise extreme caution when combining diltiazem with beta-blockers due to increased risk of significant bradyarrhythmias and heart failure. 1
Formulation-Specific Considerations
Extended-release capsules cannot be split, crushed, or chewed. 6 If a patient cannot swallow the ER capsule, alternative formulations or medications must be considered.
The once-daily ER formulation improves adherence compared to multiple daily IR doses while maintaining equivalent efficacy and safety profiles. 3, 4