Diltiazem ER Dosing Frequency
Yes, diltiazem extended-release (ER) can be taken twice daily, but the specific formulation matters—some ER products are designed for once-daily dosing while others require twice-daily administration. 1
Understanding Diltiazem ER Formulations
The term "extended-release" encompasses multiple delivery systems with different dosing schedules:
- Once-daily formulations (e.g., Cardizem CD, Dilacor XR) are designed to maintain therapeutic blood levels over 24 hours and should be dosed once daily at 120-540 mg 1, 2
- Slow-release formulations are available for divided dosing at 120-360 mg daily in 2-3 divided doses, meaning twice-daily administration is appropriate for these products 1
- The capsule formulation is typically dosed twice daily to three times daily, while extended-release tablets are dosed once daily 3
Clinical Evidence on Dosing Frequency
A 1991 study directly comparing once-daily versus twice-daily administration of slow-release diltiazem found that twice-daily dosing was significantly more effective at lowering blood pressure, particularly at higher doses. 4 In the subgroup receiving maximum doses, blood pressure levels were significantly lower with twice-daily treatment compared to once-daily administration of the same total daily dose.
However, a 1995 study demonstrated that the once-daily CD formulation was as effective as twice-daily SR formulation in lowering blood pressure over 24 hours, with the advantage of better compliance. 5 This highlights that the formulation's drug delivery system—not just the "ER" label—determines appropriate dosing frequency.
Practical Prescribing Guidance
When prescribing diltiazem ER:
- Verify the specific product name and formulation before determining dosing frequency 1
- Once-daily CD formulations start at 120-180 mg once daily and can be titrated to a maximum of 360-420 mg daily 1
- If using a slow-release formulation designed for divided dosing, twice-daily administration is appropriate and may provide superior blood pressure control 4
- Never split, crush, or open extended-release capsules, as this destroys the controlled-release mechanism 6
Critical Safety Considerations
Before prescribing any diltiazem formulation, regardless of dosing frequency:
- Absolutely contraindicated in second- or third-degree AV block without a pacemaker, sick sinus syndrome without a pacemaker, decompensated systolic heart failure or severe LV dysfunction, hypotension, and Wolff-Parkinson-White syndrome with atrial fibrillation/flutter 1
- Exercise extreme caution when combining with beta-blockers due to increased risk of significant bradyarrhythmias, profound AV block, and heart failure 1
- Monitor blood pressure and heart rate regularly during dose titration 1
Common Pitfall
The most frequent error is assuming all "ER" or "extended-release" diltiazem products have identical dosing schedules. Always check the specific product labeling—some ER formulations are engineered for once-daily dosing while others require twice-daily administration for optimal efficacy. 1, 4