Dose Conversion from Diltiazem to Amlodipine
There is no established equipotent dose conversion ratio between diltiazem and amlodipine, as these calcium channel blockers have different pharmacologic properties and cannot be directly converted on a milligram-to-milligram basis.
Key Pharmacologic Differences
These two calcium channel blockers belong to different subclasses with distinct mechanisms:
- Diltiazem is a nondihydropyridine that affects both cardiac tissue and vascular smooth muscle, causing negative chronotropic and inotropic effects 1
- Amlodipine is a dihydropyridine with greater selectivity for peripheral vascular smooth muscle, producing primarily vasodilation without significant cardiac effects 1
Recommended Conversion Approach
Starting Dose Selection
When switching from diltiazem to amlodipine, initiate amlodipine at standard starting doses regardless of the diltiazem dose 1:
- Adults: Start amlodipine 2.5-5 mg once daily 1, 2
- Pediatrics: Start amlodipine 0.1-0.3 mg/kg/day (maximum 10 mg/day) 1
Titration Strategy
- Uptitrate amlodipine gradually from the starting dose to achieve blood pressure control 1, 2
- Maximum adult dose: 10 mg once daily 1, 2
- Therapeutic range for pulmonary hypertension: up to 20 mg daily 1
- Monitor blood pressure weekly during titration to assess response 3
Clinical Considerations During Conversion
Heart rate monitoring is critical when switching between these agents 1:
- Diltiazem causes bradycardia through AV node suppression 1
- Amlodipine may cause reflex tachycardia due to peripheral vasodilation 4, 5
- Patients with baseline bradycardia on diltiazem may experience heart rate increase after switching to amlodipine 1
Evidence from Comparative Studies
Research comparing these agents demonstrates they are not equipotent:
- In head-to-head trials, amlodipine 5-10 mg once daily showed greater systolic blood pressure reduction than diltiazem 180-360 mg once daily 4
- Amlodipine produced superior antianginal efficacy at mean dose 9.25 mg daily compared to diltiazem 180 mg daily 5
- The rate-pressure product decreased 20.8% with amlodipine versus 13.1% with diltiazem 5
Practical Conversion Algorithm
- Discontinue diltiazem and start amlodipine 5 mg once daily (or 2.5 mg in elderly/hepatic impairment) 1, 2
- Monitor blood pressure at 1-2 week intervals 6, 3
- Titrate amlodipine by 2.5-5 mg increments if blood pressure remains uncontrolled 2, 3
- Anticipate dosage adjustments in approximately 60% of patients during conversion 6
- Watch for peripheral edema, which occurs more frequently with amlodipine than diltiazem 4, 5
Common Pitfalls to Avoid
- Do not attempt milligram-for-milligram conversion - these drugs have different potencies and mechanisms 1, 6
- Do not assume equivalent blood pressure control - additional titration is usually required 6, 3
- Monitor for loss of rate control in patients with atrial fibrillation, as amlodipine lacks the AV nodal blocking effects of diltiazem 1
- Anticipate increased vasodilatory side effects (flushing, headache, peripheral edema) with amlodipine 4, 5