Dose Equivalent Conversion from Amlodipine to Diltiazem
There is no established equipotent dose conversion between amlodipine and diltiazem because they are fundamentally different calcium channel blockers with distinct mechanisms, pharmacokinetics, and clinical effects—therefore, conversion requires starting diltiazem at standard initial dosing (120 mg daily) and titrating based on blood pressure response rather than using a mathematical equivalence. 1, 2
Why Direct Dose Equivalence Does Not Exist
Amlodipine is a long-acting dihydropyridine that primarily causes peripheral vasodilation with minimal cardiac effects, while diltiazem is a non-dihydropyridine that affects both vascular tone and cardiac conduction (negative chronotropic and inotropic effects). 1
The two agents have completely different pharmacokinetic profiles: amlodipine has a half-life of 30-50 hours allowing true once-daily dosing, whereas diltiazem requires extended-release formulations to achieve 24-hour coverage. 2
Clinical studies directly comparing these agents show amlodipine is more potent for systolic blood pressure reduction at standard doses (amlodipine 5-10 mg vs diltiazem 180-360 mg), but diltiazem provides additional heart rate control. 3, 4
Practical Conversion Strategy
Step 1: Discontinue Amlodipine and Initiate Diltiazem
Start diltiazem extended-release at 120-180 mg once daily regardless of the amlodipine dose, as this is the standard initial dose recommended by the American College of Cardiology. 1, 2
For a patient on amlodipine 10 mg (maximum dose), anticipate needing higher diltiazem doses (240-360 mg daily) to achieve equivalent blood pressure control. 2
Step 2: Titration Protocol
Titrate diltiazem cautiously and progressively over several weeks to reach effective blood pressure control, monitoring at each dose adjustment. 2
The maximum maintenance dose is 360 mg daily for hypertension management. 1, 2
Reassess patients 1 month after initiation or dose change, monitoring for return of elevated blood pressure. 2
Step 3: Monitor for Key Differences
Heart rate reduction will occur with diltiazem but not amlodipine—monitor for excessive bradycardia, especially if baseline heart rate is low. 1, 2
Peripheral edema is dose-related with both agents but more common with amlodipine; patients may experience improvement when switching to diltiazem. 2, 3
Blood pressure and heart rate should be checked at each visit during titration. 2
Critical Contraindications Before Converting
Do not convert to diltiazem if the patient has: 1, 2
- Second- or third-degree AV block without a functioning pacemaker
- Sick sinus syndrome without a pacemaker
- Decompensated systolic heart failure or severe left ventricular dysfunction (ejection fraction <40%)
- Wolff-Parkinson-White syndrome with atrial fibrillation/flutter
- Concurrent beta-blocker therapy (relative contraindication—requires extreme caution due to risk of profound bradycardia and heart block)
Clinical Context Matters
When Diltiazem May Be Preferred Over Amlodipine:
Baseline tachycardia or elevated resting heart rate—diltiazem provides dual benefit of blood pressure and heart rate reduction. 2
Comorbid supraventricular arrhythmias (atrial fibrillation, PSVT)—diltiazem offers rate control. 2, 5
Stable angina with normal left ventricular function—diltiazem reduces myocardial oxygen demand through heart rate reduction. 2
When Amlodipine Should Be Continued Instead:
Heart failure with reduced ejection fraction—amlodipine is safe in this population, whereas diltiazem is contraindicated. 2
Baseline bradycardia (heart rate <60 bpm)—diltiazem will worsen this. 2
Concurrent beta-blocker therapy—the combination with diltiazem significantly increases risk of bradyarrhythmias. 2
Common Pitfalls to Avoid
Do not assume mg-for-mg equivalence—amlodipine 10 mg is not equivalent to diltiazem 10 mg or any simple multiple. 6, 3
Do not combine diltiazem with beta-blockers routinely—this combination carries Class III (Harm) recommendation due to increased risk of significant bradyarrhythmias and heart block. 2
Do not use immediate-release diltiazem for hypertension—extended-release formulations (120-360 mg once daily) are required for 24-hour blood pressure control. 1, 2
Monitor for drug interactions—diltiazem is both a CYP3A4 substrate and moderate inhibitor, requiring dose adjustments of medications like simvastatin, digoxin, and certain anticoagulants. 2