What is the equivalent dose of amlodipine for a patient taking diltiazem 240mg?

Dose Conversion from Diltiazem 240mg to Amlodipine

There is no direct milligram-to-milligram dose equivalence between diltiazem 240mg and amlodipine; instead, start amlodipine at 5mg once daily regardless of the diltiazem dose, then titrate based on blood pressure response. 1

Why Direct Conversion Ratios Don't Exist

These are fundamentally different calcium channel blockers with distinct mechanisms:

• Diltiazem is a nondihydropyridine affecting both cardiac tissue and vascular smooth muscle, causing negative chronotropic (heart rate slowing) and inotropic effects 1
• Amlodipine is a dihydropyridine with greater selectivity for peripheral vascular smooth muscle, producing primarily vasodilation without significant direct cardiac effects 1

Recommended Conversion Protocol

Step 1: Discontinue diltiazem and initiate amlodipine at standard starting dose

• Start amlodipine 5mg once daily for most adults 1
• Alternative starting dose of 2.5mg once daily may be considered in elderly or frail patients 1

Step 2: Titrate based on blood pressure response

• If blood pressure remains uncontrolled, increase by 2.5-5mg increments 1
• Maximum dose is 10mg once daily 1
• Allow 1-2 weeks between dose adjustments given amlodipine's long half-life 2

Critical Monitoring During Conversion

Heart rate changes require close attention:

• Expect potential increase in heart rate when switching from diltiazem to amlodipine 1
• Diltiazem causes bradycardia through AV node suppression, while amlodipine may cause reflex tachycardia due to peripheral vasodilation 1
• Monitor heart rate at baseline and after conversion 3, 4

Blood pressure monitoring:

• Both sitting and standing blood pressures should be assessed 3
• 24-hour ambulatory monitoring may be valuable if available, as amlodipine provides smooth blood pressure control throughout the dosing interval 4, 5

Comparative Efficacy Evidence

Research demonstrates amlodipine's superior systolic blood pressure reduction compared to diltiazem:

• In head-to-head trials, amlodipine (5-10mg) reduced sitting systolic BP by 14mm Hg versus 4mm Hg with diltiazem (180-360mg) 3
• Amlodipine achieved significantly greater reductions in 24-hour ambulatory systolic and diastolic pressures compared to diltiazem 3
• Both agents were well-tolerated with comparable dropout rates 3, 4

Common Pitfalls to Avoid

Do not attempt milligram-for-milligram conversion - The pharmacologic profiles are too different to support direct dose equivalence 1

Do not start at maximum amlodipine dose - Even patients on high-dose diltiazem (240-720mg) should start amlodipine at standard doses 6

Watch for peripheral edema - Amlodipine causes more vasodilator side effects including ankle edema compared to diltiazem 4

Monitor for loss of rate control - Patients who required diltiazem's negative chronotropic effects (e.g., atrial fibrillation rate control) will lose this benefit with amlodipine and may need additional rate-controlling agents 1

Special Populations

Pulmonary arterial hypertension context:

• If converting in PAH patients, note that therapeutic doses differ substantially: diltiazem 240-720mg daily versus amlodipine up to 20mg daily 6
• These high doses apply only to vasoreactive IPAH patients and should not be extrapolated to hypertension management 6