What is the dose equivalent of verapamil (calcium channel blocker) for a patient taking diltiazem (calcium channel blocker) 120 mg?

Dose Equivalent Conversion from Diltiazem to Verapamil

When converting from diltiazem 120 mg daily to verapamil, the equivalent dose is verapamil 120 mg daily, as both medications share the same initial starting dose of 120 mg daily according to ACC/AHA guidelines. 1

Direct Dose Equivalence

The 2015 ACC/AHA/HRS guideline provides clear dosing parameters for both nondihydropyridine calcium channel blockers that establish a 1:1 ratio at the initial dosing level: 1

• Diltiazem: Initial dose 120 mg daily → Maximum 360 mg daily 1
• Verapamil: Initial dose 120 mg daily → Maximum 480 mg daily 1

Therefore, a patient taking diltiazem 120 mg should be converted to verapamil 120 mg daily. 1

Important Considerations for Conversion

Potency Differences at Higher Doses

While the initial doses are equivalent, the maximum dosing differs between these agents, suggesting verapamil may have slightly greater potency at higher dose ranges: 1

• Verapamil can be titrated up to 480 mg daily 1, 2
• Diltiazem maximum is 360 mg daily 1, 3

Clinical Evidence Supporting Equivalence

Research comparing these agents in atrial fibrillation demonstrates similar efficacy at the dose ratio being discussed: 4

• Diltiazem 270 mg/day produced comparable ventricular rate control and exercise performance to verapamil 240 mg/day 4
• This suggests roughly equivalent potency on a milligram-per-milligram basis in the therapeutic range 4

Monitoring After Conversion

After switching from diltiazem 120 mg to verapamil 120 mg, monitor for: 1, 2

• Blood pressure and heart rate regularly during the transition 2
• Signs of hypotension (most common adverse effect with both agents) 1, 2
• Bradycardia or conduction abnormalities 1, 2
• Worsening heart failure in patients with pre-existing ventricular dysfunction 1, 2

Critical Drug Interaction Differences

Verapamil has more extensive drug interactions than diltiazem and is contraindicated with dofetilide. 1

• Verapamil is a moderate CYP3A4 inhibitor and also inhibits P-glycoprotein 1
• Verapamil affects levels of dabigatran, edoxaban, rivaroxaban, flecainide, simvastatin, and many other medications 1
• Review the patient's medication list carefully before conversion, as verapamil may require dose adjustments of concomitant medications 1

Contraindications Remain Similar

Both agents share the same contraindications: 1, 2

• AV block greater than first degree or SA node dysfunction (without pacemaker) 1
• Decompensated systolic heart failure or severe LV dysfunction 1
• Hypotension 1
• Wolff-Parkinson-White syndrome with atrial fibrillation/flutter 1