Verapamil Equivalent Dose for Diltiazem 120 mg ER
For a patient taking diltiazem 120 mg ER, the equivalent dose of verapamil is 120 mg daily, using a 1:1 conversion ratio at the initial dosing level. 1
Direct Dose Conversion
- The ACC/AHA guidelines recommend a 1:1 ratio when converting from diltiazem to verapamil at the starting dose of 120 mg daily. 1
- Both diltiazem ER and verapamil SR share the same initial dose of 120 mg daily and can be administered once daily with extended-release formulations. 2
- The FDA-approved dosing for verapamil extended-release starts at 120-180 mg daily, with lower initial doses of 120 mg warranted in elderly patients or smaller individuals who may have increased drug response. 3
Titration Potential Differences
- While the initial doses are equivalent, verapamil can be titrated up to a maximum of 480 mg daily, whereas diltiazem maximum is 360 mg daily, suggesting verapamil may have slightly greater potency at higher dose ranges. 2, 1
- If your patient eventually requires dose escalation beyond 360 mg daily equivalent, verapamil offers more flexibility with its higher maximum dose. 1
Critical Monitoring After Conversion
- Monitor blood pressure and heart rate regularly during the first 1-2 weeks after switching, watching specifically for hypotension (the most common adverse effect), bradycardia, or conduction abnormalities. 4, 1
- Watch for signs of worsening heart failure in patients with pre-existing ventricular dysfunction, as this is a known side effect of verapamil. 4, 1
Important Drug Interaction Differences
- Verapamil has more extensive drug interactions than diltiazem because it is both a moderate CYP3A4 inhibitor and a P-glycoprotein inhibitor. 1
- Carefully review the patient's medication list before conversion, paying particular attention to: dabigatran, edoxaban, rivaroxaban, flecainide, and simvastatin, as verapamil will increase levels of these medications. 2, 1
- Both diltiazem and verapamil are CYP3A4 substrates and inhibitors, but verapamil's P-glycoprotein inhibition creates additional interaction concerns. 2
Shared Contraindications
- Both agents are contraindicated in: AV block greater than first degree or SA node dysfunction (without pacemaker), decompensated systolic heart failure or severe LV dysfunction, hypotension, Wolff-Parkinson-White syndrome with atrial fibrillation/flutter, and cardiogenic shock. 4, 1
- Avoid routine use with beta blockers due to increased risk of bradycardia and heart block. 2