What is the equivalent IV dose of diltiazem (Cardizem) for a 360 mg oral dose?

IV to Oral Diltiazem Conversion for 360 mg Daily Dose

There is no direct mg-to-mg equivalent conversion between IV and oral diltiazem; instead, conversion is based on achieving equivalent steady-state plasma concentrations, where a continuous IV infusion of 11 mg/hour produces plasma levels equivalent to 360 mg total daily oral dose. 1

Pharmacokinetic Basis for Conversion

The FDA label provides specific guidance on this conversion based on pharmacokinetic studies in healthy volunteers 1:

• 3 mg/hour IV infusion = 120 mg total daily oral dose
• 5 mg/hour IV infusion = 180 mg total daily oral dose
• 7 mg/hour IV infusion = 240 mg total daily oral dose
• 11 mg/hour IV infusion = 360 mg total daily oral dose 1

These equivalencies are based on steady-state plasma diltiazem concentrations, not direct dose conversion 1.

Clinical Transition Protocol

When transitioning from IV to oral diltiazem in patients with atrial fibrillation/flutter, administer the first oral dose while the IV infusion is still running, then discontinue the IV infusion 4 hours after the first oral dose. 2

Specific Transition Steps:

• Start oral long-acting diltiazem (diltiazem CD or ER) at the appropriate dose (typically 180-360 mg once daily) 2
• Continue IV infusion for 4 hours after first oral dose 2
• Monitor heart rate closely during the 48-hour transition period 2
• Success rate for maintaining rate control during transition is approximately 77% 2

Important Clinical Considerations

Dosing Differences Between Routes:

The median IV infusion rate in clinical studies was 10 mg/hour, with median oral transition dose of 300 mg/day 2. This aligns with the pharmacokinetic data showing 10 mg/hour IV approximates 300-360 mg oral daily 1.

Patient-Specific Factors:

Patients with atrial fibrillation/flutter have significantly reduced diltiazem clearance (36-42 L/hour) compared to healthy volunteers (48-65 L/hour), requiring careful dose titration. 1, 3

Contraindications Apply to Both Routes:

• Avoid in heart failure with reduced ejection fraction 4
• Contraindicated in second/third-degree AV block without pacemaker 4, 5
• Avoid in hypotension or cardiogenic shock 5, 1
• Contraindicated in WPW syndrome with atrial fibrillation/flutter 6, 5

Monitoring During Transition

• Assess heart rate at 4 hours after discontinuing IV infusion 2
• Continue monitoring for 48 hours during oral therapy stabilization 2
• Target heart rate <100 beats/min or ≥20% reduction from baseline 2
• Watch for hypotension, bradycardia, and worsening heart failure 4