What is the recommended oral dose of Cardizem (diltiazem) when converting from intravenous (IV) to oral therapy?

IV to Oral Diltiazem Conversion

When converting from IV to oral diltiazem, administer oral diltiazem CD 180-360 mg once daily (typically 300 mg) and discontinue the IV infusion 4 hours after the first oral dose. 1, 2

Conversion Protocol

The standard conversion approach involves:

• Administer the first dose of oral diltiazem CD while the patient is still on IV infusion 2
• Discontinue IV diltiazem 4 hours after the first oral dose 2
• Monitor heart rate closely during the 48-hour transition period 2

Dosing Equivalence

The median IV infusion rate of 10 mg/hour corresponds to an oral diltiazem CD dose of 300 mg/day 2

• Oral diltiazem CD dosing range: 180-360 mg once daily 1, 2
• Most patients require 300 mg/day for adequate rate control 2
• The 77% success rate for maintaining heart rate control during transition supports this dosing strategy 2

Monitoring Requirements During Transition

Monitor the following parameters during the 48-hour transition period:

• Heart rate should remain <100 beats/min or show ≥20% reduction from baseline 2
• Blood pressure for hypotension (most common adverse effect) 1
• Signs of bradycardia or heart block 1
• Symptoms of worsening heart failure in at-risk patients 1, 3

Critical Contraindications to Verify Before Conversion

Do not convert to oral diltiazem if any of the following are present:

• Second or third-degree AV block without a functioning pacemaker 1, 3
• Decompensated systolic heart failure or severe LV dysfunction 1, 3
• Cardiogenic shock 1, 3
• WPW syndrome with atrial fibrillation/flutter 1, 3
• Symptomatic hypotension 1, 3

Common Pitfalls to Avoid

Avoid combining diltiazem with beta-blockers during transition due to risk of significant bradyarrhythmias and heart failure 3

• If beta-blockers are necessary, use extreme caution and close monitoring 3
• The combination increases risk of profound bradycardia given the longer half-life of both agents 1

Do not use diltiazem in patients with PR interval >0.24 seconds 1, 3

Adjust dosing in hepatic or renal dysfunction, as diltiazem is metabolized by the liver and may require dose adjustment in renal impairment 1, 3

Alternative Dosing Considerations

If the patient was on a higher IV infusion rate (>10 mg/hour), consider starting with diltiazem CD 360 mg/day 1, 2

For patients requiring divided dosing, immediate-release diltiazem 30-90 mg every 6-8 hours can be used instead of once-daily formulations 3, 4

• Immediate-release oral diltiazem may actually have lower treatment failure rates than IV continuous infusion in some ED studies 4
• The median dose of immediate-release diltiazem at 4 hours was 30 mg 4

Drug Interactions During Transition

Diltiazem is a CYP3A4 substrate and moderate inhibitor—use caution with:

• Apixaban, itraconazole, bosutinib, ceritinib, cilostazol, cyclosporine, everolimus, ibrutinib, idelalisib, ivabradine, lomitapide, olaparib, ranolazine, rifampin, simeprevir 1, 3