What is the recommended dosing regimen for converting a patient with Atrial Fibrillation (AFib) and Rapid Ventricular Response (RVR) from inpatient to oral Cardizem (Diltiazem)?

Converting Inpatient to Oral Diltiazem for Atrial Fibrillation with Rapid Ventricular Response

For patients with atrial fibrillation and rapid ventricular response (AFib with RVR) transitioning from intravenous to oral diltiazem, start with oral diltiazem 120-360 mg daily in divided doses, administered 4 hours before discontinuing the IV infusion to ensure continuous rate control.

Dosing Conversion Protocol

Step 1: Establish IV Rate Control

• Ensure adequate rate control is achieved with IV diltiazem before transitioning
• Typical IV diltiazem dosing 1:
  • Initial bolus: 0.25 mg/kg IV over 2 minutes (typically 15-20 mg)
  • Maintenance infusion: 5-15 mg/hour, titrated to heart rate

Step 2: Initiate Oral Therapy

• Begin oral diltiazem 4 hours before discontinuing IV infusion 2
• Initial oral dosing recommendations 1:
  • 120-360 mg daily in divided doses
  • Common starting dose: 30 mg four times daily or equivalent extended-release formulation

Step 3: Determine Appropriate Oral Formulation

• Immediate-release tablets: 30-60 mg 3-4 times daily
• Extended-release formulations: 120-360 mg once daily or 60-180 mg twice daily
• Base selection on:
  1. Patient's response to IV therapy
  2. Maintenance IV infusion rate needed for control
  3. Renal/hepatic function

Step 4: Conversion Formula

• For patients with stable rate control on IV diltiazem, use this guideline 2:
  • IV rate of 5-10 mg/hour → oral diltiazem 240-300 mg/day
  • IV rate of 10-15 mg/hour → oral diltiazem 300-360 mg/day

Monitoring During Transition

• Monitor heart rate and blood pressure every 2-4 hours during transition
• Target heart rate: 60-80 bpm at rest, 90-115 bpm with moderate exercise 1
• Assess for signs of:
  • Inadequate rate control (HR >100 bpm)
  • Hypotension (SBP <90 mmHg)
  • Heart block
  • Heart failure exacerbation

Special Considerations

Heart Failure Patients

• Traditional teaching suggests avoiding diltiazem in heart failure with reduced ejection fraction
• However, recent evidence suggests diltiazem may be as safe as metoprolol in HFrEF patients with similar rate control efficacy 3, 4
• Consider cardiology consultation for patients with severe heart failure

Dosage Adjustments

• For elderly patients: Start with lower doses (e.g., 120-180 mg/day)
• For renal/hepatic impairment: Use lower doses and titrate cautiously 5
• For patients requiring higher doses: Maximum daily dose is typically 360 mg 1

Common Pitfalls to Avoid

1. Abrupt discontinuation of IV therapy: Always overlap oral and IV therapy by at least 4 hours
2. Inadequate oral dosing: Underdosing oral therapy is common and leads to rebound tachycardia
3. Failure to monitor: Regular assessment of heart rate and blood pressure during transition is essential
4. Drug interactions: Be aware of potential interactions with other medications that affect heart rate or blood pressure

Alternative Rate Control Options

If diltiazem is ineffective or contraindicated, consider:

• Beta-blockers (metoprolol, esmolol, propranolol) 1
• Digoxin (particularly in heart failure patients) 1
• Amiodarone (for refractory cases) 1

The transition from IV to oral diltiazem has shown a 77% success rate in maintaining heart rate control when properly executed 2, making it an effective strategy for managing AFib with RVR in the inpatient setting.