What is the dose of diltiazem (calcium channel blocker) for rate control in atrial fibrillation?

Diltiazem Dosing for Rate Control in Atrial Fibrillation

For acute rate control in atrial fibrillation, administer diltiazem 0.25 mg/kg IV bolus over 2 minutes (typically 20 mg for average-weight patients), followed by a second bolus of 0.35 mg/kg (typically 25 mg) after 15 minutes if needed, then initiate continuous infusion at 10 mg/hour, titrating up to 15 mg/hour as needed. 1, 2

Initial IV Bolus Dosing

• First bolus: Administer 0.25 mg/kg actual body weight IV over 2 minutes 1, 2

  • For the average patient, this translates to approximately 20 mg 2
  • Onset of action occurs within 2-7 minutes 1

• Second bolus (if inadequate response): After 15 minutes, administer 0.35 mg/kg actual body weight IV over 2 minutes 1, 2

  • For the average patient, this translates to approximately 25 mg 2
  • Some patients may respond to a lower initial dose of 0.15 mg/kg, though duration of action may be shorter 2

• Low-dose alternative: Evidence suggests that doses ≤0.2 mg/kg may be equally effective while reducing hypotension risk from 35% to 18% compared to standard dosing 3

  • However, doses ≥0.13 mg/kg achieve heart rate control significantly faster (169 minutes vs 318 minutes) without increased hypotension 4

Continuous IV Infusion

• Initial infusion rate: Start at 10 mg/hour immediately following the bolus dose 1, 2

  • Some patients may maintain response at 5 mg/hour 2

• Titration: Increase in 5 mg/hour increments up to a maximum of 15 mg/hour as needed for further heart rate reduction 1, 2

• Duration: Maintain infusion for up to 24 hours maximum 2

  • Infusion durations exceeding 24 hours and rates exceeding 15 mg/hour have not been studied and are not recommended 2

• Pharmacokinetic considerations: Diltiazem exhibits dose-dependent, non-linear pharmacokinetics with decreased systemic clearance at higher infusion rates 5

Target Heart Rate Goals

• Lenient control: <110 bpm at rest 6, 1
• Strict control: <80 bpm at rest 6, 1
• The choice between lenient versus strict control depends on symptom burden and patient tolerance 6

Transition to Oral Maintenance Therapy

• Immediate-release formulation: 120-360 mg daily in divided doses 1

• Extended-release formulation: 180-360 mg once daily 1

  • Administer the first oral dose while the IV infusion is running, then discontinue IV infusion 4 hours after the first oral dose 7
  • 77% of patients maintain heart rate control during this transition 7

Critical Contraindications (Must Screen Before Administration)

• Heart failure with reduced ejection fraction (LVEF ≤40%): Absolute contraindication due to negative inotropic effects 1

  • Use digoxin or amiodarone instead in these patients 1

• Pre-excited atrial fibrillation (Wolff-Parkinson-White syndrome): Absolute contraindication as diltiazem can accelerate conduction through accessory pathways 6, 1

• Severe hypotension: Contraindicated 1

• Second or third-degree AV block without pacemaker: Contraindicated 1

• Decompensated heart failure: Contraindicated 6

Monitoring Requirements

• Continuous monitoring during administration: Heart rate, blood pressure, and symptoms 6, 1
• Expected adverse effects:
  • Hypotension (18-42% depending on dose) 1, 3
  • Bradycardia 1
  • Heart block 1
  • Negative inotropic effects 1

Clinical Pearls and Pitfalls

• Weight-based dosing is essential: Patients with low body weights should be dosed on a mg/kg basis rather than using fixed doses 2

• Combination with beta-blockers: Use with extreme caution due to additive negative inotropic and chronotropic effects 1

• Plasma concentration-response relationship: Plasma diltiazem concentrations of 79,172, and 294 ng/mL are required to produce 20%, 30%, and 40% reductions in heart rate, respectively 5

• Class I recommendation: Diltiazem carries the highest level of evidence (Class I, Level B) for acute rate control in atrial fibrillation 1

Alternative Agents if Diltiazem Contraindicated or Ineffective

• IV beta-blockers: Metoprolol 2.5-5 mg IV bolus over 2 minutes, up to 3 doses 6

• IV verapamil: 0.075-0.15 mg/kg IV bolus over 2 minutes 6

• IV amiodarone: 300 mg IV over 1 hour, then 10-50 mg/hour for critically ill patients without pre-excitation 6