What is the recommended diltiazem dosing protocol (intravenous bolus, continuous infusion, and oral loading/maintenance) for a hemodynamically stable adult with atrial fibrillation and rapid ventricular response, and what are the contraindications?

Diltiazem Administration Protocol for Atrial Fibrillation with Rapid Ventricular Response

For hemodynamically stable adults with atrial fibrillation and rapid ventricular response, administer diltiazem as an initial IV bolus of 0.25 mg/kg (15-20 mg) over 2 minutes, followed by a second bolus of 0.35 mg/kg (20-25 mg) at 15 minutes if needed, then maintain with a continuous infusion of 5-15 mg/hour titrated to heart rate. 1

Initial Intravenous Bolus Dosing

• First bolus: 0.25 mg/kg (typically 15-20 mg) administered IV over 2 minutes 1
• Second bolus: If inadequate response after 15 minutes, give 0.35 mg/kg (typically 20-25 mg) IV over 2 minutes 1, 2
• Onset of action: Expect maximal heart rate reduction within 2-7 minutes, with median time of 4.3 minutes 1, 3
• Success rate: Approximately 75% respond to the first bolus, and 93-94% achieve adequate rate control with one or both boluses 3

Continuous Infusion Protocol

• Initial infusion rate: Start at 5 mg/hour IV 1
• Titration: Increase to 10 mg/hour if inadequate response, then to 15 mg/hour as needed 1
• Titration timing: Assess response and adjust infusion rate every 1-2 hours 4
• Maintenance goal: Titrate to achieve heart rate <100 beats per minute or a >20% reduction from baseline 4, 3
• Duration: Continue infusion until rate control is achieved and transition to oral therapy is appropriate 1

Oral Transition Strategy

After achieving initial rate control with IV therapy, transition to oral diltiazem:

• Oral immediate-release: 30 mg PO may be more effective than continuing IV infusion for sustained rate control 5
• Timing: Consider oral dosing after initial IV bolus achieves rate control, as oral therapy shows lower treatment failure rates (27% vs 46%) compared to continuous IV infusion 5
• Maintenance dosing: Typical oral maintenance is 30-60 mg every 6-8 hours, adjusted based on response 1

Absolute Contraindications

Do not administer diltiazem in the following situations:

• Heart failure with reduced ejection fraction (HFrEF) or decompensated heart failure, as it may precipitate hemodynamic collapse 1, 2
• Pre-excitation syndromes (Wolff-Parkinson-White syndrome), as diltiazem may paradoxically accelerate ventricular response and precipitate ventricular fibrillation 1, 2
• Wide-complex tachycardias or rhythms consistent with ventricular tachycardia 1
• Hemodynamic instability (systolic blood pressure <90 mmHg) 3

Monitoring Requirements

Continuous monitoring is mandatory during diltiazem administration:

• ECG monitoring: Continuous cardiac monitoring throughout bolus and infusion 2
• Blood pressure: Frequent measurements every 5-15 minutes during bolus dosing and hourly during infusion 2, 3
• Heart rate: Monitor for both inadequate response and excessive bradycardia 1

Common Adverse Effects and Management

• Hypotension: Occurs in 18-42% of patients, with 3.2% requiring intervention 2, 6

  • Lower doses (≤0.2 mg/kg) reduce hypotension risk (18%) compared to standard doses (35%) without compromising efficacy 6
  • Most hypotension is asymptomatic and does not require treatment 3

• Bradycardia: Risk increases in elderly patients and those with paroxysmal atrial fibrillation 1, 2

  • Monitor for heart rate <50 beats per minute or symptomatic bradycardia
  • May require dose reduction or discontinuation 1

• Precipitation of heart failure: Negative inotropic effects can worsen heart failure in susceptible patients 1

Dosing Considerations for Efficacy and Safety

Weight-based dosing ≥0.13 mg/kg achieves faster rate control:

• Patients receiving ≥0.13 mg/kg achieve heart rate <100 bpm in mean 169 minutes versus 318 minutes with lower doses 7
• Rate control success: 61% with ≥0.13 mg/kg versus 36% with lower doses 7
• Lower doses (≤0.2 mg/kg) maintain 70.5% efficacy while reducing hypotension risk 6

Clinical Decision Algorithm

1. Confirm hemodynamic stability (systolic BP ≥90 mmHg, no signs of shock)
2. Exclude contraindications (heart failure, pre-excitation, wide-complex rhythm)
3. Administer first bolus (0.25 mg/kg over 2 minutes)
4. Reassess at 15 minutes: If heart rate remains >100 bpm or >20% above baseline, give second bolus (0.35 mg/kg)
5. Initiate continuous infusion at 5 mg/hour if ongoing rate control needed
6. Titrate infusion every 1-2 hours (5→10→15 mg/hour) based on heart rate response
7. Transition to oral therapy once stable rate control achieved 1, 5