What is the initial bolus dose of Cardizem (diltiazem) for atrial fibrillation with rapid ventricular response (AFib RVR)?

Initial Diltiazem Bolus Dosing for Atrial Fibrillation with Rapid Ventricular Response

The initial bolus dose of diltiazem for atrial fibrillation with rapid ventricular response (AFib RVR) should be 0.25 mg/kg administered intravenously over 2 minutes (approximately 20 mg for an average adult). 1

Dosing Protocol

Initial Bolus Administration

• First bolus: 0.25 mg/kg IV over 2 minutes (20 mg for average adult) 1
• If inadequate response after 15 minutes: Second bolus of 0.35 mg/kg IV over 2 minutes (25 mg for average adult) 1
• Low body weight patients: Should be dosed strictly on a mg/kg basis 1

Continuous Infusion (After Bolus)

If continued heart rate control is needed:

• Start infusion at 10 mg/hour immediately following bolus administration 1
• Some patients may respond to 5 mg/hour 1
• Titrate in 5 mg/hour increments up to maximum of 15 mg/hour as needed 1
• Infusion can be maintained for up to 24 hours 1

Efficacy and Safety Considerations

Efficacy

• Approximately 94% of patients respond to the initial bolus dose with either:

  • 20% reduction in heart rate

  • Conversion to sinus rhythm
  • Heart rate <100 beats/min 2

Safety Profile

• Common side effects: Hypotension, heart block, heart failure 3
• Risk factors for hypotension:
  • Higher doses (>0.2 mg/kg) are associated with increased hypotension risk 4
  • Patients with pre-existing ventricular dysfunction 3
  • Patients with hypotension at baseline 3

Alternative Dosing Strategies

Recent research suggests that lower doses may be effective with fewer adverse events:

• Low-dose diltiazem (≤0.2 mg/kg) has shown similar efficacy to standard dosing (0.25 mg/kg) with significantly lower rates of hypotension (18% vs 34.9%) 4
• Some studies indicate that a standard 10 mg dose may be non-inferior to weight-based dosing for initial treatment 5

Contraindications and Precautions

Absolute contraindications:

• AV block greater than first degree or SA node dysfunction (without pacemaker) 3
• Decompensated systolic heart failure/severe LV dysfunction 3
• Hypotension 3
• Wolff-Parkinson-White (WPW) syndrome with AF/atrial flutter 3

Use with caution in:

• Patients taking other medications with SA/AV nodal blocking properties 3
• Patients with renal dysfunction 3

Target Heart Rate

• Goal of rate control: 60-80 bpm at rest and 90-115 bpm during moderate exercise 3
• Heart rate control is generally achieved when ventricular response is between 60-80 bpm at rest 3

Clinical Pearl

When administering diltiazem, strict adherence to protocol is associated with better clinical outcomes and fewer adverse events. One study showed that protocol adherence led to higher rates of clinical improvement (63% vs 46%) and lower rates of adverse events (8% vs 18%) 6.

Remember that while the FDA-approved dose is 0.25 mg/kg, some evidence suggests that lower doses (0.13-0.2 mg/kg) may provide adequate rate control with reduced risk of hypotension in selected patients 4, 7.