What dose of metoprolol (beta blocker) should I use for a patient with atrial fibrillation (A Fib) and rapid ventricular response (RVR)?

Metoprolol Dosing for Atrial Fibrillation with Rapid Ventricular Response

For atrial fibrillation with rapid ventricular response, administer metoprolol 5 mg IV over 1-2 minutes, repeated as needed every 5 minutes to a maximum dose of 15 mg, followed by oral maintenance therapy of 25-50 mg twice daily. 1, 2

IV Administration Protocol

• Initial IV dose: 5 mg over 1-2 minutes
• Repeat dosing: May repeat 5 mg every 5 minutes if needed
• Maximum IV dose: 15 mg total
• Transition to oral therapy: Begin oral metoprolol 15 minutes after the last IV dose
  • Start with 25 mg orally every 6 hours for 48 hours
  • Then transition to maintenance dose

Oral Maintenance Therapy

• Initial oral dose: 25-50 mg twice daily
• Titration: Increase dose at 2-week intervals, doubling the dose if:
  • Heart rate remains above target
  • Patient tolerates current dose
• Maximum daily dose: 200 mg (100 mg twice daily)
• Target heart rate: 50-60 beats per minute (a more lenient target of <110 bpm may be reasonable for asymptomatic patients with preserved LV function)

Special Considerations

• Heart failure patients:

  • For HFpEF: Metoprolol is recommended first-line 2
  • For HFrEF: Use IV beta blockers with caution in patients with overt congestion or hypotension 2

• Elderly patients (>70 years): Start with lower doses (12.5-25 mg) 2

• Patients with diabetes: Monitor glucose levels more frequently 2

• Patients with mild to moderate COPD/asthma: Use lower doses of metoprolol (cardioselective agent) 2

Contraindications

Metoprolol is contraindicated in patients with:

• Marked first-degree AV block
• Second or third-degree AV block without pacemaker
• Severe bradycardia
• Hypotension
• Decompensated heart failure
• Cardiogenic shock
• Severe bronchospastic disease
• Wolff-Parkinson-White syndrome (can facilitate antegrade conduction along accessory pathway) 2

Monitoring

• Immediate monitoring: Continuous ECG monitoring, frequent blood pressure checks
• Follow-up: Initial follow-up 2 weeks after starting therapy
• Parameters to monitor: Heart rate, blood pressure, symptom improvement, side effects
• ECG monitoring: At baseline and with significant dose changes

Alternative Agents

If metoprolol is contraindicated or ineffective, consider:

• Diltiazem: 0.25 mg/kg IV over 2 minutes (onset 2-7 minutes) 2
• Esmolol: 500 mcg/kg IV over 1 minute, followed by 60-200 mcg/kg/min infusion 2

Clinical Pearls

• Beta-blockers like metoprolol may be less effective in patients already on chronic beta-blocker therapy, with studies showing lower rate control success (42.4% vs 56.1% in beta-blocker naive patients) 3
• Benefits may develop slowly over 3-6 months, and temporary symptom worsening may occur during initiation 2
• Avoid abrupt discontinuation as this can lead to rebound tachycardia 2
• If rate control is not achieved with a single agent, consider adding a second agent 4