What is the dosing for Lopressor (metoprolol) in a patient with atrial fibrillation and rapid ventricular response (RVR)?

Metoprolol Dosing for Atrial Fibrillation with Rapid Ventricular Response

For atrial fibrillation with rapid ventricular response (RVR), metoprolol tartrate should be administered at 2.5-5.0 mg IV bolus over 2 minutes, which can be repeated up to 3 doses, followed by oral maintenance dosing of 25-100 mg twice daily. 1

Intravenous Dosing for Acute Management

• Initial IV dose: 2.5-5.0 mg IV bolus over 2 minutes
• Maximum IV dosing: May repeat up to 3 doses (total of 15 mg) if needed for rate control
• Onset of action: Approximately 5 minutes 1
• Target heart rate: 60-80 bpm at rest and 90-115 bpm during moderate exercise 1

Oral Maintenance Dosing

After IV administration and stabilization:

• Starting dose: 25 mg twice daily of metoprolol tartrate
• Titration: Can increase to 50 mg twice daily based on heart rate response
• Maximum dose: 100 mg twice daily 1, 2
• Alternative formulation: Metoprolol succinate (extended-release) 50-400 mg once daily 1

Efficacy Considerations

Metoprolol has been shown to be effective for rate control in AF with RVR, with several studies showing:

• Similar efficacy to diltiazem in achieving rate control within 30 minutes 3, 4
• Potentially lower failure rates compared to amiodarone 5
• Effective sustained rate control in most patients (78.9% in one study) 6

Important Monitoring Parameters

• Heart rate: Target 60-80 bpm at rest, 90-115 bpm with moderate exercise
• Blood pressure: Monitor for hypotension
• Cardiac rhythm: Assess for bradycardia or heart block
• Respiratory status: Watch for signs of bronchospasm, especially in patients with pulmonary disease

Contraindications and Precautions

• Absolute contraindications: Severe bradycardia, high-grade AV block (without pacemaker), cardiogenic shock, decompensated heart failure 2
• Use with caution: Asthma or COPD, compensated heart failure, diabetes (may mask hypoglycemia symptoms)
• Avoid in: Pre-excited atrial fibrillation (may accelerate ventricular response) 1

Special Considerations

1. Heart failure patients:

   • Metoprolol can be used in compensated heart failure
   • Start at lower doses and titrate more gradually
   • Monitor closely for signs of decompensation 2

2. Conversion from IV to oral dosing:

   • Use a 10:1 ratio (5 mg IV ≈ 50 mg oral) 2
   • Begin oral therapy as soon as the patient is stabilized

3. Alternative agents if metoprolol is contraindicated or ineffective:

   • Diltiazem: 0.25 mg/kg IV bolus over 2 min, then 5-15 mg/h infusion 1
   • Esmolol: 500 mcg/kg IV bolus over 1 min, then 50-300 mcg/kg/min 1
   • Verapamil: 0.075-0.15 mg/kg IV bolus over 2 min 1

Practical Algorithm for Management

1. Confirm diagnosis of AF with RVR (typically heart rate >120 bpm)
2. Assess hemodynamic stability:
   • If unstable: Consider immediate electrical cardioversion
   • If stable: Proceed with pharmacologic rate control
3. Administer metoprolol: 2.5-5.0 mg IV over 2 minutes
4. Reassess in 5 minutes:
   • If inadequate response: Repeat dose (up to 3 doses total)
   • If adequate response: Monitor and prepare for oral therapy
5. Transition to oral therapy: Start metoprolol tartrate 25-50 mg twice daily
6. Titrate dose based on heart rate response over subsequent days

Metoprolol is a first-line agent for AF with RVR due to its efficacy, safety profile, and Class I recommendation from major cardiology societies 1.