What is the recommended dosing frequency for Lopressor (metoprolol) in atrial fibrillation?

Metoprolol Dosing for Atrial Fibrillation Rate Control

For atrial fibrillation with rapid ventricular response, intravenous 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, 2

IV Administration Protocol

• Initial dose: 2.5-5.0 mg IV bolus over 2 minutes
• Onset of action: Approximately 5 minutes
• Maximum doses: Up to 3 doses may be administered
• Monitoring: Heart rate, blood pressure, ECG during administration
• Target heart rate: 60-80 bpm at rest and 90-115 bpm during moderate exercise

Oral Maintenance Therapy

After IV administration for acute rate control, transition to oral therapy:

• Metoprolol tartrate: 25-100 mg twice daily (BID)
• Metoprolol succinate (extended-release): 50-400 mg once daily (QD)

Dosing Conversion

• When converting from IV to oral metoprolol, use a 10:1 ratio (5 mg IV ≈ 50 mg oral) 2
• When switching between formulations, the total daily dose of tartrate can be administered as a single daily dose of succinate 2

Titration Strategy

1. Starting dose: Begin with 25 mg metoprolol tartrate twice daily
2. Titration: Increase to 50 mg twice daily based on heart rate response
3. Maximum dose: Up to 100 mg twice daily as needed for rate control
4. Monitoring: Check heart rate and blood pressure at each dose adjustment

Contraindications and Precautions

Beta-blockers like metoprolol should not be used in:

• Severe bradycardia
• High-grade AV block (without pacemaker)
• Cardiogenic shock
• Decompensated heart failure
• Pre-excited atrial fibrillation (may accelerate ventricular response) 2

Use with caution in:

• Asthma or COPD
• Compensated heart failure
• Diabetes

Alternative Agents if Metoprolol is Contraindicated

If metoprolol is ineffective or contraindicated, consider:

1. Diltiazem: 0.25 mg/kg IV bolus over 2 min, then 5-15 mg/h infusion 1, 3

   • Note: Low-dose diltiazem (≤0.2 mg/kg) may be as effective with lower risk of hypotension 3

2. Verapamil: 0.075-0.15 mg/kg IV bolus over 2 min 1

3. Esmolol: 500 mcg/kg IV bolus over 1 min, then 50-300 mcg/kg/min 1

Adverse Effects to Monitor

• Hypotension
• Bradycardia
• Heart failure exacerbation
• Bronchospasm

Important Clinical Considerations

• Do not abruptly discontinue metoprolol as this can cause rebound tachycardia 2
• For patients with heart failure, start with lower doses and titrate more gradually 2, 4
• In patients with heart failure and atrial fibrillation, metoprolol has been shown to reduce the incidence of new atrial fibrillation 5
• Metoprolol CR/XL has been shown to be effective in preventing relapse into atrial fibrillation after cardioversion 6

Monitoring Parameters

• Heart rate (target: 60-80 bpm at rest)
• Blood pressure
• Signs/symptoms of heart failure
• ECG for rhythm assessment and AV conduction

Remember that aggressive heart rate control may not always be associated with improved outcomes in patients with both chronic AF and heart failure, so careful titration based on symptoms and tolerance is essential 4.