What is the typical starting dose of metoprolol (beta blocker) for managing atrial fibrillation?

Metoprolol Dosing for Atrial Fibrillation

For oral rate control in atrial fibrillation, start metoprolol tartrate at 25-50 mg twice daily and titrate up to 200 mg twice daily, or use metoprolol succinate 50-100 mg once daily and titrate up to 400 mg daily based on heart rate response. 1, 2

Acute/Intravenous Dosing

For immediate rate control in the acute setting:

• Administer metoprolol tartrate 2.5-5 mg IV bolus over 2 minutes, which can be repeated every 2 minutes up to 3 total doses 1, 2
• This approach provides rapid ventricular rate control while assessing patient tolerance 1

Oral Maintenance Dosing

Immediate-Release Metoprolol Tartrate

• Start at 25-100 mg twice daily and titrate based on heart rate response 1, 2
• Maximum dose is 200 mg twice daily 1
• Half-life is 3-4 hours, requiring twice-daily dosing for consistent rate control 1

Extended-Release Metoprolol Succinate

• Start at 50-100 mg once daily and titrate up to 400 mg daily 1, 2
• Provides more consistent 24-hour coverage with once-daily dosing 2
• Half-life is 3-7 hours 1

Heart Rate Targets

The target resting heart rate depends on symptom burden:

• Aim for resting heart rate <80 bpm for symptomatic patients (strict control strategy) 2
• A lenient strategy targeting <110 bpm is reasonable for asymptomatic patients with preserved left ventricular function 2
• Monitor heart rate both at rest and during exercise to ensure adequate control throughout daily activities 3, 2

Titration Strategy

When initiating or adjusting metoprolol:

• Start at the lower end of the dosing range (25-50 mg twice daily for immediate-release) 2
• Assess heart rate control during exertion, not just at rest 2
• Titrate upward every 1-2 weeks based on patient response and tolerability 2
• Higher initial heart rates typically require and respond better to higher doses 4

Critical Contraindications and Cautions

Avoid metoprolol in these situations:

• Decompensated heart failure (can worsen acute HF symptoms) 2, 5
• Pre-excited atrial fibrillation (may accelerate ventricular response through the accessory pathway) 2
• Severe bradycardia or high-degree AV block without a pacemaker 3
• Severe asthma or COPD 3

Common Pitfalls

In patients with heart failure with reduced ejection fraction (HFrEF):

• Metoprolol can be used but requires careful dose titration 5
• Aggressive rate control may be difficult to achieve due to patient intolerance of higher beta-blocker doses 6
• Monitor closely for signs of worsening heart failure during titration 3, 5

If inadequate rate control despite maximum tolerated metoprolol:

• Consider adding a non-dihydropyridine calcium channel blocker (diltiazem or verapamil) or digoxin 3
• However, avoid calcium channel blockers in patients with HFrEF 1

Monitoring Parameters

During initiation and dose adjustments, assess:

• Heart rate (both resting and with exertion) 3, 2
• Blood pressure (watch for hypotension) 3
• Symptoms of bradycardia or worsening heart failure 3
• If excessive bradycardia or hypotension occurs, reduce the dose rather than changing timing 3