What is the dose of metoprolol (beta-blocker) IV for atrial fibrillation (FIB)?

Metoprolol IV Dosing for Atrial Fibrillation

For atrial fibrillation with rapid ventricular rate, administer metoprolol 5 mg IV over 1 to 2 minutes, repeated every 5 minutes as needed up to a maximum total dose of 15 mg. 1

Initial Dosing Protocol

• Start with 5 mg IV push administered over 1-2 minutes 1
• Repeat 5 mg doses every 5 minutes if arrhythmia persists or recurs 1
• Maximum cumulative dose is 15 mg (three 5 mg doses total) 1

This dosing regimen comes directly from the 2010 American Heart Association ACLS Guidelines and represents the standard approach for acute rate control in atrial fibrillation. 1

Clinical Indications

Metoprolol IV is indicated for:

• Control of ventricular rate in patients with atrial fibrillation or atrial flutter 1
• Stable, narrow-complex tachycardias if rhythm remains uncontrolled or unconverted by adenosine or vagal maneuvers 1

Monitoring Requirements

• Assess heart rate and blood pressure before each dose 2
• Monitor for hypotension (systolic BP <90 mmHg) and bradycardia (HR <50 bpm) 2
• Continuous ECG monitoring is recommended when aggressive rate control is needed 2
• Auscultate for new pulmonary rales indicating heart failure 2

Absolute Contraindications

Do not administer metoprolol IV if any of the following are present:

• Decompensated heart failure or severe left ventricular dysfunction 1, 2
• Hypotension with systolic BP <90 mmHg 1, 2
• Significant bradycardia with HR <50 bpm 1, 2
• Second or third-degree heart block without a functioning pacemaker 2
• Marked first-degree AV block (PR interval >0.24 seconds) 2
• Pre-excited atrial fibrillation or flutter (Wolff-Parkinson-White syndrome) - beta-blockers may paradoxically accelerate ventricular response through the accessory pathway 1, 2
• Active asthma or severe obstructive airway disease 1, 2

Expected Adverse Effects

Common side effects include:

• Hypotension 1
• Bradycardia 1
• Precipitation of heart failure 1

Recent meta-analysis data suggest metoprolol has a 26% lower risk of adverse events (10% total incidence) compared to diltiazem (19% total incidence), though both agents are effective. 3

Efficacy Considerations

• Beta-blocker-naive patients achieve rate control more frequently (56.1%) compared to patients on chronic beta-blocker therapy (42.4%) 4
• Rate control is defined as either ventricular rate <100 bpm or a 20% decrease in heart rate to <120 bpm 4
• Historical data show conversion to sinus rhythm occurs in approximately 12.5% of atrial fibrillation patients, with significant ventricular rate reduction in 50% of those who don't convert 5

Critical Pitfalls to Avoid

• Never combine metoprolol with other AV nodal blocking agents (diltiazem, verapamil, digoxin) that have longer duration of action, as profound bradycardia can develop 2
• Do not use in pre-excited atrial fibrillation - this can accelerate ventricular response and cause hemodynamic collapse 1, 2
• Avoid administering additional doses if signs of hypotension, bradycardia, or heart failure develop 2
• In patients with COPD or asthma history, use cautiously at reduced doses or consider alternative agents 1, 2

Alternative Agents if Metoprolol Contraindicated

• Diltiazem: 15-20 mg (0.25 mg/kg) IV over 2 minutes; may repeat 20-25 mg (0.35 mg/kg) in 15 minutes 1
• Esmolol: 500 mcg/kg (0.5 mg/kg) loading dose over 1 minute, followed by infusion starting at 50 mcg/kg/min 1