What is the maximum dose of metoprolol (Metoprolol XR) for paroxysmal tachycardia?

Maximum Dose of Metoprolol XR for Paroxysmal Tachycardia

The maximum daily dose of metoprolol XR for paroxysmal tachycardia is 400 mg once daily. 1

Dosing Guidelines

Initial Dosing

• Start with 50 mg once daily of metoprolol succinate (XR/extended-release) 1
• For acute management of paroxysmal tachycardia episodes, IV metoprolol can be administered at 5 mg over 1-2 minutes, repeated every 5 minutes to a maximum of 15 mg 1

Dose Titration

• Increase dose gradually based on clinical response
• Maintenance dose range: 50-400 mg once daily 1
• Allow adequate time between dose increases (typically 1-2 weeks) to assess efficacy and tolerability

Mechanism of Action for Tachycardia Control

Metoprolol is a beta-1 selective adrenergic receptor blocker that:

• Reduces effects of circulating catecholamines
• Reduces heart rate and AV node conduction
• Decreases blood pressure
• Acts as a negative inotrope 1

In paroxysmal tachycardia specifically, metoprolol:

• Prolongs AV nodal functional and effective refractory period
• Extends the A-H interval
• Can terminate reentrant tachycardias by disrupting the reentry circuit 2

Clinical Efficacy

Metoprolol has demonstrated effectiveness in:

• Stable, narrow-complex tachycardias uncontrolled by adenosine or vagal maneuvers
• Control of ventricular rate in atrial fibrillation or flutter
• Certain forms of polymorphic VT (associated with acute ischemia, familial LQTS, catecholaminergic) 1

Studies have shown that:

• IV metoprolol can terminate paroxysmal supraventricular tachycardia in approximately 33% of patients 3
• Oral metoprolol at doses of 50-100 mg twice daily has been effective for prophylaxis of recurrent episodes 2, 4

Important Precautions

Avoid metoprolol in patients with:

• AV block greater than first degree or SA node dysfunction (without pacemaker)
• Decompensated systolic heart failure
• Hypotension
• Reactive airway disease/asthma
• Pre-excited atrial fibrillation or flutter 1

Monitoring

When using metoprolol for paroxysmal tachycardia, monitor for:

• Hypotension
• Bradycardia
• Precipitation or worsening of heart failure
• Bronchospasm in susceptible patients 1

Common Pitfalls

1. Abrupt withdrawal: Never discontinue metoprolol abruptly as this can lead to rebound tachycardia and worsening of symptoms

2. Inadequate initial dosing: Starting with too high a dose can lead to hypotension and bradycardia

3. Failure to recognize pre-excitation: Using metoprolol in patients with WPW syndrome and pre-excited atrial fibrillation can be dangerous and is contraindicated 1

4. Overlooking comorbidities: Patients with severe COPD or asthma may experience bronchospasm with metoprolol despite its relative beta-1 selectivity

5. Drug interactions: Be aware of potential interactions with other medications that have SA and/or AV nodal-blocking properties 1

By following these guidelines, metoprolol XR can be safely and effectively used for the management of paroxysmal tachycardia with a maximum daily dose of 400 mg.