What is the equivalent intravenous (IV) dose of metoprolol (Lopressor) for a patient taking 25mg orally (PO)?

Metoprolol PO to IV Conversion

The equivalent intravenous (IV) dose of metoprolol for a patient taking 25mg orally (PO) is 5mg IV.

Dosing Conversion Rationale

Metoprolol conversion from oral to IV requires understanding the differences in bioavailability and potency between the two routes:

• According to multiple guidelines, IV metoprolol is typically administered as 5mg slow IV boluses 1
• The FDA label for metoprolol indicates that after full IV loading (15mg total), patients are typically started on 50mg PO every 6 hours 2
• This suggests an approximate 10:1 ratio when converting from IV to oral dosing

Therefore, for a patient taking 25mg PO metoprolol:

• 25mg PO ÷ 5 = 5mg IV equivalent dose

Administration Guidelines

When administering IV metoprolol:

• Give as a slow IV bolus over 1-2 minutes 1
• Monitor vital signs closely, including:
  • Blood pressure
  • Heart rate
  • ECG monitoring
  • Signs of heart failure

Clinical Considerations

Precautions

• IV metoprolol should be used with caution in patients with:
  • AV block greater than first degree
  • Sinus node dysfunction
  • Decompensated heart failure
  • Hypotension (SBP <90 mmHg)
  • Bradycardia
  • Cardiogenic shock
  • Reactive airway disease 1

Monitoring

• During IV beta-blocker therapy, perform:
  • Frequent checks of heart rate and blood pressure
  • Continuous ECG monitoring
  • Auscultation for rales and bronchospasm 1

Special Populations

• Hepatic impairment: Metoprolol blood levels increase substantially; use lower doses 2
• Elderly patients: Start with lower doses due to decreased hepatic function 2
• Renal impairment: No specific dose adjustment required 2

Common Pitfalls

1. Rapid administration: Administering IV metoprolol too quickly can cause profound hypotension and bradycardia
2. Failure to monitor: Not monitoring vital signs during and after administration
3. Inappropriate use: Using IV metoprolol in contraindicated conditions like cardiogenic shock or severe bradycardia
4. Dose confusion: Assuming 1:1 conversion between oral and IV routes

Remember that IV metoprolol is more potent than oral metoprolol due to bypassing first-pass metabolism, which is why a much lower dose is needed to achieve the same therapeutic effect.