What is the equivalent intravenous (IV) dose of Metoprolol (beta-blocker) for a patient taking 25mg of oral Metoprolol?

Metoprolol Oral to IV Conversion

The equivalent intravenous (IV) dose of metoprolol for a patient taking 25mg of oral metoprolol is 5mg IV administered as a slow bolus over 2 minutes. 1, 2

Conversion Rationale

The conversion from oral to IV metoprolol is based on several key factors:

1. Bioavailability: Oral metoprolol has a bioavailability of approximately 50% due to first-pass metabolism, meaning that IV administration requires a lower dose to achieve equivalent effects 2

2. Guideline-based dosing: According to the 2014 AHA/ACC/HRS guidelines, the standard IV metoprolol dose is 2.5-5.0 mg administered as a slow IV bolus over 2 minutes 1

3. Dose equivalence: For a patient taking 25mg oral metoprolol (which is at the lower end of the usual oral maintenance dose range of 25-100mg BID), a 5mg IV dose would provide comparable beta-blockade 1

Administration Protocol

When converting from oral to IV metoprolol:

• Administer 5mg IV metoprolol as a slow bolus over 2 minutes 1
• Monitor vital signs closely, including continuous ECG monitoring, frequent blood pressure checks, and heart rate assessment 1, 2
• If needed and tolerated, additional doses of 5mg may be given at 5-minute intervals, up to a maximum total dose of 15mg 1, 2
• Target a heart rate of 50-60 beats per minute unless limiting side effects occur 1, 2

Clinical Considerations

Precautions

• Avoid IV metoprolol in patients with:

  • Signs of heart failure or pulmonary edema
  • Significant sinus bradycardia (heart rate <50 bpm)
  • Hypotension (systolic BP <90 mmHg)
  • High-grade AV block
  • Cardiogenic shock 1, 2

• Use with caution in:

  • Elderly patients (>70 years)
  • Patients with systolic BP <120 mmHg
  • Patients with heart rate >110 bpm or <60 bpm 2

Return to Oral Therapy

If the patient tolerates the IV dose and needs to return to oral therapy:

• Begin oral metoprolol 15 minutes after the last IV dose
• Start with 25mg orally every 6 hours for 48 hours
• Then transition to maintenance dose of up to 100mg twice daily 1, 2

Special Populations

• Patients with respiratory conditions: For patients with mild wheezing or history of COPD, consider using a reduced dose (2.5mg IV) rather than completely avoiding beta-blockers 1

• Patients with uncertain tolerance: Consider using a shorter-acting beta-blocker like esmolol initially to assess tolerance before administering metoprolol 1

• Patients with hepatic impairment: Consider dose reduction as metoprolol is primarily metabolized by the liver 2

Remember that IV metoprolol has been shown to be more effective than oral administration in certain clinical scenarios due to more predictable absorption and bioavailability, particularly in post-surgical settings 3.