What is the equivalent intravenous (IV) dose of metoprolol tartrate for a patient taking 50 mg of metoprolol tartrate (metoprolol) twice daily (bid) orally?

Metoprolol Tartrate Oral to IV Conversion

When converting a patient from oral metoprolol tartrate 50 mg twice daily to intravenous administration, the equivalent IV dose is 5 mg IV metoprolol tartrate given as a bolus over 2 minutes, which can be repeated up to 3 doses (maximum 15 mg total). 1

Conversion Rationale

The conversion from oral to IV metoprolol is based on the following principles:

• According to the American College of Cardiology, 25 mg oral metoprolol tartrate is equivalent to approximately 5 mg IV metoprolol 1
• This equivalence accounts for the first-pass metabolism and bioavailability differences between oral and IV administration
• For a patient taking 50 mg oral metoprolol tartrate twice daily (100 mg total daily dose), the equivalent single IV dose would be 5-10 mg

Administration Protocol

1. Initial IV Dose: Administer 2.5-5.0 mg IV metoprolol tartrate as a bolus over 2 minutes 2
2. Repeat Dosing: Can repeat 2.5-5.0 mg IV bolus in 10 minutes, up to a maximum of 3 doses (15 mg total) 2
3. Monitoring: Continuously monitor ECG, blood pressure, and heart rate during administration
4. Target Response: Aim for heart rate control (50-60 bpm) unless limiting side effects occur 1

Transitioning Back to Oral Therapy

If the patient needs to return to oral therapy after IV administration:

1. Begin oral metoprolol 15 minutes after the last IV dose
2. Start with 25 mg orally every 6 hours for 48 hours
3. Then transition to the maintenance dose of 50 mg twice daily 1

Precautions and Contraindications

Exercise caution or avoid IV metoprolol in patients with:

• AV block greater than first degree or SA node dysfunction (without pacemaker)
• Decompensated heart failure or cardiogenic shock
• Hypotension
• Reactive airway disease
• Concomitant use of other drugs with SA/AV nodal blocking properties 2

Special Considerations

• For elderly patients (>70 years), consider starting with a lower dose (2.5 mg IV) due to potentially greater variability in drug response 1, 3
• In patients with uncertain tolerance, consider using a shorter-acting beta-blocker like esmolol initially to assess tolerance 1
• If the patient has mild wheezing or history of COPD, a reduced dose (2.5 mg IV) may be considered rather than completely avoiding beta-blockers 1

This conversion approach ensures appropriate dosing while minimizing risks of adverse hemodynamic effects that can occur with IV beta-blocker administration.