What is the equivalent intravenous (IV) dose of metoprolol for a patient taking 50mg orally (PO)?

Metoprolol PO to IV Conversion

The equivalent intravenous (IV) dose of metoprolol for a patient taking 50 mg orally (PO) is 15 mg IV, administered as three 5-mg boluses given 5 minutes apart.

Conversion Rationale

The conversion from oral to IV metoprolol is not a simple 1:1 ratio due to differences in bioavailability and first-pass metabolism. According to the ACC/AHA guidelines, the standard approach for IV metoprolol administration is:

• Administer three 5-mg boluses (total 15 mg IV)
• Give each bolus by slow IV administration over 1-2 minutes
• Space each bolus approximately 5 minutes apart
• Monitor vital signs between doses 1

This 15 mg IV dose is considered equivalent to an oral dose of 50 mg, as evidenced by the recommended transition from IV to oral therapy in the FDA drug label 2.

Administration Protocol

IV Administration

1. Initial dosing: Administer 5 mg IV over 1-2 minutes
2. Monitoring: Check heart rate, blood pressure, and ECG
3. Subsequent doses: Give second 5 mg bolus after 5 minutes if tolerated
4. Final dose: Give third 5 mg bolus after another 5 minutes if tolerated
5. Total IV dose: 15 mg

Transition to Oral Therapy

• After completing the IV regimen (15 mg total), oral therapy can be initiated 15 minutes after the last IV dose
• Begin with 50 mg PO every 6 hours for 48 hours
• Then transition to maintenance dose of 100 mg twice daily 1, 2

Monitoring Requirements

During IV metoprolol administration, the following monitoring is essential:

• Continuous ECG monitoring
• Frequent blood pressure checks
• Heart rate monitoring
• Auscultation for rales and bronchospasm 1

Important Considerations and Contraindications

Contraindications to IV Beta-Blocker Therapy

• Marked first-degree AV block (PR interval >0.24 sec)
• Second or third-degree AV block without functioning pacemaker
• History of asthma
• Severe left ventricular dysfunction or heart failure
• High risk for cardiogenic shock
• Evidence of low-output state (oliguria)
• Sinus tachycardia reflecting low stroke volume
• Significant bradycardia (HR <50 bpm)
• Hypotension (SBP <90 mmHg) 1

Special Populations

• Patients with COPD/asthma: Use with extreme caution; consider lower doses
• Elderly patients: Start with lower doses due to potential for decreased hepatic, renal, or cardiac function
• Hepatic impairment: Lower doses may be required due to reduced clearance 2

Clinical Pearls

• The bioavailability of oral metoprolol is lower than IV administration due to first-pass metabolism, which is why a higher oral dose (50 mg) is needed to achieve the same effect as the IV dose (15 mg) 3
• Patients with acute myocardial infarction may have reduced metoprolol clearance, potentially requiring dose adjustment 4
• Always have resuscitation equipment readily available when administering IV beta-blockers

This conversion protocol is based on established guidelines and is designed to maintain therapeutic efficacy while minimizing risks associated with IV beta-blocker administration.