Metoprolol PO to IV Conversion
For patients requiring conversion from oral to IV metoprolol, start with 2.5-5 mg IV bolus over 2 minutes, repeat every 5 minutes as needed based on hemodynamic response, with a maximum total dose of 15 mg—regardless of the previous oral dose. 1, 2, 3
Standard IV Dosing Protocol
The conversion from oral to IV metoprolol does not follow a direct mathematical equivalence. Instead, use a conservative approach:
- Initial dose: Administer 2.5-5 mg IV bolus slowly over 1-2 minutes 1, 2, 3
- Repeat dosing: May repeat every 5 minutes based on clinical response 1, 2, 3
- Maximum total dose: 15 mg (three 5 mg boluses) 1, 2, 3
The FDA label specifies that during the early phase of acute myocardial infarction, three bolus injections of 5 mg each should be given at approximately 2-minute intervals, with continuous monitoring of blood pressure, heart rate, and electrocardiogram. 3
Critical Contraindications Before Administration
Do not administer IV metoprolol if any of the following are present:
- Signs of heart failure, low output state, or decompensated heart failure 1, 2
- Systolic blood pressure <120 mmHg 1, 2
- Heart rate >110 bpm or <60 bpm 1, 2
- Second or third-degree AV block without a functioning pacemaker 1, 2
- PR interval >0.24 seconds 1, 2
- Active asthma or reactive airway disease 1, 2
- Evidence of cardiogenic shock risk (age >70 years, Killip class II-III) 2
Required Monitoring During IV Administration
Parenteral administration must be performed in a setting with intensive monitoring. 3 Specifically monitor:
- Continuous heart rate monitoring throughout administration 2
- Blood pressure checked frequently during and after each bolus 1, 2, 3
- Continuous ECG monitoring to detect conduction abnormalities 2, 3
- Auscultation for rales (pulmonary congestion) 2
- Auscultation for bronchospasm 1, 2
Transition Back to Oral Therapy
After completing IV administration:
- Start oral metoprolol tartrate 15 minutes after the last IV dose 2, 3
- Initial oral dose: 25-50 mg every 6 hours for 48 hours 2, 3
- For patients who tolerated the full 15 mg IV dose, the FDA label recommends 50 mg every 6 hours 3
- For patients with intolerance, use 25 mg every 6 hours or discontinue if severe intolerance occurs 3
- Maintenance dosing: Transition to 100 mg twice daily after the initial 48-hour period 3
Do not transition directly back to extended-release formulations—use immediate-release metoprolol tartrate initially. 2
Why No Direct Conversion Ratio Exists
The pharmacokinetics differ substantially between routes:
- IV metoprolol has 100% bioavailability with immediate onset (1-2 minutes) and duration of 5-8 hours 1
- Oral metoprolol has variable bioavailability (approximately 50% due to first-pass metabolism) with onset of 1 hour and prolonged absorption in acute MI patients 4, 5
- In acute MI patients receiving 15 mg IV followed by oral dosing, plasma concentrations at steady state (823 nmol/L) were substantially higher than after IV alone (248 nmol/L) 4
Common Pitfalls to Avoid
- Never administer the full 15 mg as a single rapid bolus—this significantly increases risk of hypotension and bradycardia 2
- Never give IV metoprolol to patients with decompensated heart failure—the COMMIT trial demonstrated increased cardiogenic shock risk (11 per 1000 patients), particularly in the first 24 hours 2, 6
- Never assume hemodynamic stability—reassess blood pressure and heart rate before each repeat dose 2
- Never skip the monitoring requirements—IV administration requires intensive care setting with continuous monitoring 3
Alternative for High-Risk Patients
For patients at elevated risk of adverse effects from IV metoprolol, consider esmolol instead: