What is the equivalent intravenous (IV) dose and frequency of metoprolol (beta-blocker) for a patient taking 100 mg metoprolol XL (extended-release) twice daily (bid)?

IV Metoprolol Dosing for Patients on 100 mg Metoprolol XL BID

For a patient taking 100 mg metoprolol XL (extended-release) twice daily who requires IV conversion, administer 5 mg IV bolus over 1-2 minutes, repeated every 5 minutes as needed based on hemodynamic response, with a maximum total dose of 15 mg (three 5 mg boluses). 1, 2

Critical Point: Do Not Attempt Mathematical Conversion

The key principle is that you cannot directly convert oral extended-release metoprolol to IV metoprolol using a mathematical formula. 1 Instead, use the standard IV dosing protocol regardless of the patient's oral dose, titrating based on clinical response rather than attempting equivalency calculations. 1

Standard IV Dosing Protocol

Initial Administration

• Start with 5 mg IV bolus administered slowly over 1-2 minutes 1, 2
• Repeat every 5 minutes as needed based on heart rate and blood pressure response 1, 2
• Maximum total dose is 15 mg (three 5 mg boluses) 1, 2

Required Monitoring During IV Administration

• Continuous heart rate monitoring 1
• Blood pressure monitoring with each dose 1, 2
• Continuous ECG monitoring 1
• Auscultation for new rales (pulmonary congestion) 1
• Auscultation for bronchospasm 1

Absolute Contraindications Before IV 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
• Heart rate >110 bpm or <60 bpm 1
• PR interval >0.24 seconds 1
• Second or third-degree heart block 1, 2
• Active asthma or reactive airway disease 1, 2
• Evidence of cardiogenic shock risk (age >70, Killip class II-III) 1

Transition Back to Oral Therapy

Timing and Dosing

• Begin oral metoprolol tartrate (immediate-release) 15 minutes after the last IV dose 1, 2
• Initial oral dose: 25-50 mg every 6 hours for 48 hours 1, 2
• Do not return directly to extended-release formulation immediately 1

Rationale for Immediate-Release First

The FDA label and ACC/AHA guidelines recommend transitioning to immediate-release metoprolol tartrate first rather than returning directly to the extended-release formulation, allowing for more precise titration and monitoring in the acute setting. 1, 2

Common Pitfalls to Avoid

• Never give the full 15 mg as a single rapid bolus - this significantly increases risk of hypotension and bradycardia 1
• Do not use the patient's home dose of 200 mg/day total to calculate IV equivalency - there is no reliable conversion ratio 1
• Avoid IV metoprolol in decompensated heart failure - wait until clinical stabilization 1
• Do not combine with other AV nodal blocking agents during acute administration - risk of profound bradycardia 1

Alternative for High-Risk Patients

For patients at high risk of complications (elderly, borderline blood pressure, multiple comorbidities), consider esmolol instead of IV metoprolol with a maintenance infusion of 50-300 mcg/kg/min, as it allows for rapid titration and has a shorter duration of action. 1

Why This Approach?

The bioavailability and pharmacokinetics of oral extended-release metoprolol differ substantially from IV administration. Oral metoprolol XL has approximately 50-80% bioavailability with extended absorption over 24 hours, while IV metoprolol has 100% bioavailability with immediate effect. 3, 4 The standard IV protocol of 5 mg boluses up to 15 mg total has been validated in clinical trials and provides adequate beta-blockade regardless of prior oral dosing. 1, 2