What is the equivalent intravenous (IV) dose of Lopressor (metoprolol tartrate) for a patient taking metoprolol succinate 75mg orally?

Oral to IV Metoprolol Conversion

There is no direct dose equivalency for converting metoprolol succinate 75mg oral to IV metoprolol tartrate; instead, IV metoprolol should be dosed based on clinical indication using standard protocols, typically starting with 5mg IV boluses up to a maximum of 15mg total. 1, 2

Key Principles for Conversion

Why Direct Conversion Is Not Appropriate

• Metoprolol succinate (extended-release) and metoprolol tartrate (IV formulation) are different salts with different pharmacokinetics - succinate provides sustained release over 20 hours while IV tartrate has immediate effect 3
• The FDA-approved IV dosing protocol does not use oral-to-IV conversion ratios but rather employs indication-based dosing regardless of prior oral dose 2
• IV metoprolol has significantly higher bioavailability than oral formulations, making direct dose conversion inappropriate and potentially dangerous 2

Standard IV Dosing Protocol

Acute Administration Guidelines

• For acute indications (supraventricular tachycardia, acute MI, or urgent rate control), administer 5mg IV over 1-2 minutes 1
• Repeat 5mg boluses every 5 minutes as needed, monitoring heart rate and blood pressure response 1
• Maximum total IV dose is 15mg (three 5mg boluses) 1, 2
• After IV administration, oral therapy can be initiated 15 minutes after the last IV dose at 25-50mg every 6 hours for 48 hours 1

Critical Monitoring Requirements

• Perform continuous ECG monitoring, frequent blood pressure and heart rate checks during IV administration 1, 2
• Auscultate for rales and bronchospasm during IV therapy 1
• IV metoprolol must be administered in a setting with intensive monitoring capabilities 2

Absolute Contraindications to IV Metoprolol

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
• Increased risk for cardiogenic shock (age >70 years, systolic BP <120 mmHg, sinus tachycardia >110 bpm or heart rate <60 bpm) 1
• PR interval >0.24 seconds, second or third-degree heart block without functioning pacemaker 1
• Active asthma or reactive airways disease 1
• Hypotension or evidence of low-output state 1

Common Clinical Pitfalls

• Never calculate an "equivalent" IV dose based on the oral dose - this approach is not supported by guidelines and risks serious adverse events 1, 2
• Do not assume the patient needs IV metoprolol simply because they were on oral therapy - IV administration is reserved for acute indications requiring immediate beta-blockade 2
• Avoid IV metoprolol in patients with pre-excitation and atrial fibrillation 1
• The COMMIT trial demonstrated that early IV metoprolol in acute MI patients increased risk of cardiogenic shock, particularly in high-risk patients 1

Transitioning Back to Oral Therapy

• After completing IV protocol, resume oral metoprolol 15 minutes after the last IV dose 1, 2
• For patients who tolerated full IV dose (15mg), start metoprolol tartrate 50mg every 6 hours for 48 hours 2
• For patients with intolerance to full IV dose, start 25-50mg every 6 hours depending on degree of intolerance 2
• Can transition back to metoprolol succinate extended-release formulation once stabilized, typically at equivalent or higher daily dose given once daily 4