What is the equivalent dose of metoprolol succinate (extended-release formulation) for a patient currently taking metoprolol tartrate (immediate-release formulation)?

Metoprolol Tartrate to Succinate Conversion

When converting from metoprolol tartrate (immediate-release) to metoprolol succinate (extended-release), use the same total daily dose but administer once daily instead of divided doses. 1

Conversion Principle

• A 100-mg metoprolol succinate extended-release tablet contains 95 mg of metoprolol succinate and is considered to have equivalent activity to 100 mg metoprolol tartrate. 2
• The conversion is essentially 1:1 in terms of beta-blocking activity, meaning if a patient takes metoprolol tartrate 50 mg twice daily (100 mg total daily), convert to metoprolol succinate 100 mg once daily. 1

Pharmacokinetic Rationale

• Metoprolol succinate extended-release delivers drug at a near constant rate over approximately 20 hours, producing even plasma concentrations over 24 hours without the marked peaks and troughs seen with immediate-release formulations. 3
• This leads to consistent beta1-blockade over 24 hours while maintaining cardioselectivity at doses up to 200 mg daily. 3
• The extended-release formulation disintegrates into individual pellets, with each pellet acting as a diffusion cell releasing drug at a relatively constant rate. 2

Practical Conversion Examples

• Metoprolol tartrate 25 mg twice daily (50 mg total) → Metoprolol succinate 50 mg once daily 1
• Metoprolol tartrate 50 mg twice daily (100 mg total) → Metoprolol succinate 100 mg once daily 1
• Metoprolol tartrate 100 mg twice daily (200 mg total) → Metoprolol succinate 200 mg once daily 1

Critical Formulation Distinction for Heart Failure

• For heart failure with reduced ejection fraction, ONLY metoprolol succinate CR/XL has proven mortality benefit—metoprolol tartrate showed lesser effectiveness and should NOT be used. 4
• The MERIT-HF trial demonstrated that metoprolol succinate CR/XL reduced all-cause mortality by 34%, sudden death by 41%, and death from progressive heart failure by 49%. 1, 5
• Never substitute metoprolol tartrate for metoprolol succinate in heart failure patients, as only the succinate formulation has mortality benefit. 4

Dosing by Indication

Heart Failure with Reduced Ejection Fraction

• Start metoprolol succinate 12.5-25 mg once daily, titrate every 1-2 weeks to target dose of 200 mg once daily. 1, 4
• Mean dose achieved in clinical trials was 159 mg daily. 1
• This is the ONLY formulation proven to reduce mortality in heart failure—do not use tartrate. 4

Hypertension

• Metoprolol tartrate: 25-100 mg twice daily 1
• Metoprolol succinate: 50-200 mg once daily (maximum 400 mg daily) 6
• These doses are equivalent in terms of beta-blocking activity. 1

Post-Myocardial Infarction

• After initial IV therapy, start metoprolol tartrate 50 mg every 6 hours for 48 hours, then transition to 100 mg twice daily for maintenance. 1

Common Pitfalls to Avoid

• Never abruptly discontinue either formulation—this can precipitate angina, myocardial infarction, ventricular arrhythmias, and has been associated with 50% mortality in one study. 1
• Do not use metoprolol tartrate 50 mg twice daily for heart failure—this was neither the dose nor formulation used in mortality-reducing trials. 1
• Using metoprolol succinate twice daily would be inappropriate dosing that deviates from evidence-based practice. 1
• Do not initiate in patients with decompensated heart failure, marked fluid retention, or requiring IV inotropic therapy. 1

Monitoring During Conversion

• Monitor for symptomatic hypotension (systolic BP <85-100 mmHg), symptomatic bradycardia (HR <50-60 bpm with symptoms), worsening heart failure symptoms, and fluid retention. 1
• Target resting heart rate is 50-60 beats per minute unless limiting side effects occur. 6
• If symptoms worsen, increase diuretics or ACE inhibitors before reducing beta-blocker dose. 1

Contraindications to Check Before Converting

• Signs of heart failure, low output state, or increased risk for cardiogenic shock 1
• PR interval >0.24 seconds, second or third-degree heart block 1
• Active asthma or reactive airways disease 1
• Systolic BP <100 mmHg with symptoms 1