Metoprolol Succinate to Tartrate Conversion
For a patient taking metoprolol succinate 37.5 mg twice daily (75 mg total daily), the equivalent metoprolol tartrate dose is 75 mg total daily, typically given as 37.5 mg twice daily or 25 mg three times daily.
Conversion Rationale
The FDA labeling establishes that metoprolol succinate and metoprolol tartrate are dose-equivalent on a milligram-per-milligram basis when comparing total daily doses 1, 2. The key difference lies in the formulation and dosing frequency, not in the total daily amount required.
Specific Conversion Details
- Current regimen: Metoprolol succinate 37.5 mg twice daily = 75 mg total daily
- Equivalent tartrate dose: 75 mg total daily
Practical Dosing Options for Tartrate
Given that metoprolol tartrate requires more frequent dosing due to its immediate-release formulation 2:
- Option 1: 37.5 mg twice daily (if 37.5 mg tablets available)
- Option 2: 25 mg three times daily (more standard dosing interval)
- Option 3: 50 mg in morning + 25 mg in evening
Important Pharmacokinetic Considerations
The succinate formulation delivers metoprolol at a near-constant rate over approximately 20 hours, producing even plasma concentrations without marked peaks and troughs 3. In contrast, the tartrate formulation produces higher peak levels and lower trough levels 4. Research demonstrates that metoprolol IR 50 mg produces peak plasma levels comparable to CR/XL 200 mg, despite the lower total dose 4.
Critical caveat: While the total daily dose equivalence is 1:1, the immediate-release tartrate formulation may not maintain full beta-blockade at the end of a 24-hour period with twice-daily dosing 2. This is why three-times-daily dosing is often preferred for tartrate, particularly at lower total daily doses like 75 mg.
Clinical Monitoring After Conversion
After switching formulations, monitor for:
- Blood pressure control at trough (just before next dose)
- Heart rate variability throughout the day
- Symptom breakthrough, particularly in the late afternoon/evening with twice-daily tartrate dosing
The FDA label specifically notes that lower doses of tartrate "may not maintain a full effect at the end of the 24-hour period" with once or twice daily dosing 2, making three-times-daily administration more reliable for maintaining consistent beta-blockade with this total daily dose.