Metoprolol Succinate Conversion from Metoprolol Tartrate 50 mg Every 6 Hours
When converting from metoprolol tartrate 50 mg every 6 hours (200 mg total daily dose) to metoprolol succinate, the equivalent daily dose is 200 mg of metoprolol succinate taken once daily.
Conversion Rationale
Metoprolol comes in two salt forms with different pharmacokinetic properties:
- Metoprolol tartrate (Lopressor): Immediate-release formulation typically dosed multiple times per day
- Metoprolol succinate (Toprol XL): Extended-release formulation designed for once-daily dosing
Dose Equivalence
According to the 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction 1, the conversion between these formulations should maintain the same total daily dose:
- Metoprolol tartrate 50 mg every 6 hours = 200 mg total daily dose
- The equivalent metoprolol succinate dose is 200 mg once daily
The guidelines specifically state: "Metoprolol tartrate 25 to 50 mg every 6 to 12 h orally, then transition over next 2 to 3 d to twice-daily dosing of metoprolol tartrate or to daily metoprolol succinate; titrate to daily dose of 200 mg as tolerated" 1.
Pharmacokinetic Considerations
Metoprolol succinate is designed to provide consistent plasma concentrations over 24 hours:
- The extended-release formulation releases metoprolol at a relatively constant rate over approximately 20 hours
- This provides even beta-1 blockade throughout the day without the peaks and troughs seen with immediate-release formulations
- A 100 mg metoprolol succinate tablet contains 95 mg of metoprolol succinate and is considered equivalent to 100 mg of metoprolol tartrate 2
Clinical Application
The 2022 AHA/ACC/HFSA guideline for heart failure management confirms that the target dose of metoprolol succinate extended release is 200 mg once daily 1. This is consistent across multiple guidelines.
Important Monitoring Considerations
When switching between formulations:
- Monitor for signs of heart failure exacerbation
- Watch for hypotension or bradycardia during the transition
- Assess for adequate heart rate control throughout the day
Potential Pitfalls to Avoid
Confusion between formulations: Metoprolol tartrate and succinate are NOT interchangeable at the same mg-per-mg dose without accounting for frequency.
Dosing frequency errors: Metoprolol succinate should ONLY be administered once daily, while tartrate is typically given 2-4 times daily.
Tablet splitting: Extended-release metoprolol succinate tablets should not be crushed or split as this would destroy the extended-release mechanism.
Abrupt discontinuation: Never abruptly discontinue beta-blockers; always taper to avoid rebound effects.
In summary, when converting from metoprolol tartrate 50 mg every 6 hours to metoprolol succinate, the appropriate dose is 200 mg of metoprolol succinate once daily.