Differences Between Metoprolol Succinate and Metoprolol Tartrate
Metoprolol succinate and metoprolol tartrate differ primarily in their release mechanisms, dosing frequency, and clinical outcomes in heart failure, with metoprolol succinate (extended-release) offering once-daily dosing and proven mortality benefits in heart failure that metoprolol tartrate (immediate-release) has not demonstrated in equivalent clinical trials. 1
Formulation and Pharmacokinetic Differences
Metoprolol succinate is an extended-release/controlled-release formulation designed to provide relatively constant plasma concentrations over approximately 20 hours, allowing for once-daily dosing 2
Metoprolol tartrate is available as an immediate-release formulation that typically requires twice-daily dosing due to its shorter duration of action 3, 4
A 100 mg metoprolol succinate tablet contains 95 mg of the active ingredient and is considered therapeutically equivalent to 100 mg of metoprolol tartrate 2
Metoprolol succinate tablets disintegrate into individual pellets after ingestion, with each pellet acting as a diffusion cell releasing the drug at a relatively constant rate over approximately 20 hours 2, 5
Dosing and Administration
Metoprolol succinate (XL/CR) is administered once daily, typically at doses ranging from 50-200 mg daily 1
Metoprolol tartrate requires twice-daily dosing, typically at doses of 25-100 mg twice daily 1
The extended-release nature of metoprolol succinate offers better patient compliance due to less frequent dosing 2, 5
Clinical Evidence and Outcomes
In heart failure management, only metoprolol succinate has been proven in large randomized controlled trials to reduce mortality in patients with heart failure with reduced ejection fraction (HFrEF) 1
The MERIT-HF trial demonstrated mortality benefits with metoprolol succinate, while similar benefits have not been conclusively shown with metoprolol tartrate in equivalent trials 1, 5
In a direct comparison trial (COMET), carvedilol was associated with significantly reduced mortality compared to immediate-release metoprolol tartrate in heart failure patients 1
It's important to note that the dose and formulation of metoprolol tartrate commonly prescribed for heart failure treatment were neither the dose nor the formulation used in the controlled trials that showed mortality benefits 1
Clinical Applications
Heart Failure: Guidelines specifically recommend metoprolol succinate (not tartrate) as one of three beta-blockers proven to reduce mortality in heart failure patients, along with bisoprolol and carvedilol 1
Hypertension: Both formulations are effective for blood pressure control, but metoprolol succinate offers the advantage of once-daily dosing 1
Atrial Fibrillation: Both formulations can be used for rate control, with metoprolol succinate offering the convenience of once-daily dosing 1
Practical Considerations
When switching between formulations, it's important to note that metoprolol succinate 100 mg once daily is approximately equivalent to metoprolol tartrate 50 mg twice daily 1, 3
Despite the fourfold greater starting dose of metoprolol succinate used in some studies, both formulations produce similar hemodynamic and clinical effects acutely and chronically 3
For patients with heart failure, metoprolol succinate is preferred due to its proven mortality benefits in clinical trials 1
Common Pitfalls
A common mistake is assuming that all metoprolol formulations have equivalent effects on mortality in heart failure patients. Only metoprolol succinate has demonstrated mortality benefits in large clinical trials 1
Prescribers should avoid substituting metoprolol tartrate for metoprolol succinate in heart failure patients, as the evidence for mortality benefit is specific to the succinate formulation 1
When prescribing metoprolol for heart failure, guidelines specifically recommend using one of the three beta-blockers with proven mortality benefits: metoprolol succinate (not tartrate), bisoprolol, or carvedilol 1