Metoprolol succinate vs tartrate pharmacokinetics
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Pharmacokinetic Differences: Metoprolol Succinate vs Tartrate
Metoprolol is available in two main salt forms: metoprolol succinate and metoprolol tartrate. The key pharmacokinetic difference between these forms lies in their release profiles and dosing schedules. Metoprolol succinate is formulated as an extended-release (ER) or controlled-release (CR) tablet, designed for once-daily dosing, while metoprolol tartrate is an immediate-release (IR) formulation, typically taken twice daily 1246.
Absorption and Plasma Concentration Profiles
Metoprolol succinate (CR/ER) provides a steady, almost constant release of the drug over 24 hours, resulting in more stable plasma concentrations with lower peaks and higher troughs compared to the immediate-release tartrate form. This means that metoprolol succinate avoids the sharp rises and falls in drug levels seen with metoprolol tartrate, which can lead to more consistent therapeutic effects throughout the day 146.
In contrast, metoprolol tartrate produces higher peak plasma concentrations shortly after dosing, followed by a more rapid decline, which can result in fluctuations in drug effect and potentially more side effects related to peak concentrations 14.
Systemic Availability and Efficacy
Although the controlled-release succinate formulation shows lower overall systemic availability compared to the immediate-release tartrate, the total therapeutic effect over the dosing interval (measured as area under the efficacy curve) is similar for both forms when dosed appropriately . The extended-release succinate formulation is more efficient in maintaining effective plasma concentrations, especially at the end of the dosing interval, which is beneficial for conditions requiring constant β1-blockade 146.
Clinical Implications and Dosing
Both metoprolol succinate and tartrate provide similar clinical and hemodynamic effects when dosed to achieve equivalent β1-blockade. However, the once-daily dosing of metoprolol succinate offers greater convenience and may improve adherence, especially in chronic conditions like heart failure and hypertension 1468. Studies have shown that both forms are well tolerated and effective, but the smoother plasma profile of the succinate form may be preferred in patients who benefit from steady drug levels 1468.
Bioequivalence and Analytical Considerations
Recent studies confirm that different brands of metoprolol succinate extended-release tablets are bioequivalent, showing similar pharmacokinetic profiles under both fasting and fed conditions . Analytical methods for measuring metoprolol in plasma are robust and can reliably track the differences in plasma concentrations resulting from the two formulations .
Conclusion
Metoprolol succinate (extended-release) and metoprolol tartrate (immediate-release) differ mainly in their pharmacokinetic profiles. Succinate provides a more stable and sustained plasma concentration, allowing for once-daily dosing and potentially better adherence, while tartrate requires more frequent dosing and results in greater fluctuations in drug levels. Both forms are effective and safe when used appropriately, but the choice of formulation should be tailored to the clinical needs and lifestyle of the patient 1468.
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