From the Guidelines
Metoprolol tartrate has a half-life of approximately 3-4 hours. This relatively short half-life means that metoprolol tartrate is typically dosed twice daily for most indications, usually at 25-200 mg per dose depending on the condition being treated, as outlined in the 2023 ACC/AHA/ACCP/HRS guideline for the diagnosis and management of atrial fibrillation 1. The half-life of metoprolol tartrate is an important consideration in its dosing, as it needs to be administered frequently enough to maintain therapeutic levels. Some key points to consider about metoprolol tartrate include:
- Its half-life is shorter compared to some other beta-blockers like atenolol, bisoprolol, or carvedilol, which have half-lives ranging from 6-12 hours 1.
- Metoprolol tartrate is extensively metabolized in the liver, primarily by the CYP2D6 enzyme, which can lead to variability in its half-life among individuals based on genetic factors.
- The drug is primarily eliminated through the kidneys, with about 95% of a dose being excreted in urine, which may necessitate dose adjustments in patients with significant kidney impairment.
- For patients with atrial fibrillation, metoprolol tartrate can be used for rate control, with an initial intravenous administration of 2.5–5 mg bolus over 2 min, up to 3 doses, followed by an oral maintenance dose of 25–200 mg, twice daily 1.
From the FDA Drug Label
Elimination of metoprolol is mainly by biotransformation in the liver The mean elimination half-life of metoprolol is 3 to 4 hours; in poor CYP2D6 metabolizers the half-life may be 7 to 9 hours. The half-life of metoprolol (Lopressor) tartrate is 3 to 4 hours in most subjects, but may be 7 to 9 hours in poor CYP2D6 metabolizers 2.
From the Research
Half-Life of Metoprolol Tartrate
- The half-life of metoprolol tartrate is approximately 3.5 hours, as reported in a study published in 1976 3.
- Another study published in 1997 found that the terminal half-life of unchanged metoprolol ranged from 2.5 to 8.5 hours in patients with ECG signs of transmural myocardial damage, and from 2.2 to 5.2 hours in patients without ST changes 4.
- The mean metoprolol half-life was found to be 4.5 hours in patients with ECG signs of transmural myocardial damage, and 3.7 hours in patients without ST changes 4.
Factors Affecting Half-Life
- The half-life of metoprolol tartrate may be affected by factors such as age, body weight, and metabolism, as suggested by a study published in 1976 3.
- A study published in 1985 found that the metabolism of metoprolol is polymorphic, with poor metabolizers having a longer half-life than extensive metabolizers 5.
Pharmacokinetics
- The pharmacokinetics of metoprolol tartrate have been studied in various populations, including healthy volunteers and patients with hypertension or angina pectoris 6, 5, 3, 4, 7.
- The bioavailability of metoprolol tartrate has been found to be affected by the route of administration, with rectal administration resulting in a higher bioavailability than oral administration 7.