Half-Life of Metoprolol Tartrate
The half-life of metoprolol tartrate is 3 to 4 hours in most individuals, but may extend to 7 to 9 hours in poor CYP2D6 metabolizers. 1
Pharmacokinetic Properties
Metoprolol tartrate is a selective beta-1 adrenergic receptor blocker with the following key pharmacokinetic properties:
- Absorption: Oral bioavailability is approximately 50% due to pre-systemic metabolism 1
- Distribution: Volume of distribution is 3.2 to 5.6 L/kg with about 10% bound to serum albumin 1
- Metabolism: Primarily metabolized by CYP2D6 in the liver 1
- Exhibits stereoselective metabolism dependent on oxidation phenotype
- Poor CYP2D6 metabolizers (approximately 8% of Caucasians) have several-fold higher plasma concentrations
- Elimination: Mainly through biotransformation in the liver 1
- In extensive metabolizers (most people), less than 10% of an intravenous dose is excreted unchanged in urine
- In poor metabolizers, up to 30-40% may be excreted unchanged
Clinical Implications of Half-Life
The relatively short half-life of metoprolol tartrate has important clinical implications:
- Dosing frequency: Requires twice-daily (BID) dosing for optimal therapeutic effect 2
- Duration of action: Approximately 6-12 hours after oral administration 2
- Onset of action: Within 1 hour after oral administration 2
- Peak effect: 2-4 hours after administration 2
This contrasts with metoprolol succinate (extended-release formulation), which has a duration of approximately 24 hours, allowing for once-daily dosing 2.
Special Populations
The half-life of metoprolol tartrate may be affected in certain patient populations:
- Elderly patients: May show slightly higher plasma concentrations due to decreased metabolism and reduced hepatic blood flow, though this is generally not clinically significant 1
- Renal impairment: Half-life does not differ significantly from normal subjects 1
- Hepatic impairment: Half-life can be considerably prolonged, up to 7.2 hours depending on severity 1
Practical Considerations
When administering metoprolol tartrate:
- Standard oral dosing is typically 25-100 mg BID for hypertension and angina 3
- For intravenous administration, the dose is 2.5-5.0 mg IV bolus over 2 minutes 3
- When converting between formulations, metoprolol tartrate 25-50 mg twice daily is approximately equivalent to metoprolol succinate 50-100 mg once daily 2
The short half-life of metoprolol tartrate makes it useful in situations where more precise titration or shorter duration of action is desired, but necessitates more frequent dosing compared to extended-release formulations.