From the Guidelines
Metoprolol begins to work within 1 hour after oral administration, with peak effects occurring at approximately 2-4 hours, as supported by the most recent guidelines 1. When given intravenously, the onset of action is much faster, typically within minutes. The medication works by blocking beta-1 adrenergic receptors in the heart, which reduces heart rate, blood pressure, and cardiac workload. For immediate-release tablets, therapeutic effects are noticeable within 1-2 hours, while extended-release formulations provide a more gradual onset but longer duration of action. Some key points to consider when using metoprolol include:
- The choice of beta blocker for an individual patient is based primarily on pharmacokinetic and side effect criteria, as well as on physician familiarity 1.
- Patients with marked first-degree AV block, any form of second- or third-degree AV block in the absence of a functioning implanted pacemaker, a history of asthma, severe LV dysfunction or HF, or at high risk for shock should not receive beta blockers on an acute basis 1.
- Intravenous metoprolol may be given in 5-mg increments by slow intravenous administration, repeated every 5 min for a total initial dose of 15 mg, with oral therapy initiated 15 min after the last intravenous dose at 25 to 50 mg every 6 h for 48 h 1.
- The target resting heart rate is 50 to 60 beats per minute unless a limiting side effect is reached, and selection of the oral agent should include the clinician's familiarity with the agent 1. Overall, metoprolol is a useful medication for managing various cardiovascular conditions, including angina, arrhythmias, and hypertension, with its onset of action and dosing frequency influencing its clinical use 1.
From the Research
Onset Time of Metoprolol
- The onset time of metoprolol is not explicitly stated in the provided studies, but the effects of metoprolol on heart rate and blood pressure can be observed within a few hours after administration 2.
- A study comparing ordinary metoprolol tablets and metoprolol sustained-release tablets found that the antihypertensive effect of metoprolol was more rapid in onset after the ordinary tablet formulation, but less marked at 12 hours than at 24 hours after the sustained-release formulation 2.
- The pharmacokinetic properties of extended-release metoprolol succinate suggest that it produces even plasma concentrations over a 24-h period, without the marked peaks and troughs characteristically observed with the immediate-release formulation 3.
- A study comparing immediate-release metoprolol and extended-release metoprolol CR/XL found that metoprolol CR/XL 200 mg once daily gave more pronounced suppression of peak heart rate, with lower peak and less variation in peak to trough plasma levels 4.
Key Findings
- Metoprolol CR/XL 200 mg once daily showed lower peak and less variation in peak to trough plasma levels compared to multiple dosing of metoprolol IR with the same AUC 4.
- The trough plasma metoprolol levels were comparable for metoprolol CR/XL 200 mg once daily and metoprolol IR 50 mg four times daily, but lower for metoprolol IR 100 mg twice daily 4.
- Both treatments were well tolerated, suggesting that metoprolol CR/XL may be used as an alternative to metoprolol IR in patients with myocardial infarction 4.