Beta-blocker · Rate control · Antihypertensive
Metoprolol (Lopressor)
Also called Lopressor
Indications
- Rate control of AF or flutter with rapid ventricular response (IV use off-label)
- Acute MI in hemodynamically stable patients, IV then oral, to lower cardiovascular mortality
- SVT after vagal maneuvers and adenosine, and multifocal atrial tachycardia (IV use off-label)
- Perioperative tachycardia or myocardial ischemia (off-label)
- Oral: hypertension and angina; HFrEF with the succinate form only
Dosing
| Where | Dose |
|---|---|
| Rhythm control | Metoprolol: 2.5–5 mg IV over 2 min, repeat every 5 min to 15 mg |
| Blood pressure boluses | Metoprolol: 5 mg IV every 5 min up to 15 mg |
On the quick cards
Mechanism of action
Metoprolol is a competitive β1-selective adrenergic antagonist with no intrinsic sympathomimetic activity; membrane-stabilizing effects appear only far above therapeutic levels. Blocking β1 receptors in the SA node, AV node and ventricles lowers Gs–adenylyl cyclase–cAMP signaling, so the sinus rate, AV conduction and contractility fall and juxtaglomerular renin release drops. Selectivity is relative: at higher concentrations it also blocks β2 receptors in bronchial and vascular smooth muscle.
Pharmacology
- Cardiovascular: slows sinus rate and AV conduction, lowers contractility and BP, and cuts myocardial oxygen demand
- Cardiovascular: long-term metoprolol succinate lowers mortality in HFrEF (MERIT-HF); the tartrate lacks that evidence
- Respiratory: β2 blockade and bronchospasm become likelier as doses rise
- CNS: enters the CSF: fatigue, dizziness, depression and vivid dreams
- Metabolic: masks the tachycardia of hypoglycemia and thyrotoxicosis
Pharmacokinetics
| Onset | IV: within minutes; maximal β-blockade about 20 min after a 10-min infusion |
|---|---|
| Duration | Several hours; longer in CYP2D6 poor metabolizers |
| Half-life | 3–4 h; 7–9 h in CYP2D6 poor metabolizers |
| Distribution | Vd 3.2–5.6 L/kg; CSF levels about 78% of plasma |
| Protein binding | About 10–12%, to albumin |
| Metabolism | Mainly hepatic CYP2D6 (stereoselective); metabolites have little β-blocking effect. About 8% of White people and 2% of most others lack CYP2D6 |
| Elimination | Urine; about 10% unchanged after IV doses, under 5% after oral |
| Bioavailability | About 50% orally (saturable first pass); oral and IV doses match at about 2.5:1 |
| Organ failure | Kidney failure barely changes clearance; liver disease raises levels |
Chemistry
- Aryloxypropanolamine with a para-methoxyethyl ether, which, unlike esmolol's ester, blood esterases cannot cut
- Racemic; β-blockade comes mainly from the S-enantiomer
- pKa about 9.6 (secondary amine): mostly ionized at pH 7.4; moderately lipophilic (log P about 1.9)
- Two salts: tartrate (immediate-release tablets and the injection) and succinate (extended release)
- Injection 1 mg/mL in saline; protect from light and heat
Adverse effects and cautions
In the one-pagers
- Heart FailureHFrEF: the four pillars: Beta-blocker: Carvedilol, metoprolol succinate, bisoprolol: Bradycardia; not started on IV inotropes; never stop abruptly
- Rhythm GalleryAtrial rhythms: PACs, MAT, flutter and AF: MAT shows three or more P-wave shapes, varying PR and R–R intervals and a rate over 100; the distinct P waves separate it from AF. It follows decompensated lung disease, hypoxemia, low K⁺ or Mg²⁺ and theophylline. Treat those: cardioversion fails, and IV metoprolol or verapamil is reasonable for rate (2015 ACC/AHA/HRS SVT guideline, 2a).
- Obstetric EmergenciesPeripartum cardiomyopathy: Beta-blocker: Yes (metoprolol): Yes
- Perioperative CareFasting and medications: the reasons: Beta-blockers: continuing a long-term beta-blocker through surgery was the one Class I recommendation of the 2014 ACC/AHA and ESC guidelines, and the 2014 ACC/AHA guideline advised against starting one on the day of surgery (Sherafati 2017). The reason is POISE: metoprolol begun just before surgery prevented some heart attacks but raised cardiovascular deaths
- Pharmacology by Class and SuffixHeart and blood pressure: -olol: β-blocker (metoprolol): Apical pulse 1 min; hold if <60 unless ordered: Bradycardia, low BP; hides hypoglycemia tachycardia; never stop abruptly
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Sources
- FDA label: metoprolol tartrate injection (2026)
- FDA label: Lopressor (2023)
- COMMIT, Lancet (2005)
- PubChem: metoprolol
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow the order, the label and your institution's protocols.