Metoprolol (Lopressor)

Emergency & Prehospital

• AF or atrial flutter with rapid ventricular response: Hemodynamically stable, with no pre-excitation. An IV β-blocker or a nondihydropyridine calcium channel blocker is first-line. Pick the β-blocker when LVEF is <40% (or LV dysfunction is known to be moderate or severe). Not when heart failure is decompensated (off-label).
• Regular narrow-complex SVT: once vagal maneuvers and adenosine have failed, or the rhythm keeps coming back. For stable narrow-QRS tachycardia, the 2025 AHA adult tachyarrhythmia algorithm lists a β-blocker or calcium channel blocker (off-label).

ED / ICU / Transport

• Acute coronary syndrome or MI: the standard is an oral β-blocker started within 24 hr. Skip it only if a contraindication applies (2025 ACC/AHA ACS guideline).
• IV regimen in definite or suspected acute MI: The FDA label covers hemodynamically stable patients, and it rests on a pre-reperfusion-era trial. The label says to start in a coronary care or similar unit. This is not routine, and it is not a routine prehospital STEMI drug. Consider it only once hemodynamics are stable, with no heart failure, low-output state or shock risk. COMMIT showed net harm in unstable patients. The older 2013 ACCF/AHA STEMI guideline limited early IV use to hypertension or ongoing ischemia. Confirm current use with cardiology.
• Oral rate control after IV loading: move to tartrate or extended-release succinate once the rate is under control.
• AF rate control in pregnancy: metoprolol is a reasonable first-line rate-control agent, per the 2023 AF guideline.

Other Uses

• Hypertension: oral tartrate or extended-release succinate. It is not an acute antihypertensive.
• Chronic angina pectoris: oral
• Heart failure with reduced ejection fraction (HFrEF): extended-release succinate only. Start it in stable, euvolemic patients.
• Pediatric hypertension, age 6 years and older: extended-release succinate

Doses vary by protocol; follow local protocols and medical direction.

Available Forms

• IV injection (metoprolol tartrate): 1 mg/mL in 5 mL (5 mg) single-dose vial. This is the form EMS and transport carry.
• Immediate-release tablets (tartrate): Lopressor 12.5 mg is the only strength in the label updated January 26, 2026. Generics come in other strengths. Check the label on the product in hand.
• Oral solution (tartrate): 10 mg/mL (Lopressor)
• Extended-release tablets (succinate): Toprol-XL and generics, 25, 50, 100 and 200 mg, with strength stated as the tartrate equivalent. They're scored and may be split. Never crush or chew them.

Adult Dosing

Dosing weight: Adult doses are fixed. Weight does not change them.

Pediatric Dosing

Preparation & Administration

• Dilution: none required. The 1 mg/mL vial goes in by direct IV injection (2.5 mg = 2.5 mL).
• Push rate: give each dose over 2 min for rate control. In the labeled MI regimen, the 5 mg boluses sit about 2 min apart.
• Line and flush: a peripheral IV. Flush with 0.9% sodium chloride before and after. Watch BP, HR and ECG during IV administration.
• Oral: tartrate goes in with or right after meals. ER succinate may be split along the score. Never crush or chew it.

Contraindications

• Heart rate <45 bpm, severe bradycardia, or sick sinus syndrome without a pacemaker
• Second- or third-degree AV block without a functioning pacemaker; significant first-degree block (PR ≥0.24 sec)
• SBP <100 mmHg, cardiogenic shock or decompensated heart failure
• Acute MI with heart failure (Killip II–IV), a low-output state or risk of cardiogenic shock: no early or IV β-blocker. COMMIT produced the shock-risk markers, which show up in the 2013 ACCF/AHA STEMI and 2014 AHA/ACC NSTE-ACS guidelines: age >70 yr, SBP <120 mmHg, sinus tachycardia >110 or HR <60 bpm, longer time since symptom onset. Reassess for oral therapy after 24 hr
• Pre-excited AF or flutter (WPW): AV nodal blockers can trigger VF (harm per the 2023 AF guideline).
• Hypersensitivity to metoprolol or other β-blockers (cross-sensitivity can occur)

Precautions

• Asthma or bronchospasm (relative): generally avoid it. In COPD, it is reasonable. Start at the lowest dose, with a bronchodilator in hand.
• Diabetes, fasting or vomiting patients, children: it hides hypoglycemia and makes it last longer.
• Pheochromocytoma: only once an α-blocker is running. Unopposed α can raise BP.
• Thyrotoxicosis: it hides the tachycardia. Stopping abruptly can trigger thyroid storm.
• Peripheral arterial disease: claudication can get worse.
• History of anaphylaxis: reactions can be harsher, and usual epinephrine doses may fall short.
• Noncardiac surgery: skip a high-dose regimen. It brings more stroke and death. Do not routinely stop chronic therapy.

Hold / Reassess If

• HR <45 bpm, a pause or new AV block, or PR ≥0.24 sec: No further doses.
• SBP <100 mmHg or signs of hypoperfusion: hold it and treat as low output.
• Suspected MI: the label limits (HR <45 bpm, SBP <100 mmHg, PR ≥0.24 sec) are minimums only. A heart failure sign or shock-risk marker above means no IV dose.
• Crackles, falling SpO₂ or new wheeze: stop the dose.

Common

• Hypotension (SBP <90 mmHg in 27% vs 23% with placebo in the IV MI trial)
• Bradycardia (HR <40 bpm in 16% vs 7% with placebo)
• First-degree AV block (PR ≥0.26 sec in 5% vs 2%)
• Tiredness, dizziness, shortness of breath
• Diarrhea (about 5%); nausea, dry mouth or constipation (about 1%)
• Pruritus or rash (about 5%)
• Cold extremities or Raynaud-type symptoms, depression, nightmares, insomnia

Serious / Life-Threatening

Overdose & Toxicity Management

• Signs: severe bradycardia, AV block, hypotension, cardiogenic shock, heart failure, bronchospasm, hypoxia, depressed consciousness or coma, nausea and vomiting; hypoglycemia, especially in children.
• Know the home product: immediate-release tartrate starts β-blockade within 1 hr. ER succinate (Toprol-XL) is built to release drug over 24 hr. Toxicity can start late and last a long time. Plan prolonged monitoring with the poison center (1-800-222-1222).
• Metoprolol vs propranolol: metoprolol's membrane-stabilizing (sodium-channel) effect only shows up far above therapeutic levels. QRS widening and seizures point more toward propranolol. Still check the QRS and glucose.
• Hypotension: Use IV fluids and vasopressors such as norepinephrine (AHA 2025 Class 1, C-EO). Expect resistance to adrenergic drugs.
• Hypotension refractory to vasopressors: high-dose insulin (AHA 2025 Class 1, C-LD): regular insulin 1 unit/kg IV bolus, then 1 unit/kg/hr, increased by 1 unit/kg/hr every 20–30 min up to 10 units/kg/hr. Targets: SBP above 90, MAP above 65, HR above 50. Give dextrose to keep glucose at 100–200 mg/dL; check glucose every 20 min in the first hour and during titration, then hourly; check potassium hourly during titration and replace if below 3 mmol/L. Differs from FDA label: Novolin R is labeled for IV infusion at 0.05–1 unit/mL.
• Bradycardia or hypotension, adjunct: glucagon (AHA 2025 2a, C-LD), after vasopressors and high-dose insulin: 2–10 mg IV, then 1–15 mg/hr in adults; children 0.05–0.15 mg/kg bolus, not above the adult dose. Expect vomiting, protect the airway. Differs from glucagon-injection and beta-blocker labels (50–150 mcg/kg then 1–5 mg/hr, or 5–10 mg then 5 mg/hr): both sit inside or below the AHA range. Atropine and pacing are standard ALS for bradycardia; the 2025 AHA toxicology recommendations no longer list them for β-blocker poisoning.
• Refractory cardiogenic shock: VA-ECMO is reasonable (AHA 2025 2a, C-LD adults). Whether lipid emulsion helps is uncertain (2b, C-EO), and it is not routine. Calcium may be reasonable (2b, C-EO). Calcium chloride 2,000 mg (20 mL of 10%) IV. Child 20 mg/kg (0.2 mL/kg), not above the adult dose. Infusion 20–40 mg/kg/hr (0.2–0.4 mL/kg/hr), titrated to blood pressure, via a central line where possible. Details are on the calcium chloride page.
• Decontamination and removal: the evidence for activated charcoal is limited. Decide with the poison center. Hemodialysis is unlikely to help.

Clinically Significant Interactions

IV Compatibility

• Give it undiluted by direct IV injection. The label lists no diluents and no Y-site data. Flush with 0.9% sodium chloride. Never mix it in a syringe with other drugs.
• Verify it with an institutional compatibility resource.

• Pediatrics: Neither IV nor immediate-release use is established. ER succinate carries a label for hypertension from age 6 years. Children face a higher hypoglycemia risk on β-blockers. See the Pediatric Dosing table.
• Pregnancy: Observational studies find no link to major malformations. Reports on growth restriction and preterm birth disagree with each other. Metoprolol crosses the placenta. Watch the newborn for bradycardia, hypotension, hypoglycemia and respiratory depression. It is a reasonable first-line rate-control drug in pregnancy. Do not withhold it in a maternal emergency.
• Lactation: It shows up in milk at 0.5–2% of the maternal weight-adjusted dose. No infant harm has been identified. If the mother is a slow CYP2D6 metabolizer, watch the infant for bradycardia.
• Older Adults: Start at the low end of the range. Titrate with caution.
• Renal Impairment: No dose adjustment. Renal failure does not meaningfully change availability or half-life.
• Hepatic Impairment: levels can climb a lot. Start low and titrate slowly.
• Obesity / Dosing Weight: adult doses are fixed. There is no weight adjustment.
• CYP2D6 Poor Metabolizers: About 8% of people of European ancestry and 2% of most other groups. They run several-fold higher levels, a longer half-life and less cardioselectivity.
• Heart Failure: contraindicated when decompensated. If heart failure worsens during oral up-titration, increase diuretics and lower or pause the dose. With AF and LVEF <40% (or known moderate–severe LV dysfunction), pick a β-blocker over IV diltiazem or verapamil. Adding IV magnesium to standard rate-control measures is reasonable in any AF with rapid ventricular response (2a). When β-blockers and nondihydropyridine CCBs are ineffective or contraindicated (decompensated HF, hypotension), consider IV digoxin (2a). Or consider IV amiodarone in critically ill or decompensated HF patients (2b). Weigh the risk of cardioversion and stroke (2023 AF guideline).

• Scope: paramedics in some systems, ED and ICU RNs, and critical-care transport. Scope varies by state and agency protocol.
• Storage & Stability: store at 20–25°C (68–77°F). Don't freeze it. Protect it from light and keep vials in the carton. Shield it from vehicle heat.
• Carried Concentration: 1 mg/mL in a 5 mL vial. One full vial is one 5 mg dose. Draw 2.5 mL for 2.5 mg.
• No quick offset: each IV dose acts for hours. There is no quick off switch. When BP or ventricular function is uncertain, talk through a titratable agent such as esmolol with medical control.
• Handoff Essentials: dose times and total IV mg, HR and BP response, last oral dose and formulation (tartrate vs succinate), other nodal blockers given, and any ingestion details (product, amount, time).

Mechanism of Action

• Competitive β₁-blockade at the SA node, AV node and myocardium. The result is a slower sinus rate and AV conduction, with less contractility. That gives rate control and lower myocardial oxygen demand.
• Relative β₁-selectivity: not absolute. β₂-blockade in the bronchi and vessels rises at higher concentrations, in poor CYP2D6 metabolizers and with CYP2D6 inhibitors.
• No intrinsic sympathomimetic activity; membrane-stabilizing activity shows up only far above therapeutic levels.

Pharmacokinetics

• Half-life: about 3–4 hr (labels range 3–7 hr). Poor CYP2D6 metabolizers run 7–9 hr.
• Metabolism: hepatic, mainly through CYP2D6 (stereoselective). Oral immediate-release bioavailability is about 50% (first-pass).
• Active metabolites: none with meaningful β-blocking activity.
• Elimination: renal, as metabolites. Under 5% of an oral dose, or about 10% of an IV dose, comes out unchanged.
• Distribution: about 10–12% protein bound. Vd 3.2–5.6 L/kg. It crosses the blood-brain barrier and placenta.

Generic Name

Metoprolol tartrate (IV, immediate-release tablets, oral solution); metoprolol succinate (extended-release tablets)

Brand Names

Lopressor (tartrate); Toprol-XL (succinate); many generics

Pharmacologic Class

Cardioselective (β₁-selective) adrenergic blocker; Vaughan Williams class II

Therapeutic Class

Rate-control agent; antianginal; antihypertensive; heart failure therapy (succinate)

Controlled Substance

Not controlled

ISMP High-Alert

Yes: ISMP high-alert medication (adrenergic antagonists, IV), per the ISMP acute care high-alert list (2024)

Look-Alike / Sound-Alike

Metoprolol succinate / metoprolol tartrate; Toprol-XL / Topamax; Lopressor / Lyrica (ISMP list of confused drug names, 2024)