Metoprolol
Metoprolol tartrate, Metoprolol succinate
Also known as: Lopressor · Toprol XL · CGP-2175E · H-93/26
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For rate control in chronic atrial fibrillation | 0.25-1 mg/kg PO q1224h. | PO | q1224h | — | 🌎 NA |
| For CHF (early/mild or well-controlled) | 0.2 mg/kg PO twice daily, with slow titration upwards every 2-3 weeks up to 0.4-6.6 mg/kg PO three times a day. | PO | BID to TID | — | 🌎 NA |
| To decrease the incidence of atrial fibrillation and flutter in dogs undergoing valve surgery | 0.4-1 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
- For rate control in chronic atrial fibrillation: Note: 'q1224h' is transcribed exactly as it appears in the source text, likely a typo for q12-24h.
- For CHF (early/mild or well-controlled): Many dogs will not tolerate this upward titration.
- To decrease the incidence of atrial fibrillation and flutter in dogs undergoing valve surgery: Using sustained release metoprolol (ToprolXR) administered before and as soon as feasible after surgery.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| As an oral beta blocker | 2-15 mg (total dose) PO q8h | PO | q8h | — | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Metoprolol is a cardioselective (beta1-specific) adrenergic receptor blocker widely used in veterinary medicine for the management of various cardiovascular conditions.
Key clinical applications include:
- Management of supraventricular tachyarrhythmias and premature ventricular contractions (PVCs/VPCs).
- Treatment of systemic hypertension.
- Management of hypertrophic cardiomyopathy (HCM) in cats, where it helps reduce dynamic left ventricular outflow tract obstruction and improves diastolic filling time.
Because of its relative beta1-selectivity, metoprolol is generally considered safer than non-selective beta-blockers (like propranolol) in patients with concurrent bronchoconstrictive disease (e.g., feline asthma), though caution is still warranted at higher doses where selectivity may be lost.
Mechanism of action
Metoprolol competitively blocks beta1-adrenergic receptors located primarily in the myocardium.
Mechanism Pathway: Blockade of beta1-receptors → decreased activation of adenylyl cyclase → reduced intracellular cAMP → decreased intracellular calcium influx.
This results in:
- Negative chronotropy: Decreased sinus heart rate.
- Negative dromotropy: Slowed atrioventricular (AV) conduction.
- Negative inotropy: Decreased myocardial contractility and cardiac output.
- Decreased myocardial oxygen demand and reduced blood pressure.
Clinical Pearl: Metoprolol lacks intrinsic sympathomimetic activity (ISA) and membrane-stabilizing activity. At higher dosages, its cardioselectivity diminishes, leading to beta2-receptor blockade in bronchial smooth muscle → potential bronchoconstriction.
Safety & warnings
Contraindications
- Overt or unstable heart failure
- Hypersensitivity to beta-blockers
- Greater than first-degree heart block
- Sinus bradycardia
Adverse effects
- Bradycardia
- Lethargy and depression
- Impaired AV conduction
- Congestive heart failure (CHF) or worsening of heart failure
- Hypotension
- Hypoglycemia
- Bronchoconstriction (at high doses)
- Syncope
- Diarrhea
Precautions
Withdrawal Warning: Do not abruptly discontinue metoprolol therapy in chronic users. Abrupt cessation can lead to rebound tachycardia and exacerbation of clinical signs; taper the dose gradually.
- Respiratory Disease: Use with caution in patients with bronchospastic lung disease, even though it is relatively beta1-selective.
- Hepatic Impairment: Use cautiously in patients with significant hepatic insufficiency due to extensive hepatic metabolism.
- Endocrine: Can mask clinical signs of hypoglycemia and thyrotoxicosis. Use cautiously in labile diabetic patients as it can cause hypoglycemia or hyperglycemia.
- Cardiac: Use cautiously in patients with sinus node dysfunction or compensated CHF.
Drug interactions
Increased risk for heart failure and hypotension due to additive myocardial depressant effects.
Concurrent use should be done with caution; additive negative inotropic and chronotropic effects, particularly in patients with preexisting cardiomyopathy or CHF.
May increase negative effects on SA or AV node conduction.
May increase the hypotensive effect of metoprolol.
May increase the risks for pulmonary hypertension in uremic patients.
May increase metoprolol plasma concentrations.
Potential for additive effects including hypotension and bradycardia.
May increase metoprolol plasma concentrations.
May have their actions blocked by metoprolol, and they may in turn reduce the efficacy of the beta-blocker.
Monitoring
- Cardiac function
- Pulse rate
- ECG (if necessary)
- Blood pressure (if indicated)
- Signs of toxicity (bradycardia, hypotension, lethargy)
Pharmacokinetics
Half-life
Absorption
Rapidly and nearly completely absorbed from the GI tract, but undergoes a high first-pass effect (50%), reducing systemic bioavailability.
Distribution
Very low protein binding (5-15%). Distributes well into most tissues. Crosses the blood-brain barrier (CSF levels are ~78% of serum levels). Crosses the placenta, and milk concentrations are 3-4 times higher than plasma.
Metabolism
Primarily biotransformed in the liver.
Elimination
Unchanged drug and metabolites are principally excreted in the urine.
Overdose
Overdosage primarily results in extensions of the drug's pharmacologic effects: hypotension, bradycardia, bronchospasm, cardiac failure, and potentially hypoglycemia.
Treatment:
- Decontamination: If recent oral ingestion, consider emptying the gut and administering activated charcoal. Caution: Inducing emesis can be risky as coma and seizures may develop rapidly.
- Monitoring: Continuous ECG, blood pressure, blood glucose, and potassium.
- Cardiovascular Support: Treat symptomatically. Use IV fluids and pressor agents for hypotension.
- Bradycardia: Treat with atropine. If atropine fails, isoproterenol may be given cautiously. A transvenous pacemaker may be necessary.
- Cardiac Failure: May be treated with digitalis glycosides, diuretics, and oxygen.
- Antidote: Glucagon (5-10 mg IV - human dose) may increase heart rate and blood pressure and reduce the cardiodepressant effects of metoprolol.
Available products
Formulations
- Oral tablets (tartrate)
- Extended-release oral tablets (succinate)
- Injection (tartrate)
- Compounded oral suspension
Human-labeled
- Metoprolol Tartrate Oral Tablets: 25 mg, 50 mg & 100 mg (Lopressor, generic)
- Metoprolol Succinate Extended-Release Tablets: 25 mg, 50 mg, 100 mg & 200 mg (Toprol XL, generic)
- Metoprolol Tartrate Injection: 1 mg/mL in 5 mL amps and Carpuject sterile cartridge units (Lopressor, generic)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store all products protected from light. Store tablets in tight, light-resistant containers at room temperature. Avoid freezing the injection. Compounded oral suspensions (10 mg/mL) retain >95% potency for 60 days when stored at 4°C or 25°C and protected from light.
Client information
Important Information for Pet Owners
- Consistency is Key: To be effective, your pet must receive all doses exactly as prescribed by your veterinarian.
- Do Not Stop Abruptly: Never suddenly stop giving this medication without consulting your veterinarian, as it can cause a dangerous spike in heart rate or worsen heart conditions.
- What to Watch For: Contact your veterinarian immediately if your pet becomes unusually lethargic, tires easily during exercise, develops shortness of breath or a cough, or shows a sudden change in behavior or attitude.
- Diabetic Pets: If your pet is diabetic, monitor their blood sugar closely, as this medication can hide the normal signs of low blood sugar (hypoglycemia).
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.