Metoprolol Tartrate — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	0.5-2 mg/kg	q12h (every 12 hours)	Duration: Variable; often long-term for chronic conditions Notes: Start at low end and titrate to effect. Monitor heart rate and blood pressure. For arrhythmias, use higher end.
Cat	PO	2.5-5 mg/cat (approximately 0.5-1 mg/kg)	q12h	Duration: Variable; often long-term for HCM Notes: Titrate based on heart rate and clinical response. Use with caution in cats with bronchoconstrictive disease.
Horse	PO	0.5-1 mg/kg	q12h	Duration: Variable; for atrial fibrillation, may be used until conversion or long-term for rate control Notes: Monitor ECG and heart rate. Adjust dose based on response.
Cattle	PO	Not established	Not established	Duration: Not established Notes: Not commonly used; avoid in food animals due to lack of withdrawal data.
Small Ruminants	PO	Not established	Not established	Duration: Not established Notes: Not commonly used; avoid in food animals due to lack of withdrawal data.
Rabbit	PO	0.5-1 mg/kg	q12h	Duration: Variable Notes: Limited data; use with caution and monitor for bradycardia.
Bird/Poultry	PO	Not established	Not established	Duration: Not established Notes: Not commonly used; avoid in food birds due to lack of withdrawal data.
Exotic/Other	PO	Not established	Not established	Duration: Not established Notes: Use with caution; consult specialist.

Clinical Indications & Species Uses

General Indications

Treatment of hypertension
Management of tachyarrhythmias (supraventricular and ventricular)
Reduction of myocardial oxygen demand in ischemic heart disease
Adjunctive therapy for hypertrophic cardiomyopathy

Dog (Canine)

Treatment of hypertension (systemic)
Management of hypertrophic cardiomyopathy (HCM) (adjunctive)
Control of supraventricular arrhythmias (e.g., atrial fibrillation, atrial tachycardia)
Reduction of myocardial oxygen demand in ischemic heart disease
Treatment of dynamic left ventricular outflow tract obstruction (e.g., in HCM)

Cat (Feline)

Management of hypertrophic cardiomyopathy (HCM) (especially with outflow obstruction or tachycardia)
Control of supraventricular arrhythmias (e.g., atrial fibrillation, atrial tachycardia)
Treatment of hypertension (adjunctive)
Reduction of myocardial oxygen demand in ischemic heart disease

Horse (Equine)

Management of atrial fibrillation (rate control)
Treatment of ventricular arrhythmias
Management of hypertension (uncommon)

Pharmacology & Mechanism of Action

Drug Class: Beta-adrenergic blocking agent (beta-blocker) | Pharmacological Group: Cardiovascular agent, antiarrhythmic (class II)

Mechanism of Action: Metoprolol is a selective beta-1 adrenergic receptor antagonist. At therapeutic doses, it selectively blocks beta-1 receptors in the heart, reducing the effects of catecholamines (epinephrine and norepinephrine). This results in decreased heart rate, myocardial contractility, and cardiac output, thereby reducing myocardial oxygen demand. It also slows conduction through the atrioventricular node, prolonging the refractory period. At higher doses, it may also block beta-2 receptors in bronchial and vascular smooth muscle, but this is less prominent than with non-selective beta-blockers.

Pharmacodynamics: Metoprolol produces a dose-dependent reduction in heart rate and blood pressure. It decreases cardiac output at rest and during exercise, reduces exercise-induced tachycardia, and lowers systolic and diastolic blood pressure. It also reduces myocardial oxygen demand, which is beneficial in ischemic heart disease. In addition, it has antiarrhythmic properties, particularly in controlling ventricular rate in atrial fibrillation and in suppressing ventricular ectopy. It does not have intrinsic sympathomimetic activity and has a membrane-stabilizing effect at high doses.

⚡ Pharmacokinetics Summary

Absorption: Metoprolol is rapidly and completely absorbed after oral administration. However, it undergoes extensive first-pass metabolism in the liver, resulting in a systemic bioavailability of approximately 50% in dogs and cats. Food can increase the bioavailability of the tartrate salt. Peak plasma concentrations occur within 1-2 hours after oral administration.

Distribution: Metoprolol is widely distributed throughout the body. It crosses the blood-brain barrier and placenta and is distributed into milk. The volume of distribution is approximately 4-5 L/kg in dogs. It is moderately lipophilic.

Metabolism: Metoprolol is extensively metabolized in the liver by the cytochrome P450 enzyme CYP2D6 in humans, but in animals, the specific isoenzymes may vary. The major metabolic pathways include oxidative deamination, O-dealkylation, and hydroxylation. The metabolites are inactive.

Excretion: Metoprolol and its metabolites are primarily excreted in the urine. In dogs, approximately 95% of an oral dose is excreted in the urine within 72 hours, with about 10% as unchanged drug. Fecal excretion is minimal.

Half-Life: The elimination half-life of metoprolol is approximately 3-4 hours in dogs, 4-5 hours in cats, and 3-4 hours in horses. In humans, it is about 3-7 hours.

Bioavailability: Oral bioavailability is approximately 50% in dogs and cats due to first-pass metabolism. In horses, bioavailability is about 40-50%.

Protein Binding: Metoprolol has low protein binding, approximately 12% in humans. In dogs, it is about 10-15%.

Available Formulations & Strengths

Oral Tablet 25 mg, 50 mg, 100 mg (PO)

Extended-release Tablet (succinate) 25 mg, 50 mg, 100 mg, 200 mg (PO)

Injectable Solution 1 mg/mL (for IV use) (IV)

Contraindications & Clinical Warnings

Contraindications:

Known hypersensitivity to metoprolol or other beta-blockers
Sinus bradycardia (heart rate < 60 bpm in dogs/cats) unless due to digitalis toxicity
Second- or third-degree atrioventricular block
Cardiogenic shock
Uncompensated congestive heart failure
Severe bronchospastic disease (e.g., asthma, COPD) - use with extreme caution
In animals with pheochromocytoma (unless alpha-blockade is established)

Warnings & Clinical Precautions:

Do not discontinue abruptly; taper dose over 1-2 weeks to avoid rebound tachycardia, hypertension, or exacerbation of angina.
Use with caution in animals with diabetes mellitus; beta-blockers may mask signs of hypoglycemia (tachycardia).
Use with caution in animals with hepatic impairment; dose reduction may be necessary.
Use with caution in animals with renal impairment; monitor for adverse effects.
May mask clinical signs of hyperthyroidism (tachycardia).
In animals with congestive heart failure, use only if compensated and under close monitoring.
In cats, use with caution in those with bronchoconstrictive disease (e.g., asthma).
In horses, use with caution in those with respiratory disease.
Safety in pregnant or lactating animals has not been established; use only if clearly needed.

Adverse Effects & Reactions

Common:

Bradycardia
Hypotension
Lethargy or fatigue
Gastrointestinal upset (vomiting, diarrhea)
Decreased exercise tolerance

Serious / Severe:

Severe bradycardia or heart block
Exacerbation of congestive heart failure
Bronchospasm (especially in animals with reactive airway disease)
Hypoglycemia (may mask signs)
Mental depression or disorientation

Rare:

Hepatotoxicity
Blood dyscrasias (thrombocytopenia, leukopenia)
Alopecia
Peyronie's disease (in humans, not reported in animals)

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Other beta-blockers	Additive effects on heart rate and blood pressure; increased risk of bradycardia and hypotension.	High
Calcium channel blockers (e.g., diltiazem, verapamil)	Additive negative inotropic and chronotropic effects; increased risk of bradycardia, AV block, and heart failure.	High
Digoxin	Additive bradycardia; may increase risk of AV block.	Moderate
Antiarrhythmic agents (e.g., amiodarone, sotalol)	Additive effects on cardiac conduction; increased risk of proarrhythmia.	High
Sympathomimetics (e.g., epinephrine, dobutamine)	Antagonism of beta-adrenergic effects; may result in unopposed alpha-adrenergic effects (vasoconstriction, hypertension).	Moderate
NSAIDs (e.g., flunixin, carprofen)	May reduce antihypertensive effect of beta-blockers due to inhibition of renal prostaglandins.	Mild
Cimetidine	May increase metoprolol plasma levels by inhibiting hepatic metabolism.	Mild
Phenobarbital or other enzyme inducers	May increase metabolism of metoprolol, reducing its efficacy.	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Severe bradycardia
Hypotension
Cardiac conduction disturbances (AV block)
Heart failure
Bronchospasm
Hypoglycemia
Seizures (in severe cases)
Coma

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Induce emesis if recent oral ingestion and animal is conscious. Administer activated charcoal to reduce absorption. For bradycardia and hypotension, administer atropine (0.04 mg/kg IV) and fluids. If unresponsive, consider glucagon (50-150 mcg/kg IV bolus followed by CRI) which has positive inotropic and chronotropic effects independent of beta-receptors. For severe cases, use dobutamine or isoproterenol. Bronchospasm can be treated with aminophylline or albuterol. Monitor ECG, blood pressure, and blood glucose. In severe refractory cases, consider temporary cardiac pacing.

Food Animal Withdrawal Times

Metoprolol is not approved for use in food animals. Withdrawal times have not been established. Do not use in food-producing animals.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (20-25°C, 68-77°F). Protect from moisture.

Handling & Special Conditions: Keep in a tightly closed container. Do not freeze.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Metoprolol tartrate is FDA-approved for human use. It is not FDA-approved for veterinary use, but it is commonly used extra-label in veterinary medicine.

Extra-Label (Off-Label) Use: In the US, extra-label use of metoprolol in animals is permitted under the Animal Medicinal Drug Use Clarification Act (AMDUCA) provided there is a valid veterinarian-client-patient relationship, and the drug is not used in feed. For food animals, extra-label use is prohibited if the drug is not approved for that species and no withdrawal times are established.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Metoprolol tartrate is a selective beta-1 blocker used in veterinary medicine primarily for the management of cardiac conditions such as hypertrophic cardiomyopathy (especially in cats), supraventricular arrhythmias, and hypertension. It is important to titrate the dose carefully based on heart rate and clinical response. In cats with HCM, metoprolol may be preferred over atenolol in some cases due to its shorter half-life, allowing for more rapid dose adjustments. However, atenolol is often preferred in cats because it is also beta-1 selective and has a longer duration of action. Metoprolol should be used with caution in animals with bronchospastic disease, diabetes mellitus, or heart failure. Abrupt discontinuation should be avoided. Monitoring parameters include heart rate, blood pressure, ECG, and clinical signs. In food animals, metoprolol should not be used due to lack of withdrawal data. Always consult current veterinary drug references for the most up-to-date dosing and safety information.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)