Metoprolol
**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.
Mecanismo: 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.
Dosificación por especie
- As an oral beta blocker · 2-15 mg (total dose) PO q8h · PO · q8h
- For rate control in chronic atrial fibrillation · 0.25-1 mg/kg PO q1224h. · PO · q1224h · 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) · 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 · Many dogs will not tolerate this upward titration.
- To decrease the incidence of atrial fibrillation and flutter in dogs undergoing valve surgery · 0.4-1 mg/kg PO q24h · PO · q24h · Using sustained release metoprolol (ToprolXR) administered before and as soon as feasible after surgery.
Las dosis son una referencia clínica para médicos veterinarios. Confirme siempre con la información vigente del producto y el paciente individual.
Vías de administración
Contraindicaciones
- Overt or unstable heart failure
- Hypersensitivity to beta-blockers
- Greater than first-degree heart block
- Sinus bradycardia
Efectos adversos
- Bradycardia
- Lethargy and depression
- Impaired AV conduction
- Congestive heart failure (CHF) or worsening of heart failure
- Hypotension
- Hypoglycemia
- Bronchoconstriction (at high doses)
- Syncope
- Diarrhea
Interacciones farmacológicas
- General Anesthetics · Increased risk for heart failure and hypotension due to additive myocardial depressant effects.
- Calcium-Channel Blockers (e.g., diltiazem, verapamil, amlodipine) · Concurrent use should be done with caution; additive negative inotropic and chronotropic effects, particularly in patients with preexisting cardiomyopathy or CHF.
- Digoxin · May increase negative effects on SA or AV node conduction.
- Diuretics (thiazides, furosemide) · May increase the hypotensive effect of metoprolol.
- Hydralazine · May increase the risks for pulmonary hypertension in uremic patients.
- Quinidine · May increase metoprolol plasma concentrations.
- Reserpine · Potential for additive effects including hypotension and bradycardia.
- SSRI Antidepressants (e.g., fluoxetine, sertraline, paroxetine) · May increase metoprolol plasma concentrations.
- Sympathomimetics (e.g., metaproterenol, terbutaline, epinephrine, phenylpropanolamine) · May have their actions blocked by metoprolol, and they may in turn reduce the efficacy of the beta-blocker.
Monitoreo
- Cardiac function
- Pulse rate
- ECG (if necessary)
- Blood pressure (if indicated)
- Signs of toxicity (bradycardia, hypotension, lethargy)
Sobredosis
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.
La referencia de fármacos de VetSheet está destinada a médicos veterinarios como apoyo a la decisión clínica; no sustituye el juicio profesional ni la información vigente del fabricante.