Mexiletine
Mexiletine is an oral **Class IB antiarrhythmic** agent that shares a very similar electrophysiologic profile to lidocaine. Because lidocaine undergoes extensive first-pass metabolism and cannot be given orally, mexiletine is often considered the "oral lidocaine" for chronic management of arrhythmias. In veterinary medicine, it is primarily used to treat **ventricular arrhythmias** (such as premature ventricular complexes [PVCs] and ventricular tachycardia) in dogs. It is particularly notable for its use in Boxers with Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) and Doberman Pinschers with Dilated Cardiomyopathy (DCM). It is frequently combined with beta-blockers (like atenolol) or sotalol for synergistic effects. Additionally, mexiletine is utilized to treat certain rare inherited myopathies, including **myotonia congenita** (seen in Chow Chows and Miniature Schnauzers) and **myokymia** (seen in Jack Russell Terriers).
Mecanismo: Mexiletine is a **Class IB antiarrhythmic**. * **Mechanism**: It binds to and inhibits the inward **fast sodium channels (Na+)** in the myocardial cell membrane. * **Electrophysiologic Effects**: By blocking these channels, it reduces the rate of rise of the action potential (**Phase 0**). In Purkinje fibers, it decreases automaticity, shortens the action potential duration, and decreases the effective refractory period. * **Selectivity**: Like lidocaine, it is highly selective for diseased, ischemic, or rapidly firing myocardial tissue, making it effective at suppressing ventricular ectopic pacemakers without significantly depressing normal sinus node function or conduction (unless pre-existing abnormalities exist).
Dosificación por especie
- Treating or assisting in treatment of ventricular arrhythmias · 5-8 mg/kg · PO · q8h
- Treating or assisting in treatment of ventricular arrhythmias · 4-10 mg/kg · PO · q8h
- Ventricular arrhythmias in Boxers · 5-7.5 mg/kg · PO · three times daily · Given with sotalol at 1.5-3 mg/kg twice daily; was successful in 7/8 dogs treated in study.
- Treating or assisting in treatment of ventricular arrhythmias · 4-8 mg/kg · PO · q8h · Combined with atenolol (0.5 mg/kg PO q12-24h).
- Familial arrhythmic cardiomyopathy of Boxers (ARVC) · 5-8 mg/kg · PO · q8h · Given with atenolol at 12.5 mg (total dose) q12h.
- Treating or assisting in treatment of ventricular arrhythmias · 5-6 mg/kg · PO · q8h · Always give with food to avoid nausea.
- Myotonia congenita or myokymia · 8.3 mg/kg · PO · q8h · Most studied in Chow Chows, miniature schnauzers, and Jack Russell terriers.
Las dosis son una referencia clínica para veterinarios colegiados. Confirme siempre con la ficha técnica vigente y el paciente individual.
Vías de administración
Contraindicaciones
- Pre-existing 2nd or 3rd degree AV block (without a pacemaker)
- Cardiogenic shock
- Known hypersensitivity to mexiletine
Efectos adversos
- Vomiting (very common)
- Nausea
- Trembling/Tremors
- Unsteadiness/Ataxia
- Dizziness
- Depression/Lethargy
- Shortness of breath
- Proarrhythmia (PVCs)
- Chest pain
- Seizures (rare)
- Agranulocytosis (rare)
- Thrombocytopenia (rare)
Interacciones farmacológicas
- Antacids (Aluminum-Magnesium) · May slow the absorption of mexiletine.
- Atropine · May reduce the rate of oral absorption.
- Cimetidine · May increase or decrease mexiletine blood levels.
- Griseofulvin · May accelerate the metabolism of mexiletine.
- Lidocaine · May cause additive adverse effects (especially CNS toxicity).
- Metoclopramide · May accelerate the absorption of mexiletine.
- Opiates · May slow the absorption of mexiletine.
- Phenobarbital · May accelerate the metabolism of mexiletine.
- Primidone · May accelerate the metabolism of mexiletine.
- Phenytoin · May accelerate the metabolism of mexiletine.
- Rifampin · May accelerate the metabolism of mexiletine.
- Theophylline · Mexiletine may reduce the metabolism of theophylline, potentially leading to theophylline toxicity.
- Urinary Acidifying Drugs (e.g., methionine, ammonium chloride) · May accelerate the renal excretion of mexiletine.
Monitorización
- Electrocardiogram (ECG) to assess antiarrhythmic efficacy and monitor for proarrhythmia
- Clinical signs of adverse effects (especially GI and CNS signs)
- Plasma concentrations (Therapeutic range in humans: 0.5-2 mcg/mL; note that toxicity may be noted even at therapeutic levels)
- Liver enzymes (AST may transiently increase in a small percentage of patients)
Sobredosis
Toxicity associated with overdosage can be significant and life-threatening. * **Clinical Signs**: In human case reports, **CNS signs (tremors, seizures, depression) always preceded cardiovascular signs** (hypotension, bradycardia, heart block). * **Treatment**: * Perform GI tract emptying protocols (emesis/gastric lavage) if indicated and safe. * Administer supportive therapy. * Acidification of the urine may be considered to enhance urinary excretion. * **Atropine** may be useful if severe hypotension or bradycardia occurs.
La referencia de fármacos de VetSheet está destinada a veterinarios colegiados como apoyo a la decisión clínica, no sustituye el juicio profesional ni la ficha técnica vigente del fabricante.