Mexiletine
Mexiletine hydrochloride
Also known as: Mexilen · Mexitilen · Myovek · Ritalmex · Ko-1173 · mexiletini hydrochloridum
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 |
|---|---|---|---|---|---|
| Treating or assisting in treatment of ventricular arrhythmias | 5-8 mg/kg | PO | q8h | — | 🌎 NA |
| Treating or assisting in treatment of ventricular arrhythmias | 4-10 mg/kg | PO | q8h | — | 🌎 NA |
| Ventricular arrhythmias in Boxers | 5-7.5 mg/kg | PO | three times daily | — | 🌎 NA |
| Treating or assisting in treatment of ventricular arrhythmias | 4-8 mg/kg | PO | q8h | — | 🌎 NA |
| Familial arrhythmic cardiomyopathy of Boxers (ARVC) | 5-8 mg/kg | PO | q8h | — | 🌎 NA |
| Treating or assisting in treatment of ventricular arrhythmias | 5-6 mg/kg | PO | q8h | — | 🌎 NA |
| Myotonia congenita or myokymia | 8.3 mg/kg | PO | q8h | — | 🌎 NA |
- Ventricular arrhythmias in Boxers: 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: Combined with atenolol (0.5 mg/kg PO q12-24h).
- Familial arrhythmic cardiomyopathy of Boxers (ARVC): Given with atenolol at 12.5 mg (total dose) q12h.
- Treating or assisting in treatment of ventricular arrhythmias: Always give with food to avoid nausea.
- Myotonia congenita or myokymia: Most studied in Chow Chows, miniature schnauzers, and Jack Russell terriers.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
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).
Mechanism of action
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).
Safety & warnings
Contraindications
- Pre-existing 2nd or 3rd degree AV block (without a pacemaker)
- Cardiogenic shock
- Known hypersensitivity to mexiletine
Adverse effects
- Vomiting (very common)
- Nausea
- Trembling/Tremors
- Unsteadiness/Ataxia
- Dizziness
- Depression/Lethargy
- Shortness of breath
- Proarrhythmia (PVCs)
- Chest pain
- Seizures (rare)
- Agranulocytosis (rare)
- Thrombocytopenia (rare)
Precautions
Use with extreme caution in patients with severe congestive heart failure, acute myocardial infarction, hepatic function impairment, hypotension, intraventricular conduction abnormalities, sinus node function impairment, or a pre-existing seizure disorder.
Clinical Note: Mexiletine is secreted into maternal milk; use of a milk replacer is recommended if the nursing mother is receiving the drug. FDA Pregnancy Category C.
Drug interactions
May slow the absorption of mexiletine.
May reduce the rate of oral absorption.
May increase or decrease mexiletine blood levels.
May accelerate the metabolism of mexiletine.
May cause additive adverse effects (especially CNS toxicity).
May accelerate the absorption of mexiletine.
May slow the absorption of mexiletine.
May accelerate the metabolism of mexiletine.
May accelerate the metabolism of mexiletine.
May accelerate the metabolism of mexiletine.
May accelerate the metabolism of mexiletine.
Mexiletine may reduce the metabolism of theophylline, potentially leading to theophylline toxicity.
May accelerate the renal excretion of mexiletine.
May reduce the urinary excretion of mexiletine.
Monitoring
- 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)
Pharmacokinetics
Absorption
Relatively well absorbed from the gastrointestinal tract with a low first-pass effect.
Distribution
Moderately bound to plasma proteins (60-75% in humans).
Metabolism
Metabolized in the liver to inactive metabolites.
Elimination
Excreted via the kidneys. Renal excretion rate is dependent on urinary pH (acidification accelerates excretion, alkalinization reduces it).
Overdose
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.
Available products
Formulations
- Oral Capsules: 150 mg, 200 mg, 250 mg
Human-labeled
- Mexiletine Oral Capsules: 150 mg, 200 mg & 250 mg (generic)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Mexiletine capsules should be stored in tight containers at room temperature.
Client information
- Always give with food: This medication frequently causes stomach upset, nausea, and vomiting. Giving it with a full meal significantly reduces this risk.
- Strict Adherence: Do not skip doses or stop the medication without consulting your veterinarian. Ventricular arrhythmias can be life-threatening and may return rapidly if the drug is discontinued.
- Monitor for Side Effects: Contact your veterinarian immediately if your pet experiences persistent vomiting, trembling, unsteadiness, dizziness, extreme lethargy, or shortness of breath.
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.