Mexiletine: veterinary dose and monograph

At a glance

Drug class

Cardiovascular

Also known as

Mexitil, Mexilen

Species with doses

Dogs

General dose range

5–8 mg/kg PO q8h — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Ventricular premature complexes / ventricular tachycardia (chronic oral control)
• Ventricular arrhythmias of dilated cardiomyopathy (often Boxer/Dobermann/large breeds)
• Combination antiarrhythmic therapy (with sotalol/atenolol) for refractory ventricular ectopy

Mexiletine dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Ventricular arrhythmia (chronic): Plumb’s p.833: 5–8 mg/kg PO q8h (Fox); 4–10 mg/kg q8h (Hogan); Boxers 5–7.5 mg/kg three times daily with sotalol 1.5–3 mg/kg twice daily, or 5–8 mg/kg q8h with atenolol. Papich 5e: 6 mg/kg q8–12h PO. Always give with food. No safe cat dose (Papich).
• Neuropathic pain / myotonia: Papich 5e: chronic pain from nerve injury 4–10 mg/kg PO q8h. Plumb’s p.833 (Lorenz 2007): myotonia congenita / myokymia 8.3 mg/kg PO q8h.

Contraindications

High-grade AV block / severe bradyarrhythmia without pacing. Cardiogenic shock. Significant hepatic impairment (hepatic metabolism). Seizure disorders (CNS effects). Known hypersensitivity. Caution combining multiple antiarrhythmics.

Adverse effects

• GI upset (vomiting, anorexia) — give with food
• CNS: tremor, ataxia, disorientation (lidocaine-like)
• Proarrhythmia (less than many agents)
• Rare: thrombocytopenia, hepatopathy

Drug interactions

• Sotalol / atenolol: synergistic ventricular arrhythmia control (common, beneficial combination)
• Hepatic enzyme inducers (phenobarbital, rifampin): lower mexiletine levels
• CYP inhibitors / cimetidine: raise levels
• Other antiarrhythmics: additive cardiac and proarrhythmic effects

Pregnancy and lactation

Limited data; use only if the maternal arrhythmia risk outweighs potential fetal risk.

Monitoring

• ECG / Holter for efficacy and proarrhythmia
• GI tolerance (give with food)
• CNS signs (tremor/ataxia)
• Liver values on long-term therapy

Toxicity and overdose

Overdose causes CNS toxicity (tremor, ataxia, disorientation, seizures) and cardiac effects (bradycardia, hypotension, proarrhythmia). GI upset is the common nuisance at therapeutic doses. Narrow-ish margin warrants titration and ECG follow-up.

Management: No specific antidote. Supportive — control seizures with benzodiazepines, IV fluids, ECG monitoring and cardiovascular support; manage bradyarrhythmia conventionally. Effects abate as the drug is metabolised.

Clinical pearls

• Think "oral lidocaine" — the practical way to chronically suppress ventricular ectopy after lidocaine has controlled it acutely
• Frequently combined with sotalol (or atenolol) for synergistic ventricular arrhythmia control in DCM/Boxer ARVC
• Give with food to limit GI upset; titrate with Holter monitoring
• Watch for lidocaine-like CNS signs (tremor, ataxia) as the toxicity cue

Mechanism of action

Class IB antiarrhythmic that blocks fast voltage-gated sodium channels (preferentially in depolarised/ischaemic tissue), shortening the action potential and effective refractory period and suppressing abnormal ventricular automaticity and re-entry — with minimal effect on normal conduction or the ECG intervals. Its oral bioavailability gives the chronic-therapy advantage lidocaine lacks.

Formulations and products

• 50 mg capsule
• 150 mg capsule
• Mexitil — 50 / 150 mg capsule, Capsule (human-label)

Storage

Capsules: 15–30 °C, dry, protect from light.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other cardiovascular drugs

• Enalapril
• Esmolol
• Hydralazine
• Metoprolol
• Nitroglycerin (Glyceryl Trinitrate)
• Norepinephrine (Noradrenaline)
• Phenylephrine
• Pimobendan

Frequently asked questions