# Mexiletine: veterinary dose and monograph

> Mexiletine is a veterinary cardiovascular drug. Oral class IB antiarrhythmic — essentially an orally available analogue of lidocaine — used in dogs for chronic suppression of VENTRICULAR tachyarrhythmias (ventricular premature complexes, ventricular tachycardia), commonly in dilated… Indications include 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. This monograph lists 2 reference doses for dogs, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/mexiletine · Last reviewed: 2026-10-01

## 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

*Mexiletine doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Ventricular arrhythmia (chronic) | 5–8 mg/kg | PO | q8h | — |
| Neuropathic pain / myotonia | 4–10 mg/kg | PO | q8h | — |

- 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

> **Caution:** 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.

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- [Phenylephrine](https://vetmasterji.com/drugs/phenylephrine)
- [Pimobendan](https://vetmasterji.com/drugs/pimobendan)

## Frequently asked questions

### What is the dose of Mexiletine for dogs?

Reference doses for Mexiletine in dogs: 5–8 mg/kg PO q8h (Ventricular arrhythmia (chronic)); 4–10 mg/kg PO q8h (Neuropathic pain / myotonia). Confirm against the label and the patient before use.

### When should Mexiletine not be used?

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.

### What are the side effects of Mexiletine in animals?

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

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.