Mexiletine

How it works

It blocks fast sodium channels, preferentially in active or depolarised tissue, shortening the action potential duration and reducing abnormal myocardial and muscle membrane excitability.

Prescribing in practice

• Like other antiarrhythmics it is proarrhythmic and should be used with caution under specialist guidance, particularly with bradyarrhythmias, conduction disturbance or significant heart failure.
• Gastrointestinal and central nervous system effects such as nausea, tremor and dizziness are common and may limit treatment.
• Plasma concentrations are affected by hepatic enzyme activity and by changes in urinary pH; consult the SPC for cautions and interactions.

Monitoring

Monitor the ECG and clinical response, with assessment of liver function and consideration of plasma-level checks in selected patients.

Counselling the patient

• Advise taking the medicine with food to reduce stomach upset.
• Tell the patient to report fainting, palpitations or new rashes promptly.

Evidence & guidelines

Mexiletine is an established class Ib antiarrhythmic; refer to the SPC and current prescribing references for indications and cautions.