Mexiletine is an oral class IB antiarrhythmic used mainly for certain ventricular arrhythmias, and it also has limited off-label roles in neuropathic pain and muscle stiffness disorders.
It works by blocking sodium channels and stabilizing cardiac electrical activity, but it can cause notable side effects, especially gastrointestinal and neurologic ones.
Mexiletine is an oral analogue of lidocaine that blocks voltage‑gated sodium channels, shortening action potential duration and refractory period in ventricular myocardium and Purkinje fibers.
Bioavailability is about 90%, peak levels at 2–4 hours, with a mean half‑life around 10–12 hours and predominantly hepatic metabolism.
Documented, life‑threatening ventricular arrhythmias (e.g., sustained VT), generally as second‑line or adjunctive therapy.
Mexiletine a sodium channel blocker is widely used in the long QT syndrome type 3 and reduces the risk of an arrhythmia by shortening the QTC.
Almost 70% of patients with long QT syndrome type 2 have a reduction in the QTC interval with mexiletine .
A mexiletine trial can indicate the efficacy of the drug before starting on long-term institution.
Off‑label: myotonia in myotonic dystrophy and non‑dystrophic myotonias; has also been used for certain chronic neuropathic pain syndromes.
Limited off-label use for chronic pain, peripheral neuropathy, and myotonia/muscle stiffness.
Dosing
Ventricular arrhythmias: often initiated at 200 mg orally every 8 hours; may load with 400 mg, then 200 mg every 8 hours, with titration based on response and tolerability.
Many patients can be down‑titrated to twice‑daily dosing once stable; always individualized and started under close monitoring, often inpatient.
Adverse effects and risks Common: GI upset (nausea, vomiting, heartburn), dizziness/lightheadedness, tremor, ataxia, paresthesias, headache, blurred vision, nervousness, insomnia.
Serious: can exacerbate arrhythmias, seizures, hepatotoxicity, blood dyscrasias, and increased mortality post‑MI similar to other class I agents; therefore reserved for clearly life‑threatening arrhythmias.
Taken with food or milk/antacid to reduce GI side effects and aim for evenly spaced dosing to maintain stable levels.
Monitor by ECG, rhythm burden, blood pressure, neurologic status, and liver function; use caution in structural heart disease, significant hepatic dysfunction, or severe conduction abnormalities. It is usually taken by mouth as capsules, often 2 to 3 times daily.
It is commonly taken with food or an antacid to reduce stomach upset.
It is metabolized in the liver, so liver impairment can increase toxicity risk.