Mexiletine (INN) (sold under the brand names Mexitil and Namuscla) is a medication used to treat abnormal heart rhythms, chronic pain, and some causes of muscle stiffness.

It works as a non-selective voltage-gated sodium channel blocker and belongs to the Class IB group of anti-arrhythmic medications.

[5][6] Common side effects of mexiletine include abdominal pain, chest discomfort, drowsiness, headache, nausea and skin reactions.

The pharmacokinetics of mexiletine are preserved with even moderate to severe renal impairment, but dose adjustment may be required when creatinine clearance falls below 10 mL/minute.

[medical citation needed] It is commonly used for the treatment of arrhythmogenic right ventricular cardiomyopathy (ARVC) in Boxer dogs in combination with sotalol.