Mexiletine (

INN Inns are generally establishments or buildings where travelers can seek lodging, and usually, food and drink. Inns are typically located in the country or along a highway; before the advent of motorized transportation they also provided accommo ...

) (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. Common side effects include abdominal pain, chest discomfort, drowsiness, headache, and nausea. It works as a non-selective voltage-gated sodium channel blocker and belongs to the Class IB group of anti-arrhythmic medications.

Medical uses

Mexiletine has several uses including the treatment of abnormal heart rhythms or

arrhythmias Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...

, chronic pain, and

myotonia Myotonia is a symptom of a small handful of certain neuromuscular disorders characterized by delayed relaxation (prolonged contraction) of the skeletal muscles after voluntary contraction or electrical stimulation. Myotonia is the defining sym ...

. In general when treating arrhythmias, mexiletine is reserved for use in dangerous heart rhythm disturbances such as ventricular tachycardia. It is of particular use when treating arrhythmias caused by long QT syndrome. The LQT3 form of long QT syndrome is amenable to treatment with mexiletine as this form is caused by defective sodium channels that continue to release a sustained current rather than fully inactivating, however other forms of long QT syndrome can also be treated with this medication. Mexiletine has been used to treat chronic pain and may also be used to treat muscle stiffness resulting from

myotonic dystrophy Myotonic dystrophy (DM) is a type of muscular dystrophy, a group of genetic disorders that cause progressive muscle loss and weakness. In DM, muscles are often unable to relax after contraction. Other manifestations may include cataracts, intell ...

(Steinert's disease) or nondystrophic myotonias such as myotonia congenita (Thomsen syndrome or Becker syndrome).

Adverse effects

Common side effects of mexiletine include abdominal pain, chest discomfort, drowsiness, headache, nausea and skin reactions. Uncommon or rare side effects include seizures and liver dysfunction.

Pharmacology

Mexiletine is an oral analogue of

lidocaine Lidocaine, also known as lignocaine and sold under the brand name Xylocaine among others, is a local anesthetic of the amino amide type. It is also used to treat ventricular tachycardia. When used for local anaesthesia or in nerve blocks, li ...

. It is a class IB

antiarrhythmic Antiarrhythmic agents, also known as cardiac dysrhythmia medications, are a group of pharmaceuticals that are used to suppress abnormally fast rhythms ( tachycardias), such as atrial fibrillation, supraventricular tachycardia and ventricular ta ...

which shorten the refractory period and action potential duration (APD). Decrease in APD more than that of ERP so there is increase ERP/APD ratio. The drug has a bioavailability of 90%, and peak plasma concentrations are seen after 2–4 hours. The mean drug half-life is approximately 11 hours. Mexiletine is predominantly

metabolised Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

by the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

. The

pharmacokinetics Pharmacokinetics (from Ancient Greek ''pharmakon'' "drug" and ''kinetikos'' "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to determining the fate of substances administered ...

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.

Synthesis

Society and culture

Mexiletine is available for human use in the US, and has been reintroduced in the UK as a licensed product, having previously only been available as a 'named patient' import. The drug is sold under the trade name Mexitil for use in arrhythmias and NaMuscla for use in myotonia.

Veterinary uses

Mexiletine is available to veterinarians in the US for the treatment of heart disease in dogs and cats. It is commonly used for the treatment of arrhythmogenic right ventricular cardiomyopathy (ARVC) in

Boxer dogs The Boxer is a medium to large, short-haired dog breed of mastiff-type, developed in Germany. The coat is smooth and tight-fitting; colors are fawn, brindled, or white, with or without white markings. Boxers are brachycephalic (they have broad ...

in combination with

sotalol Sotalol, sold under the brand name Betapace among others, is a medication used to treat and prevent abnormal heart rhythms. It is only recommended in those with significant abnormal heart rhythms due to potentially serious side effects. Evidence ...

References

External links

* {{Portal bar , Medicine Analgesics Antiarrhythmic agents Local anesthetics Phenol ethers Sodium channel blockers