Description
Mexiletine is a voltage-gated sodium channel blocker and class Ib antiarrhythmic agent that preferentially binds to open/inactive channels.
1 It inhibits aconitine-induced dysrhythmias in mice with ED
50 values of 57 and 107 mg/kg for intraperitoneal and oral administration, respectively.
2 Mexiletine decreases or inhibits conduction across the Purkinje fiber-muscle junction, shortens action potential duration, and decreases the refractory period when used at concentrations less than 5 μg/ml in isolated canine Purkinje fiber and ventricular muscle preparations.
3
Chemical Properties
White to Off-White Solid
Originator
Mexitil,Boehringer Ingelheim,US,1976
Uses
Antiarrhythmic (class IB)
Definition
ChEBI: A hydrochloride composed of equimolar amounts of mexiletine and hydrogen chloride.
Manufacturing Process
The sodium salt of dimethyl phenol was reacted with chloroacetone and this
product with hydroxylamine to give the starting material.
245 g of this 1-(2',6'-dimethyl-phenoxy)-propanone-(2)-oxime were dissolved
in 1,300 cc of methanol, and the solution was hydrogenated at 5 atmospheres
gauge and 60°C in the presence of Raney nickel. After the calculated amount
of hydrogen had been absorbed, the catalyst was filtered off, the methanol
was distilled out of the filtrate,and the residue, raw 1-(2',6'-dimethylphenoxy)-2-amino-propane, was dissolved in ethanol. The resulting solution
was acidified with ethereal hydrochloric acid, the acidic solution was allowed
to cool, and the precipitate formed thereby was collected by vacuum filtration.
The filter cake was dissolved in ethanol and recystallized therefrom by
addition of ether. 140.5 g (51.5% of theory) of a substance having a melting
point of 203°C to 205°C were obtained, which was identified to be 1-(2',6'-
dimethyl-phenoxy)-2-anino-propane hydrochloride.
Brand name
Mexitil (Boehringer Ingelheim).
Therapeutic Function
Antiarrhythmic
General Description
Mexiletine hydrochloride,1-methyl-2-(2,6-xylyloxy)ethylamine hydrochloride (Mexitil)(pKa 8.4), is a class IB antiarrhythmic agent that is effectivewhen given either intravenously or orally. It resembles lidocainein possessing a xylyl moiety but otherwise is differentchemically. Mexiletine hydrochloride is an ether and is notsubject to the hydrolysis common to the amides lidocaineand tocainide. Its mean half-life on oral administration isapproximately 10 hours.
Although not subject to hydrolysis, mexiletine hydrochlorideis metabolized by oxidative and reductiveprocesses in the liver. Its metabolites, p-hydroxymexiletineand hydroxymethylmexiletine, are not pharmacologicallyactive as antiarrhythmic agents.
Biological Activity
Use-dependent sodium channel blocker (IC 50 values are 75.3 and 23.6 μ M for tonic and use-dependent block respectively). Class Ib antiarrhythmic, neuroprotective and antimyotonic agent.
Biochem/physiol Actions
Mexiletine is a potent sodium channel blocker. It is a cardiac antiarrhythmic and is used as an adjuvant in headache and neuropathic pain Mexiletine is used for treating myotonia in sodium channelopathies and reduces the cardiac action potential depolarization but shows no impact on atrial refractoriness. Its inhibitory effect on sodium channels is effective in treating potassium aggravated myotonia.
Clinical Use
Mexiletine hydrochloride, like class I antiarrhythmicagents, blocks the fast Na channel in cardiac cells. It isespecially effective on the Purkinje fibers in the heart. Thedrug increases the threshold of excitability of myocardialcells by reducing the rate of rise and amplitude of the actionpotential and decreases automaticity.
Mexiletine hydrochloride is used for long-term oral prophylaxisof ventricular tachycardia. The drug is given in200- to 400-mg doses every 8 hours.
storage
Desiccate at +4°C
