Mexiletine HCl

Mexiletine is a local anesthetic, antiarrhythmic agent (Class Ib), structurally similar to lidocaine, but orally active. Mexiletine, inhibits the inward sodium current required for the initiation and conduction of impulses, thus reducing the rate of rise of the action potential. It achieves this reduced sodium current by inhibiting sodium channels. Mexiletine decreases the effective refractory period (ERP) in Purkinje fibers in the heart. The decrease in ERP is of lesser magnitude than the decrease in action potential duration (APD), which results in an increase in the ERP/APD ratio. It does not significantly affect resting membrane potential or sinus node automaticity, left ventricular function, systolic arterial blood pressure, atrioventricular (AV) conduction velocity, or QRS or QT intervals. ^[1]

Mexiletine has fast onset and offset kinetics, meaning that they have little or no effect at slower heart rates, and more effects at faster heart rates. It shortens the action potential duration, reduces refractoriness, and decreases Vmax in partially depolarized cells with fast response action potentials. Mexiletine either does not change the action potential duration, or decreases the action potential duration. Mexiletine is well absorbed (bioavailability 90%) from the gastrointenstinal tract. ^[2]