Mexiletine, antiarrhythmic action

Tocainide and mexiletine also show stereoselectivity in their action with the R(—) enantiomers being four and two times, respectively, more potent than their antipodes in sodium channel blocking activity (Table 8). In contrast, there is no stereoselectivity in the main antiarrhythmic action of encainide, flecainide, and propafenone (Table 8). 

Some cardiac arrhythmias result from many stimuli present in the myocardium. Some of these are weak or of low intensity but are still able to excite myocardial tissue Lidocaine, by raising the threshold of myocardial fibers, reduces the number of stimuli that will pass along these fibers and therefore decreases the pulse rate and corrects the arrhythmia Mexiletine (Mexitil) and tocadnide (Tonocard) are also antiarrhythmic drag s with actions similar to those of lidocaine... 

ATROPINE ANTIARRHYTHMICS - MEXILETINE Delayed absorption of mexiletine Anticholinergic effects delay gastric emptying and absorption May slow the onset of action of the first dose of mexiletine, but is not of clinical significance for regular dosing (atropine does not 1 total dose absorbed)... 

Mexiletine hydrochloride, like cla.ss I antiarrhythmic agents, blocks the fast Na channel in cardiac cells. It is especially effective on the Purkinje fibers in the heart. The drug increases the threshold of excitability of myocardial cells by reducing the rale of rise and amplitude of the action potential and decreases aulomaliciiy. 

The third member of this class IB trio, mexiletine (No. 5), which was marketed in 1986, was first found to have anticonvulsant properties. Examination of its electrophysiological behavior led to its characterization as a strong ventricular antiarrhythmic. As the other drugs in this subclass, mexiletine blocks Na+ influx and reduces the maximal impulse velocity of phase O of the action potential. 

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