Mexiletine resources

Interactions for Mexiletine:

Since MEXITIL is a substrate for the metabolic pathways involving CYP2D6 and CYP1A2 enzymes, inhibition or induction of either of these enzymes would be expected to alter mexiletine plasma concentrations. In a formal, single-dose interaction study (n = 6 males) the clearance of mexiletine was decreased by 38% following the coadministration of fluvoxamine, an inhibitor of CYP1A2. In another formal study (n = 8 extensive and n = 7 poor metabolizers of CYP2D6), coadministration of propafenone did not alter the kinetics of mexiletine in the poor CYP2D6 metabolizer group. However, the metabolic clearance of mexiletine in the extensive metabolizer phenotype decreased by about 70% making the poor and extensive metabolizer groups indistinguishable. In this crossover steady state study, the pharmacokinetics of propafenone were unaffected in either phenotype by the coadministration of mexiletine. Addition of mexiletine to propafenone did not lead to further electrocardiographic parameters changes of QRS, QTc, RR, and PR intervals than propafenone alone. When concomitant administration of either of these two drugs with mexiletine is initiated, the dose of mexiletine should be slowly titrated to desired effect.

In a large compassionate use program Mexitil^® has been used concurrently with commonly employed antianginal, antihypertensive, and anticoagulant drugs without observed interactions. A variety of antiarrhythmics such as quinidine or propranolol were also added, sometimes with improved control of ventricular ectopy. When phenytoin or other hepatic enzyme inducers such as rifampin and phenobarbital have been taken concurrently with Mexitil^®, lowered Mexitil^® plasma levels have been reported. Monitoring of Mexitil^® plasma levels is recommended during such concurrent use to avoid ineffective therapy.

In a formal study, benzodiazepines were shown not to affect Mexitil^® plasma concentrations. ECG intervals (PR, QRS, and QT) were not affected by concurrent Mexitil^® and digoxin, diuretics, or propranolol.

Concurrent administration of cimetidine and Mexitil^® has been reported to increase, decrease, or leave unchanged Mexitil^® plasma levels; therefore patients should be followed carefully during concurrent therapy.

Mexitil^® does not alter serum digoxin levels but magnesium-aluminum hydroxide, when used to treat gastrointestinal symptoms due to Mexitil^®, has been reported to lower serum digoxin levels.

Concurrent use of Mexitil^® and theophylline may lead to increased plasma theophylline levels. One controlled study in eight normal subjects showed a 72% mean increase (range 35-136%) in plasma theophylline levels. This increase was observed at the first test point which was the second day after starting Mexitil^®. Theophylline plasma levels returned to pre-Mexitil^® values within 48 hours after discontinuing Mexitil^®. If Mexitil and theophylline are to be used concurrently, theophylline blood levels should be monitored, particularly when the Mexitil^® dose is changed. An appropriate adjustment in theophylline dose should be considered.

Additionally, in one controlled study in five normal subjects and seven patients, the clearance of caffeine was decreased 50% following the administration of Mexitil^®.