Test Catalog

Test ID: MEX    
Mexiletine, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Assessing achievement of optimal therapeutic concentrations


Assessing potential toxicity

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Mexiletine is a class I B antiarrhythmic with electrophysiologic properties similar to lidocaine and is useful in suppression of ventricular arrhythmias.


The drug exhibits a high degree of oral bioavailability, is approximately 60% protein bound, and undergoes renal clearance at a rate of 10.3 mL/min/kg. Mexiletine has a volume of distribution of 9.5 L/kg at a half-life of 11 hours. Myocardial infarction and uremia reduce the rate of clearance and increase the half-life of mexiletine, requiring dosage adjustment guided by drug monitoring.


Mexiletine toxicity occurs at concentrations above 2.0 mcg/mL (trough value) and is characterized by symptoms of nausea, hypotension, sinus bradycardia, paresthesia, seizures, intermittent left bundle branch block, and temporary asystole.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Trough Value

0.5-2.0 mcg/mL: Therapeutic concentration

>2.0 mcg/mL: Toxic concentration

Interpretation Provides information to assist in interpretation of the test results

Optimal response to mexiletine occurs when the serum concentration is within the range of 0.8 to 2.0 mcg/mL (trough value).

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Specimens that are obtained from gel tubes or anticoagulate collections can cause assay interference.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Nader R, Horwath AR, Wittwer CT: In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Sixth edition. St. Louis: Elsevier 2018

2. Burtis CA, Ashwood ER, Bruns DE, et al: In Tietz Textbook of Clinical Chemistry and Molecular Diagnosis. Fifth edition. St Louis: Elsevier. USA 2012

3. Josephson ME, Buxton AE, Marchlinski FE: The tachyarrhythmias: tachycardias. In Harrison's Principles of Internal Medicine. 12th edition. Edited by JD Wilson, E Braunwald, KJ Isselbacher, et al: New York, McGraw-Hill Book Company, 1991, p 915

4. Valdes R Jr, Jortani SA, Gheorghiade M, et al: Standards of Laboratory Practice: Cardiac Drug Monitoring. Clin Chem 1998;44(5):1096-1099

5. Joseph SP, Holt DW: Electrophysiological properties of mexiletine assessed with respect to plasma concentrations. Eur J Cardiol 1980 Feb;11(2):115-121