CPT: 80299
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Expected Turnaround Time

2 - 4 days

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Specimen Requirements


Serum or plasma


3 mL

Minimum Volume

1.1 mL


Red-top tube, lavender-top (EDTA) tube, or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.


Transfer separated serum or plasma to a plastic transport tube.

Storage Instructions

Room temperature

Stability Requirements



Room temperature

7 days


14 days


14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Gel-barrier tube

Test Details


This Class 1B drug is used to suppress premature ventricular arrhythmias and may be as effective as quinidine or procainamide for this purpose. Mexiletine is less effective in patients with recurrent refractory ventricular tachycardia and fibrillation, and extracardiac side effects may limit its long-term usefulness. Approximately 45% of all patients experience side effects within the commonly accepted therapeutic range of 0.5−2.0 μg/mL.1 Concurrent administration of a Class 1A antiarrhythmic drug (eg, quinidine, disopyramide) or propranolol may provide better control of the arrhythmia and permit a reduction in the dose of mexiletine, thus reducing side effects. Supraventricular arrhythmias are not controlled by mexiletine.


This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.


High-pressure liquid chromatography (HPLC)

Reference Interval

Therapeutic: 0.75−2.00 μg/mL

Critical Value

Potentially toxic: >2.00 μg/mL

Additional Information

Mexiletine is a racemic mixture with equal parts of the (R) and (S) enantiomers, but will be present in plasma in unequal parts due to stereoselective hepatic metabolism. The ratio of the two enantiomers is genetically determined and differs between individuals.1 Toxic effects include dizziness, vomiting, confusion, tremor, bradycardia, and hypotension. Metabolism of mexiletine is accelerated by rifampin, phenobarbital, and phenytoin and retarded by cimetidine and ketoconazole. Half-life is 8 to 17 hours and is urine pH dependent. Acidic urine accelerates elimination.


1. Jurgens G, Graudal NA, Kampmann JP. Therapeutic monitoring of antiarrhythmic drugs. Clin Pharmacokinet. 2003; 42(7):647-663. 12844326


American Medical Association, Division of Drugs and Toxicology. Drug Evaluations Subscription. Chicago, Ill: AMA, Winter 1993.


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
716076 Mexiletine (Mexitil), Serum 3819-0 716077 Mexiletine, Serum ug/mL 3819-0

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