Find Locations
For hours, walk-ins and appointments.Expected Turnaround Time
2 - 4 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Related Documents
Specimen Requirements
Specimen
Serum or plasma
Volume
3 mL
Minimum Volume
1.1 mL
Container
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.
Collection
Transfer separated serum or plasma to a plastic transport tube.
Storage Instructions
Room temperature
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 7 days |
Refrigerated | 14 days |
Frozen | 14 days |
Freeze/thaw cycles | Stable x3 |
Causes for Rejection
Gel-barrier tube
Test Details
Use
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.
Limitations
This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.
Methodology
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.
Footnotes
1. Jurgens G, Graudal NA, Kampmann JP. Therapeutic monitoring of antiarrhythmic drugs. Clin Pharmacokinet. 2003; 42(7):647-663. 12844326
References
American Medical Association, Division of Drugs and Toxicology. Drug Evaluations Subscription. Chicago, Ill: AMA, Winter 1993.
LOINC® Map
| 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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