Mexiletine (Mexitil®)

Test ID: 

703846

CPT code:

80375

Clinical 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.

Test 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.

Specimen Type:

Serum or plasma

Requested Volume: 

3 mL

Minimum Volume: 

1.1 mL

Container Type: 

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

Rejection Criteria:

Gel-barrier tube.

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