Lamotrigine, Serum or Plasma

CPT: 80175
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Test Details

Synonyms

  • Lamictal®

Methodology

Liquid chromatography/tandem mass spectrometry (LC/MS-MS)

Reference Interval

Therapeutic: trough: 2.0−20.0 μg/mL

Additional Information

Lamotrigine is an antiepileptic drug (AED) of the phenyltriazine class that is chemically unrelated to existing AEDs. The precise mechanism of action is unknown although it has been postulated that lamotrigine inhibits voltage-sensitive sodium channels thereby stabilizing neuronal membranes and consequently modulating presynaptic transmitter release of excitatory amino acids (eg, glutamate, aspartate). Lamotrigine is 55% bound to plasma proteins and is metabolized predominantly to an inactive 2-N-glucuronide conjugate. Peak plasma concentration occurs at 1.4 to 4.8 hours following oral administration.1 The elimination half-life varies from 12 to 70 hours. The longer half-lives are observed in patients on concomitant valproic acid therapy. Accordingly, if lamotrigine is coadministered with valproic acid, the dose of lamotrigine must be reduced to less than half the normal dosage. The most common adverse reactions are associated with the use of lamotrigine in combination with other anticonvulsants, and include dizziness, diplopia, ataxia, blurred vision, nausea and vomiting, somnolence, headache, and rash. The anticonvulsants phenytoin, phenobarbital, primidone, and carbamazepine can reduce lamotrigine levels when coadministered.2 Conversely, lamotrigine can reduce levels of levetiracetam when coadministered.3 In children, investigators4 have found large differences in lamotrigine plasma levels in patients with improvement in seizure frequency, but patients who were seizure-free had higher lamotrigine levels than other patients in the study.

Specimen Requirements

Specimen

Serum or plasma

Volume

1 mL

Minimum Volume

0.3 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

Maintain specimen at room temperature.

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Gel-barrier tube

Clinical Information

Footnotes

1. Lensmeyer GL, Gidal BE, Wiebe DA. Optimized high-performance liquid chromatographic method for determination of lamotrigine in serum with concomitant determination of phenytoin, carbamazepine, and carbamazepine epoxide. Ther Drug Monit. 1997 Jun; 19(3):292-300. 9200770
2. Bourgeois BF. Pharmacokinetic properties of current antiepileptic drugs. What improvements are needed? Neurology. 2000; 55(11 Suppl 3):S11-S16. 11147563
3. May TW, Rambeck B, Jürgens U. Serum concentrations of levetiracetam in epileptic patients: The influence of dose and comedication. Ther Drug Monit. 2003 Dec; 25(6):690-699. 14639055
4. Bartoli A, Guerrini R, Belmonte A, Alessandri MG, Gatti G, Perucca E. The influence of dosage, age, and comedication on steady state plasma lamotrigine concentrations in epileptic children: A prospective study with preliminary assessment of correlations with clinical response. Ther Drug Monit. 1997 Jun; 19(3):252-260. 9200763

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
716944 Lamotrigine (Lamictal), Serum 6948-4 716945 Lamotrigine, Serum ug/mL 6948-4

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