Felbamate, Serum or Plasma

CPT: 80339
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Test Details

Synonyms

  • Felbatol®

Use

Evaluate toxicity; monitor therapeutic levels

Methodology

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

Reference Interval

Therapeutic: 25−104 μg/mL; steady-state trough levels are dose proportional in adults. Multiple daily doses of 1200, 2400, and 3600 mg/day gave trough levels of 25−35, 47−63, and 62−104 μg/mL, respectively. Steady-state peak concentrations are dose proportional in children ages 4 to 12 years over a range of 15, 30, 45 mg/kg/day. The dose proportional peak concentrations were reported as 17, 32, and 49 μg/mL, respectively at two to six hours postdose. Co-administration of carbamazepine, phenytoin, phenobarbital, or primidone can cause a decrease in felbamate plasma concentrations; conversely, valproic acid can increase concentrations.1 In children, a similar effect was found with carbamazepine and phenytoin decreasing levels and an opposite effect with valproic acid.2

Additional Information

Following oral administration, felbamate is 25% bound to serum albumin. Approximately 40% to 50% of the absorbed dose appears unchanged in the urine. The rest is present as nonactive metabolites, including parahydroxyfelbamate, 2-hydroxyfelbamate, and felbamate monocarbamate. Felbamate has an elimination half-life of 20 to 23 hours. The apparent volume of distribution is 0.7−1.0 L/kg.

Specimen Requirements

Specimen

Serum or plasma

Volume

2 mL

Minimum Volume

0.6 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

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Gel-barrier tube

Clinical Information

Footnotes

1. Bourgeois BF. Pharmacokinetic properties of current antiepileptic drugs: What improvements are needed? Neurology. 2000; 55(Suppl 3):S11-S16. 11147563
2. Kelley MT, Walson PD, Cox S, Dusci LJ. Population pharmacokinetics of felbamate in children. Ther Drug Monit. 1997 Feb; 19(1):29-36. 9029743

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
716530 Felbamate (Felbatol(R)), Serum 6899-9 716531 Felbamate, Serum ug/mL 6899-9

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