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Test ID: FELBA Felbamate (Felbatol), Serum

Reporting Name

Felbamate (Felbatol), S

Useful For

Determining whether a poor therapeutic response is attributable to noncompliance or lack of drug effectiveness

 

Monitoring changes in serum concentrations resulting from interactions with coadministered drugs such as barbiturates and phenytoin

Clinical Information

Felbamate is an anticonvulsant drug approved for treatment of partial seizures with or without secondary generalization in persons 14 years of age and older. It is also approved for Lennox-Gastout syndrome in children 2 years of age and older. Felbamate is well absorbed (>90%) and is metabolized by the hepatic cytochrome P450 system. Metabolites lack anticonvulsant activity. The elimination half-life of felbamate ranges from 13 to 23 hours.

 

Optimal response to felbamate is seen with serum concentrations between 30 mcg/mL to 60 mcg/mL. Patients who are elderly or have renal dysfunction may require reduced dosing; felbamate should not be given to individuals with hepatic disease. Toxicity can be severe, including life-threatening aplastic anemia or liver failure; toxic concentration has been established at concentrations greater than 120 mcg/mL.

 

Coadministration of felbamate increases the concentration of phenytoin and valproic acid, decreases carbamazepine concentration, and increases carbamazepine-10,11-epoxide (its active metabolite). Conversely, coadministration of phenytoin or carbamazepine causes a decrease in felbamate concentration.

Interpretation

Optimal response to felbamate is associated with serum concentrations of 30 mcg/mL to 60 mcg/mL.

 

Toxic serum concentrations for felbamate have been established at concentrations greater than 120 mcg/mL.

Analytic Time

Same day/1 day

Day(s) and Time(s) Performed

Monday, Wednesday, Friday; 3 p.m.

Clinical Reference

1. Johannessen, SI, Tomson, T: Pharmacokinetic Variability of Newer Antiepileptic Drugs: When is Monitoring Needed? Clin Pharmacokinet 2006;45 (11):1061-1075

2. Schmidt D: Felbamate: successful development of a new compound for the treatment of epilepsy. Epilepsia 1996;34(Suppl 7):S30-S33

3. Patsalos PN: Antiepileptic drugs--best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia. 2008 Jul;49(7):1239-1276

4. Nader R, Horwath AR, Wittwer CT: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Sixth edition. Elsevier, St. Louis, 2018

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Specimen Type

Serum


Specimen Required


Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions:

1. Draw blood immediately before next scheduled dose.

2. Centrifuge and separate serum from cells or gel within 2 hours of collection.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 28 days
  Ambient  28 days
  Frozen  28 days

Reference Values

30.0-60.0 mcg/mL

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

80299

LOINC Code Information

Test ID Test Order Name Order LOINC Value
FELBA Felbamate (Felbatol), S 6899-9

 

Result ID Test Result Name Result LOINC Value
80782 Felbamate (Felbatol), S 6899-9

Forms

If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

-Neurology Specialty Testing Client Test Request (T732)

-Therapeutics Test Request (T831)

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-Epilepsy, mml-Neuro-oncology