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HelpTest ID: FELBA Felbamate (Felbatol), Serum
Reporting Name
Felbamate (Felbatol), SUseful 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 and older. It is also approved for Lennox-Gastout syndrome in children 2 years 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 16 to 22 hours.
Optimal response to felbamate is seen with serum concentrations between 30 mcg/mL to 80 mcg/mL. Patients who are older adults or have kidney 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 100 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 80 mcg/mL.
Toxic serum concentrations for felbamate have been established at concentrations greater than 100 mcg/mL.
Report Available
Same day/1 to 3 daysDay(s) Performed
Monday, Wednesday, Friday
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;49(7):1239-1276
4. Rifai N, Horwath AR, Wittwer CT, eds: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018
5. Hiemke C, Bergemann N, Clement HW, et al. Consensus guidelines for therapeutic drug monitoring in neuropsychopharmacology: Update 2017. Pharmacopsychiatry. 2018;51(1-02):9-62
Method Name
Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
Specimen Type
SerumSpecimen Required
Supplies: Sarstedt Aliquot Tube 5 mL (T914)
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. Within 2 hours of collection, centrifuge the specimen.
3. For red-top tubes, immediately aliquot serum into a plastic vial.
4. For serum-gel tubes, aliquot serum into a plastic vial within 24 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
30.0-80.0 mcg/mL
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
80167
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)
mml-Epilepsy, mml-Neuro-oncology