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HelpTest Code 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
Method Name
Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
Performing Laboratory
Mayo Clinic Laboratories in Rochester
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 |
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | OK |
| Gross icterus | OK |
Reference Values
30.0-80.0 mcg/mL
Day(s) Performed
Monday, Wednesday, Friday
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 |
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.
Cautions
No significant cautionary statements
Method Description
Samples are diluted and extracted online by high turbulence liquid chromatography with detection by tandem mass spectrometry.(Unpublished Mayo method)