Felbamate (Felbatol), Serum
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 Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Felbamate is an anticonvulsant drug approved for treatment of partial seizures with or without secondary generalization in persons >14 years of age. It is also approved for Lennox-Gastout syndrome in children >2 years of age. 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, but no defined toxic concentration has been established.
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.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Optimal response to felbamate is associated with serum concentrations of 30 mcg/mL to 60 mcg/mL.
Toxic serum concentrations for felbamate have not been established.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
No significant cautionary statements
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Johannessen, SI, Tomson, T: Pharmacokinetic Variability of Newer Antiepileptic Drugs: When is Monitoring Needed? Clin Pharmacokinet 2006; 45 (11): 1061-10752. Schmidt D: Felbamate: successful development of a new compound for the treatment of epilepsy. Epilepsia 1996;34(Suppl 7):S30-S33
2. 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