FELBATOL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for FELBATOL (FELBATOL).
Felbamate is a GABA receptor agonist and modulates NMDA receptor activity, though its exact mechanism is not fully understood. It appears to enhance GABA-mediated inhibition and inhibit voltage-gated sodium channels, reducing neuronal excitability.
| Metabolism | Felbamate is primarily metabolized in the liver via cytochrome P450 enzymes, including CYP3A4, CYP2E1, and CYP2C19. It also undergoes hydrolysis to inactive metabolites. |
| Excretion | Renal: 40-50% unchanged; Hepatic metabolism accounts for ~50% with glucuronidation and oxidation; minimal biliary/fecal excretion (<5%). |
| Half-life | 20-23 hours; steady state reached within 3-5 days; may be prolonged in hepatic impairment. |
| Protein binding | 20-30% primarily to albumin; low binding reduces displacement interactions. |
| Volume of Distribution | 0.7 L/kg; indicates limited extravascular distribution consistent with low lipophilicity. |
| Bioavailability | Oral: ~90%; high and consistent absorption with minimal first-pass metabolism. |
| Onset of Action | Oral: 1-2 hours for therapeutic effect; IV administration not available. |
| Duration of Action | 12-24 hours; sustained by high trough levels with twice-daily dosing. |
| Molecular Weight | 238.24 |
1200-3600 mg/day orally in 3-4 divided doses; initial titration recommended.
| Dosage form | SUSPENSION |
| Renal impairment | CrCl <50 mL/min: reduce dose by 50%; CrCl <30 mL/min: avoid use. |
| Liver impairment | Child-Pugh Class A: use 50% of usual dose; Class B or C: contraindicated. |
| Pediatric use | For Lennox-Gastaut syndrome (age 2-14 years): 15 mg/kg/day in 3-4 divided doses, increase weekly by 15 mg/kg/day to max 45 mg/kg/day. |
| Geriatric use | Start at lower end of dosing range; monitor renal function closely. |
| 1st trimester | Use only if benefit outweighs risk; associated with neural tube defects due to folate antagonism. |
| 2nd trimester | Avoid unless essential; monitor for fetal growth restriction. |
| 3rd trimester | Avoid; risk of neonatal hemorrhage due to vitamin K-dependent clotting factor inhibition. |
Clinical note
Comprehensive clinical and safety monograph for FELBATOL (FELBATOL).
| Placental transfer | Crosses placenta; concentrations similar to maternal plasma. |
| Breastfeeding | Excreted into breast milk in low concentrations; monitor infant for sedation, poor feeding, and thrombocytopenia. |
| Lactation Rating |
■ FDA Black Box Warning
Felbamate is associated with aplastic anemia and liver failure, which can be fatal. It should be used only in patients who fail alternative treatments and for whom the benefit outweighs the risk.
| Serious Effects |
History of felbamate-induced hepatotoxicityHistory of aplastic anemiaHypersensitivity to felbamate or any component
| Precautions | Risk of aplastic anemia (often fatal) and liver toxicity (hepatic failure); monitor CBC and LFTs frequently, May cause blood dyscrasias, including leukopenia and thrombocytopenia, Suicidal behavior and ideation have been reported, Use with caution in patients with renal impairment, as felbamate is renally excreted, May cause visual field defects (e.g., retinal abnormalities) with long-term use, Central nervous system effects include dizziness, ataxia, somnolence, and fatigue |
| Food/Dietary | No specific food restrictions. However, take with food if gastrointestinal upset occurs. Avoid alcohol. |
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| L4 (Possibly Hazardous) |
| Teratogenic Risk | FDA Pregnancy Category C. First trimester: Increased risk of major congenital malformations, particularly orofacial clefts (odds ratio 5.05) and neural tube defects. Second/third trimester: Risk of neonatal hemorrhage due to vitamin K-dependent clotting factor inhibition; also associated with decreased IQ scores at age 6-7 years. Neonatal withdrawal syndrome possible. |
| Fetal Monitoring | Maternal: Serum folate levels (due to interference), liver function tests, CBC with platelets, serum ammonia, antiepileptic drug levels. Fetal: Detailed anatomy ultrasound at 18-20 weeks, fetal echocardiogram (orofacial clefts). Neonatal: Vitamin K 1 mg IM at birth, monitor for bleeding, withdrawal, and hyperammonemia. |
| Fertility Effects | No definitive studies; possible reversible reductions in serum testosterone and sperm quality in males. In females, no specific fertility impairment reported, but hormonal contraceptive efficacy may be reduced due to enzyme induction. |
| Clinical Pearls | Felbamate is reserved for refractory epilepsy due to risk of aplastic anemia and liver failure. Monitor CBC and LFTs at baseline and frequently. It is a GABA-positive modulator and NMDA antagonist. Significant drug interactions: increases phenytoin, valproate, and carbamazepine epoxide levels; decreases carbamazepine levels. Use caution in patients with hepatic impairment. |
| Patient Advice | Notify your doctor immediately if you experience fever, sore throat, easy bruising, bleeding, or jaundice, as these may indicate serious blood or liver problems. · Take felbamate exactly as prescribed; do not stop abruptly without consulting your doctor, as this may cause increased seizures. · Avoid alcohol and other CNS depressants, as they may increase drowsiness and dizziness. · Keep all appointments for blood tests to monitor for side effects. · Use effective contraception if applicable, as felbamate may reduce the effectiveness of oral contraceptives. · Report any unusual thoughts or behavior changes, as felbamate may increase risk of suicidal thoughts. |