Felbamate

Trade Names:
Felbatol
- Tablets 400 mg
- Tablets 600 mg
- Suspension 600 mg/5 mL

Pharmacology

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May reduce seizure spread in generalized tonic-clonic or partial seizures and may increase seizure threshold in absence seizures.

Pharmacokinetics

Distribution

Vd is about 756 mL/kg and the drug is 22% to 25% bound to plasma proteins.

Metabolism

About 40% to 50% is excreted unchanged in the urine.

About 40% is unidentified metabolites and conjugates and about 15% is parahydroxy-felbamate, 2-hydroxyfelbamate, and felbamate monocarbamate; none have significant anticonvulsant activity.

Elimination

The t _{1/ 2} is 20 to 23 h. Cl is about 30 mL/h/kg.

Special Populations

Decreased felbamate Cl and increased t _{1/ 2} were associated with diminishing renal function.

Indications and Usage

Monotherapy or adjunctive therapy in treatment of partial seizures with and without generalization in epileptic adults. Adjunctive therapy in treatment of partial and generalized seizures associated with Lennox-Gastaut syndrome in children.

Contraindications

Hypersensitivity to felbamate or ingredients of this product; hypersensitivity reactions to other carbamates; history of any blood dyscrasia or hepatic dysfunction.

Dosage and Administration

Because of reports of aplastic anemia, it has been recommended to stop use of this drug unless health care provider decides that withdrawal would cause greater risk.

PO 1,200 mg/day in 3 or 4 divided doses; increase in 600 mg increments every 2 wk to 2,400 mg/day and then 3,600 mg/day if indicated.

PO 1,200 mg/day in 3 or 4 divided doses, reducing dose of other antiepileptic drugs by 1/ 3 . At wk 2, increase felbamate to 2,400 mg/day and at week 3, increase to 3,600 mg/day; continue to reduce dose of other antiepileptic drugs as indicated.

PO 1,200 mg/day in 3 or 4 divided doses; reduce original dose of other antiepileptic drugs by 20% to 33% for 1 wk. At week 2, increase felbamate to 2,400 mg/day and at week 3, increase to 3,600 mg/day if needed; reduce dosage of other antiepileptic drugs as clinically indicated.

PO 15 mg/kg/day in 3 or 4 divided doses while reducing other antiepileptic drugs at least 20%. Increase felbamate by 15 mg/kg/day increments at weekly intervals up to 45 mg/kg/day; continue to reduce dosage of other antiepileptic drugs as needed.

General Advice

• Instruct patient to take tablet whole with full glass of water; do not crush or chew.
• May administer tablet with food.
• Administer suspension if patient is unable to swallow tablets.
• Shake suspension prior to administration.

Storage/Stability

Store at room temperature in tightly closed container away from excessive heat, direct sunlight, and moisture.

Drug Interactions

Felbamate may increase blood levels of phenytoin and valproic acid and decrease blood levels of carbamazepine. Phenytoin or carbamazepine may increase clearance of felbamate.

Laboratory Test Interactions

None well documented.

Adverse Reactions

CNS

Insomnia; headache; anxiety; somnolence; dizziness; nervousness; tremor; abnormal gait; depression; paresthesia; ataxia; dry mouth; stupor; thinking abnormalities; emotional lability.

Dermatologic

Acne; rash; pruritus.

EENT

Diplopia; abnormal vision; miosis; otitis media; rhinitis; sinusitis; taste perversion; pharyngitis.

GI

Dyspepsia; vomiting; constipation; diarrhea; nausea; anorexia; abdominal pain; hiccoughs.

Genitourinary

Urinary incontinence; intramenstrual bleeding; UTI.

Hematologic

Aplastic anemia; purpura; leukopenia.

Hepatic

Increased ALT and AST; acute liver failure.

Respiratory

Upper respiratory tract infection; coughing.

Miscellaneous

Fatigue; weight decrease; facial edema; fever; chest pain; pain; hypophosphatemia; myalgia.

Precautions

Pregnancy

Category C .

Lactation

Excreted in breast milk.

Children

Safety and efficacy not established other than for adjunctive therapy of Lennox-Gastaut syndrome.

Elderly

Use caution and start with low doses. Clinical experience is limited.

Hypersensitivity

Administer drug with caution to patients with prior hypersensitivity reactions to carbamates.

Carcinogenesis

Drug may have carcinogenic potential.

Discontinuation

Withdraw drug slowly to avoid increased seizure frequency.

Pre-existing liver failure

8 cases of acute liver failure have occurred, including 4 deaths, in association with the use of felbamate. Evaluate patients prior to treatment initiation for evidence of pre-existing liver damage; avoid use in patients with pre-existing liver pathology. Immediately withdraw the drug in patients who develop lab findings indicating liver injury.

Patient Information

• Instruct patient to drink at least 1 full glass of water with each dose.
• Remind patient to take tablet whole; do not crush.
• Inform patient that tablet may be taken with food.
• Caution patient to not stop taking this medication suddenly because of possibility of increasing seizure frequency.
• Advise patient to avoid exposure to sunlight or sunlamps and to use sunscreen or wear protective clothing to avoid photosensitivity reaction.
• Instruct patient and family that if seizures occur, they should protect patient from injury.
• Inform patient to report these symptoms to health care provider: loss of appetite, nausea, vomiting, indigestion, constipation, diarrhea, weight loss/gain, anxiety, nervousness, tremors, dizziness, depression, chest pain, fever, headache, poor coordination, drowsiness, sleeplessness, edema (fluid retention), intramenstrual bleeding (women), dry mouth, vision problems and any changes in seizure activity.
• Advise patient that drug may cause drowsiness, dizziness, and vision problems, and to use caution while driving or performing other tasks requiring mental alertness.

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