FELBAMATE

FELBAMATE (fel'ba-mate) Felbatol Classifications: anticonvulsant; Therapeutic:anticonvulsant Prototype: Phenytoin Pregnancy Category: C

Availability

400 mg, 600 mg tablets; 600 mg/5 mL suspension

Action

Anticonvulsant mechanism has not been identified. Blocks repetitive firing of neurons and increases seizure threshold; prevents seizure spread.

Therapeutic Effect

Increases seizure threshold and prevents seizure spread.

Uses

Treatment of Lennox–Gastaut syndrome and partial seizures.

Unlabeled Uses

Monotherapy or in combination with other anticonvulsants for the treatment of generalized tonic/clonic seizures.

Contraindications

Hypersensitivity to felbamate, history of blood dyscrasia or hepatic dysfunction; pregnancy (category C).

Cautious Use

Renal impairment, renal failure; older adults; hypersensitivity to other carbamates; thrombocytopenia; iron-deficiency anemia; lactation. Safety and effectiveness in children other than those with Lennox–Gastaut syndrome are not established.

Route & Dosage

Partial Seizures Adult: PO Initiate with 1200 mg/d in 3–4 divided doses, may increase by 600 mg/d q2wk (max: 3600 mg/d); when converting to monotherapy, reduce dose of concomitant anticonvulsants by 1/3 when initiating felbamate, then continue to decrease other anticonvulsants by 1/3 with each increase in felbamate q2wk; when using as adjunctive therapy, decrease other anticonvulsants by 20% when initiating felbamate and note that further reductions in other anticonvulsants may be required to minimize side effects and drug interactions Lennox–Gastaut Syndrome Child: PO Start at 15 mg/kg/d in 3 or 4 divided doses, reduce concurrent antiepileptic drugs by 20%, further reductions may be required to minimize side effects due to drug interactions, may increase felbamate by 15 mg/kg/d at weekly intervals (max: 45 mg/kg/d)

Administration

Oral

• Do not give this drug to anyone with a history of blood dyscrasia or hepatic dysfunction.
• Titrate dose under close clinical supervision.
• Shake suspension well before giving a dose.
• Store in airtight container at room temperature, 15°–30° C (59°–86° F).

Adverse Effects (≥1%)

CNS: Mild tremors, headache, dizziness, ataxia, diplopia, blurred vision; agitation, aggression, hallucinations, fatigue, psychological disturbances. Endocrine: Slight elevation of serum cholesterol, hyponatremia, hypokalemia, weight gain and loss. GI: Nausea and vomiting, anorexia, constipation, hiccup, taste disturbance, indigestion, esophagitis, increased appetite, acute liver failure. Hematologic: Aplastic anemia.

Interactions

Drug: Felbamate reduces serum carbamazepine levels by a mean of 25%, but increases levels of its active metabolite, increases serum phenytoin levels approximately 20%, and increases valproic acid levels. Herbal: Gingko may decrease anticonvulsant effectiveness.

Pharmacokinetics

Absorption: 90% from GI tract. Absorption of tablet not affected by food. Onset: Therapeutic effect approximately 14 d. Peak: Peak plasma levels at 1–6 h. Distribution: 20–25% protein bound, readily crosses the blood–brain barrier. Metabolism: In the liver via the cytochrome P-450 system. Elimination: 40–50% excreted unchanged in urine, rest excreted in urine as metabolites. Half-Life: 20–23 h.

Nursing Implications

Assessment & Drug Effects

• Lab tests: Obtain baseline values for liver function and complete hematologic studies before initiating therapy, repeat frequently during therapy, and for a lengthy period after discontinuation of felbamate. Monitor serum sodium and potassium levels periodically because hyponatremia and hypokalemia have been reported.
• Report immediately any hematologic abnormalities.
• Monitor results of hepatic function tests throughout therapy.
• Note: When used concomitantly with either phenytoin or carbamazepine, carefully monitor serum levels of these drugs when felbamate is added, when adjustments in felbamate dosing are made, or when felbamate is discontinued.
• Note: A reduction in phenytoin of 10–40% is usually needed when felbamate is added to the regimen.
• Monitor weight, because both weight gain and loss have been reported.
• Monitor for S&S of drug toxicity including GI distress and CNS toxicity.

Patient & Family Education

• Note: It is highly recommended that patients and physicians review the indication for treatment, risks associated with the drug, and the importance of undergoing regular blood monitoring.
• Report unusual changes (e.g., blurred vision, dysplopia) to physician.
• Report S&S of hypersensitivity including pruritus, urticaria, and (rarely) photosensitivity allergic reaction to physician.
• Learn adverse effects and report these to physician immediately.

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Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug