As with most anticonvulsants, the precise mechanism is unknown. It has a weak inhibitory effect on GABA receptor binding sites.
August 1993. Felbamate was approved for partial seizures with and without secondary generalization in adults and for Lennox-Gastaut Syndrome, a serious form of childhood epilepsy. Over the following year 150,000 people were started on felbamate therapy and a third of these became established.
August 1 1994. It was urgently withdrawn  after 10 cases of aplastic anemia. A "Dear Doctor" letter was sent to 240,000 physicians.
September 27 1994. Felbamate had a limited redemption in another "Dear Doctor" letter sent to 260,000 physicians. It was recommended that the drug remain available only for patients with severe epilepsy for whom the benefits outweigh the risks, and that changes be made to the product's labelling to reflect the newly recognized risk . This redemption came with an additional warning since there had been 10 cases acute liver failure (4 of which were fatal). At this point, 10,000 to 12,000 people remained on the drug.
The drug is only available on a limited named-patient basis.
Indications and usage
Adults: Monotherapy or adjunctive therapy in the treatment of partial seizures, with and without generalization.
Children: Adjunctive therapy in the treatment of partial and generalized seizures associated with Lennox-Gastaut syndrome.
Felbamate is available in tablets (400 mg and 600 mg) and as a peach-coloured oral suspension (600 mg/5 mL).
Adults (> 14 years): begin with 1,200 mg daily given every 6 to 8 hours
Children (2 > 14 years): 15 to 45 mg per kg per day given every 6 to 8 hours
Adverse reactions include decreased appetite, vomiting, insomnia, nausea, dizziness, somnolence, and headache. Many patients report increased alertness with the drug.
Two rare but very serious effects include aplastic anemia and hepatic (liver) failure. The risk of aplastic anemia is between 1:3,600 and 1:5,000, of which 30% of cases are fatal. The risk of hepatic failure is between 1:24,000 to 1:34,000, of which 40% of cases are fatal.
Felbamate interacts with other AEDs, the dose of which may be reduced in order to avoid adverse effects.
Felbamate for partial seizures: results of a controlled clinical trial.
Leppik IE, Dreifuss FE, Pledger GW, Graves NM, Santilli N, Drury I, Tsay JY, Jacobs MP, Bertram E, Cereghino JJ, et al.
[Abstract]. Neurology. 1991 Nov;41(11):1785–9.
RxList: Felbamate contains extensive information including the patient warning and a sample consent form.
Hard Choices with Felbamate
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