Felbamate (Felbatol, Carter-Wallace)
Felbamate, released in 1994, was the first new antiepileptic medication in the United States in 15 years. Hopes were initially high, based upon clinical trials that showed good safety and efficacy. Clinical trials, are performed on two to five thousand individuals, and low-incidence side effects may not become evident until the medication is in the field.
As the drug approached 100,000 patient years of exposure, it became clear that complications were occurring. Thirty-one cases of aplastic anemia (serious injury to the blood and bone marrow) were reported, along with several cases of liver failure. A few of these complications were fatal. The drug was almost withdrawn from the market, but the FDA decided to let it stay with stern labeling, since it was the only effective drug for some individuals with epilepsy.
Prior to the concern about aplastic anemia, it was evident that felbamate had a unique profile of common side effects, including GI upset, weight loss, insomnia, and tendency to induce behavior problems, particularly in mentally impaired children and adults. Some individuals who are troubled by weight gain and sleepiness find felbamate particularly useful.
Felbamate indications were broad spectrum for a variety of seizure types. It has efficacy against atonic seizures, as well as partial and secondarily generalized seizures. Felbamate has substantial drug interactions, which make it difficult to use in conjunction with other medications.
A typical adult dose of felbamate is 400 - 1200 mg orally three times per day (total of 1200 - 3600 mg per day). Frequent monitoring of blood counts and liver tests are necessary if felbamate is to be used. It should only be used when all other reasonable alternatives have been tried and found inadequate.
Summary Data for Felbamate
Pill sizes: 400, 600 (scored) mg tan capsules.
Liquid for oral: suspension 600 mg/5ml.
Injectable: none
Typical adult dose: 900 mg divided as ˝ of a 600 mg tablet three times per day. Increase 300 mg daily every 3-7 days to a target dose of 1,800 mg divided into 3 doses. Dosing can go as high as 3,600 mg per day.
Typical pediatric dose: 15 mg/kg/d in 3 divided doses, increase as tolerated up to 45 mg/kg/d.
Metabolism: 50% by various liver systems and 50% kidney and other routes.Half-life: 12-18 hours.
Serum levels: not established.
Pregnancy: Category C - can cause birth defects in animals, unknown in humans.
Drugs that raise FLB levels: Valproate
Drugs that lower FLB levels: phenytoin, carbamazepine (but raises epoxide metabolite levels), phenobarbital.
FLB increases effects of: phenobarbital, phenytoin, valproate, carbamazepine epoxide.
FLB decreases effects of other drugs: oral contraceptives.
Dangerous Side Effects
Aplastic anemia, liver failure. The risk of a serious, and potentially fatal, complication is estimated at 1-in-2000.
Common Side Effects
GI upset, headache, insomnia, weight loss.
Other Side Effects
Behavior and personality changes (especially in children), sexual dysfunction, rash or itching, blurred vision, unsteadiness, dizziness, anxiety, depression, altered taste.