Felbatol
Felbamate · Tablet · Oral
Uses
Felbatol ® is not indicated as a first line antiepileptic treatment (see Warnings ). Felbatol ® is recommended for use only in those patients who respond inadequately to alternative treatments and whose epilepsy is so severe that a substantial risk of aplastic anemia and/or liver failure is deemed acceptable in light of the benefits conferred by its use. If these criteria are met and the patient has been fully advised of the risk and has provided written acknowledgment, Felbatol ® can be considered for either monotherapy or adjunctive therapy in the treatment of partial seizures, with and without generalization, in adults with epilepsy and as adjunctive therapy in the treatment of partial and generalized seizures associated with Lennox-Gastaut syndrome in children.
Dosage and administration
Felbatol ® (felbamate) has been studied as monotherapy and adjunctive therapy in adults and as adjunctive therapy in children with seizures associated with Lennox-Gastaut syndrome. As Felbatol ® is added to or substituted for existing AEDs, it is strongly recommended to reduce the dosage of those AEDs in the range of 20–33% to minimize side effects (see Drug Interactions subsection). Dosage Adjustment in the Renally Impaired Felbamate should be used with caution in patients with renal dysfunction. In the renally impaired, starting and maintenance doses should be reduced by one-half (see CLINICAL PHARMACOLOGY/Pharmacokinetics and PRECAUTIONS ). Adjunctive therapy with medications which affect felbamate plasma concentrations, especially AEDs, may warrant further reductions in felbamate daily doses in patients with renal dysfunction. Adults (14 years of age and over) The majority of patients received 3600 mg/day in clinical trials evaluating its use as both monotherapy and adjunctive therapy. Monotherapy: (Initial therapy) Felbatol ® (felbamate) has not been systematically evaluated as initial monotherapy. Initiate Felbatol ® (felbamate) at 1200 mg/day in divided doses three or four times daily. The prescriber is advised to titrate previously untreated patients under close clinical supervision, increasing the dosage in 600-mg increments every 2 weeks to 2400 mg/day based on clinical response and thereafter to 3600 mg/day if clinically indicated. Conversion to Monotherapy: Initiate Felbatol ® at 1200 mg/day in divided doses three or four times daily. Reduce the dosage of concomitant AEDs by one-third at initiation of Felbatol ® therapy. At week 2, increase the Felbatol ® dosage to 2400 mg/day while reducing the dosage of other AEDs up to an additional one-third of their original dosage. At week 3, increase the Felbatol ® dosage up to 3600 mg/day and continue to reduce the dosage of other AEDs as clinically indicated. Adjunctive Therapy: Felbatol ® should be added at 1200 mg/day in divided doses three or four times daily while reducing present AEDs by 20% in order to control plasma concentrations of concurrent phenytoin, valproic acid, phenobarbital, and carbamazepine and its metabolites. Further reductions of the concomitant AEDs dosage may be necessary to minimize side effects due to drug interactions. Increase the dosage of Felbatol ® by 1200 mg/day increments at weekly intervals to 3600 mg/day. Most side effects seen during Felbatol ® adjunctive therapy resolve as the dosage of concomitant AEDs is decreased. Table 6 Dosage Table (adults) Dosage reduction of concomitant AEDs WEEK 1 REDUCE original dose by 20–33% See Adjunctive and Conversion to Monotherapy sections. WEEK 2 REDUCE original dose by up to an additional 1/3 WEEK 3 REDUCE as clinically indicated Felbatol ® Dosage 1200 mg/day Initial dose 2400 mg/day Therapeutic dosage range 3600 mg/day Therapeutic dosage range While the above Felbatol ® conversion guidelines may result in a Felbatol ® 3600 mg/day dose within 3 weeks, in some patients titration to a 3600 mg/day Felbatol ® dose has been achieved in as little as 3 days with appropriate adjustment of other AEDs. Children with Lennox-Gastaut Syndrome (Ages 2–14 years) Adjunctive Therapy: Felbatol ® should be added at 15 mg/kg/day in divided doses three or four times daily while reducing present AEDs by 20% in order to control plasma levels of concurrent phenytoin, valproic acid, phenobarbital, and carbamazepine and its metabolites. Further reductions of the concomitant AEDs dosage may be necessary to minimize side effects due to drug interactions. Increase the dosage of Felbatol ® by 15 mg/kg/day increments at weekly intervals to 45 mg/kg/day. Most side effects seen during Felbatol ® adjunctive therapy resolve as the dosage of concomitant AEDs is decreased.
Contraindications
Felbatol ® is contraindicated in patients with known hypersensitivity to Felbatol ® , its ingredients, or known sensitivity to other carbamates. It should not be used in patients with a history of any blood dyscrasia or hepatic dysfunction.
Warnings
See Boxed Warning regarding aplastic anemia and hepatic failure. Antiepileptic drugs should not be suddenly discontinued because of the possibility of increasing seizure frequency. Suicidal Behavior and Ideation Antiepileptic drugs (AEDs) including Felbatol ® , increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Patients treated with any AED for any indication should be monitored for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior. Pooled analyses of 199 placebo-controlled clinical trials (mono- and adjunctive therapy) of 11 different AEDs showed that patients randomized to one of the AEDs had approximately twice the risk (adjusted Relative Risk 1.8, 95% CI:1.2, 2.7) of suicidal thinking or behavior compared to patients randomized to placebo. In these trials, which had a median treatment duration of 12 weeks, the estimated incidence rate of suicidal behavior or ideation among 27,863 AED-treated patients was 0.43%, compared to 0.24% among 16,029 placebo-treated patients, representing an increase of approximately one case of suicidal thinking or behavior for every 530 patients treated. There were four suicides in drug-treated patients in the trials and none in placebo-treated patients, but the number is too small to allow any conclusion about drug effect on suicide. The increased risk of suicidal thoughts or behavior with AEDs was observed as early as one week after starting drug treatment with AEDs and persisted for the duration of treatment assessed. Because most trials included in the analysis did not extend beyond 24 weeks, the risk of suicidal thoughts or behavior beyond 24 weeks could not be assessed. The risk of suicidal thoughts or behavior was generally consistent among drugs in the data analyzed. The finding of increased risk with AEDs of varying mechanisms of action and across a range of indications suggests that the risk applies to all AEDs used for any indication. The risk did not vary substantially by age (5-100 years) in the clinical trials analyzed. Table 1 shows absolute and relative risk by indication for all evaluated AEDs. Table 1 Risk by Indication for Antiepileptic Drugs in the Pooled Analysis Indication Placebo Patients with Events Per 1000 Patients Drug Patients with Events Per 1000 Patients Relative Risk: Incidence of Events in Drug Patients/Incidence in Placebo Patients Risk Difference: Additional Drug Patients with Events Per 1000 Patients Epilepsy 1.0 3.4 3.5 2.4 Psychiatric 5.7 8.5 1.5 2.9 Other 1.0 1.8 1.9 0.9 Total 2.4 4.3 1.8 1.9 The relative risk for suicidal thoughts or behavior was higher in clinical trials for epilepsy than in clinical trials for psychiatric or other conditions, but the absolute risk differences were similar for the epilepsy and psychiatric indications. Anyone considering prescribing Felbatol ® or any other AED must balance the risk of suicidal thoughts or behavior with the risk of untreated illness. Epilepsy and many other illnesses for which AEDs are prescribed are themselves associated with morbidity and mortality and an increased risk of suicidal thoughts and behavior. Should suicidal thoughts and behavior emerge during treatment, the prescriber needs to consider whether the emergence of these symptoms in any given patient may be related to the illness being treated. Patients, their caregivers, and families should be informed that AEDs increase the risk of suicidal thoughts and behavior and should be advised of the need to be alert for the emergence or worsening of the signs and symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self-harm. Behaviors of concern should be reported immediately to healthcare providers.
Precautions
Dosage Adjustment in the Renally Impaired A study in otherwise healthy individuals with renal dysfunction indicated that prolonged half-life and reduced clearance of felbamate are associated with diminishing renal function. Felbamate should be used with caution in patients with renal dysfunction (see DOSAGE AND ADMINISTRATION ). Information for Patients Patients should be informed that the use of Felbatol ® is associated with aplastic anemia and hepatic failure, potentially fatal conditions acutely or over a long term. The physician should obtain written acknowledgment prior to initiation of Felbatol ® therapy (see PATIENT/PHYSICIAN ACKNOWLEDGMENT FORM section). Patients should be instructed to read the Medication Guide supplied as required by law when Felbatol ® is dispensed. The complete text of the Medication Guide is reprinted at the end of this document. Aplastic anemia in the general population is relatively rare. The absolute risk for the individual patient is not known with any degree of reliability, but patients on Felbatol ® may be at more than a 100 fold greater risk for developing the syndrome than the general population. The long term outlook for patients with aplastic anemia is variable. Although many patients are apparently cured, others require repeated transfusions and other treatments for relapses, and some, although surviving for years, ultimately develop serious complications that sometimes prove fatal (e.g., leukemia). At present there is no way to predict who is likely to get aplastic anemia, nor is there a documented effective means to monitor the patient so as to avoid and/or reduce the risk. Patients with a history of any blood dyscrasia should not receive Felbatol ® . Patients should be advised to be alert for signs of infection, bleeding, easy bruising, or signs of anemia (fatigue, weakness, lassitude, etc.) and should be advised to report to the physician immediately if any such signs or symptoms appear. Hepatic failure in the general population is relatively rare. The absolute risk for an individual patient is not known with any degree of reliability but patients on Felbatol ® are at a greater risk for developing hepatic failure than the general population. At present, there is no way to predict who is likely to develop hepatic failure, however, patients with a history of hepatic dysfunction should not be started on Felbatol ® . Patients should be advised to follow their physician’s directives for liver function testing both before starting Felbatol ® and at frequent intervals while taking Felbatol ® . Patients should be advised to be alert for signs of liver dysfunction (jaundice, anorexia, gastrointestinal complaints, malaise, etc.) and to report them to their doctor immediately if they should occur. Laboratory Tests Full hematologic evaluations should be performed before Felbatol ® therapy, frequently during therapy, and for a significant period of time after discontinuation of Felbatol ® therapy. While it might appear prudent to perform frequent CBCs in patients continuing on Felbatol ® , there is no evidence that such monitoring will allow early detection of marrow suppression before aplastic anemia occurs. (see Boxed Warnings ). Complete pretreatment blood counts, including platelets and reticulocytes should be obtained as a baseline. If any hematologic abnormalities are detected during the course of treatment, immediate consultation with a hematologist is advised. Felbatol ® should be discontinued if any evidence of bone marrow depression occurs. See Box Warnings for recommended monitoring of serum transaminases. If significant, confirmed liver abnormalities are detected during the course of Felbatol ® treatment, Felbatol ® should be discontinued immediately with continued liver function monitoring until values return to normal. (see PATIENT/PHYSICIAN ACKNOWLEDGMENT FORM ). Suicidal Thinking and Behavior Patients, their caregivers, and families should be counseled that AEDs, including Felbatol ® , may increase the risk of suicidal thoughts and behavior and should be advised of the need to be alert for the emergence or worsening of symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self-harm. Behaviors of concern should be reported immediately to healthcare providers. Pregnancy Patients should be encouraged to enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry if they become pregnant. This registry is collecting information about the safety of antiepileptic drugs during pregnancy. To enroll, patients can call the toll free number 1-888-233-2334 (see Pregnancy section). Drug Interactions The drug interaction data described in this section were obtained from controlled clinical trials and studies involving otherwise healthy adults with epilepsy. Use in Conjunction with Other Antiepileptic Drugs (see DOSAGE AND ADMINISTRATION ) The addition of Felbatol ® to antiepileptic drugs (AEDs) affects the steady-state plasma concentrations of AEDs. The net effect of these interactions is summarized in Table 2: Table 2 Steady-State Plasma Concentrations of Felbatol When Coadministered With Other AEDs AED Coadministered AED Concentration Felbatol ® Concentration Phenytoin ↑ ↓ Valproate ↑ ↔ No significant effect. Carbamazepine (CBZ) Not administered, but an active metabolite of carbamazepine. CBZ epoxide ↓ ↑ ↓ Phenobarbital ↑ ↓ Specific Effects of Felbatol® on Other Antiepileptic Drugs Phenytoin Felbatol ® causes an increase in steady-state phenytoin plasma concentrations. In 10 otherwise healthy subjects with epilepsy ingesting phenytoin, the steady-state trough (C min ) phenytoin plasma concentration was 17±5 micrograms/mL. The steady-state C min increased to 21±5 micrograms/mL when 1200 mg/day of felbamate was coadministered. Increasing the felbamate dose to 1800 mg/day in six of these subjects increased the steady-state phenytoin C min to 25±7 micrograms/mL.
Side effects
To report SUSPECTED ADVERSE REACTIONS, contact Viatris at 1-877-446-3679 (1-877-4-INFO-RX) or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. The most common adverse reactions seen in association with Felbatol ® (felbamate) in adults during monotherapy are anorexia, vomiting, insomnia, nausea, and headache. The most common adverse reactions seen in association with Felbatol ® in adults during adjunctive therapy are anorexia, vomiting, insomnia, nausea, dizziness, somnolence, and headache. The most common adverse reactions seen in association with Felbatol ® in children during adjunctive therapy are anorexia, vomiting, insomnia, headache, and somnolence. The dropout rate because of adverse experiences or intercurrent illnesses among adult felbamate patients was 12 percent (120/977). The dropout rate because of adverse experiences or intercurrent illnesses among pediatric felbamate patients was six percent (22/357). In adults, the body systems associated with causing these withdrawals in order of frequency were: digestive (4.3%), psychological (2.2%), whole body (1.7%), neurological (1.5%), and dermatological (1.5%). In children, the body systems associated with causing these withdrawals in order of frequency were: digestive (1.7%), neurological (1.4%), dermatological (1.4%), psychological (1.1%), and whole body (1.0%). In adults, specific events with an incidence of 1% or greater associated with causing these withdrawals, in order of frequency were: anorexia (1.6%), nausea (1.4%), rash (1.2%), and weight decrease (1.1%). In children, specific events with an incidence of 1% or greater associated with causing these withdrawals, in order of frequency was rash (1.1%). Incidence in Clinical Trials The prescriber should be aware that the figures cited in the following table cannot be used to predict the incidence of side effects in the course of usual medical practice where patient characteristics and other factors differ from those which prevailed in the clinical trials. Similarly, the cited frequencies cannot be compared with figures obtained from other clinical investigations involving different investigators, treatments, and uses including the use of Felbatol ® (felbamate) as adjunctive therapy where the incidence of adverse events may be higher due to drug interactions. The cited figures, however, do provide the prescribing physician with some basis for estimating the relative contribution of drug and nondrug factors to the side effect incidence rate in the population studied. Adults Incidence in Controlled Clinical Trials – Monotherapy Studies in Adults The table that follows enumerates adverse events that occurred at an incidence of 2% or more among 58 adult patients who received Felbatol ® monotherapy at dosages of 3600 mg/day in double-blind controlled trials. Table 3 presents reported adverse events that were classified using standard WHO-based dictionary terminology. Table 3 Adults Treatment-Emergent Adverse Event Incidence in Controlled Monotherapy Trials Felbatol ® 3600 mg/day (N=58) Low Dose Valproate 15 mg/kg/day (N=50) Body System/Event % % Body as a Whole Fatigue Weight Decrease Face Edema 6.9 3.4 3.4 4.0 0 0 Central Nervous System Insomnia Headache Anxiety 8.6 6.9 5.2 4.0 18.0 2.0 Dermatological Acne Rash 3.4 3.4 0 0 Digestive Dyspepsia Vomiting Constipation Diarrhea SGPT Increased 8.6 8.6 6.9 5.2 5.2 2.0 2.0 2.0 0 2.0 Metabolic/Nutritional Hypophosphatemia 3.4 0 Respiratory Upper Respiratory Tract Infection Rhinitis 8.6 6.9 4.0 0 Special Senses Diplopia Otitis Media 3.4 3.4 4.0 0 Urogenital Intramenstrual Bleeding Urinary Tract Infection 3.4 3.4 0 2.0 Incidence in Controlled Add-On Clinical Studies in Adults Table 4 enumerates adverse events that occurred at an incidence of 2% or more among 114 adult patients who received Felbatol ® adjunctive therapy in add-on controlled trials at dosages up to 3600 mg/day. Reported adverse events were classified using standard WHO-based dictionary terminology. Many adverse experiences that occurred during adjunctive therapy may be a result of drug interactions. Adverse experiences during adjunctive therapy typically resolved with conversion to monotherapy, or with adjustment of the dosage of other antiepileptic drugs. Table 4 Adults Treatment-Emergent Adverse Event Incidence in Controlled Add-On Trials Felbatol ® (N=114) Placebo (N=43) Body System/Event % % Body as a Whole Fatigue Fever Chest Pain 16.8 2.6 2.6 7.0 4.7 0 Central Nervous System Headache Somnolence Dizziness Insomnia Nervousness Tremor Anxiety Gait Abnormal Depression Paraesthesia Ataxia Mouth Dry Stupor 36.8 19.3 18.4 17.5 7.0 6.1 5.3 5.3 5.3 3.5 3.5 2.6 2.6 9.3 7.0 14.0 7.0 2.3 2.3 4.7 0 0 2.3 0 0 0 Dermatological Rash 3.5 4.7 Digestive Nausea Anorexia Vomiting Dyspepsia Constipation Diarrhea Abdominal Pain SGPT Increased 34.2 19.3 16.7 12.3 11.4 5.3 5.3 3.5 2.3 2.3 4.7 7.0 2.3 2.3 0 0 Musculoskeletal Myalgia 2.6 0 Respiratory Upper Respiratory Tract Infection Sinusitis Pharyngitis 5.3 3.5 2.6 7.0 0 0 Special Senses Diplopia Taste Perversion Vision Abnormal 6.1 6.1 5.3 0 0 2.3 Children Incidence in a Controlled Add-On Trial in Children with Lennox-Gastaut Syndrome Table 5 enumerates adverse events that occurred more than once among 31 pediatric patients who received Felbatol ® up to 45 mg/kg/day or a maximum of 3600 mg/day. Reported adverse events were classified using standard WHO-based dictionary terminology.
Drug interactions
Drug Interactions The drug interaction data described in this section were obtained from controlled clinical trials and studies involving otherwise healthy adults with epilepsy. Use in Conjunction with Other Antiepileptic Drugs (see DOSAGE AND ADMINISTRATION ) The addition of Felbatol ® to antiepileptic drugs (AEDs) affects the steady-state plasma concentrations of AEDs. The net effect of these interactions is summarized in Table 2: Table 2 Steady-State Plasma Concentrations of Felbatol When Coadministered With Other AEDs AED Coadministered AED Concentration Felbatol ® Concentration Phenytoin ↑ ↓ Valproate ↑ ↔ No significant effect. Carbamazepine (CBZ) Not administered, but an active metabolite of carbamazepine. CBZ epoxide ↓ ↑ ↓ Phenobarbital ↑ ↓ Specific Effects of Felbatol® on Other Antiepileptic Drugs Phenytoin Felbatol ® causes an increase in steady-state phenytoin plasma concentrations. In 10 otherwise healthy subjects with epilepsy ingesting phenytoin, the steady-state trough (C min ) phenytoin plasma concentration was 17±5 micrograms/mL. The steady-state C min increased to 21±5 micrograms/mL when 1200 mg/day of felbamate was coadministered. Increasing the felbamate dose to 1800 mg/day in six of these subjects increased the steady-state phenytoin C min to 25±7 micrograms/mL. In order to maintain phenytoin levels, limit adverse experiences, and achieve the felbamate dose of 3600 mg/day, a phenytoin dose reduction of approximately 40% was necessary for eight of these 10 subjects. In a controlled clinical trial, a 20% reduction of the phenytoin dose at the initiation of Felbatol ® therapy resulted in phenytoin levels comparable to those prior to Felbatol ® administration. Carbamazepine Felbatol ® causes a decrease in the steady-state carbamazepine plasma concentrations and an increase in the steady-state carbamazepine epoxide plasma concentration. In nine otherwise healthy subjects with epilepsy ingesting carbamazepine, the steady-state trough (C min ) carbamazepine concentration was 8±2 micrograms/mL. The carbamazepine steady-state C min decreased 31% to 5±1 micrograms/mL when felbamate (3000 mg/day, divided into three doses) was coadministered. Carbamazepine epoxide steady-state C min concentrations increased 57% from 1.0±0.3 to 1.6±0.4 micrograms/mL with the addition of felbamate. In clinical trials, similar changes in carbamazepine and carbamazepine epoxide were seen. Valproate Felbatol ® causes an increase in steady-state valproate concentrations. In four subjects with epilepsy ingesting valproate, the steady-state trough (C min ) valproate plasma concentration was 63±16 micrograms/mL. The steady-state C min increased to 78±14 micrograms/mL when 1200 mg/day of felbamate was coadministered. Increasing the felbamate dose to 2400 mg/day increased the steady-state valproate C min to 96±25 micrograms/mL. Corresponding values for free valproate C min concentrations were 7±3, 9±4, and 11±6 micrograms/mL for 0, 1200, and 2400 mg/day Felbatol ® , respectively. The ratios of the AUCs of unbound valproate to the AUCs of the total valproate were 11.1%, 13.0%, and 11.5%, with coadministration of 0, 1200, and 2400 mg/day of Felbatol ® , respectively. This indicates that the protein binding of valproate did not change appreciably with increasing doses of Felbatol ® . Phenobarbital Coadministration of felbamate with phenobarbital causes an increase in phenobarbital plasma concentrations. In 12 otherwise healthy male volunteers ingesting phenobarbital, the steady-state trough (C min ) phenobarbital concentration was 14.2 micrograms/mL. The steady-state C min concentration increased to 17.8 micrograms/mL when 2400 mg/day of felbamate was coadministered for one week. Effects of Other Antiepileptic Drugs on Felbatol ® Phenytoin Phenytoin causes an approximate doubling of the clearance of Felbatol ® (felbamate) at steady-state and, therefore, the addition of phenytoin causes an approximate 45% decrease in the steady-state trough concentrations of Felbatol ® as compared to the same dose of Felbatol ® given as monotherapy. Carbamazepine Carbamazepine causes an approximate 50% increase in the clearance of Felbatol ® at steady-state and, therefore, the addition of carbamazepine results in an approximate 40% decrease in the steady-state trough concentrations of Felbatol ® as compared to the same dose of Felbatol ® given as monotherapy. Valproate Available data suggest that there is no significant effect of valproate on the clearance of Felbatol ® at steady-state. Therefore, the addition of valproate is not expected to cause a clinically important effect on Felbatol ® (felbamate) plasma concentrations. Phenobarbital It appears that phenobarbital may reduce plasma felbamate concentrations. Steady-state plasma felbamate concentrations were found to be 29% lower than the mean concentrations of a group of newly diagnosed subjects with epilepsy also receiving 2400 mg of felbamate a day. Effects of Antacids on Felbatol ® The rate and extent of absorption of a 2400 mg dose of Felbatol ® as monotherapy given as tablets was not affected when coadministered with antacids. Effects of Erythromycin on Felbatol ® The coadministration of erythromycin (1000 mg/day) for 10 days did not alter the pharmacokinetic parameters of C max , C min , AUC, Cl/kg or T max at felbamate daily doses of 3000 or 3600 mg/day in 10 otherwise healthy subjects with epilepsy. Effects of Felbatol ® on Low-Dose Combination Oral Contraceptives A group of 24 nonsmoking, healthy white female volunteers established on an oral contraceptive regimen containing 30 µg ethinyl estradiol and 75 µg gestodene for at least 3 months received 2400 mg/day of felbamate from midcycle (day 15) to midcycle (day 14) of two consecutive oral contraceptive cycles. Felbamate treatment resulted in a 42% decrease in the gestodene AUC 0-24, but no clinically relevant effect was observed on the pharmacokinetic parameters of ethinyl estradiol.
Pregnancy
Pregnancy Patients should be encouraged to enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry if they become pregnant. This registry is collecting information about the safety of antiepileptic drugs during pregnancy. To enroll, patients can call the toll free number 1-888-233-2334 (see Pregnancy section). Pregnancy The incidence of malformations was not increased compared to control in offspring of rats or rabbits given doses up to 13.9 times (rat) and 4.2 times (rabbit) the human daily dose on a mg/kg basis, or 3 times (rat) and less than 2 times (rabbit) the human daily dose on a mg/m 2 basis. However, in rats, there was a decrease in pup weight and an increase in pup deaths during lactation. The cause for these deaths is not known. The no effect dose for rat pup mortality was 6.9 times the human dose on a mg/kg basis or 1.5 times the human dose on a mg/m 2 basis. Placental transfer of felbamate occurs in rat pups. There are, however, no studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed. To provide information regarding the effects of in utero exposure to Felbatol ® , physicians are advised to recommend that pregnant patients taking Felbatol enroll in the NAAED Pregnancy Registry. This can be done by calling the toll free number 1-888-233-2334, and must be done by patients themselves. Information on the registry can also be found at the website http://www.aedpregnancyregistry.org/.
Pediatric use
Pediatric Use The safety and effectiveness of Felbatol ® in children other than those with Lennox-Gastaut syndrome has not been established.
Geriatric use
Geriatric Use No systematic studies in geriatric patients have been conducted. Clinical studies of Felbatol ® did not include sufficient numbers of patients aged 65 and over to determine whether they respond differently from younger patients. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dosage selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.
Overdosage
Four subjects inadvertently received Felbatol ® (felbamate) as adjunctive therapy in dosages ranging from 5400 to 7200 mg/day for durations between 6 and 51 days. One subject who received 5400 mg/day as monotherapy for 1 week reported no adverse experiences. Another subject attempted suicide by ingesting 12,000 mg of Felbatol ® in a 12-hour period. The only adverse experiences reported were mild gastric distress and a resting heart rate of 100 bpm. No serious adverse reactions have been reported. General supportive measures should be employed if overdosage occurs. It is not known if felbamate is dialyzable.
Description
Felbatol ® (felbamate) is an antiepileptic available as 400 mg and 600 mg tablets and as a 600 mg/5 mL suspension for oral administration. Its chemical name is 2-phenyl-1,3-propanediol dicarbamate. Felbamate is a white to off-white crystalline powder with a characteristic odor. It is very slightly soluble in water, slightly soluble in ethanol, sparingly soluble in methanol, and freely soluble in dimethyl sulfoxide. The molecular weight is 238.24; felbamate’s molecular formula is C 11 H 14 N 2 O 4 ; its structural formula is: The inactive ingredients for Felbatol ® (felbamate) Tablets 400 mg and 600 mg are starch, microcrystalline cellulose, croscarmellose sodium, lactose, magnesium stearate, FD&C Yellow No. 6, D&C Yellow No. 10, and FD&C Red No. 40 (600 mg tablets only). The inactive ingredients for Felbatol ® (felbamate) Oral Suspension 600 mg/5 mL are sorbitol, glycerin, microcrystalline cellulose, carboxymethylcellulose sodium, simethicone, polysorbate 80, methylparaben, saccharin sodium, propylparaben, FD&C Yellow No. 6, FD&C Red No. 40, flavorings, and purified water. Felbamate Structural Formula
Mechanism of action
Mechanism of Action The mechanism by which felbamate exerts its anticonvulsant activity is unknown, but in animal test systems designed to detect anticonvulsant activity, felbamate has properties in common with other marketed anticonvulsants. Felbamate is effective in mice and rats in the maximal electroshock test, the subcutaneous pentylenetetrazol seizure test, and the subcutaneous picrotoxin seizure test. Felbamate also exhibits anticonvulsant activity against seizures induced by intracerebroventricular administration of glutamate in rats and N-methyl-D,L-aspartic acid in mice. Protection against maximal electroshock-induced seizures suggests that felbamate may reduce seizure spread, an effect possibly predictive of efficacy in generalized tonic-clonic or partial seizures. Protection against pentylenetetrazol-induced seizures suggests that felbamate may increase seizure threshold, an effect considered to be predictive of potential efficacy in absence seizures. Receptor-binding studies in vitro indicate that felbamate has weak inhibitory effects on GABA-receptor binding, benzodiazepine receptor binding, and is devoid of activity at the MK-801 receptor binding site of the NMDA receptor-ionophore complex. However, felbamate does interact as an antagonist at the strychnine-insensitive glycine recognition site of the NMDA receptor-ionophore complex. Felbamate is not effective in protecting chick embryo retina tissue against the neurotoxic effects of the excitatory amino acid agonists NMDA, kainate, or quisqualate in vitro. The monocarbamate, p-hydroxy, and 2-hydroxy metabolites were inactive in the maximal electroshock-induced seizure test in mice. The monocarbamate and p-hydroxy metabolites had only weak (0.2 to 0.6) activity compared with felbamate in the subcutaneous pentylenetetrazol seizure test. These metabolites did not contribute significantly to the anticonvulsant action of felbamate.
How supplied
Felbatol ® (felbamate) Tablets, 400 mg, are yellow, scored, capsule-shaped tablets, debossed 0430 on one side and FELBATOL 400 on the other; available in bottles of 100 (NDC 0037 0430-01). Felbatol ® (felbamate) Tablets, 600 mg, are peach-colored, scored, capsule-shaped tablets, debossed 0431 on one side and FELBATOL 600 on the other; available in bottles of 100 (NDC 0037-0431-01). Felbatol ® (felbamate) Oral Suspension, 600 mg/5 mL, is peach-colored; available in 8 oz bottles (NDC 0037-0442-67) and 32 oz bottles (NDC 0037-0442-17). Shake suspension well before using. Store at controlled room temperature 20°–25°C (68°–77°F). Dispense in tight container.
Patient information
Information for Patients Patients should be informed that the use of Felbatol ® is associated with aplastic anemia and hepatic failure, potentially fatal conditions acutely or over a long term. The physician should obtain written acknowledgment prior to initiation of Felbatol ® therapy (see PATIENT/PHYSICIAN ACKNOWLEDGMENT FORM section). Patients should be instructed to read the Medication Guide supplied as required by law when Felbatol ® is dispensed. The complete text of the Medication Guide is reprinted at the end of this document. Aplastic anemia in the general population is relatively rare. The absolute risk for the individual patient is not known with any degree of reliability, but patients on Felbatol ® may be at more than a 100 fold greater risk for developing the syndrome than the general population. The long term outlook for patients with aplastic anemia is variable. Although many patients are apparently cured, others require repeated transfusions and other treatments for relapses, and some, although surviving for years, ultimately develop serious complications that sometimes prove fatal (e.g., leukemia). At present there is no way to predict who is likely to get aplastic anemia, nor is there a documented effective means to monitor the patient so as to avoid and/or reduce the risk. Patients with a history of any blood dyscrasia should not receive Felbatol ® . Patients should be advised to be alert for signs of infection, bleeding, easy bruising, or signs of anemia (fatigue, weakness, lassitude, etc.) and should be advised to report to the physician immediately if any such signs or symptoms appear. Hepatic failure in the general population is relatively rare. The absolute risk for an individual patient is not known with any degree of reliability but patients on Felbatol ® are at a greater risk for developing hepatic failure than the general population. At present, there is no way to predict who is likely to develop hepatic failure, however, patients with a history of hepatic dysfunction should not be started on Felbatol ® . Patients should be advised to follow their physician’s directives for liver function testing both before starting Felbatol ® and at frequent intervals while taking Felbatol ® . Patients should be advised to be alert for signs of liver dysfunction (jaundice, anorexia, gastrointestinal complaints, malaise, etc.) and to report them to their doctor immediately if they should occur. PATIENT/PHYSICIAN ACKNOWLEDGMENT FORM FELBATOL ® (felbamate) SHOULD NOT BE USED BY PATIENTS UNTIL THERE HAS BEEN A COMPLETE DISCUSSION OF THE RISKS. All patients treated with Felbatol should acknowledge that they understand the risks and other information about Felbatol discussed below, and physicians should acknowledge this discussion. IMPORTANT INFORMATION AND WARNING: Felbatol ® , taken by itself or with other prescription and/or non-prescription drugs, can result in a severe, potentially fatal blood abnormality (“aplastic anemia”) and/or severe, potentially fatal liver damage. PATIENT ACKNOWLEDGMENT: Do not sign this form if there is anything you do not understand about the information you have received. Ask your doctor about anything you do not understand before you initial any of the items below or sign this form. My [My son, daughter, ward, __________________________________________________’s] treatment with Felbatol ® has been personally explained to me by Dr. ______________________________. The following points of information, among others, have been specifically discussed and made clear and I have had the opportunity to ask any questions concerning this information: 1. I, __________________________________________________________(Patient’s Name), understand that Felbatol ® is used to treat certain types of seizures and my physician has told me that I have this type(s) of seizures; INITIALS: __________ 2. I understand that Felbatol ® is being used because my seizures have not been satisfactorily treated with other antiepileptic drugs; INITIALS: __________ 3. I understand that there is a serious risk that I could develop aplastic anemia and/or liver failure, both of which are potentially fatal, by using Felbatol ® ; INITIALS: __________ 4. I understand that there are no laboratory tests which will predict if I am at an increased risk for one of the potentially fatal conditions; INITIALS: __________ 5. I understand that I should have the recommended blood work before my treatment with Felbatol ® is begun (baseline) and periodically thereafter as clinical judgement warrants. I understand that although this blood work may help detect if I develop one of these conditions, it may do so only after significant, irreversible and potentially fatal damage has already occurred; INITIALS: __________ 6. If I am currently taking other antiepileptic drugs, I understand that the manufacturer of Felbatol ® recommends that the dosage of these other drugs be decreased by a certain amount when Felbatol ® is started; if my physician determines that this should not be done in my case, he/she has explained the reason(s) for this decision; INITIALS: __________ 7. I understand that I must immediately report any unusual symptoms to Dr._______________ and be especially aware of any rashes, easy bruising, bleeding, sore throats, fever, and/or dark urine; INITIALS: __________ 8. I understand that antiepileptic drugs such as Felbatol ® may increase the risk of suicidal thoughts and behavior. I understand that I must immediately report any unusual changes in mood or behavior, symptoms of depression or thoughts about self-harm to Dr._________________.
Label text from the FDA structured product label by Viatris Specialty LLC (revised Aug 15, 2025). Long sections are shortened; the complete label is on DailyMed.
Active ingredients
- Felbamate in 2 products
Felbatol NDC products (2)
| NDC | Strength & form | Labeler | Type |
|---|---|---|---|
| 0037-0430 | Felbamate 400 mg/1 Tablet | Viatris Specialty LLC | NDA |
| 0037-0431 | Felbamate 600 mg/1 Tablet | Viatris Specialty LLC | NDA |
Frequently asked questions
What is Felbatol used for?
Felbatol ® is not indicated as a first line antiepileptic treatment (see Warnings ). Felbatol ® is recommended for use only in those patients who respond inadequately to alternative treatments and whose epilepsy is so severe that a substantial risk of aplastic anemia and/or liver failure is deemed acceptable in light of the benefits conferred by its use. If these criteria are met and the patient…
What are the side effects of Felbatol?
To report SUSPECTED ADVERSE REACTIONS, contact Viatris at 1-877-446-3679 (1-877-4-INFO-RX) or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. The most common adverse reactions seen in association with Felbatol ® (felbamate) in adults during monotherapy are anorexia, vomiting, insomnia, nausea, and headache. The most common adverse reactions seen in association with Felbatol ® in adults during… See the full label for the complete list.
Who makes Felbatol?
Felbatol is listed by 1 labeler in the FDA NDC directory, including Viatris Specialty LLC.