Felbamate

INDICATIONS AND USAGE Felbamate tablets, USP are not indicated as a first line antiepileptic treatment (see WARNINGS ). Felbamate tablets, USP are 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 acknowledgement, felbamate tablets, USP 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 Felbamate tablets, USP have been studied as monotherapy and adjunctive therapy in adults and as adjunctive therapy in children with seizures associated with Lennox-Gastaut syndrome. As felbamate tablets, USP are added to or substituted for existing AEDs, it is strongly recommended to reduce the dosage of those AEDs in the range of 20% to 33% to minimize side effects (see Drug Interactions subsection). Dosage Adjustment in the Renally Impaired: Felbamate, USP 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, USP plasma concentrations, especially AEDs, may warrant further reductions in felbamate, USP 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) Felbamate tablets, USP have not been systematically evaluated as initial monotherapy. Initiate felbamate tablets, USP 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 felbamate tablets, USP at 1200 mg/day in divided doses three or four times daily. Reduce the dosage of concomitant AEDs by one-third at initiation of felbamate tablets, USP therapy. At week 2, increase the felbamate tablets, USP 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 felbamate tablets, USP dosage up to 3600 mg/day and continue to reduce the dosage of other AEDs as clinically indicated. Adjunctive Therapy: Felbamate tablets, USP 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 felbamate, USP by 1200 mg/day increments at weekly intervals to 3600 mg/day. Most side effects seen during felbamate tablets, USP 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% to 33%* WEEK 2 REDUCE original dose by up to an additional 1/3* WEEK 3 REDUCE as clinically indicated Felbamate Tablet, USP Dosage 1200 mg/day Initial dose 2400 mg/day Therapeutic dosage range 3600 mg/day Therapeutic dosage range *See Adjunctive and Conversion to Monotherapy sections. While the above felbamate tablets, USP conversion guidelines may result in a felbamate tablet, USP 3600 mg/day dose within 3 weeks, in some patients titration to a 3600 mg/day felbamate tablets, USP dose has been achieved in as little as 3 days with appropriate adjustment of other AEDs. Children with Lennox-Gastaut Syndrome (Ages 2 to 14 years) Adjunctive Therapy: Felbamate tablets, USP 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 felbamate tablets, USP by 15 mg/kg/day increments at weekly intervals to 45 mg/kg/day. Most side effects seen during felbamate tablets, USP adjunctive th …

CONTRAINDICATIONS Felbamate tablets, USP is contraindicated in patients with known hypersensitivity to felbamate tablets, 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.

ADVERSE REACTIONS To report SUSPECTED ADVERSE REACTIONS, contact Amneal Pharmaceuticals at 1-877-835-5472 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . The most common adverse reactions seen in association with felbamate in adults during monotherapy are anorexia, vomiting, insomnia, nausea and headache. The most common adverse reactions seen in association with felbamate in adults during adjunctive therapy are anorexia, vomiting, insomnia, nausea, dizziness, somnolence and headache. The most common adverse reactions seen in association with felbamate 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%). 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 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 felbamate 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 Felbamate* (N=58) Low Dose Valproate** (N=50) Body System Event % % Body as a Whole Fatigue 6.9 4 Weight Decrease 3.4 0 Face Edema 3.4 0 Central Nervous System Insomnia 8.6 4 Headache 6.9 18 Anxiety 5.2 2 Dermatological Acne 3.4 0 Rash 3.4 0 Digestive Dyspepsia 8.6 2 Vomiting 8.6 2 Constipation 6.9 2 Diarrhea 5.2 0 SGPT Increased 5.2 2 Metabolic/Nutritional Hypophosphatemia 3.4 0 Respiratory Upper Respiratory Tract Infection 8.6 4 Rhinitis 6.9 0 Special Senses Diplopia 3.4 4 Otitis Media 3.4 0 Urogenital Intramenstrual Bleeding 3.4 0 Urinary Tract Infection 3.4 2 *3600 mg/day, ** 15 mg/kg/day 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 felbamate 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 adjunctiv …

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 felbamate to antiepileptic drugs (AEDs) affects the steady-state plasma concentrations of AEDs. The net effect of these interactions is summarized in Table 2: *Not administered but an active metabolite of carbamazepine. **No significant effect. Table 2 Steady-State Plasma Concentrations of Felbamate When Coadministered With Other AEDs AED Coadministered AED Concentration Felbamate Concentration Phenytoin ↑ ↓ Valproate ↑ ↔** Carbamazepine (CBZ) *CBZ epoxide ↓ ↑ ↓ Phenobarbital ↑ ↓ Specific Effects of Felbamate on Other Antiepileptic Drugs: Phenytoin: Felbamate 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 felbamate therapy resulted in phenytoin levels comparable to those prior to felbamate administration. Carbamazepine: Felbamate 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: Felbamate 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 felbamate, 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 felbamate, respectively. This indicates that the protein binding of valproate did not change appreciably with increasing doses of felbamate. 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 Felbamate: Phenytoin: Phenytoin causes an approximate doubling of the clearance of felbamate at steady-state and, therefore, the addition of phenytoin causes an approximate 45% decrease in the steady-state trough concentrations of fel …

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.

DESCRIPTION Felbamate is an antiepileptic available as 400 mg and 600 mg tablets for oral administration. Its chemical name is 2-phenyl-1,3-propanediol dicarbamate. Felbamate, USP is white to off-white powder. It is freely soluble in dimethyl sulfoxide, sparingly soluble in methanol, slightly soluble in acetonitrile and very slightly soluble in water. Felbamate's molecular weight is 238.24, its molecular formula is C 11 H 14 N 2 O 4 and its structural formula is: Each felbamate tablet, USP contains felbamate, USP 400 mg or 600 mg and following inactive ingredients: colloidal silicon dioxide, ferric oxide yellow, FD & C red no. 40 aluminum lake, lactose monohydrate, microcrystalline cellulose, magnesium stearate, povidone K 30, pregelatinised starch (botanical source: corn) and sodium starch glycolate type A (botanical source: potato). Apart from this felbamate tablets USP, 600 mg also contain D & C yellow no. 10 aluminum lake. Felbamate Tablets

OVERDOSAGE Four subjects inadvertently received felbamate as adjunctive therapy in dosages ranging from 5,400 mg/day to 7,200 mg/day for durations between 6 and 51 days. One subject who received 5,400 mg/day as monotherapy for 1 week reported no adverse experiences. Another subject attempted suicide by ingesting 12,000 mg of felbamate 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.

HOW SUPPLIED Felbamate Tablets USP, 400 mg are off-white to pale yellow colored, capsule shaped biconvex tablets, debossed with "10" and "53" separated by breakline on one side and plain on other and are supplied as: NDC 72578-056-06 in bottles of 30 tablets with child-resistant closures NDC 72578-056-16 in bottles of 90 tablets with child-resistant closures NDC 72578-056-01 in bottles of 100 tablets with child-resistant closures NDC 72578-056-05 in bottles of 500 tablets NDC 72578-056-77 in cartons of 100 tablets (10 x 10 unit-dose) Felbamate Tablets USP, 600 mg are light pink to pink colored, capsule shaped biconvex tablets debossed with "10" and "54" separated by breakline on one side and plain on other and are supplied as: NDC 72578-057-06 in bottles of 30 tablets with child-resistant closures NDC 72578-057-16 in bottles of 90 tablets with child-resistant closures NDC 72578-057-01 in bottles of 100 tablets with child-resistant closures NDC 72578-057-28 in bottles of 180 tablets NDC 72578-057-05 in bottles of 500 tablets NDC 72578-057-77 in cartons of 100 tablets (10 x 10 unit-dose) Store at 20°C to 25°C (68°F to 77°F) [See USP Controlled Room Temperature]. Dispense in tight container. Manufactured by: Zydus Lifesciences Ltd. Matoda, Ahmedabad, India. Distributed by: Viona Pharmaceuticals Inc. Cranford, NJ 07016 Rev.: 08/22