DOSAGE AND ADMINISTRATION 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 felbamate is 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 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) Felbamate has not been systematically evaluated as initial monotherapy. Initiate felbamate at 1200 mg/day in divided doses three or 4 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 at 1200 mg/day in divided doses 3 or 4 times daily. Reduce the dosage of concomitant AEDs by one-third at initiation of felbamate therapy. At week 2, increase the felbamate 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 dosage up to 3600 mg/day and continue to reduce the dosage of other AEDs as clinically indicated. Adjunctive Therapy Felbamate should be added at 1200 mg/day in divided doses 3 or 4 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 by 1200 mg/day increments at weekly intervals to 3600 mg/day. Most side effects seen during felbamate 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% 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 Felbamate Dosage 1200 mg/day Initial dose 2400 mg/day Therapeutic dosage range 3600 mg/day Therapeutic dosage range While the above felbamate conversion guidelines may result in a felbamate 3600 mg/day dose within 3 weeks, in some patients titration to a 3600 mg/day felbamate 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 should be added at 15 mg/kg/day in divided doses 3 or 4 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 by 15 mg/kg/day increments at weekly intervals to 45 mg/kg/day. Most side effects seen during felbamate adjunctive therapy resolve as the dosage of concomitant AEDs is decreased.