Four randomized, controlled, double-blind, multicenter trials, conducted in a predominately adult population, demonstrated the efficacy of oxcarbazepine as monotherapy. Two trials compared oxcarbazepine to placebo and 2 trials used a randomized withdrawal design to compare a high dose (2400 mg) with a low dose (300 mg) of oxcarbazepine, after substituting oxcarbazepine 2400 mg/day for 1 or more antiepileptic drugs (AEDs). All doses were administered on a twice-a-day schedule. A fifth randomized, controlled, rater-blind, multicenter study, conducted in a pediatric population, failed to demonstrate a statistically significant difference between low and high dose oxcarbazepine treatment groups.

One placebo-controlled trial was conducted in 102 patients (11 to 62 years of age) with refractory partial-onset seizures who had completed an inpatient evaluation for epilepsy surgery. Patients had been withdrawn from all AEDs and were required to have 2 to 10 partial-onset seizures within 48 hours prior to randomization. Patients were randomized to receive either placebo or oxcarbazepine given as 1500 mg/day on Day 1 and 2400 mg/day thereafter for an additional 9 days, or until 1 of the following 3 exit criteria occurred: 1) the occurrence of a fourth partial-onset seizure, excluding Day 1, 2) 2 new-onset secondarily generalized seizures, where such seizures were not seen in the 1-year period prior to randomization, or 3) occurrence of serial seizures or status epilepticus. The primary measure of effectiveness was a between-group comparison of the time to meet exit criteria. There was a statistically significant difference in favor of oxcarbazepine (see Figure 1), p=0.0001.

Figure 1: Kaplan-Meier Estimates of Exit Rate by Treatment Group

The second placebo-controlled trial was conducted in 67 untreated patients (8 to 69 years of age) with newly-diagnosed and recent-onset partial seizures. Patients were randomized to placebo or oxcarbazepine, initiated at 300 mg twice a day and titrated to 1200 mg/day (given as 600 mg twice a day) in 6 days, followed by maintenance treatment for 84 days. The primary measure of effectiveness was a between-group comparison of the time to first seizure. The difference between the 2 treatments was statistically significant in favor of oxcarbazepine (see Figure 2), p=0.046.

Figure 2: Kaplan-Meier Estimates of First Seizure Event Rate by Treatment Group

A third trial substituted oxcarbazepine monotherapy at 2400 mg/day for carbamazepine in 143 patients (12 to 65 years of age) whose partial-onset seizures were inadequately controlled on carbamazepine (CBZ) monotherapy at a stable dose of 800 to 1600 mg/day, and maintained this oxcarbazepine dose for 56 days (baseline phase). Patients who were able to tolerate titration of oxcarbazepine to 2400 mg/day during simultaneous carbamazepine withdrawal were randomly assigned to either 300 mg/day of oxcarbazepine or 2400 mg/day oxcarbazepine. Patients were observed for 126 days or until 1 of the following 4 exit criteria occurred: 1) a doubling of the 28-day seizure frequency compared to baseline, 2) a 2-fold increase in the highest consecutive 2-day seizure frequency during baseline, 3) a single generalized seizure if none had occurred during baseline, or 4) a prolonged generalized seizure. The primary measure of effectiveness was a between-group comparison of the time to meet exit criteria. The difference between the curves was statistically significant in favor of the oxcarbazepine 2400 mg/day group (see Figure 3), p=0.0001.

Figure 3: Kaplan-Meier Estimates of Exit Rate by Treatment Group

Another monotherapy substitution trial was conducted in 87 patients (11 to 66 years of age) whose seizures were inadequately controlled on 1 or 2 AEDs. Patients were randomized to either oxcarbazepine 2400 mg/day or 300 mg/day and their standard AED regimen(s) were eliminated over the first 6 weeks of double-blind therapy. Double-blind treatment continued for another 84 days (total double-blind treatment of 126 days) or until 1 of the 4 exit criteria described for the previous study occurred. The primary measure of effectiveness was a between-group comparison of the percentage of patients meeting exit criteria. The results were statistically significant in favor of the oxcarbazepine 2400 mg/day group (14/34; 41.2%) compared to the oxcarbazepine 300 mg/day group (42/45; 93.3%) (p<0.0001). The time to meeting one of the exit criteria was also statistically significant in favor of the oxcarbazepine 2400 mg/day group (see Figure 4), p=0.0001.

Figure 4: Kaplan-Meier Estimates of Exit Rate by Treatment Group

A monotherapy trial was conducted in 92 pediatric patients (1 month to 16 years of age) with inadequately-controlled or new-onset partial seizures. Patients were hospitalized and randomized to either oxcarbazepine 10 mg/kg/day or were titrated up to 40 to 60 mg/kg/day within 3 days while withdrawing the previous AED on the second day of oxcarbazepine. Seizures were recorded through continuous video-EEG monitoring from Day 3 to Day 5. Patients either completed the 5- day treatment or met 1 of the 2 exit criteria: 1) three study-specific seizures (i.e., electrographic partial-onset seizures with a behavioral correlate), 2) a prolonged study-specific seizure. The primary measure of effectiveness was a between-group comparison of the time to meet exit criteria in which the difference between the curves was not statistically significant (p=0.904). The majority of patients from both dose groups completed the 5-day study without exiting.

Although this study failed to demonstrate an effect of oxcarbazepine as monotherapy in pediatric patients, several design elements, including the short treatment and assessment period, the absence of a true placebo, and the likely persistence of plasma levels of previously administered AEDs during the treatment period, make the results uninterpretable. For this reason, the results do not undermine the conclusion, based on pharmacokinetic/pharmacodynamic considerations, that oxcarbazepine is effective as monotherapy in pediatric patients 4 years old and older.