[Slow release versus immediate release oxcarbazepine in difficult-to-treat focal epilepsy: a multicenter, randomized,...

The aim of the study was an assessment of the tolerability and efficacy of slow release oxcarbazepine (OXC-MR) versus immediate release OXC (OXC-IR) after forced titration in patients with focal epileptic seizures with and without secondary generalization who had previously not become seizure-free under OXC-IR with or without concomitant antiepileptic drugs. The primary study variable was to assess the maximum tolerated dosage with OXC-MR and OXC-IR.

This was designed as a multicenter, randomized, open, controlled, parallel group phase III study. After randomization patients received OXC-MR or OXC-IR for a study period of 26 days. The initial dosage of 900 mg, 1,200 mg or 1,500 mg OXC was increased every 5 days by 300 mg up to a maximum daily dosage of 2,700 mg. In cases of intolerable adverse events dosage could be reduced by 150 mg 2 days after an increase. Adverse events and executive abilities were assessed with the questionnaire "Adverse Event Profile plus" and with the Epitrack® test protocol. Serum concentrations of OXC and its active metabolite were measured in a part of the patient group.

The 71 patients (54% male, age: 19-70 years) enrolled in the study were randomized. The maximum mean daily OXC dosage at the end of the study period was 1,950 mg with OXC-MR and thus statistically significantly higher than in OXC-IR group (1,650 mg, p = 0.022). The number of causally related adverse events was lower in the OXC-MR group (n = 104 versus n = 138 with OXC-IR) and CNS-related adverse events such as dizziness, tremor, somnolence and headache occurred significantly less often with OXC-MR (OXC-MR 65.7%, OXC-IR 88.9%, p = 0.01). Fluctuations of serum concentrations of the active metabolite were less pronounced under the OXC-MR regimen.

Due to better tolerability OXC-MR allowed higher maintenance dosages to be reached than OXC-IR. In spite of a higher mean daily dosage adverse events and especially CNS-related adverse events occurred less often than with OXC-IR.