This study was planned as a single-dose, open label phase (Phase A) followed by a multiple-dose, double-blind, randomised, placebo-controlled, two-way crossover phase (Phase B) study in patients taking phenytoin. Phase B consisted of two 14-day treatment periods separated by a washout period of 10 to 15 days. Subjects continued their usual phenytoin scheme and received a single dose of ESL 1200 mg (Phase A) and either ESL (600 mg from Day 1 to 7 and 1200 mg from Day 8 to 14) or matching placebo once-daily for 14 days in each period.