At the completion of the maintenance period, subjects who did not enter Part II were to be tapered off study drug while maintaining the blind according to the following down titration procedure: subjects on 800 mg were down titrated to 400 mg for a duration of 2 weeks, and subjects on 1200 mg were down titrated to 800 mg for 1 week and then down-titrated to 400 mg for 1 week and subjects in the placebo group received placebo QD for 2 weeks. During Part I, 1 to 2 concomitant AEDs were allowed in this study and were to be kept stable during the course of the study.