This is an eight week, randomized, double blind, placebo-controlled, exploratory study. Patients randomized to rufinamide (SYN111) will receive 250 mg BID (total daily dose 500mg) for one week then have their dose increased to 500 mg BID (total daily dose 1000mg) for the remaining 7 weeks of the study. If the 500 mg BID dose is not tolerated, one dose reduction is allowed.