8. If felbamate is used as a concomitant AED, participants must be on felbamate for at least 2 years, with a stable dose for 8 weeks prior to Visit 1. They must not have a history of white blood cell (WBC) count below 2500/L (2.50 x 10^9/L), platelets below 100,000, liver function tests (LFTs) above 3 times the upper limit of normal (ULN), or other indication of hepatic or bone marrow dysfunction while receiving felbamate. If participants received felbamate in the past, it must have been discontinued 8 weeks prior to Visit 1