Qualified subjects will be screened and upon fulfilling inclusion/exclusion criteria and signing the informed consent will be enrolled into the study and enter the randomization phase (2-30 days). Subjects will be randomized according to a sealed allocation list that will be balanced for sequence and provided to each site prior to the first subject enrollment. Subjects that withdraw prior to completing the second period will be replaced in a randomized manner. The randomization list will be generated by the study statistical group. There are four test periods in two sequences for a sequence-randomized study. During two test periods subjects will receive twice daily dosing of the "low" generic product and during the other two periods subjects will receive twice daily dosing of the "high" generic product. Each subject will return at the end of the 14+/-1 day stable dosing period for an in-facility 12-hour pharmacokinetic (PK) session to collect samples to determine Cmax and AUCs (area under curve). Each in-facility pharmacokinetic testing will be separated by a 14+/-1 day stable dosing period. A final follow-up phone evaluation will be conducted 12-16 days (target 14 days) after the last dose of study medication. A single make-up period will be permitted if there are issues during any single period. During the study the subjects will continue their usual concomitant medications, including AEDs (anti epilepsy drugs), without change.