 When the randomized allocation requires a switch, the AEDs currently taken carbamazepine, valproic acid, topiramate, oxcarbazepine, levetiracetam andor lamotrigine will be substituted, starting with the morning dose on day 2, with an equivalent formulation available in the market. Namely, a brand product will be switched to a generic, randomly chosen among those available in the market, while maintaining unaltered the dosing regimen and times of administration.Likewise, a generic product will be switched to the brand or another generic, as determined by the randomization scheme, while maintaining unaltered the dosing regimen and times of administration. For AEDs which are commercially available both as immediate-release as well as sustained-release dose forms, the substituted product brand of generic will have equivalent release characteristics. The newly allocated treatments will be continued unchanged for 4 days days 2,3,4 and 5 or 5 days days 2,3,4, 5 and 6 for patients receiving lamotrigine or topiramate without enzyme inducers, or lamotrigine combined with enzyme inducers plus valproate. No changes in concomitant treatments will be allowed during the 56 days of the study, although addition, withdrawal or dose modification of drugs not interacting pharmacokinetically with the medications taken by the subject will be permitted. 