Levetiracetam Versus Topiramate as Adjunctive Therapy to Evaluate Efficacy and Safety in Subjects With Refractory Partial Onset Seizures

Inclusion Criteria: * Male or female subjects from 16 to 80 years, inclusive. Subjects under 20 years may only be included where legally permitted and ethically accepted * Subjects with refractory epilepsy with partial onset seizure classifiable according to the International League Against Epilepsy (ILAE). * Subjects having at least 2 partial onset seizures whether or not secondarily generalized during the 8 weeks historical baseline preceding V1 according to ILAE classification * Subjects having at least 1 partial onset seizures whether or not secondarily generalized per 4 weeks preceding V2 according to ILAE classification * Subjects with each interval of partial onset seizures less than 6 weeks during entire 12 weeks (8 weeks preceding V1 and 4 weeks preceding V2) * Subjects being uncontrolled while treated by 1 to 3 permitted concomitant AEDs. * Permitted concomitant AEDs having been stable and at optimal dosage for the subject from at least 4 week before V1 and during 4 weeks preceding V2 and expected to be kept stable during the Treatment Period. Exclusion Criteria: * Subjects presenting any generalized epilepsies classified as type II according to the ILAE classification (ref to publication from 1981) * Subjects suffering from epilepsies and syndromes undetermined whether focal or generalized (classification III according to the ILAE classification) * Subjects suffering from special syndromes (classification IV according to the ILAE classification) * History or occurring only in clusters (too frequently or indistinctly separated to be reliably counted) before V2. * Presence of exclusively type IA non-motor seizures. * History or presence of status epilepticus within last 3 months preceding V1 or during Baseline * History or presence of known pseudo-seizures * Subjects who are currently on vigabatrin. (Subjects who received vigabatrin in the past and have a normal visual field test are allowed.) * Subject taking 1 or more of the following medications on a regular basis within 28 days prior to Visit 1: antipsychotics drugs, and psychostimulant (amphetamine derivatives)