Study With Subjects 18-65 Years Old With Partial Onset Seizures Who Are Currently Taking Levetiracetam

Inclusion Criteria: * Males/Females from 18 to 65 years of age (minimum body weight of 40 kg) * Subjects with a confirmed diagnosis of epilepsy suffering from partial onset seizures whether or not secondarily generalized * Subjects who have been treated for epilepsy for \>= 6 months and are currently uncontrolled while being treated with 1-3 concomitant AED(s), inclusive of levetiracetam (LEV) * Female subjects without childbearing potential or those who are using an acceptable contraceptive method Exclusion Criteria: * Seizures occurring in clusters. Status epilepticus within 6 months of Visit 1. History of non-epileptic seizures * Subjects on vigabatrin * Subjects on felbamate, unless treatment has been continuous for \>2 years * Ongoing psychiatric disease other than mild controlled disorders * Subjects with clinically significant organ dysfunction * Known allergic reaction or intolerance to pyrrolidine derivatives and/or excipients * Pregnant or lactating women * Use of benzodiazepines (for any indication) taken at a higher frequency than an average of once a week, unless counted as one of the concomitant Antiepileptic Drug (AEDs).