• Percent reduction in the average monthly seizure rate from baseline to end of treatment
  

• Percent of patients responding to treatment (>= 50% reduction in seizure rate from baseline to end of treatment); patient's and investigator's global assessments at end of study; incidence of adverse events throughout study
  

Epilepsy is characterized by seizures, which are abnormal electrical discharges in the brain that temporarily disrupt normal brain function. Seizures are classified as "generalized," originating in both sides of the brain simultaneously, or "partial-onset," starting in one area of the brain. Antiepilepsy medications, such as topiramate, are selected based on seizure type. This study is designed to study patients with partial epilepsy. This is a double-blind, placebo-controlled study that includes a baseline phase and a treatment phase. During the baseline phase (8 weeks duration), patients receive one or two standard antiepileptic drugs (AEDs), such as phenytoin, carbamazepine, phenobarbital, primidone, or valproic acid. Patients who continue to have seizures during treatment with standard AEDs proceed into the double-blind treatment phase. Patients then receive topiramate or placebo at a dosage of 100-milligrams (mg) once daily, increasing gradually to 3 tablets twice daily (600 mg/day, maximum) for 12 weeks (total duration of double-blind phase), while continuing on their standard AED regimen. Assessments of effectiveness include the percent reduction in the average monthly seizure rate, percent of patients responding to treatment (having equal to or greater than 50% reduction in seizure rate), and the patient's and investigator's global assessments of medication at end of study. Safety assessments include the incidence of adverse events throughout the study, clinical laboratory tests (hematology, serum chemistry, urinalysis), neurologic examinations, and vital sign measurements (blood pressure, pulse, temperature) weekly during the treatment phase. The study hypothesis is that topiramate, taken as add-on therapy to treatment with AEDs, will significantly reduce seizure frequency, compared with placebo, in patients with refractory partial epilepsy: that is, in patients who continue to have seizures despite treatment with a first-line AEDs. In addition, it is hypothesized that topiramate is well-tolerated. Topiramate, 100 milligrams (mg) oral tablets. Dosage begins at 100 mg once daily and increases gradually over 4 weeks to 3 tablets twice daily (600 mg/day, maximum) or maximum tolerated dose for an additional 8 weeks.