• Changes in length of time between the onset and cessation of painful migraine symptoms (migraine period) from the baseline. Safety evaluations conducted throughout the study.
  

• Proportion of patients responding to the treatment. Changes from baseline to double-blind phase in number of monthly migraine attacks, monthly migraine days, number of days/month requiring rescue medication, and Health-Related Quality of Life measures.
  

This is a randomized, double-blind, placebo-controlled, parallel-group, multi-center study to evaluate the effectiveness and safety of three different doses of topiramate (50mg, 100mg, and 200mg daily) in migraine prophylaxis. The study consists of five phases: baseline (determination of whether patients meet the eligibility criteria and tapering of any migraine medication patients are already taking); initial titration and double-blind phase (8 weeks) which begins with 25 mg/daily increasing to the assigned (50, 100, 200 mg/day topiramate); followed by a maintenance period at the target dose (18 weeks); tapering transition phase (up to 7 weeks); and open-label extension up to 6 months (to a maximum topirmate dose of 1600 mg/day); doses are adjusted to maximize effectiveness and minimize side effects. The primary study hypothesis is that one or more of the three doses of topiramate (50, 100, 200 mg/day) will be superior to placebo in the prophylaxis of migraine based on the change in monthly (28 day) migraine period rate from the prospective baseline period to the double-blind phase and that topiramate treatment is well tolerated.

During the titration period (8 weeks), doses are increased to target dose of daily topiramate (50 milligrams[mg], 100, or 200mg) or placebo, taken twice daily by mouth. Doses are continued for 18 weeks, adjusted over 7 weeks, and continued for up to 6 months during the Open-Label Extension.