Topiramate (Topamax®)
Health Canada's Health Protection Branch has granted marketing clearance for Topamax® (topiramate), a new antiepileptic drug (AED) proven to reduce the frequency of seizure in adults, particularly among people whose seizures are not controlled by other AEDs. Topiramate is indicated as an adjunctive therapy for those people.
Although the exact mechanism of action is not known, topiramate appears to work in 3 ways. It blocks voltage-sensitive sodium channels, thereby reducing the magnitude and duration of electrical discharges from nerve cells in the brain. It enhances the activity of gamma-aminobutyric acid (GABA), a neurotransmitter that inhibits nerve-cell excitation in the brain. It blocks the action of glutamate, a neurotransmitter that increases nerve-cell excitation in the brain.
Topiramate has been studied in more than 2,000 people worldwide. It has been established as a useful add-on therapy in adults with partial onset seizures, with or without secondarily generalized seizures. In one test (of 743 people who were being treated with traditional AEDs and had an average seizure frequency of 11 per month), 5% who tried it became completely seizure-free (0% in placebo group), 21% had at least a 75% reduction in seizure frequency (4% in placebo group), 44% had at least a 50% reduction (12% in placebo group), and 57% of people with secondarily generalized tonic-clonic seizures had at least a 50% reduction in seizure frequency (while the placebo group experienced an increase of 3%).
Clinical trials indicate that topiramate is well-tolerated and has few clinically significant interactions with other AEDs.
The most commonly reported side effects relate to the central nervous system. These include difficulty concentrating, drowsiness, dizziness and coordination problems. Most were "mile to moderate in severity and usually disappeared over time."
in 1,715 people who took topiramate in clinical trials, 1.5% reported the development of kidney stones.
Topamax® is available in 25, 100 and 200 mg tablets in bottles of 60 tablets. Suggested therapy begins with 50 mg daily, gradually increasing to 200 to 400 mg daily. The daily maximum recommended dose is 800 mg.
Topamax® is available in Canada by prescription. It will be "competitively priced with other new generation antiepileptic drugs."
