Topamax (topiramate) is approved by government regulatory agencies as monotherapy and adjunctive (add-on) therapy for many types of seizures in both adults and children. These include partial seizures (with and without secondary generalization), primary generalized tonic-clonic seizures, and seizures associated with Lennox-Gastaut syndrome.

In a number of randomized, controlled clinical trials in the 1990s, Topamax was significantly more effective than a placebo as add-on therapy for people with frequent partial seizures. In reports combining several such studies, about 44% of the people who took Topamax reduced their seizure frequency by half or more, compared to about 12% of those who added a placebo. The rate of unwanted side effects was rather high, but many of these people were given higher doses than are usually given now, with more rapid dose increases.

Topamax has the advantage of providing good control of both primary generalized tonic-clonic seizures and partial-onset seizures. In an add-on study that added Topamax or a placebo to other medications, the rate of primary generalized tonic-clonic seizures was reduced by at least half in 56% of those who took Topamax, versus 20% of those who added a placebo. Other types of generalized seizures were similarly reduced in these people.

Children with Lennox-Gastaut syndrome have various types of difficult-to-control seizures, including tonic and atonic seizures with stiffening or falling. When Topamax was added to previous medication, the frequency of major seizures was reduced by at least half for 33% of these children. Only 8% of those who added a placebo had a similar improvement.

No single combination of seizure medicines is perfect for everyone. Sometimes, a series of combinations must be tried before finding what is best for the individual. Adding Topamax generally does not have an important effect on the level of other seizure medicines in the blood. If a person starts or stops taking certain other medications while taking Topamax, however, the doctor probably will need to adjust the dose of Topamax. The most common medications with this kind of effect are carbamazepine (Tegretol, Carbatrol) and phenytoin (Dilantin, Phenytek).

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