How does topiramate interact with prescription and over-the-counter medications?
Only a few interactions between topiramate and other drugs have been identified. Topiramate may increase the plasma level of phenytoin (Dilantin). Phenytoin lowers the concentration of topiramate in the blood by about 50%. While topiramate has little effect on the plasma level of carbamazepine, the latter may decrease the plasma level of topiramate by about 50%. Valproate lowers the plasma level of topiramate by about 15%. Topiramate may lead to decreased effectiveness of some oral anticontraceptives. Interactions with other prescription and over-the-counter drugs are not known at this time.
