Drug–Drug Interactions: Antiseizure Medications

Abstract

Abstract Antiseizure medications (ASMs) can affect other ASMs by affecting the amount of active metabolite in various ways. The most common way is via an increase in metabolism due to enzyme induction. ASMs that are CYP inducers can lower the level of another ASM if that ASM is metabolized by that enzyme. Alternatively, others may act as inhibitors of metabolism, thereby resulting in an increase in the level of an ASM. Some ASMs are thought to work synergistically due to such interactions, such as valproate and lamotrigine. On the other hand, some, such as valproate and phenytoin, compete for protein-binding, affecting free levels and active metabolites. In addition to direct interactions, medications with similar side-effect profiles, and/or mechanisms of action, may be more difficult to tolerate at escalating doses and one may have to be reduced to compensate for an increase in dose of the other. It is crucial to consider these interactions when pursuing polypharmacy or transition of ASMs.