Drug-resistant Epilepsy: Which Drugs are Substrates of P-glycoprotein and Which are Not?

One of the accepted factors of antiseizure medication resistance is the action of P-glycoprotein (P-gp), limiting the access of drugs to the nervous system. But if we ask which antiseizure medications are substrates of P-gp and which are not, the available bibliography will not allow us to obtain a clear answer. In this review, we focus on clarifying this response. The reviewed studies have been conducted both in cell lines and in mice that have been administered a P-gp inhibitor, artificially induced with drug-resistant epilepsy, or had a P-gp gene knockout. A limited number of studies have been conducted in dogs, primates, brain sections of known epilepsies, or human volunteers, including pharmacokinetic studies in healthy volunteers and symptomatic response to treatment. Notably, in human cases, allele variation studies check if having one allele or another of P-gp varies the pharmacokinetics in question. As we see, the approach to P-gp and antiseizure medication can be done using very different methods, which undoubtedly complicates the interpretation of the findings. We cannot be categorical in our results, but we can mention probabilities. Regarding the weighting of studies, we will consider those conducted in humans as more important, followed by animal studies, and we will give less weight to studies showing contradictory results compared to the general bibliographic base. Based on the published bibliography, we propose that, among the anticrisis medications, the following are likely substrates of P-glycoprotein: Phenytoin, Phenobarbital, Oxcarbazepine, Lamotrigine, Topiramate, and Lacosamide (less evidence). The following are probably not substrates: Brivaracetam, Zonisamide, Valproic acid, Perampanel, Gabapentin, and Vigabatrin. We have not obtained enough information about: Carbamazepine, Eslicarbazepine, Levetiracetam, Tiagabine, Felbamate, Pregabalin, Rufinamide, Ezogabine, and Retigabine.