The isoenzyme CYP3A5 is functionally and quantitatively related to CYP3A4, which has been connected with the expression of glycoprotein P and the resistance to AEDs; thus, it seems that also the polymorphism of CYP3A5 may have its share in the drug resistance mechanisms in epilepsy [15, 16, 29, 30]. This evidence concerns the gene ABCB1 and epilepsy.