The three enzymes are polymorphically expressed and the genetic variants are responsible for changes in the enzyme activity.
Natalia Guevara, Cecilia Maldonado, Manuel Uría, Raquel González, Manuel Ibarra, SilvanaAlvariza, Antonella Carozzi, Carlos Azambuja, Pietro Fagiolino, Marta Vázquez 2017, 'Role of CYP2C9, CYP2C19 and EPHX Polymorphism in the Pharmacokinetic of Phenytoin:A Study on Uruguayan Caucasian Subjects', Pharmaceuticalshttps://www.mdpi.com/1424-8247/10/3/73. Retrieved from DOAJ CC BY 4.0 (https://creativecommons.org/licenses/by-sa/4.0/legalcode)