Pharmacogenetics analyzes how an individual’s genetic makeup affects responses to drugs. Knowledge of gene variants causing differences in drug response among patients has the potential to allow “personalized” drug therapy.
There are several genes responsible for differences in drug metabolism and response. Among the most common are the cytochrome P450 (CYP) genes. They encode the cytochrome P450 class of metabolic enzymes found primarily in the human liver. Many of these enzymes play an instrumental role in the breakdown and clearance of clinically prescribed drugs.
Cytochrome P450 2D6 is estimated to be active in the breakdown of 20-25% of all medications prescribed.1 The potential benefit of CYP2D6 genotype testing is that patients with genotypes that are associated with a higher risk of ineffective therapy or of an adverse event may be identified, and alternative drug may be administered to these patients.
Cytochrome P450 2C19 metabolizes 5% of the prescription drugs in use today. Some of the commonly used and largest selling therapeutics for heart disease, depression, and fungal treatments are all metabolized by CYP2C19. Understanding a patient’s CYP2C19 genotype may provide insight into how they will respond to drugs.2