Phenotype Frequency

Genetic Variations in Cytochromes Affect
Drug Metabolism

More than 85% of patients have significant genetic variations in the most important cytochromes – CYP2D6, CYP2C9, CYP2C19, CYP3A4 and CYP3A5. For example, CYP3A4 and CYP3A5 affect the metabolism of one-half of the drugs in clinical use, and this variance is profoundly affected based on patient ethnicity.

Gene Variant Activity Caucasian Asian African
CYP3A4 Decreased 5.3% 0% 0%
CYP3A5 Decreased 93% 75% 27-50%

The YouScript® Personalized Prescribing System tests these cytochromes (CYPs), which are responsible for metabolizing most commonly prescribed medications. Once tested, each patient is classified as a Poor, Intermediate, Normal, Rapid, or Ultra-rapid Metabolizer. These classifications describe a patient’s inherent drug metabolizing capacity, a major contributor to adverse drug events.

Gene Poor Metabolizer Intermediate Metabolizer Normal Metabolizer Rapid or Ultrarapid Metabolizer
CYP2D6 10% 35% 48% 7%
CYP2C9 2-4% >35% ~60% N/A
CYP2C19* 2-20% 24-36% 14-44% 30%

*CYP2C19 variability depends on ethnicity.


The chart below describes effects that may be seen in patients with each of these phenotypes.

*Prodrugs must be metabolized in order to become active.

Until recently, you had little choice but to try medications without knowing in advance how patients might genetically respond. But no more: with personalized prescribing by YouScript, you’ll know upfront what medications will likely prove the most effective for your patient – and which ones will not. And you’ll know how medications will interact with the prescriptions and supplements she’s already taking.

YouScript is typically covered by Medicare and most private insurers.