Risk of a Type 1 ADR

How Drug Metabolism Can Affect the Risk of a Type 1 ADR

Type of metabolic reaction

Drug-gene pair examples

Pharmacogenetic phenotype predicted

Poor metabolizer

Rapid metabolizer

Drug is activated by metabolism

Codeine and CYP2D6


Clopidogrel and CYP2C19

Reduced drug activation; therapeutic failure likely

Accelerated drug activation; excess active drug accumulates; dose-related toxicity possible

Drug is inactivated by metabolism

Nortriptyline and CYP2D6


Phenytoin and CYP2C9

Poor drug inactivation; dose-related toxicity possible

Accelerated drug elimination; therapeutic failure possible