Pharmacogenetic Phenotypes: Alterations in Pharmacokinetics, Drug Targets and Biologic Milieu

Genetic variations influence drug response through pharmacokinetics, receptor interactions, and the biologic milieu.

Pharmacokinetic alterations affect drug concentration.

For instance, individuals with the non-functional CYP2C9 variant require lower warfarin doses due to an increased bleeding risk. Similarly, the CYP2C19 variant impairs clopidogrel activation, leading to a higher risk of thrombosis.

Drug receptor variations also modify the response.

For instance, TYMS polymorphisms with the 2R/2R genotype can impact treatment outcomes. They affect both the toxicity and efficacy of anticancer agents that target TYMS.

Modifications in the biologic milieu also alter drug response. For example, MTHFR polymorphisms elevate homocysteine levels, increasing the risk of thrombosis.

Polymorphisms in ion channels, although not direct drug targets, prolong baseline QT intervals, increasing susceptibility to cardiac arrhythmias.

This predisposition is particularly concerning when using antiarrhythmics or certain noncardiovascular drugs.