While numerous factors may influence patient responses to medications, treatment response likely depends on the relationship between the pharmacokinetics, pharmacodynamics, and pharmacogenetics for each individual patient. 

Jeffrey Fudin, PharmD, FCCP, FASHP, clinical pharmacy specialist and director of the PGY-2 Pharmacy Pain Residency Program at the Stratton Veterans Administration Medical Center in Albany, New York, discussed pharmacogenetic testing as part of a presentation on dosage thresholds.

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Pharmacogenetic testing can serve as a tool that provides information in terms of how genetic variability affects individual responses to medications, specifically, Dr. Fudin explained, by helping clinicians determine how medications may be metabolized.  

Traditionally 4 common phenotypes designate how an individual will metabolize medications: normal or extensive metabolizers, poor metabolizers, intermediate metabolizers, and ultrarapid metabolizers.

Practitioners need to understand the clinical effect of genetic polymorphisms in metabolizing enzymes, Dr. Fudin said, which can vary depending on the phenotype and the specific medication. 

In discussing poor metabolizers, Dr. Fudin said, “for a medication that has an active parent compound, the potential clinical consequences in general include increased efficacy and the potential for lower doses to provide efficacy, or increased toxicity as a result of buildup of the active parent compound.”

For a medication for which the parent drug has little or no activity, he said, the clinical consequences in general may include decreased toxicity, little or no efficacy, and the potential need for higher doses if the drug is even a useful option.

This article originally appeared on MPR