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Steps to Implementing Pharmacogenomics (PGx) in Your Practice
FDA Labeling with PGx Information
Pharmacogenomic (PGx) information is increasingly being incorporated into FDA-approved drug labelling (package inserts). Drug labelling may now contain information on genomic "biomarkers." A biomarker, or biological marker, generally refers to a measurable indicator of some biological state or condition. In the case of PGx, it refers to the alleles, or polymorphisms. These polymorphisms can play an important role in identifying responders and non-responders to medications, avoiding adverse events, and optimizing drug dose; this is important to improve drug efficacy and/or safety.
There are currently over 160 unique drugs listed in the FDA table with some having multiple entries for multi-gene information. Drug labeling may contain information on genomic biomarkers and can describe:
- Drug exposure and clinical response variability
- Risk for adverse events
- Genotype-specific dosing
- Mechanisms of drug action
- Polymorphic drug target and disposition genes
- Trial design features
The FDA table is available at:
https://www.fda.gov/Drugs/ScienceResearch/ResearchAreas/
Pharmacogenetics/ucm083378.htm
An even more detailed version is available at:
https://www.fda.gov/downloads/Drugs/ScienceResearch/ResearchAreas/
Pharmacogenetics/UCM545881.pdf
The labeling for some, but not all, of the products includes specific actions to be taken based on the biomarker information. PGx information can appear in different sections of the labeling, depending on the actions.
Biomarkers in the table include but are not limited to:
- Germ-line or somatic gene variants (polymorphisms, mutations)
- Functional deficiencies with a genetic etiology, gene expression differences
- Chromosomal abnormalities; selected protein biomarkers that are used to select treatments for patients are also included
For drugs that are available in multiple dosage forms, salts, or combinations, a single representative product is listed. In the case of combination products, the single agent associated with the biomarker is listed, unless the agent is only approved as a combination product, in which case all agents are listed.
The table is a great resource but its limitations include:
- Frequency of table updates
- Lack of consistency for the type of PGx information included
- Genetic markers listed for drugs which may not be directly affected by that gene
One must carefully analyze the chart to avoid accidental misinterpretation.
Another valuable website we mentioned two weeks ago is PharmGKB, The Pharmacogenomics Knowledge base, at:
https://www.pharmgkb.org/
We will discuss this very valuable website in more detail later.
Loyd V. Allen, Jr., PhD, RPh
Editor-in-Chief
International Journal of Pharmaceutical Compounding
Remington: The Science and Practice of Pharmacy Twenty-second edition
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