Pharmacogenetics

Pharmacogenetics is the study of inherited genetic differences in metabolic pathways which can affect individual responses to drugs, both in terms of therapeutic effect as well as adverse effects.

Individual patient response to medications is influenced by genetic variation in the enzymes responsible for drug metabolism as well as targeted receptors and transporters.

The majority of drugs enter the body and have to be metabolized before giving good therapy.  Knowing what genetic variants are present or not, leads to more effective medication prescribing.

Alterations in enzyme function are categorized info four phenotypes.  Knowing a patient’s metabolic phenotype and its impact on drug metabolism can empower clinical treatment decisions, increase drug efficacy and reduce the risk of adverse events.

  • Extensive Metabolizers: (EM) carry 2 functional genes and have normal enzyme activity.  Standard medication dosing is appropriate for extensive metabolizers.
  • Poor Metabolizers (PM) have severely reduced or no functional capacity to metabolize substrate medications. Poor metabolizers are at risk for side effects due to toxic drug accumulation and may require lower doses.
  • Intermediate Metabolizers (IM) also have a severely reduced capacity to metabolize drugs and therefore may also require modified drug doses.
  • Ultra-Rapid Metabolizers (UM) typically carry multiple copies of the same gene and have elevated enzyme activity and may need increasing drug dosing or decreased drug dosing, in the case of pro-drugs, in order to offset the higher rate of metabolism.

Variations in metabolism can cause life-threatening toxicity in one person and reduce drug effectiveness in another. Genetic testing provides physicians with valuable patient-specific information to provide better therapeutic treatment decisions to determine, right drug, at the right dose, for the right person.

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Why is genomic information helpful?

Each gene provides the blueprint for the production of a certain protein in the body. A particular protein may have an important role in drug treatment for one of several reasons, including the following:

  1. The protein plays a role in breaking down the drug.
  2. It helps with the absorption or transport of the drug.
  3. The protein is the actual target of the drug.
  4. It has some role in a series of molecular events triggered by the drug.

When researchers compare the genomes of people taking the same drug, they may discover that a set of people who share a certain genetic variation also share a common treatment response, such as:

  • A greater risk of side effects
  • Severe side effects at relatively low doses
  • The need for a higher dose to achieve a therapeutic effect
  • No benefit from the treatment
  • A greater or more likely benefit from the treatment
  • The optimal duration of treatment

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