What are the recent findings on pharmacogenetic testing in psychiatry?

From the Guidelines

Pharmacogenetic testing in psychiatry is a valuable tool for personalized treatment, particularly for patients who have failed multiple medication trials or experienced unusual side effects, as it can help predict how patients metabolize certain psychiatric medications, potentially reducing adverse effects and improving treatment outcomes. The most recent and highest quality study on this topic is from 2016, which discusses the implementation of pharmacokinetic pharmacogenetic guidelines for antidepressants primarily metabolized by CYP2D6 and CYP2C19 1.

Key Points to Consider

• The study highlights the importance of genetic variation in CYP2D6 and CYP2C19 in determining the metabolism of antidepressants, such as fluoxetine and paroxetine, which are commonly prescribed medications in the United States.
• The article notes that providing greater precision to pharmacotherapeutic recommendations for individual patients can potentially reduce adverse effect toxicity profiles and increase response rates and overall effectiveness.
• The study also mentions that genetic testing can help identify patients who are poor, intermediate, normal, or ultrarapid metabolizers, which can inform treatment decisions.

Implementation of Pharmacogenetic Testing

• Clinicians should consider pharmacogenetic testing for patients who have failed multiple medication trials or experienced unusual side effects.
• Testing typically involves a simple cheek swab or blood sample, with results available within 1-2 weeks.
• However, it's essential to understand that these tests don't predict which medication will be most effective for a specific condition, but rather how a patient might metabolize certain drugs.

Limitations and Future Directions

• While pharmacogenetic testing can provide valuable information about metabolism status, clinical judgment remains essential as genetic factors account for only part of medication response variability.
• Other factors like environmental influences, drug interactions, and individual physiology still play crucial roles in treatment outcomes.
• The field is evolving rapidly, and further research is needed to fully understand the clinical utility of pharmacogenetic testing in psychiatry.

From the Research

Recent Articles on Pharmacogenetic Testing in Psychiatry

• A recent article published in 2021 2 discusses the use of pharmacogenetic testing in psychiatry, highlighting the importance of testing for human leukocyte antigen (HLA)-A and HLA-B before initiating carbamazepine and oxcarbazepine due to the risk of serious skin reactions.
• The article also mentions that limited evidence suggests testing for variation in metabolism through CYP2D6 and CYP2D19 for psychotropic medications metabolized through the liver.
• Another article published in 2023 3 focuses on pediatric considerations for pharmacogenetic selective serotonin reuptake inhibitors clinical decision support, highlighting the need for consideration of evidence for pharmacogenetic associations, medication indications, and appropriate alternative therapies.

Implementation of Pharmacogenetic Testing in Psychiatry

• A review of pharmacogenetic tests in psychiatry published in 2008 4 discusses the evaluation of these tests in clinical practice, cost-effectiveness, and regulatory oversight.
• The review highlights the need for more robust studies to assess the potential benefits of adopting pharmacogenetics in health systems and services.
• A more recent overview of reviews published in 2021 5 also emphasizes the need for more robust studies to assess the potential benefits of pharmacogenetic testing in psychiatry and neurology.

Pharmacogenetics of Selective Serotonin Reuptake Inhibitors

• An early study published in 1993 6 discusses the pharmacogenetics of selective serotonin reuptake inhibitors, highlighting the importance of cytochrome P450 enzymes in the elimination of these drugs.
• The study notes that paroxetine and fluoxetine are potent inhibitors of cytochrome P4502D6, which can cause serious interactions with other drugs metabolized by this isozyme.