Pharmacogenomics in Psychiatry

Pharmacogenomics in Psychiatry - Gene-Drug Dance Intro

• Pharmacogenomics (PGx): The study of how an individual's unique genetic makeup (genome) influences their response to medications.
• Primary Goals in Psychiatry:
  • Personalize treatment selection and dosing.
  • Maximize therapeutic efficacy.
  • Minimize adverse drug reactions (ADRs) and improve tolerability.
• Core Principle: Genetic variations can alter drug metabolism (pharmacokinetics) and drug action sites (pharmacodynamics).

⭐ PGx testing helps predict how patients might respond to certain psychiatric medications, guiding more informed prescribing and reducing trial-and-error approaches.

Pharmacogenomics in Psychiatry - Star Players & Meds

• Cytochrome P450 (CYP) Enzymes: Key for psychotropic metabolism; variants alter drug levels.
  • CYP2D6:
    • Meds: TCAs, fluoxetine, paroxetine, risperidone, aripiprazole, atomoxetine.
    • PMs (Poor Metabolizers): ↑ levels, ↑ side effects. Consider ~50% dose ↓.
    • UMs (Ultrarapid Metabolizers): ↓ levels, ↓ efficacy. Alternative or dose ↑.
  • CYP2C19:
    • Meds: Citalopram, escitalopram, sertraline, TCAs, diazepam.
    • PMs: ↑ side effect risk (e.g., QTc with citalopram).
    • UMs: ↓ efficacy.
  • CYP1A2:
    • Meds: Clozapine, olanzapine, duloxetine.
    • Inducer: Smoking (↓ levels).
• Serotonin Transporter (SLC6A4/5-HTTLPR):
  • Impacts SSRI response/side effects.
  • S-allele: Potentially ↓ SSRI efficacy, ↑ side effects.
• Human Leukocyte Antigen (HLA) Alleles: Predict severe ADRs.
  • HLA-B*1502: Carbamazepine-SJS/TEN in Asians. Screen pre-use.
  • HLA-A*3101: Carbamazepine hypersensitivity (DRESS) in Europeans.

⭐ HLA-B*1502 testing: vital for Asians pre-carbamazepine to prevent SJS/TEN.

Pharmacogenomics in Psychiatry - Guiding Rx Choices

Pharmacogenomics (PGx) tailors drug choices and dosages based on an individual's genetic makeup, aiming to optimize efficacy and minimize adverse drug reactions (ADRs).

• Core Principle: Match drug to patient genetics for personalized psychiatric treatment.
• Clinical Utility:
  • Predicting drug metabolism rates (e.g., CYP2D6, CYP2C19 variants affecting SSRIs, TCAs).
  • Identifying risk for severe ADRs (e.g., HLA-B*1502 and carbamazepine-induced SJS/TEN in specific populations).
  • Guiding dosage adjustments (e.g., ↓ dose for Poor Metabolizers) or alternative drug selection.
• Key Guidelines:
  • CPIC (Clinical Pharmacogenetics Implementation Consortium).
  • DPWG (Dutch Pharmacogenetics Working Group).
• Interpretation: Genotype (e.g., CYP2D6*4/*4) → Phenotype (e.g., Poor Metabolizer) → Clinical recommendation.
  • UM: Ultrarapid Metabolizer (may need ↑ dose or alternative).
  • PM: Poor Metabolizer (needs ↓ dose or alternative to avoid toxicity).

⭐ For many SSRIs (e.g., paroxetine, fluvoxamine) and TCAs (e.g., nortriptyline, amitriptyline), CYP2D6 genotype significantly impacts plasma concentrations; poor metabolizers may require ~50% dose reduction.

• Limitations: Not all psychotropics have PGx guidelines; cost; test turnaround time; PGx is one factor among many - clinical judgment is paramount.

Pharmacogenomics in Psychiatry - Roadblocks & Horizons

• Roadblocks:
  • Cost & accessibility (esp. India).
  • Evidence gaps; need for diverse population data.
  • Interpretation complexity; unclear clinical guidelines.
  • Ethical, Legal, Social Implications (ELSI) e.g., privacy, discrimination.
• Horizons:
  • Personalized drug choice/dose; ↓Adverse Drug Reactions (ADRs).
  • ↑Efficacy; predicting non-response; guiding refractory cases.
  • Research: novel drug targets, better disease understanding.
  • Future: potential for ↑cost-effectiveness by optimizing treatment selection.

⭐ CYP2D6 & CYP2C19 are key pharmacogenes affecting metabolism of many psychotropics like SSRIs & TCAs, influencing both efficacy and side effects.

High‑Yield Points - ⚡ Biggest Takeaways

• CYP2D6 & CYP2C19 are key enzymes metabolizing many psychotropics like SSRIs, TCAs, and antipsychotics.
• Poor metabolizers (PMs) risk ↑ side effects/toxicity; Ultrarapid metabolizers (UMs) risk ↓ drug efficacy.
• HLA-B*1502 allele: high risk of carbamazepine-induced SJS/TEN in Asian populations.
• HLA-A*3101 allele: another important marker for carbamazepine hypersensitivity reactions.
• Pharmacogenomic testing guides drug selection and optimal dosing, aiming to minimize ADRs.
• Particularly valuable for treatment-resistant conditions or patients with a history of significant ADRs.