ANTIDEPRESSANT PHARMACOGENOMICS

Antidepressant Response — CYP2D6 and CYP2C19 variants determine whether an antidepressant reaches therapeutic levels, causes toxicity, or never works at the prescribed dose.

Whole genome sequencing provides complete CYP2D6 and CYP2C19 diplotypes — the two genes that govern the metabolism of most commonly prescribed SSRIs, SNRIs, and tricyclic antidepressants — before the first prescription is written.

CYP2D6
CYP2C19

About this condition

Antidepressant Response — CYP2D6 & CYP2C19

The pharmacological response to antidepressants varies dramatically between individuals, and a substantial proportion of that variance is genetically determined. Two cytochrome P450 enzymes — CYP2D6 and CYP2C19 — are responsible for the primary metabolic clearance of the majority of antidepressants in widespread clinical use. CYP2D6 metabolizes fluoxetine (Prozac), paroxetine (Paxil), venlafaxine (Effexor), duloxetine (Cymbalta), tricyclic antidepressants including amitriptyline and nortriptyline, and several antipsychotics used as adjuncts in treatment-resistant depression. CYP2C19 metabolizes citalopram (Celexa), escitalopram (Lexapro), sertraline (Zoloft), amitriptyline, and clomipramine.

CYP2D6 metabolizer phenotypes span a wide spectrum. Poor metabolizers (PM) carry two loss-of-function alleles and cannot clear CYP2D6-substrate antidepressants at normal rates — they accumulate drug at standard doses, experiencing toxicity including QT prolongation, serotonin syndrome risk, and adverse effects that lead to drug discontinuation. Ultra-rapid metabolizers (UM) carry duplicate or multiply duplicated functional CYP2D6 alleles and clear drugs so rapidly they never achieve therapeutic plasma concentrations at standard dosing. Intermediate metabolizers have an attenuated intermediate phenotype. CYP2C19 PMs accumulate escitalopram and citalopram — the FDA issued a dose-limiting guidance for citalopram specifically referencing CYP2C19 poor metabolizer status in 2012, capping the maximum dose to reduce QTc prolongation risk.

CPIC guidelines (Level A) provide prescribing recommendations for CYP2D6 and CYP2C19 across multiple antidepressants: alternatives or dose adjustments are recommended for PMs and UMs for tricyclic antidepressants; dose reductions are recommended for CYP2C19 PMs on citalopram and escitalopram; and alternative agents are recommended for CYP2D6 PMs on paroxetine and fluoxetine. Psychiatric pharmacogenomics testing is increasingly standard of care for treatment-resistant depression — studies show that genotype-guided antidepressant selection reduces medication switches and reduces time to remission compared to standard trial-and-error prescribing.

CYP2D6 has over 100 named star alleles with highly variable activity. Gene copy number variation — including complete gene deletions and multiplications — is common and determines the ultra-rapid and poor metabolizer phenotypes that have the most dramatic antidepressant response consequences.

Gene locus: CYP2D6 (22q13.2), CYP2C19 (10q23.33)

Standard psychiatry genetic panels test a limited set of CYP2D6 and CYP2C19 variants. Whole genome sequencing resolves the complete star-allele diplotype — including copy number variants and rare alleles missed by fixed panels.

CYP2D6 gene copy number variants require genome-level detection

CYP2D6 ultra-rapid metabolizer status most commonly arises from gene duplication — an individual carries 3, 4, or more copies of a functional CYP2D6 allele. Standard SNP-based pharmacogenomics panels can identify the major loss-of-function alleles but often cannot reliably quantify CYP2D6 copy number or distinguish genotypes with intermediate copy numbers. Whole genome sequencing provides both variant identification and copy number analysis across the CYP2D6 locus, enabling complete diplotype assignment including the duplication alleles that define ultra-rapid metabolizer status — the phenotype where standard antidepressant doses fail entirely.

One genome result covers every antidepressant you may ever be prescribed

Psychiatric medication management is rarely a single-drug decision. Most patients with depression try multiple agents over their lifetime — SSRIs, SNRIs, augmentation with atypical antipsychotics, TCAs for refractory cases. Each new drug introduces a new pharmacogenomic question. A complete CYP2D6 and CYP2C19 diplotype from whole genome sequencing answers the metabolizer question for all CYP2D6 and CYP2C19 substrate medications simultaneously and permanently — the result applies to every future prescribing decision, not just the current one.

Antidepressant Response — CYP2D6 and CYP2C19 variants determine whether an antidepressant reaches therapeutic levels, causes toxicity, or never works at the prescribed dose.

Antidepressant Response — CYP2D6 & CYP2C19

Standard psychiatry genetic panels test a limited set of CYP2D6 and CYP2C19 variants. Whole genome sequencing resolves the complete star-allele diplotype — including copy number variants and rare alleles missed by fixed panels.

CYP2D6 gene copy number variants require genome-level detection

One genome result covers every antidepressant you may ever be prescribed

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