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Exploring the role of drug-metabolising enzymes in antidepressant side effects

Research output: Contribution to journalArticle

Karen Hodgson, Katherine E. Tansey, Rudolf Uher, Mojca Zvezdana Dernovšek, Ole Mors, Joanna Hauser, Daniel Souery, Wolfgang Maier, Neven Henigsberg, Marcella Rietschel, Anna Placentino, Ian W. Craig, Katherine J. Aitchison, Anne Farmer, Richard J B Dobson, Peter McGuffin

Original languageEnglish
Pages (from-to)2609-2617
Number of pages9
Issue number14
Early online date12 Mar 2015
StatePublished - Jul 2015

King's Authors


Rationale: Cytochrome P450 enzymes are important in the metabolism of antidepressants. The highly polymorphic nature of these enzymes has been linked to variability in antidepressant metabolism rates, leading to hope regarding the use of P450 genotyping to guide treatment. However, evidence that P450 genotypic differences underlie the variation in treatment outcomes is inconclusive.

Objectives: We explored the links between both P450 genotype and serum concentrations of antidepressant with antidepressant side effects, using data from the Genome-Based Therapeutic Drugs for Depression Project (GENDEP), which is a large (n = 868), pharmacogenetic study of depressed individuals treated with escitalopram or nortriptyline.

Methods: Patients were genotyped for the enzymes CYP2C19 and CYP2D6, and serum concentrations of both antidepressant and primary metabolite were measured after 8 weeks of treatment. Side effects were assessed weekly. We investigated associations between P450 genotypes, serum concentrations of antidepressants and side effects, as well as the relationship between P450 genotype and study discontinuation.

Results: P450 genotype did not predict total side effect burden (nortriptyline: n = 251, p = 0.5638, β = −0.133, standard error (SE) = 0.229; escitalopram: n = 340, p = 0.9627, β = −0.004, SE = 0.085), study discontinuation (nortriptyline n = 284, hazard ratio (HR) = 1.300, p = 0.174; escitalopram n = 376, HR = 0.870, p = 0.118) or specific side effects. Serum concentrations of antidepressant were only related to a minority of the specific side effects measured: dry mouth, dizziness and diarrhoea.

Conclusions: In this sample where antidepressant dosage is titrated using clinical judgement, P450 genotypes do not explain differences between patients in side effects with antidepressants. Serum drug concentrations appear to only explain variability in the occurrence of a minority of specific side effects.

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