CYP2D6 Genotyping and Inhibition as Predictors of Adverse Drug Reactions in Depressive Disorders

The primary aim of this study was to examine the association between the different predicted phenotypes of the polymorphic CYP2D6 gene and the prevalence of adverse drug reactions in patients suffering from depressive disorders. The secondary aim was to investigate if comedication with CYP2D6 inhibitors resulted in more adverse drug reactions due to phenoconversion.

Between January 2012 and December 2021, 415 patients with a depressive disorder and insufficient treatment response in secondary psychiatric care were included in the naturalistic observational study Genes, Depression, and Suicidality (GEN-DS). The patients were subjected to a semistructured interview and diagnosed according to DSM-IV. Patients were also required to complete the self-rating version of the UKU Side Effect Rating Scale. All patients were genotyped for CYP2D6 and assigned a corresponding predicted CYP2D6 phenotype.

Out of the 415 patients, 147 patients with available genotyping and UKU scale results were also prescribed 1 or more drugs metabolized by CYP2D6. We did not find any evidence of an effect of the predicted CYP2D6 phenotype on the total burden of adverse drug reactions or in any of the specific symptom domains as measured with the UKU scale among these patients. We also investigated if comedication with 1 or more substances that inhibited the effect of the CYP2D6 enzyme resulted in more reported adverse drug reactions due to phenoconversion. Even though the rate of phenotypic PMs increased from 13 to 38 patients, we did not find any support for increased adverse drug reactions in this group.

We did not find that CYP2D6 phenotype could predict the occurrence of adverse drug reactions in patients with depressive disorders in this naturalistic setting. However, information about CYP2D6 genotype may still be important in antidepressant treatment for the selection of appropriate drugs, for dosing recommendations of certain medications, or when the patient is suffering from severe adverse reactions.