Influence of combined CYP2C19 and CYP2D6 phenotypes on adverse drug reactions in patients with major depressive disorder: a clinical cohort study

CYP2C19, CYP2D6 (combined phenotypes + phenoconversion)

Combined CYP2C19 IM/PM + CYP2D6 PM phenotypes → cumulative reduction in antidepressant metabolism → plasma accumulation → ADRs; CYP2D6 phenoconversion (inhibition by fluoxetine/antipsychotics) in 48.6% of patients

Clinical cohort study (n=35 patients, Frankfurt University Hospital) evaluating the impact of combined CYP2C19/CYP2D6 metabolizer status on antidepressant adverse drug reactions in major depression. Non-normal metabolizers present significantly more ADRs (OR=2.99; CI 1.38-6.46; p=0.039). The CYP2C19 IM/CYP2D6 PM combination presents the highest risk (OR=9.04; CI 2.7-30.3; p=0.044). Critical point: phenoconversion rate of 48.6% — drug-mediated enzymatic inhibition altered the actual phenotype regardless of genotype.

Synthesis written by Geno'X. For the full original abstract, please refer to the source publication.

Phenoconversion, often overlooked in clinical practice, is as important as genotype for predicting ADRs. Nearly one in two depressed patients was functionally a PM due to co-prescriptions (fluoxetine, antipsychotics). Key message: always check co-prescribed CYP2D6/CYP2C19 inhibitors, regardless of genomic result. Limitation: n=35, single center.

CPIC Level A (CYP2D6 + CYP2C19) +2; documented phenoconversion (48%) +2; OR=9.04 for double PM +2; Pharmacogenomics J +1