Klin Farmakol Farm. 2025;39(4):206-212 | DOI: 10.36290/far.2025.073

TDM as a tool for pharmacogenetic patient profiling: a case report of phenoconversion

Ivana Tašková^{1, 2}, Nicole Šafářová^{1, 3, 4}

¹ Oddělení klinické farmacie, Psychiatrická nemocnice Bohnice, Praha

² Katedra sociální a klinické farmacie, Farmaceutická fakulta Univerzity Karlovy v Hradci Králové

³ Národní ústav duševního zdraví, Klecany

⁴ 3. lékařská fakulta Univerzity Karlovy, Praha

Pharmacogenetics and therapeutic drug monitoring (TDM) are essential tools of personalised medicine in psychiatry. While pharmacogenetic testing enables the prediction of genetically determined enzyme activity, TDM provides a direct view of actual plasma drug concentrations and individual pharmacokinetics. These two methods are complementary; TDM can be utilised not only for dose optimisation but also to estimate the patient's metabolic phenotype or detect phenoconversion - a situation where the observed metabolic profile does not align with the genotype-predicted enzymatic activity. This case report details a patient with obsessive-compulsive disorder who underwent a phenoconversion to a poor metaboliser under the influence of a strong CYP2D6 inhibitor (paroxetine), despite being genetically classified as a normal metaboliser. By employing elimination half-life calculations and a validated phenoconversion prediction tool, we identified a significant metabolic slowdown necessitating thera­peutic adjustment. This case illustrates the practical value of TDM in interpreting pharmacogenetic findings and underscores the role of the clinical pharmacist in evaluating complex pharmacokinetic scenarios in psychiatric patients.

Keywords: pharmacogenetics, pharmacokinetics, therapeutic drug monitoring, psychopharmacology, phenoconversion.

Received: September 22, 2025; Revised: December 13, 2025; Accepted: December 15, 2025; Published: December 22, 2025  Show citation