Effect of CYP2D6 and CYP2C19 genotypes on atomoxetine serum levels - a study based on therapeutic drug monitoring data.

CYP2D6 genotype has a great impact on atomoxetine exposure, where our real-world data suggest atomoxetine dose requirements to be around half and one-tenth in CYP2D6 IM and PM vs. NM patients, respectively. When adding CYP2C19 genotype as a factor of relevance for personalized atomoxetine dosing, CYP2C19*2 carriers should further reduce the dose by a third. These findings suggest that pre-emptive CYP2D6/CYP2C19 genotyping should be performed to individualize atomoxetine dosing and prevent adverse effects.