New guideline concerning CYP2D6 and atomoxetine

In March 2019, the Clinical Pharmacogenetics Implementation Consortium (CPIC) published a new guideline concerning CYP2D6 and atomoxetine, a non-stimulant medication used in the treatment of some people with attention-deficit/hyperactivity disorder. Currently, this drug is included in the TreatGx pharmacogenetic report and precision prescribing software, and we provide relevant information to CYP2D6 poor metabolizers based on the Dutch Pharmacogenetics Working Group (DPWG) therapeutic recommendations.

Aside from making these recommendations to CYP2D6 poor metabolizers, the new CPIC guideline also provides therapeutic guidance for CYP2D6 intermediate metabolizers (0.5 score) and normal or intermediate metabolizers (1.0 score) with a *10 allele. These changes will be reflected in our pharmacogenetic report. 

In the TreatGx software, personalized atomoxetine dosing for ADHD medication is already adjusted based on CYP2D6 phenotype, in addition to other factors including concomitant use of a CYP2D6 strong inhibitor medication, hepatic function, and weight. Following the DPWG guidelines, we currently recommend a slower titration schedule for those who are CYP2D6 poor metabolizers. The new CPIC guidelines groups some CYP2D6 normal and intermediate metabolizers (who have the *10 allele) into this group of patients who should follow a slower titration schedule.

In our upcoming TreatGx Version 3 release, scheduled for later in summer 2019, we will be including this new stratification of *10 allele presence or absence in combination with CYP2D6 phenotype; this will bring the TreatGx medication decision support software in line with the report.

Our aim is to improve the safety and effectiveness of medication therapy, and this update in atomoxetine dosing will provide clinicians with the information to help them achieve that.