Abstract
The Dutch Pharmacogenetics Working Group (DPWG) aims to facilitate pharmacogenetics implementation in clinical practice by developing evidence-based guidelines to optimize pharmacotherapy based on pharmacogenetic test results. The current guideline describes the gene-drug interaction between CYP2D6 and venlafaxine, mirtazapine and duloxetine. In addition, the interaction between CYP2C19 and mirtazapine and moclobemide is presented. The DPWG identified a gene-drug interaction that requires therapy adjustment for CYP2D6 and venlafaxine. However, as the side effects do not appear to be related to plasma concentrations, it is not possible to offer a substantiated advice for dose reduction. Therefore, the DPWG recommends avoiding venlafaxine for CYP2D6 poor and intermediate metabolisers. Instead, an alternative antidepressant, which is not, or to a lesser extent, metabolized by CYP2D6 is recommended. When it is not possible to avoid venlafaxine and side effects occur, it is recommended to reduce the dose and monitor the effect and side effects or plasma concentrations. No action is required for ultra-rapid metabolisers as kinetic effects are minimal and no clinical effect has been demonstrated. In addition, a gene-drug interaction was identified for CYP2D6 and mirtazapine and CYP2C19 and moclobemide, but no therapy adjustment is required as no effect regarding effectiveness or side effects has been demonstrated for these gene-drug interactions. Finally, no gene-drug interaction and need for therapy adjustment between CYP2C19 and mirtazapine and CYP2D6 and duloxetine were identified. The DPWG classifies CYP2D6 genotyping as being "potentially beneficial" for venlafaxine, indicating that genotyping prior to treatment can be considered on an individual patient basis.