PharmacoKINEtics of TAMoxifen and Its Metabolites in Breast Cancer Patients: the Influence of a Dose Increase in Phenotypic Poor Metabolizers of CYP2D6 (KINETAM)

Summary

All women on tamoxifen receive the standard dose of 20mg QD, irrespective of the use of potential CYP2D6 inhibitors, and are not tested for CYP2D6 polymorphisms prior to start of tamoxifen treatment.However CYP2D6 polymorphisms and/or the use of CYP2D6 inhibitors as co-medication may influence the treatment outcome of tamoxifen. The investigators propose a prospective study in women taking tamoxifen at a dose of 20mg QD. In each woman, information will be collected on endoxifen levels, CYP2D6 status, adherence and use of co-medication. In women who are phenotypically poor metabolizers of tamoxifen, a dose increase to 40mg QD will be applied and the effect of this intervention on tamoxifen pharmacokinetics will be evaluated after 4 weeks.

Timeline

Start

2010-07

Primary completion

2011-05

Completion

2012-05

Publications

• Results Welzen ME, Dezentje VO, van Schaik RH, Colbers AP, Guchelaar HJ, van Erp NP, den Hartigh J, Burger DM, van Laarhoven HW. The Effect of Tamoxifen Dose Increment in Patients With Impaired CYP2D6 Activity. Ther Drug Monit. 2015 Aug;37(4):501-7. doi: 10.1097/FTD.0000000000000195.

Drugs

Indications