Patients who were taking oral anticoagulants were not excluded from the phase-3-clinical trials of abemaciclib. However, we do not have specific safety or efficacy data in these patients.1,2

Abemaciclib inhibits P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in vitro. Based on this observation, an in-vivo interaction of abemacicilib with narrow therapeutic index substrates of these transporters, such as the oral anticoagulant dabigatran etexilate, and others, may occur.3

Dabigatran etexilate is an anticoagulant and a substrate of P-gp. The information in the Summary of Product Characteristics (SmPC) that DDI between abemaciclib and dabigatran etexilate may occur is based on the observation that

• abemaciclib is known to inhibit P-gp transporter in vitro and
• abemaciclib increased loperamide as another P-gp substrate to an extent that was considered not to be clinically relevant.

However, the DDI of abemaciclib with dabigatran has not been tested in patients and therefore the actual extent of increase in dabigatran plasma exposure when administered in combination with abemaciclib has not been established in vivo.3

Please refer to the SmPC of the respective oral anticoagulant for full prescribing information.

We did not systematically study interactions between abemaciclib and oral anticoagulants, therefore the following considerations are of theoretical nature based on the safety profile of abemaciclib. We do not know if these considerations are clinically relevant. 

Please note that abemaciclib indicated for the treatment of women with hormone receptor positive (HR+), human epidermal growth factor receptor 2 (HER2) negative locally advanced or metastatic breast cancer in combination with 

• an aromatase inhibitor, or 
• fulvestrant.3

Please check the SmPCs of all concomitantly used medications.