Xtandi™ (enzalutamide) interference with laboratory test CMIA leading to falsely elevated digoxin plasma levels

A Dear Healthcare Professional Letter has been issued by Astellas Pharma Singapore Pte. Ltd. to inform healthcare professionals that Xtandi^TM (enzalutamide) may interfere with the chemiluminescent microparticle immunoassay (CMIA) laboratory test method. This interference can lead to falsely elevated digoxin plasma level results in patients taking enzalutamide, regardless of whether the patient is actually taking digoxin. Healthcare professionals are advised to confirm the serum digoxin levels using another type of assay before determining the need for discontinuation or dose adjustments of digoxin in patients taking enzalutamide. Enzalutamide may also inhibit the efflux transporter P-glycoprotein (P-gp), leading to increased serum levels of digoxin, a P-gp substrate. Digoxin should therefore be used with caution when administered concomitantly with enzalutamide and may require dose adjustment to maintain optimal plasma concentrations. Please refer to the letter for details.

Only abstracts of the Dear Healthcare Professional Letters (DHCPL) are provided on this website. Details of these letters can be found in the MOH Alert System, which is accessible via the Health Professionals Portal (HPP), a one-stop portal for all healthcare professionals in Singapore. Dentists, medical doctors and pharmacists may access HPP at https://hpp.moh.gov.sg ↗ (opens in new tab) and follow the procedures below to access the MOH Alert system.

Step 1: Select your profession under ‘For Healthcare Professionals’.

Step 2: Click on ‘Useful links’.

Step 3: Click on ‘MOH Alert’ and log in via Singpass.

Step 4: Click on ‘Drug Alerts’ or ‘Med Device Alerts’ to view the DHCPLs.