The Health Sciences Authority (HSA) has informed healthcare professionals that the prostate cancer drug Xtandi (enzalutamide) can cause falsely elevated results in certain laboratory tests.

• Technical Interference: The drug interferes with the chemiluminescent microparticle immunoassay (CMIA) method used to measure plasma digoxin levels.
• Clinical Guidance: Doctors should use alternative assay types to confirm digoxin levels before making dose adjustments.
• Drug Interaction: Enzalutamide may also raise actual serum digoxin levels by inhibiting P-glycoprotein, necessitating careful monitoring.

This summary is based on a Dear Healthcare Professional Letter issued by Astellas Pharma Singapore Pte Ltd via the HSA.