Zongertinib in the Context of Hepatic Impairment, Polypharmacy, and Hepatitis B Reactivation Risk

William takes 7 daily medications (metformin, lisinopril, amlodipine, atorvastatin, entecavir, aspirin, omeprazole) and has baseline aspartate aminotransferase (AST) elevation (1.3× upper limit of normal [ULN]) and total bilirubin 1.2× ULN from chronic hepatitis B. The drug–drug interaction that matters most is atorvastatin–zongertinib.

Zongertinib is both a breast cancer resistance protein (BCRP) substrate and a BCRP inhibitor. Atorvastatin is a BCRP substrate, so zongertinib can raise atorvastatin exposure and increase the risk of myalgias and creatine kinase (CK) elevations. Management options: lower the atorvastatin dose, discontinue it if it is not clinically essential, or switch to a non-BCRP-substrate statin such as pravastatin. Dr. Wu reports no clinically meaningful interactions between zongertinib and metformin, lisinopril, amlodipine, aspirin, or omeprazole; however, clinicians should remain aware that zongertinib is a strong cytochrome P450 3A4 (CYP3A4) inducer, so co-administered CYP3A4 substrates warrant review.

Hepatotoxicity is the second major issue. In the Beamion LUNG study, 27% of patients experienced some hepatotoxicity on zongertinib. Atorvastatin and entecavir can independently contribute to liver dysfunction. The label requires checking AST, alanine aminotransferase (ALT), and total bilirubin at baseline, every 2 weeks for the first 12 weeks, then monthly.

On hepatitis B reactivation: no cases were reported in the zongertinib trial and no published cases exist to Dr. Wu's knowledge, but TKIs as a class carry a 10%–15% reactivation risk. He favors continuing entecavir prophylactically. For monitoring logistics with a patient 50 miles from clinic, Dr. Wu partners with the primary care provider or a local reference lab (Quest, Clinical Labs) for every-2-week labs, reviews results remotely, and uses phone or telemedicine visits between in-person appointments.

In the next episode, “Second-Line Sequencing After Progression on Zongertinib: ADC, TKI Switch, or Chemotherapy,” Dr. Wu discusses the limited evidence for within-class TKI switching and the rationale for crossing drug classes at progression.