Monitoring of blood levels in patients administered CYP3A4 inhibitor during the maintenance phase of venetoclax administration

Objective: Venetoclax, an oral dose adjustment when combined with a CYP3A4 inhibitor; however, the dosing regimen remains unclear on adding a CYP3A4 inhibitor after venetoclax administration. Case summary: We present a case report of a patient who was simultaneously treated with a CYP3A4 inhibitor and a steady daily dose of venetoclax. A 30-year-old male diagnosed with acute myeloid leukemia received a combination of venetoclax and azacitidine as remission induction therapy. He was prescribed 400 mg/day venetoclax at a steady daily dose, with fosfluconazole initiated on day 18. Given that fosfluconazole can induce moderate CYP3A4 inhibitory effects, the venetoclax dosage was reduced to 200 mg/day on the same day. Despite dose reduction, plasma trough levels of venetoclax continued rising gradually. Nearly 10 days were required to decrease blood levels to a steady state. Conclusion: The risk of elevated venetoclax blood levels needs to be considered when initiating CYP3A4 inhibitors and reducing venetoclax dosage on the same day.