Clinical impact of potential drug-drug interactions between midostaurin and posaconazole in FLT3-mutated AML

ABSTRACT To determine midostaurin and posaconazole plasma concentrations and investigate adverse events (AEs) resembling drug-drug interactions (DDI) when both drugs were administered concomitantly during induction chemotherapy for acute myeloid leukemia (AML). Patients with FLT3-mutated AML who received midostaurin and posaconazole concomitantly between May 2019 and December 2022 were included and followed up to March 2023. Twice-weekly trough levels for midostaurin and posaconazole were measured with validated liquid chromatography–tandem mass spectrometry methods. Potential DDIs were independently reviewed by two physicians and attributed using the Drug Interaction Probability Scale (DIPS). Population pharmacokinetics analysis was done via nonlinear mixed-effect modeling. In 29 patients, concentrations ranged from 0.6 to 24.5 mg/L for midostaurin and from <30 to 2,572 µg/L for posaconazole. A total of 375 AEs in 66 midostaurin cycles, with 280 AEs classified as grade ≥3, were recorded. Probable DDI with a DIPS score of ≥5 was attributed in 14/375 AEs; no highly probable AEs were registered. Eight AEs led to dose modification or discontinuation of midostaurin in seven patients. Clearance for midostaurin during co-administration with posaconazole was 0.52 L/h (95% CI, 0.42–0.62 L/h). A breakthrough fungal infection was recorded in eight patients (27.5%). DDI of midostaurin and posaconazole is clinically meaningful but infrequent. High inter- and intra-individual variabilities of midostaurin and posaconazole plasma exposure were observed. Midostaurin clearance was delayed during co-administration. Midostaurin therapeutic drug monitoring may serve for decision-making when DDI with CYP3A4 inhibitors is suspected.