Venetoclax is safe and tolerable as post-transplant maintenance therapy for AML patients at high risk for relapse.

Relapse is the most common cause of mortality in acute myeloid leukemia (AML) patients after allogeneic stem cell transplant (SCT). Post-SCT maintenance strategies that prevent relapse are desirable but must be well tolerated and convenient to administer. We hypothesized single agent venetoclax (ven) may be an effective maintenance therapy among high relapse risk patients. Between February 2019 and December 2021, we administered post-SCT ven maintenance to 49 AML patients at high-risk for relapse as a prospectively defined off-label practice at our institution. Ven was planned to be administered until 1-year post-SCT. While temporary interruptions were common (67.3% of all patients), of those with >1 year follow up, 22/25 (88%) completed the full year of planned therapy. Cytopenias (40.8%) and gastrointestinal adverse events (34.7%) were the most common toxicities. At 1-year post-SCT, overall survival (OS) and relapse-free survival (RFS) were 70% and 67% respectively. Our experience demonstrates single agent ven is a safe, tolerable, and feasible maintenance therapy that may improve RFS and OS in high relapse risk post-SCT patients.

Evaluation of the Pharmacokinetic Interaction Between Letermovir and Tacrolimus in Allogeneic Hematopoietic Cell Transplantation Recipients.

Data describing the magnitude of the pharmacokinetic interaction between letermovir and tacrolimus in allogeneic hematopoietic cell transplantation (allo-HCT) recipients are limited, and varying outcomes have been reported. The need for empiric dose adjustment of tacrolimus on initiation of letermovir has not been established; instead, guidelines suggest closely monitoring the tacrolimus trough concentration and adjusting the dose as needed. A better understanding of this interaction is imperative to accurately manage the narrow therapeutic window of tacrolimus post-transplantation. The primary objective of this study was to determine the percent change in tacrolimus concentration-to-dose ratio over the 14-day period after initiation of letermovir. Secondary objectives were to describe the frequency of tacrolimus dose adjustments after initiation of letermovir, the percent change in daily tacrolimus dose over the 14-day period after initiation of letermovir, and the incidence of both subtherapeutic and supratherapeutic tacrolimus trough concentrations. This retrospective chart review included adult allo-HCT recipients at our institution who received tacrolimus in combination with oral letermovir and had been taking tacrolimus for at least 5 days before letermovir initiation. Patients receiving strong CYP3A4 inhibitors or i.v. tacrolimus were excluded. Thirty-five patients were included in the analysis. The median percent increase in tacrolimus concentration-to-dose ratio over the 14-day period after initiation of letermovir was 22% on days 2 to 4, 47% on days 5 to 7, 66% on days 8 to 11, and 81% on days 12 to 14. The mean frequency of tacrolimus dose adjustments was 0.66 on days 2 to 4, 0.69 on days 5 to 7, 1.06 on days 8 to 11, and 0.57 on days 12 to 14. The results of this study show that the pharmacokinetic interaction between tacrolimus and letermovir is substantial and continues to affect tacrolimus concentration over the 14-day period after letermovir initiation. Close monitoring of tacrolimus trough concentration on initiation of letermovir should be considered.