Tacrolimus dose modification in patients receiving concomitant isavuconazole after hematopoietic stem cell transplantation

Coadministration of isavuconazole and sirolimus in allogeneic hematopoietic stem cell transplant recipients

Background

Invasive fungal infections (IFIs) represent a major cause of morbidity among allogeneic hematopoietic stem cell transplantation (allo-HSCT). Isavuconazole (ISA) is a broad-spectrum triazole with favorable safety profile.

Objectives and design

Herein, we evaluate the real life coadministration of ISA and sirolimus in allo-HSCT recipients in a single-center retrospective analysis, describing clinical efficacy, safety, and therapeutic drug monitoring (TDM) of both drugs.

Methods

All consecutive allo-HSCT recipients who received the coadministration of ISA and sirolimus for at least 2 weeks between July 2017 and December 2022 were included in this retrospective analysis. TDM was longitudinally performed during treatment. IFIs were classified according to the revised European Organization for Research and Treatment of Cancer/Mycoses Study Group consensus criteria.

Results

A total of 51 recipients were included in the analysis. A total of 17 patients received ISA as continuous antifungal treatment for IFI diagnosed before transplant: one patient experienced a probable invasive pulmonary aspergillosis, and one patient switched from ISA to liposomal amphotericin B for a possible IFI. A total of 34 patients started ISA as antifungal therapy for IFI diagnosed after transplant. Sixteen of 34 were treated for a proven/probable breakthrough IFI during mold-active prophylaxis: 6/16 patients died for IFI after a median of 51 days of ISA. Eighteen of 34 started ISA as empirical therapy for a possible IFI: 15/18 patients were alive with resolution of infection after 6 weeks, 1 died for disease progression, and 2 had empirically changed antifungal therapy due to pneumonia progression. Clinical and radiological response rate was 68% after 90 days from IFI diagnosis. No toxicities related to drug-drug interaction have been registered in patients reaching concomitant therapeutic levels of ISA and sirolimus.

Conclusion

The coadministration of ISA and sirolimus was safe and feasible in this cohort, confirming favorable clinical efficacy in patients with multiple-drug coadministration.

Isavuconazole-tacrolimus drug-drug interactions in HSCT patients

OBJECTIVES

Because tacrolimus has a narrow therapeutic window and exhibits both intraindividual and interindividual variability, we attempted to establish the percentage of calcineurin inhibitor (CNI) dose reduction to prevent toxicity and ensure stem cell engraftment when using this immunosuppressant with the antifungal isavuconazole (ISA). By calculating the tacrolimus concentration/dose (C/D) ratio, we expected to demonstrate the magnitude of change in the C/D ratio from baseline after ISA administration.

METHODS

We evaluated the interaction between ISA, a new triazole antifungal used in prophylaxis for invasive fungal infections, and the CNI class of immunosuppressive drugs, specifically tacrolimus, in 11 blood samples from HSCT recipients.

RESULTS

The mean tacrolimus C/D ratio increased 1.44-fold from baseline 48 h after ISA administration (P = 0.001).

CONCLUSIONS

Although further investigation is needed, the results of this study suggest that a reduction of 18% in tacrolimus may be recommended.

Impact of Pharmacogenetics on Intravenous Tacrolimus Exposure and Conversions to Oral Therapy

CYP3A5 and CYP3A4 are the predominant enzymes responsible for tacrolimus metabolism; however only a proportion of the population expresses CYP3A5 secondary to genetic variation. CYP3A5 is expressed in both the intestine and the liver and has been shown to impact both the bioavailability and metabolism of orally administered tacrolimus. Increasing the initial tacrolimus dose by 50% to 100% is recommended in patients who are known CYP3A5 expressers; however, whether this dose adjustment is appropriate for i.v. tacrolimus administration is unclear. The objective of this study was to evaluate the impact of CYP3A5 genotype as well as other pharmacogenes on i.v. tacrolimus exposure to determine whether the current genotype-guided dosing recommendations are appropriate for this formulation. In addition, this study aimed to investigate dose conversion requirements among CYP3A5 genotypes when converting from i.v. to p.o. tacrolimus. This study is a retrospective chart review of all patients who underwent allogeneic stem cell transplantation at Michigan Medicine between June 1, 2014, and March 1, 2018, who received i.v. tacrolimus at the time of their transplantation. Secondary use samples were obtained for genotyping CYP3A5, CYP3A4, and ABCB1. Patient demographic information, tacrolimus dosing and trough levels, and concomitant medications received at the time of tacrolimus trough were collected retrospectively from the patients' medical records. The i.v. dose-controlled concentration (C/D) and the i.v.:p.o. exposure ratio was calculated for all tacrolimus doses and patients, respectively. The impact of CYP3A5, CYP3A4, and ABCB1 genotypes on the i.v. C/D were evaluated with linear mixed modeling. The impact of CYP3A5 genotype on the i.v.:p.o. ratio was evaluated while controlling for age and concomitant use of an azole inhibitor. CYP3A5 and CYP3A4 genotypes were significantly associated with the i.v. C/D, with CYP3A5 expressers and CYP3A4 rapid metabolizers having 20% lower tacrolimus exposure. Neither genotype remained significant in the multivariable model, although age, hematocrit, and concomitant use of strong azole inhibitors were associated with increased i.v. C/D. When controlling for patient age and sex, CYP3A5 expressers had significantly higher i.v.:p.o. ratios than CYP3A5 nonexpressers (3.42 versus 2.78; P = .04). Post hoc analysis showed that the i.v.:p.o. ratio may differ among different CYP3A5 genotypes and azole inhibitor combinations. This study demonstrates that the current genotype-guided tacrolimus dose adjustment recommendations are inappropriate for CYP3A5 expressers receiving i.v. tacrolimus. Although CYP3A5 genotype is likely a minor contributor to i.v. tacrolimus exposure, genotype, in addition to capturing concomitant CYP3A inhibitors, would likely improve i.v.:p.o. dose conversion selection. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.