Utilization of a Population Pharmacokinetic Model to Improve a Busulfan Test-Dose Strategy in Allogeneic Hematopoietic Cell Transplant Recipients.

Busulfan is an alkylating agent used as part of conditioning chemotherapy regimens prior to allogeneic hematopoietic cell transplant (allo-HCT). Pharmacokinetic (PK)-guided test-dose strategies have been shown to improve the number of patients achieving busulfan exposure goals and improve clinical outcomes. However, current practices require extensive PK sampling. In this study, PK data were retrospectively collected from busulfan drug monitoring records from adult allo-HCT recipients who received once-daily intravenous busulfan at the University of North Carolina Medical Center (UNCMC). A population pharmacokinetic (popPK) model was developed to identify sources of interindividual variability and evaluate alternative PK sampling strategies. A 2-compartment model, with covariate effects of actual body weight and sex, best described the data. The typical value of clearance for an 83 kg male was estimated to be 11.21 L/h. Fifty-nine percent of allo-HCT recipients were estimated to have met the UNCMC institutional myeloablative conditioning (MAC) exposure goal based on model post hoc estimates of clearance using all PK samples obtained following MAC dosing. Fifty-seven percent of patients were estimated to have met this goal based on post hoc estimates using a single PK sample. Our results indicate once-daily, intravenous busulfan PK in adult allo-HCT recipients receiving MAC dosing can be reasonably described by a popPK model, and the use of a sparse PK sampling strategy may be feasible for determining target exposure attainment following MAC dosing. Use of a popPK model and sparse PK sampling strategy to carry out busulfan test-dose procedures could reduce health care costs and inconvenience to patients.

Correlation of Engraftment and Time from Melphalan Administration to Stem Cell Infusion.

Single-agent, high-dose melphalan continues to be the most commonly used conditioning regimen for transplantation-eligible patients with multiple myeloma undergoing autologous stem cell transplantation. The timing of melphalan administration with respect to stem cell infusion has not been clearly defined. Many institutions require a minimum of 24 hours between melphalan administration and stem cell infusion; however, some institutions have adopted shorter intervals based on melphalan's short half-life. Some studies have suggested that shortening the interval between melphalan administration and stem cell infusion may contribute to delays in engraftment, but this correlation has not been clearly evaluated or defined. This multicenter retrospective cohort study evaluated the times to neutrophil and platelet engraftment in patients who received stem cells at least 24 hours after melphalan (≥24 hours cohort) compared with those who received stem cells within 24 hours of melphalan (<24 hours cohort. The study included a total of 723 adult patients, 502 patients in the ≥24 hours cohort and 221 in the <24 hours cohort, treated at 3 transplantation centers between January 1, 2016, and September 30, 2019. Patient characteristics were summarized using descriptive statistics. The Fisher exact test was used to compare nominal categorical variables between the 2 cohorts, and the nonparametric van der Waerden test or Mood median test was used to compare ordinal or continuous variables. The median time to neutrophil engraftment was 12 days for both the ≥24 hours cohort (interquartile range [IQR], 11 to 12 days) and the <24 hours cohort (IQR, 11 to 13 days) (P = .07). The median time to platelet engraftment was 19 days for both the ≥24 hours cohort (IQR, 17 to 22 days) and <24 hours cohort (IQR, 17 to 20 days) (P = .25). The median time between melphalan administration and stem cell infusion in the <24 hours cohort was 18 hours, with a minimum time of 12 hours. The existing literature has not clearly defined the impact of the timing between melphalan administration and stem cell infusion on engraftment in autologous transplantation. The ability to safely shorten the interval between chemotherapy and transplantation could increase logistical flexibility and/or decrease the length of hospital stay. This large multicenter retrospective study did not identify a statistical or clinical impact on engraftment when melphalan was infused <24 hours or ≥24 hours before autologous stem cell infusion.

Plerixafor strategies for autologous hematopoietic cell transplant mobilization: A comparison of efficacy and cost.

Addition of plerixafor (P) to granulocyte colony stimulating factor (G-CSF) during peripheral blood mobilization of hematopoietic stem cells (HSC) increases the number of patients meeting collection goals prior to autologous stem cell transplant (aSCT). However, use of P is not universal among transplant centers due to cost. This study aims to compare clinical and financial impacts of using an algorithm-based P mobilization strategy versus use in all patients. This was a single center, retrospective analysis of adult patients with myeloma or amyloidosis receiving aSCT who received apheresis of their HSC between 3/1/2017 and 3/1/2019. Patients prior to 3/1/2018 were classified as receiving P "per algorithm" and those after this date were classified as "up-front" P. For the per-algorithm group, P was given for a pre-apheresis CD34+ cell count of <20 cells/µL on mobilization day 5 and patients returned on day 6 for apheresis. Of the 129 patients included, 55 received P per-algorithm and 74 received up-front P. There was a reduction in median number of apheresis days (1.5 vs 1 day, p < 0.001) and an increase in median number of CD34+ cells collected (6.6 vs 8.5 × 106 cells/kg, p < 0.001) with up-front P. Up-front P increased drug cost but reduced apheresis costs, which resulted in a net savings of $121 per patient in total mobilization costs. These findings suggest that use of up-front P for mobilization significantly reduces apheresis days and increases HSC collection yield without increasing overall cost per patient.

Chimeric Antigen Receptor T Cell Therapy: A Comprehensive Review of Clinical Efficacy, Toxicity, and Best Practices for Outpatient Administration.

Chimeric antigen receptor T cell (CAR T) therapy has been integrated into treatment algorithms for acute leukemia, lymphoma, and, most recently, multiple myeloma. The number of clinical trials in both hematologic and solid tumor malignancies for new products and potential indications continues to grow. The clinical toxicities of CAR T therapy include cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome, which often warrant inpatient admission for close monitoring and treatment. Consequently, many centers have built processes around the administration of these cells in the inpatient setting. As new products gain Food and Drug Administration approval with more manageable toxicity profiles, and as institutions gain experience with the management of these toxicities, outpatient administration and monitoring should be expected. In addition, payor reimbursements for inpatient treatment have put the sustainability of inpatient CAR T therapy in jeopardy, especially for centers with a payor mix that includes a high proportion of Medicare patients. This has the serious potential to limit access to care. As the use of CAR T therapy continues to expand, changes in payment models, care settings, or both are needed to ensure the sustainability of safe, efficient, and cost-effective treatment. This review outlines the efficacy and toxicity of currently approved products, as well as best practices to optimize the management of CAR T cell therapy in the outpatient setting.

Evaluation of mobilization efficacy with an extended interval following plerixafor administration.

Plerixafor is a hematopoietic stem cell mobilizing agent used in combination with granulocyte-colony stimulating factor to improve collection for autologous stem cell transplantation. Despite a recommendation for administration 11 h prior to apheresis per package labeling, logistical challenges lead many institutions to administer plerixafor at an extended interval. The purpose of this study was to determine if plerixafor effectively and efficiently mobilizes CD34+ cells when given at an extended interval prior to apheresis. This was a retrospective evaluation of adult patients who received plerixafor based on an algorithm reserving daily plerixafor only for patients with a pre-apheresis CD34+ count of < 20 cells/µL (pre-apheresis plerixafor) or with a low CD34+ yield after the first apheresis session (rescue plerixafor). The primary outcome was achievement of a disease-specific collection goal of ≥ 6 ×106 CD34+ cells/kg for multiple myeloma and ≥ 4 ×106 CD34+ cells/kg for lymphoma. The mean interval between plerixafor administration and apheresis was 17 h in this study. Despite this extended interval, 64% of patients met their disease-specific collection goal. A minimum collection goal of ≥ 2 ×106 CD34+ cells/kg was achieved by 95% of patients. Mobilization remained efficient with a median of two days to complete collection. Based on this data, plerixafor effectively and efficiently mobilizes CD34+ cells when given at an extended interval prior to apheresis.

Influence of Germline Genetics on Tacrolimus Pharmacokinetics and Pharmacodynamics in Allogeneic Hematopoietic Stem Cell Transplant Patients.

Tacrolimus exhibits high inter-patient pharmacokinetics (PK) variability, as well as a narrow therapeutic index, and therefore requires therapeutic drug monitoring. Germline mutations in cytochrome P450 isoforms 4 and 5 genes (CYP3A4/5) and the ATP-binding cassette B1 gene (ABCB1) may contribute to interindividual tacrolimus PK variability, which may impact clinical outcomes among allogeneic hematopoietic stem cell transplantation (HSCT) patients. In this study, 252 adult patients who received tacrolimus for acute graft versus host disease (aGVHD) prophylaxis after allogeneic HSCT were genotyped to evaluate if germline genetic variants associated with tacrolimus PK and pharmacodynamic (PD) variability. Significant associations were detected between germline variants in CYP3A4/5 and ABCB1 and PK endpoints (e.g., median steady-state tacrolimus concentrations and time to goal tacrolimus concentration). However, significant associations were not observed between CYP3A4/5 or ABCB1 germline variants and PD endpoints (e.g., aGVHD and treatment-emergent nephrotoxicity). Decreased age and CYP3A5*1/*1 genotype were independently associated with subtherapeutic tacrolimus trough concentrations while CYP3A5*1*3 or CYP3A5*3/*3 genotypes, myeloablative allogeneic HSCT conditioning regimen (MAC) and increased weight were independently associated with supratherapeutic tacrolimus trough concentrations. Future lines of prospective research inquiry are warranted to use both germline genetic and clinical data to develop precision dosing tools that will optimize both tacrolimus dosing and clinical outcomes among adult HSCT patients.

Drug-Drug Interaction Between Isavuconazole and Tacrolimus: Is Empiric Dose Adjustment Necessary?

A paucity of data currently exists regarding drug-drug interaction (DDI) with tacrolimus and isavuconazole coadministration. Current literature provides conflicting recommendations on whether an empiric tacrolimus dose reduction is necessary when coadministered with isavuconazole. A 47-year-old African American female with acute lymphoblastic leukemia underwent an allogenic stem cell transplant (alloSCT) and was subsequently placed on routine posttransplant therapy including tacrolimus for immunosuppression and posaconazole for antifungal prophylaxis. Tacrolimus was empirically dose reduced due to the expected DDI with posaconazole based on current recommendations. Due to a persistently prolonged QTc interval and need for mold coverage, antifungal prophylaxis was ultimately changed to isavuconazole at standard recommended dosing. Tacrolimus was empirically dose reduced by 40% based on limited available literature at the time; however, tacrolimus trough concentrations subsequently declined, requiring an increase in tacrolimus dose to maintain therapeutic trough concentrations. Adequate isavuconazole absorption was documented through pharmacokinetic and pharmacodynamic data by measuring an isavuconazole trough concentration and directly observing isavuconazole's shortening effect on the QTc interval, respectively. Our experience in an alloSCT patient suggests that an empiric tacrolimus dose reduction is not required when isavuconazole is initiated, but close tacrolimus therapeutic drug monitoring should rather be performed to guide tacrolimus dosing.

Evaluation of a Test Dose Strategy for Pharmacokinetically-Guided Busulfan Dosing for Hematopoietic Stem Cell Transplantation.

Targeted busulfan dosing helps limit chemotherapy-related toxicity and optimize disease outcomes in hematopoietic stem cell transplantation (HCT). The objective of this study was to evaluate busulfan exposure from a pharmacokinetic (PK)-guided dosing strategy using a test dose. This retrospective evaluation included adult patients who underwent HCT at our institution with busulfan-based myeloablative (>9 mg/kg) conditioning between January 2014 and October 2015. A weight-based test dose of 0.8 mg/kg was used with PK assessments to predict area under the curve (AUCpred) achieved with weight-based dosing, with a target AUC of 4800 µM*minute (AUCtarget). PK from the test dose was then used to calculate a PK-guided first myeloablative busulfan dose. PK assessments were also done after the first dose to assess if the goal area under the curve (AUC) had been achieved (AUCfirst). A PK-guided first dose resulted in achievement of target AUC with target ranges of ±10% in 50% of patients, ±15% in 75%, and ±20% in 94%. This was an improved rate of target achievement compared with the 33%, 44%, and 63% of patients who achieved the desired AUC for these respective target ranges when using weight-based dosing (P = .12, .004, and <.001, respectively). The PK-guided strategy also decreased the variability of AUC from 3.6-fold in AUCpred from the weight-based test doses (2700.8 to 9631 µM*minute; SD, 1211.6 µM*minute) to 1.8-fold in AUCfirst from the PK-guided first doses (3672.1 to 6609.8 µM*minute; SD, 574.7 µM*minute). This reflects a 2-fold improvement in AUC variability with a PK-guided dosing strategy. This is also improved from the 3-fold variability in AUC reported in other studies. Weight and body surface area were significantly associated with the likelihood of AUCfirst being within the ±10% target range (P = .04 for both associations). There was no significant association between AUCfirst and death, relapse, or a composite of the two. These results demonstrate a significant improvement in target AUC attainment and less interpatient variability with PK-guided dosing using a test dose strategy compared with weight-based dosing.

Evaluation of Hematopoietic Stem Cell Mobilization Rates with Early Plerixafor Administration for Adult Stem Cell Transplantation.

The addition of plerixafor to high-dose colony-stimulating growth factor has been shown to improve stem cell mobilization rates in autologous transplant patients with multiple myeloma and non-Hodgkin lymphoma. This study evaluates the change in administration time of plerixafor to determine if cell mobilization rates are similar between the US Food and Drug Administration-approved administration time of 11 hours before apheresis and an earlier administration time of 16 hours before apheresis. Medical records of patients age ≥ 18 years undergoing autologous stem cell transplantation requiring the use of plerixafor after at least 4 days of granulocyte colony-stimulating factor therapy to complete stem cell mobilization from January 1, 2010 through September 30, 2014 were retrospectively reviewed. The primary outcome was CD34+ cell mobilization success rates when plerixafor was administered 11 ± 2 hours (standard administration group) compared with 16 ± 2 hours before cell apheresis (early administration group), as defined as collection of ≥2 × 106 CD34+ cells/kg. Secondary outcomes included the number of plerixafor therapy days required to collect a total of ≥2 × 106 CD34+ cells/kg, the number of apheresis cycles required to achieve ≥2 × 106 CD34+ cells/kg, the median CD34+ cells/kg collected in each apheresis session, and the rates of reported adverse events that occurred in the standard administration time group compared with the early administration time group. Of the 197 patients included, 114 patients received plerixafor 11 ± 2 hours before apheresis and 83 patients received plerixafor 16 hours ± 2 hours before apheresis. Ninety-four percent of patients in the early administration group achieved successful stem cell mobilization compared with 81.6% in the standard administration group (P = .0111). The median number of plerixafor days to reach the collection goal of ≥2 × 106 CD34+ cells/kg was 1 day for each group (P = .323), and the median number of apheresis days to reach the collection goal was 2 days for the standard administration group compared with 1 day for the early administration group (P = .0156). Most adverse events were similar between the 2 groups except for fever, which occurred in 4.8% of the patients in the early administration group and none of the patients in the standard administration group. This study demonstrates plerixafor effectively mobilizes peripheral blood stem cells when given at an early administration time of 16 hours before apheresis compared with standard administration of 11 hours before apheresis. However, further prospective studies could strengthen these results.