Retrospective analysis of the correlation between tacrolimus concentrations measured in whole blood and variations of blood cell counts in patients undergoing allogeneic haematopoietic stem cell transplantation

Effect of early post-hematopoietic stem cell transplant tacrolimus concentration on transplant outcomes in pediatric recipients: One facility's ten-year experience of immunosuppression with tacrolimus

Acute graft-versus-host disease (GVHD) is a common life-threatening complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT), ranking as the second leading cause of death among recipients, surpassed only by disease relapse. Tacrolimus is commonly used for GVHD prophylaxis, but achieving therapeutic blood levels is challenging, particularly in pediatrics, due to the narrow therapeutic window and the high interindividual variability. The retrospective study conducted at IRCCS "Burlo Garofolo" in Italy aimed to assess the impact of early post-HSCT tacrolimus levels on transplant-related outcomes in pediatric recipients. The population pharmacokinetic model (POP/PK) was set up to describe tacrolimus pharmacokinetics. Elevated tacrolimus (>12-15 ng/ml) levels within the initial weeks post-HSCT are associated with reduced post-transplant infections (p < 0.0001) and decreased incidence of early transplant-related events (p < 0.01), including a lower incidence of acute GVHD (p < 0.05 on day 0). High tacrolimus exposure can lead to an increased risk of chronic GVHD (p < 0.0001) and reduced overall survival (p < 0.01). Personalized dosing and therapeutic monitoring of tacrolimus are crucial to ensure optimal outcomes. POP/PK could help achieve this goal, giving us a model by which we can balance immunosuppression while looking at the patient's general well-being and providing the necessary treatment.

Change in Tacrolimus Concentration Measured in Whole Blood Correlates With Changes in Red Blood Cell Parameters After Red Blood Cell Transfusion in Kidney Transplant Recipients

BACKGROUND

Tacrolimus (TAC) is a narrow therapeutic range drug that requires therapeutic drug monitoring. TAC concentration is measured using whole blood owing to its high red blood cell (RBC) transfer rate of 95%. The distribution and whole-blood TAC concentration may be affected by the transfusion of red cell concentrates (RCCs); however, this has not been studied in kidney transplant recipients (KTR). Therefore, we investigated the relationship between changes in whole-blood TAC concentration and RBC parameters before and after RCC transfusion in KTR.

METHODS

Fifteen KTR who received TAC and RCC transfusions were enrolled. The change rates of RBC parameters (RBC count, hemoglobin [Hgb], hematocrit [Hct]), and TAC concentration/dose before and after transfusion were calculated. The correlation between each RBC parameter and the TAC rate was evaluated.

RESULTS

The TAC concentration and rate increased after RCC transfusion. Moreover, the TAC rate showed a significant and strong correlation with RBC count, Hgb, and Hct, with RBC count showing the highest correlation coefficient (r = 0.811, 0.766, and 0.764, respectively; p < .01). Serum creatinine and potassium levels remained stable, suggesting the absence of typical adverse effects associated with TAC, such as acute kidney injury or hyperkalemia.

CONCLUSION

Changes in whole-blood TAC concentration and RBC parameters were correlated, and whole-blood TAC concentration increased after RCC transfusion. Therefore, the TAC dose should be adjusted accordingly.

Elevation of tacrolimus concentration after administration of methotrexate for treatment of graft-versus-host disease in pediatric patients received allogeneic hematopoietic stem cell transplantation

BACKGROUND

Methotrexate (MTX) is used to treat graft-versus-host disease (GVHD) following allogeneic hematopoietic stem cell transplantation (allo-HSCT). Recently, a case was encountered in which the blood concentration of tacrolimus (TCR) at steady state increased after intravenous MTX administration for GVHD treatment (therapeutic IV-MTX administration). Therefore, this study aimed to investigate the effect of therapeutic IV-MTX administration on the pharmacokinetics of TCR.

METHODS

This single-center, retrospective, observational study included patients who underwent allo-HSCT and received therapeutic IV-MTX administration during immunosuppressive therapy with continuous intravenous infusion (CIV) of TCR from April 2004 to December 2021. Here, each therapeutic IV-MTX administration was defined as a case and independently subjected to subsequent analyses. The blood concentration of TCR at steady state (Css), ratio of Css to daily TCR dose (C/D), and clinical laboratory data were compared before and after therapeutic IV-MTX administration. In addition, dose changes in the TCR after therapeutic IV-MTX administration were evaluated.

RESULTS

Ten patients (23 cases) were included in this study. The C/D value significantly increased after therapeutic IV-MTX administration (median: 697 vs. 771 (ng/mL)/(mg/kg), 1.16-fold increase, P < 0.05), indicating a reduction in the apparent clearance of TCR. Along with the increase in C/D, significant increases were observed in aspartate transaminase level (median: 51.0 vs. 92.9 U/L, P < 0.01) and alanine aminotransferase level (median: 74.5 vs. 99.4 U/L, P < 0.01) indicating that liver injury after therapeutic IV-MTX administration contributes to the observed C/D increase. In addition, the daily dose of TCR was reduced in 11 cases (47.8%) after therapeutic IV-MTX administration, and the relative frequency of dose reduction tended to be higher than that of dose increase (median: 37.5% vs. 0.0%, P = 0.0519, permuted Brunner-Munzel test). The magnitude of dose reduction was 18.8% (7.4-50.0%) in the 11 cases with dose reduction.

CONCLUSIONS

Therapeutic IV-MTX administration cause a significant increase in C/D, which requires TCR dose reduction. Careful therapeutic drug monitoring of TCR is needed after therapeutic IV-MTX administration in patients receiving immunosuppressive therapy with TCR after allo-HSCT.

Effects of CYP3A5 Genotypes on Thrombocytopenia in Liver Transplantation Patients Treated with Tacrolimus

BACKGROUND

Thrombocytopenia is a complication after liver transplantation. This study's aims were to evaluate the role of CYP3A5 genotypes on tacrolimus-induced thrombocytopenia after orthotopic liver transplantation.

METHODS

In this retrospective case-control study, data from 100 patients who underwent deceased-donor liver transplantation (DDLT) were divided into CYP3A5*3 genotype (donor/recipient) tacrolimus fast- (A*/A*, n = 22), intermediate- (A*/GG, n = 20; GG/A*, n = 31) and slow-metabolizer (GG/GG, n = 27) groups. Platelet count changes and prognosis for 180 days after surgery were compared.

RESULTS

Platelet counts declined significantly after DDLT, especially on postoperative day (POD) 3, and continued at low levels for a week thereafter in all groups. In the GG/GG group, platelet counts on POD3 (50.29 ± 5.44 × 109/L) were the lowest among the groups (A*/A*, 71.00 ± 6.22 × 109/L; A*/GG, 57.95 ± 6.21 × 109/L; GG/A*, 75.90 ± 5.56 × 109/L) (p = 0.006). Compared with the A*/A* genotype, tacrolimus nadir levels were significantly higher in GG/GG genotype patients, who also exhibited a higher incidence of hemorrhage (22.2%, p = 0.011). A combination of a nadir blood concentration of tacrolimus ≥ 4.74 ng/mL and spleen size ≥ 165.5 mm was a risk factor for increased thrombocytopenia after DDLT on POD3, with an AUC of 0.735 (sensitivity, 77.2%; specificity, 41.7%).

CONCLUSIONS

A high blood concentration of tacrolimus after the early stage of DDLT is a major risk factor for hemorrhage. For the CYP3A5 genotype (GG/GG), controlling the blood concentration of tacrolimus below the target concentration until POD3 can avoid thrombocytopenia-related complications.

Relationship between CYP3A5 Polymorphism and Tacrolimus Blood Concentration Changes in Allogeneic Hematopoietic Stem Cell Transplant Recipients during Continuous Infusion

A polymorphism in the gene encoding the metabolic enzyme cytochrome P450 family 3 subfamily A member 5 (CYP3A5) is a particularly influential factor in the use of tacrolimus in Japanese patients. Those who are homozygotic for the *3 mutation lack CYP3A5 activity, which results in substantial individual differences in tacrolimus metabolism. The aim of this study was to analyze the relationship between individual differences in tacrolimus blood concentration changes and CYP3A5 polymorphisms in allogeneic hematopoietic stem cell transplantation recipients during the period of increasing blood concentration of the drug following treatment onset. This was a prospective observational cohort study, involving 20 patients administered tacrolimus by continuous infusion. The subjects were divided into the *1/*3 and *3/*3 groups based on CYP3A5 polymorphism analysis. The tacrolimus blood concentration/dose (C/D) ratio increased from day 1 and was largely stable on day 5, and a significant difference was observed between the *1/*3 and *3/*3 groups in the time course of the C/D ratio during this period (p < 0.05). This study reveals the effects of CYP3A5 polymorphism on continuous changes in tacrolimus blood concentration.

Role of FK506 Binding Protein on Tacrolimus Distribution in Red Blood Cells

PURPOSE

Tacrolimus is distributed mainly in red blood cells (RBCs) after transfer into blood. This study aimed to evaluate the effect of FK506-binding proteins (FKBPs) on RBC distribution of tacrolimus in a physiological environment.

METHODS

Human RBCs were isolated from fresh blood samples from healthy volunteers. The effect of FKBPs on each process of the RBC distribution of tacrolimus was evaluated in vitro. Effect of intracellular FKBPs was assessed by inhibition experiment with rapamycin, which competitively inhibits the binding of tacrolimus to FKBPs. Effect of extracellular FKBPs was examined by pre-exposure of RBCs to FKBP and preincubation of tacrolimus with FKBP.

RESULTS

Pretreatment with rapamycin significantly reduced the rate of tacrolimus distribution in RBCs in a concentration-dependent manner. Pre-exposure of RBCs to FKBP12 followed by exposure to tacrolimus significantly decreased tacrolimus distribution in RBCs in a concentration-dependent manner. In addition, preincubation of tacrolimus with FKBP12 significantly reduced the rate of tacrolimus distribution in RBCs.

CONCLUSIONS

FKBP played an important role in the distribution of tacrolimus in RBCs. The effect of intracellular and extracellular FKBPs on RBC distribution of tacrolimus in circulating blood was substantial. FKBP was shown as a potential biomarker for predicting the pharmacokinetics and pharmacodynamics of tacrolimus.