Clinical determinants of calcineurin inhibitor disposition: a mechanistic review

Tacrolimus intra-patient variability measures and its associations with allograft clinical outcomes in kidney transplantation

AIMS

Tacrolimus (Tac) is commonly prescribed in solid organ transplantation to prevent immune-mediated damage to the graft. However, its pharmacokinetics show substantial variability between and within patients. Intra-patient variability of tacrolimus (Tac-IPV) has emerged as a novel marker to predict transplant outcomes. Numerous studies report varying associations between Tac-IPV and clinical outcomes, with Tac-IPV measures showing wide discrepancies among these studies. This inconsistency could be a significant factor that influences the various outcomes reported in different studies. Our review comprehensively assesses the relationship between various Tac-IPV measures and their associations with clinical outcomes in transplant patients.

METHODS

A comprehensive literature search was conducted using the PubMed and Embase databases, covering the period from 2004 to March 31, 2023. The search focused on studies that examined the relationship between Tac-IPV and clinical outcomes in kidney transplantation (KT). The inclusion criteria were specific to studies addressing Tac-IPV, including measures such as standard deviation (SD), coefficient of variation (CV), time-weighted coefficient of variability (CV), mean absolute deviation (MAD), and Tac variability score (TVS). Clinical outcomes included the development of de novo donor-specific antibodies (dnDSA), rejection episodes, graft loss, and graft failure.

RESULTS

Among the 33 studies that met the inclusion criteria, a notable proportion presented conflicting findings in their assessment of various Tac-IPV measures regarding dnDSA, rejection episodes, graft loss, and graft failure.

CONCLUSIONS

Most studies have identified a correlation between high Tac-IPV and poor clinical outcomes; however, this relationship is multifactorial. Influencing factors include the metabolic status of KT patients, the timing of Tac-IPV calculations, and the criteria for defining high and low Tac-IPV thresholds, including the size and selection method. CV, MAD, and TWCV are the metrics that are most frequently used to determine Tac-IPV. Additionally, most of the methods for establishing Tac-IPV thresholds typically employ receiver operating characteristic (ROC) curves and median values. It is also notable that studies examining the clinical significance of Tac-IPV often include tacrolimus levels measured six months after kidney transplantation.

Clinical Pharmacokinetics and Pharmacodynamics of Letermovir in Allogenic Hematopoietic Cell Transplantation

Letermovir is a newly developed antiviral agent used for the prophylaxis of human cytomegalovirus infections in patients undergoing allogeneic hematopoietic cell transplantation. This novel anti-cytomegalovirus drug, used for the prophylaxis of cytomegalovirus reactivation until approximately 200 days after transplantation, effectively reduces the risk of clinically significant cytomegalovirus infection. No human counterpart exists for the terminase complex; letermovir is virus specific and lacks some toxicities previously observed with other anti-cytomegalovirus drugs, such as cytopenia and nephrotoxicity. The absolute bioavailability of letermovir in healthy individuals is estimated to be 94% based on a population-pharmacokinetic analysis. In contrast, oral administration of letermovir to patients undergoing hematopoietic cell transplantation results in lower exposure than that in healthy individuals. Renal or hepatic impairment does not influence the intrinsic clearance of letermovir. Co-administration of letermovir may alter the plasma concentrations of other drugs, including itself, as it acts as a substrate and inhibitor/inducer of several drug-metabolizing enzymes and transporters. In particular, attention should be paid to the drug-drug interactions between letermovir and calcineurin inhibitors or azole antifungal agents, which are commonly used in patients undergoing hematopoietic cell transplantation. This article reviews and summarizes the clinical pharmacokinetics and pharmacodynamics of letermovir, focusing on patients undergoing hematopoietic cell transplantation, healthy individuals, and specific patient subsets.

Tacrolimus-induced posterior reversible encephalopathy syndrome following liver transplantation

In this editorial, we talk about a compelling case focusing on posterior reversible encephalopathy syndrome (PRES) as a complication in patients undergoing liver transplantation and treated with Tacrolimus. Tacrolimus (FK 506), derived from Streptomyces tsukubaensis, is a potent immunosuppressive macrolide. It inhibits T-cell transcription by binding to FK-binding protein, and is able to amplify glucocorticoid and progesterone effects. Tacrolimus effectively prevents allograft rejection in transplant patients but has adverse effects such as Tacrolimus-related PRES. PRES presents with various neurological symptoms alongside elevated blood pressure, and is primarily characterized by vasogenic edema on neuroimaging. While computed tomography detects initial lesions, magnetic resonance imaging, especially the Fluid-Attenuated Inversion Recovery sequence, is superior for diagnosing cortical and subcortical edema. Our discussion centers on the incidence of PRES in solid organ transplant recipients, which ranges between 0.5 to 5 +ACU-, with varying presentations, from seizures to visual disturbances. The case of a 66-year-old male status post liver transplantation highlights the diagnostic and management challenges associated with Tacrolimus-related PRES. Radiographically evident in the parietal and occipital lobes, PRES underlines the need for heightened vigilance among healthcare providers. This editorial emphasizes the importance of early recognition, accurate diagnosis, and effective management of PRES to optimize outcomes in liver transplant patients. The case further explores the balance between the efficacy of immunosuppression with Tacrolimus and its potential neurological risks, underlining the necessity for careful monitoring and intervention strategies in this patient population.

Therapeutic drug monitoring in kidney and liver transplantation: current advances and future directions

INTRODUCTION

Immunosuppressive drugs (ISD) present a narrow therapeutic window and extremely high inter- and intra-individual pharmacokinetic variability, which complicates their use in solid organ transplant recipients. In order to find a narrow appropriate equilibrium for each patient with the aim of maintaining clinical efficacy and reducing the risk of adverse drug reactions, a complex both clinical and biological monitoring is required, in particular through the use of therapeutic drug monitoring (TDM).

AREA COVERED

This review provides an overview of the available information on the relationship between exposure to immunosuppressive drugs and their efficacy and/or toxicity in kidney and liver transplantation. The aim of the review is to describe the pharmacodynamic/pharmacokinetic relationship that exists for immunosuppressive drugs, to summarize the studies that assess the value of TDM for these drugs in clinical practice, and to present the target and monitoring strategies aimed at optimizing patient immunosuppression, which could help to take a step forward in the field of solid organ transplant patient care.

EXPERT OPINION

To improve the care of transplant patients, several TDM innovations can be pursued by investigators. Among these, the development of microsampling methods for TDM or the combination of pharmacodynamic biomarkers with ISD exposure measurements appear to be relevant strategies.

A Comprehensive Mixed-Method Approach to Characterize the Source of Diurnal Tacrolimus Exposure Variability in Children: Systematic Review, Meta-analysis, and Application to an Existing Data Set

Tacrolimus is widely reported to display diurnal variation in pharmacokinetic parameters with twice-daily dosing. However, the contribution of chronopharmacokinetics versus food intake is unclear, with even less evidence in the pediatric population. The objectives of this study were to summarize the existing literature by meta-analysis and evaluate the impact of food composition on 24-hour pharmacokinetics in pediatric kidney transplant recipients. For the meta-analysis, 10 studies involving 253 individuals were included. The pooled effect sizes demonstrated significant differences in area under the concentration-time curve from time 0 to 12 hours (standardized mean difference [SMD], 0.27; 95% confidence interval [CI], 0.03-0.52) and maximum concentration (SMD, 0.75; 95% CI, 0.35-1.15) between morning and evening dose administration. However, there was significant between-study heterogeneity that was explained by food exposure. The effect size for minimum concentration was not significantly different overall (SMD, -0.09; 95% CI, -0.27 to 0.09) or across the food exposure subgroups. A 2-compartment model with a lag time, linear clearance, and first-order absorption best characterized the tacrolimus pharmacokinetics in pediatric participants. As expected, adding the time of administration and food composition covariates reduced the unexplained within-subject variability for the first-order absorption rate constant, but only caloric composition significantly reduced variability for lag time. The available data suggest food intake is the major driver of diurnal variation in tacrolimus exposure, but the associated changes are not reflected by trough concentrations alone.

Adequate cumulative exposure to tacrolimus and low tacrolimus variability decrease the incidence of biliary complications after liver transplantation

BACKGROUND

Nonearly biliary complications (BCs) after liver transplantation (LT) are highly associated with immunological status. Tacrolimus is the main immunosuppressant. Whether and how tacrolimus bioavailability affects BCs is unclear.

METHODS

LT recipients receiving tacrolimus-free immunosuppressants or developing BCs within 3 months after LT were excluded. Tacrolimus-related variables included trough concentration (C0), variability and cumulative exposure to tacrolimus (CET). Receiver operating characteristic (ROC) curves defined cutoff values of CET and variability. The values divided patients into adequate and low CET groups, also high and low-variability groups. Inverse probability of treatment weighting (IPTW) was used to reduce bias. Logistic regression identified risk factors. Kaplan-Meier curves were generated for survival comparison.

RESULTS

409 patients were enrolled, and 39 (9.5 %) suffered from BCs. The mean C0 values were 6.9 and 7.2 ng/mL in the BCs and BCs-free groups, respectively. CET within 3 postoperative months was 550.0 and 608.6 ng.day/mL, while the tacrolimus variability was 0.4 and 0.3, respectively. The cutoff values for CET within 3 months and variability predicting BCs were 660.5 and 0.54, respectively. Multivariable logistic regression revealed that low CET within 3 months (p = 0.005, p = 0.002) and high variability (p < 0.001, p < 0.001) were associated with BCs before and after IPTW. Appropriate CET and low variability were associated with better overall survival (p = 0.009 and 0.029). Subgroup analysis indicated that long cold ischemia time (CIT), high bilirubin and low CET had a higher relative risk and raised the incidence of BCs.

CONCLUSIONS

Adequate CET and low variability of tacrolimus ameliorated nonearly BCs incidence and improved survival.

Effects of CYP3A4*22 and POR*28 variations on the pharmacokinetics of tacrolimus in renal transplant recipients: a meta-analysis of 18 observational studies

PURPOSE

This study aimed to investigate the association between cytochrome P450 (CYP) 3A4*22 and cytochrome P450 oxidoreductase (POR)*28 variations and the pharmacokinetics of tacrolimus.

METHODS

Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science (SCI), MEDLINE, and Embase were systematically searched from inception to August 2022. The outcomes were weight-adjusted daily dose and dose-adjusted trough concentration (C0/Dose).

RESULTS

The study included 2931 renal transplant recipients from 18 publications. Weight-adjusted daily dose of CYP3A4*1/*1 carriers was 0.04 (WMD = 0.04, 95% CI: 0.02 to 0.06), 0.03 (WMD = 0.03, 95% CI: 0.02 to 0.05), 0.02 (WMD = 0.02, 95% CI: 0.01 to 0.03), or 0.02 mg/kg/day (WMD = 0.02, 95% CI: 0.00 to 0.04) higher than CYP3A4*22 carriers in Caucasians at 1 month, 3 months, 6 months, or 12 months post-transplantation. Conversely, C0/Dose was lower for CYP3A4*1/*1 carriers at 3 days (SMD = -0.35, 95% CI: -0.65 to -0.06), 1 month (SMD = -0.67, 95% CI: -1.16 to -0.18), 3 months (SMD = -0.60, 95% CI: -0.89 to -0.31), 6 months (SMD = -0.76, 95% CI: -1.49 to -0.04), or 12 months post-transplantation (SMD = -0.69, 95% CI: -1.37 to 0.00). Furthermore, C0/Dose of POR*1/*1 carriers was 22.64 (WMD = 22.64, 95% CI: 2.54 to 42.74) or 19.41 (ng/ml)/(mg/kg/day) (WMD = 19.41, 95% CI: 9.58 to 29.24) higher than POR*28 carriers in CYP3A5 expressers at 3 days or 7 days post-transplantation, and higher in Asians at 6 months post-transplantation (SMD = 0.96, 95% CI: 0.50 to 1.43).

CONCLUSIONS

CYP3A4*22 variant in Caucasians restrains the metabolism of tacrolimus, while POR*28 variant in CYP3A5 expressers enhances the metabolism of tacrolimus for renal transplant recipients. However, further well-designed prospective studies are necessary to substantiate these conclusions given some limitations.

A Population Pharmacokinetic Model to Predict the Individual Starting Dose of Tacrolimus for Tunisian Adults after Renal Transplantation

BACKGROUND

Tacrolimus is the most frequently used immunosuppressive drug for preventing renal rejection. However, its use is hampered by its narrow therapeutic index and large intra and interpatient variability in pharmacokinetics. The objective of this study was to externally validate a tacrolimus population pharmacokinetic model developed for the Dutch population and adjust the model for the Tunisian population for use in predicting the starting dose requirement after kidney transplantation.

METHODS

Data on tacrolimus exposure were obtained from kidney transplant recipients (KTRs) during the first 3 months post-transplantation. External validation of the Dutch model and its adjustment for the Tunisian population was performed using nonlinear mixed-effects modeling.

RESULTS

In total, 1901 whole-blood predose tacrolimus concentrations from 196 adult KTRs were analyzed. According to a visual predictive check, the Dutch model underestimated the starting dose for the Tunisian adult population. The effects of age, together with the CYP3A5*3 and CYP3A4*22 genotypes on tacrolimus clearance were significantly different in the Tunisian population than in the Dutch population. Based on a bodyweight-based dosing, only 21.9% of tacrolimus concentrations were within the target range, whereas this was estimated to be 54.0% with the newly developed model-based dosing. After adjustment, the model was successfully validated internally in a Tunisian population.

CONCLUSIONS

A starting-dose population pharmacokinetic model of tacrolimus for Tunisian KTRs was developed based on a previously published Dutch model. Using this starting dose could potentially increase the percentage of patients achieving target tacrolimus concentrations after the initial starting dose.

Population pharmacokinetic models of tacrolimus in paediatric solid organ transplant recipients: A systematic review

AIMS

This study aimed to provide up-to-date information on paediatric population pharmacokinetic models of tacrolimus and to identify factors influencing tacrolimus pharmacokinetic variability.

METHODS

Systematic searches in the Web of Science, PubMed, Scopus, Science Direct, Cochrane, EMBASE databases and reference lists of articles were conducted from inception to March 2023. All population pharmacokinetic studies of tacrolimus using nonlinear mixed-effect modelling in paediatric solid organ transplant patients were included.

RESULTS

Of the 21 studies reviewed, 62% developed from liver transplant recipients and 33% from kidney transplant recipients. Most studies used a 1-compartment model to describe tacrolimus pharmacokinetics. Body weight was a significant predictor for tacrolimus volume of distribution (Vd/F). The estimated Vd/F for 1-compartment models ranged from 20 to 1890 L, whereas the peripheral volume of distribution (Vp/F) for 2-compartment models was between 290 and 1520 L. Body weight, days post-transplant, CYP3A5 genotype or haematocrit were frequently reported as significant predictors of tacrolimus clearance. The estimated apparent clearance values range between 0.12 and 2.18 L/h/kg, with inter-individual variability from 13.5 to 110.0%. Only 29% of the studies assessed the generalizability of the models with external validation.

CONCLUSION

This review highlights the potential factors, modelling approaches and validation methods that impact tacrolimus pharmacokinetics in a paediatric population. The clinician could predict tacrolimus clearance based on body weight, CYP3A5 genotype, days post-transplant or haematocrit. Further research is required to determine the relationship between pharmacogenetics and tacrolimus pharmacodynamics in paediatric patients and confirm the applicability of nonlinear kinetics in this population.

Modelling changes in the pharmacokinetics of tacrolimus during pregnancy after kidney transplantation: A retrospective cohort study

AIMS

Pregnancy after kidney transplantation is realistic but immunosuppressants should be continued to prevent rejection. Tacrolimus is safe during pregnancy and is routinely dosed based on whole-blood predose concentrations. However, maintaining these concentrations is complicated as physiological changes during pregnancy affect tacrolimus pharmacokinetics. The aim of this study was to describe tacrolimus pharmacokinetics throughout pregnancy and explain the changes by investigating covariates in a population pharmacokinetic model.

METHODS

Data of pregnant women using a twice-daily tacrolimus formulation following kidney transplantation were retrospectively collected from 6 months before conception, throughout gestation and up to 6 months postpartum. Pharmacokinetic analysis was performed using nonlinear mixed effects modelling. Demographic, clinical and genetic parameters were evaluated as covariates. The final model was evaluated using goodness-of-fit plots, visual predictive checks and a bootstrap analysis.

RESULTS

A total of 260 whole-blood tacrolimus predose concentrations from 14 pregnant kidney transplant recipients were included. Clearance increased during pregnancy from 34.5 to 41.7 L/h, by 15, 19 and 21% in the first, second and third trimester, respectively, compared to prior to pregnancy. This indicates a required increase in the tacrolimus dose by the same percentage to maintain the prepregnancy concentration. Haematocrit and gestational age were negatively correlated with tacrolimus clearance (P ≤ 0.01), explaining 18% of interindividual and 85% of interoccasion variability in oral clearance.

CONCLUSIONS

Tacrolimus clearance increases during pregnancy, resulting in decreased exposure to tacrolimus, which is explained by gestational age and haematocrit. To maintain prepregnancy target whole-blood tacrolimus predose concentrations during pregnancy, increasing the dose is required.

Tacrolimus population pharmacokinetics in adult heart transplant patients

INTRODUCTION

Tacrolimus is an immunosuppressant largely used in heart transplantation. However, the calculation of its exposure based on the area under the curve (AUC) requires the use of a population pharmacokinetic (PK) model. The aims of this work were (i) to develop a population PK model for tacrolimus in heart transplant patients, (ii) to derive a maximum a posteriori Bayesian estimator (MAP-BE) based on a limited sampling strategy (LSS) and (iii) to estimate probabilities of target attainment (PTAs) for AUC and trough concentration (C0).

MATERIAL AND METHODS

Forty-seven PK profiles (546 concentrations) of 18 heart transplant patients of the Pharmacocinétique des Immunosuppresseurs chez les patients GREffés Cardiaques study receiving tacrolimus (Prograf®) were included. The database was split into a development (80%) and a validation (20%) set. PK parameters were estimated in MONOLIX® and based on this model a Bayesian estimator using an LSS was built. Simulations were performed to calculate the PTA for AUC and C0.

RESULTS

The best model to describe the tacrolimus PK was a two-compartment model with a transit absorption and a linear elimination. Only the CYP3A5 covariate was kept in the final model. The derived MAP-BE based on the LSS (0-1-2 h postdose) yielded an AUC bias ± SD = 2.7 ± 10.2% and an imprecision of 9.9% in comparison to the reference AUC calculated using the trapezoidal rule. PTAs based on AUC or C0 allowed new recommendations to be proposed for starting doses (0.11 mg·kg-1 ·12 h-1 for the CYP3A5 nonexpressor and 0.22 mg·kg1 ·12 h-1 for the CYP3A5 expressor).

CONCLUSION

The MAP-BE developed should facilitate estimation of tacrolimus AUC in heart transplant patients.

Bridging the Worlds of Pharmacometrics and Machine Learning

Precision medicine requires individualized modeling of disease and drug dynamics, with machine learning-based computational techniques gaining increasing popularity. The complexity of either field, however, makes current pharmacological problems opaque to machine learning practitioners, and state-of-the-art machine learning methods inaccessible to pharmacometricians. To help bridge the two worlds, we provide an introduction to current problems and techniques in pharmacometrics that ranges from pharmacokinetic and pharmacodynamic modeling to pharmacometric simulations, model-informed precision dosing, and systems pharmacology, and review some of the machine learning approaches to address them. We hope this would facilitate collaboration between experts, with complementary strengths of principled pharmacometric modeling and flexibility of machine learning leading to synergistic effects in pharmacological applications.

Beyond Immunosuppression: The Intricate Relationship Between Tacrolimus and Microangiopathy

Tacrolimus, widely known as Prograf, has become the preferred immunosuppressant for preventing graft rejection in solid organ transplant recipients, particularly in steroid-sparing regimens. Its efficacy and reduced risk of acute and chronic rejection compared to cyclosporine have made it the preferred treatment option for transplant patients. However, tacrolimus has drawbacks as it is associated with adverse effects, such as renal tubular necrosis, kidney failure, hypertension, metabolic acidosis, and new-onset diabetes mellitus. Among the less common but potentially severe complications is thrombotic microangiopathy linked to tacrolimus usage. Identifying and addressing this condition early on is crucial given its severity and potential complications. Manifestations of this microangiopathy can vary, encompassing renal, neurological, cardiac, and respiratory symptoms, and, in some cases, presenting as pancreatitis, intestinal ischemia, or skin abnormalities. Although conventional management often involves plasma exchange as the primary therapeutic option, recent insights into the pathophysiology have led to newer drugs, such as eculizumab and belatacept, offering promising outcomes. In this narrative review, we delve deeper into the underlying pathophysiological mechanisms of tacrolimus-induced thrombotic microangiopathy and aim to provide clinicians with valuable recommendations for efficient and timely treatment strategies. By understanding the complexities of this condition and staying abreast of the latest advancements in therapeutic options, healthcare providers can optimize patient outcomes and ensure safer tacrolimus administration in solid organ transplant recipients.

Physiologically based pharmacokinetic model combined with reverse dose method to study the nephrotoxic tolerance dose of tacrolimus

Nephrotoxicity is the most common side effect that severely limits the clinical application of tacrolimus (TAC), an immunosuppressive agent used in kidney transplant patients. This study aimed to explore the tolerated dose of nephrotoxicity of TAC in individuals with different CYP3A5 genotypes and liver conditions. We established a human whole-body physiological pharmacokinetic (WB-PBPK) model and validated it using data from previous clinical studies. Following the injection of 1 mg/kg TAC into the tail veins of male rats, we developed a rat PBPK model utilizing the drug concentration-time curve obtained by LC-MS/MS. Next, we converted the established rat PBPK model into the human kidney PBPK model. To establish renal concentrations, the BMCL5 of the in vitro CCK-8 toxicity response curve (drug concentration range: 2-80 mol/L) was extrapolated. To further investigate the acceptable levels of nephrotoxicity for several distinct CYP3A5 genotypes and varied hepatic function populations, oral dosing regimens were extrapolated utilizing in vitro-in vivo extrapolation (IVIVE). The PBPK model indicated the tolerated doses of nephrotoxicity were 0.14-0.185 mg/kg (CYP3A5 expressors) and 0.13-0.155 mg/kg (CYP3A5 non-expressors) in normal healthy subjects and 0.07-0.09 mg/kg (CYP3A5 expressors) and 0.06-0.08 mg/kg (CYP3A5 non-expressors) in patients with mild hepatic insufficiency. Further, patients with moderate hepatic insufficiency tolerated doses of 0.045-0.06 mg/kg (CYP3A5 expressors) and 0.04-0.05 mg/kg (CYP3A5 non-expressors), while in patients with moderate hepatic insufficiency, doses of 0.028-0.04 mg/kg (CYP3A5 expressors) and 0.022-0.03 mg/kg (CYP3A5 non-expressors) were tolerated. Overall, our study highlights the combined usage of the PBPK model and the IVIVE approach as a valuable tool for predicting toxicity tolerated doses of a drug in a specific group.

Tacrolimus-why pharmacokinetics matter in the clinic

The calcineurin inhibitor (CNI) Tacrolimus (Tac) is the most prescribed immunosuppressant drug after solid organ transplantation. After renal transplantation (RTx) approximately 95% of recipients are discharged with a Tac-based immunosuppressive regime. Despite the high immunosuppressive efficacy, its adverse effects, narrow therapeutic window and high intra- and interpatient variability (IPV) in pharmacokinetics require therapeutic drug monitoring (TDM), which makes treatment with Tac a major challenge for physicians. The C/D ratio (full blood trough level normalized by daily dose) is able to classify patients receiving Tac into two major metabolism groups, which were significantly associated with the clinical outcomes of patients after renal or liver transplantation. Therefore, the C/D ratio is a simple but effective tool to identify patients at risk of an unfavorable outcome. This review highlights the challenges of Tac-based immunosuppressive therapy faced by transplant physicians in their daily routine, the underlying causes and pharmacokinetics (including genetics, interactions, and differences between available Tac formulations), and the latest data on potential solutions to optimize treatment of high-risk patients.

Rifaximin stimulates nitrogen detoxification by PXR-independent mechanisms in human small intestinal organoids

BACKGROUND AND AIMS

Recurrent hepatic encephalopathy (HE) is characterized by hyperammonaemia in combination with neuropsychiatric abnormalities and is treated with lactulose and rifaximin. Rifaximin is a pregnane X receptor (PXR) agonist with low systemic and high intestinal bioavailability. The mechanisms by which it alleviates HE are unclear. We used human small intestinal (hSI) organoids to study whether rifaximin, via PXR activation, affects the epithelial biotransformation machinery, and to gain understanding of its low systemic availability.

METHODS

We generated PXR knockdown hSI organoids via lentiviral delivery of short hairpin RNAs. Organoids were cultured for 24 h with rifaximin or rifampicin. RNA-sequencing and metabolomics were performed to analyse gene expression and amino acid metabolism. Luminal rifaximin was quantified by photospectrometry.

RESULTS

Treatment of wild-type hSI organoids with rifaximin resulted in >twofold differential expression of 131 genes compared to DMSO. These effects were largely PXR independent and related to amino acid metabolism. Rifaximin decreased expression of glutaminase-2 and increased expression of asparagine synthetase and solute carrier 7A11, thereby increasing intracellular glutamine and asparagine concentrations, indicating active ammonia detoxification. Rifaximin was apically excreted into the lumen in an ATP binding cassette B1 (ABCB1)-dependent manner.

CONCLUSIONS

Rifaximin-after uptake into enterocytes-stimulates intracellular nitrogen detoxification by PXR-independent mechanisms. Active apical excretion of rifaximin by ABCB1 into the intestinal lumen explains its low systemic bioavailability. Our study implies that rifaximin, next to modulation of the microbiome, has direct effects on ammonia scavenging in the human small intestinal epithelium.

Population Pharmacokinetics of Tacrolimus in Pediatric Patients With Umbilical Cord Blood Transplant

Tacrolimus was frequently used in pediatric patients with umbilical cord blood transplant for the prevention of graft-versus-host disease. The aim of the present study was to evaluate the population pharmacokinetics of tacrolimus among pediatric patients with umbilical cord blood transplant and find potential influenced factors. A total of 275 concentrations from 13 pediatric patients were used to build a polulation pharmacokinetic model using a nonlinear mixed-effects modeling approach. The impact of demographic features, biological characteristics, and concomitant medications, including sex, age, body weight, postoperative day, white blood cell count, red blood cell count, hemoglobin, platelets, hematocrit, blood urea nitrogen, creatinine, aspartate transaminase, alanine transaminase, total bilirubin, albumin, and total protein were investigated. The pharmacokinetics of tacrolimus were best described by a 1-compartment model with first- and zero-order mixed absorption and first-order elimination. The clearance and volume of distribution of tacrolimus were 1.93 L/h and 75.1 L, respectively. A covariate analysis identified that postoperative day and co-administration with trimethoprim-sulfamethoxazole were significant covariates influencing clearance of tacrolimus. Frequent blood monitoring and dose adjustment might be needed with the prolongation of postoperative day and coadministration with trimethoprim-sulfamethoxazole.

Comparison of P-glycoprotein function in peripheral blood mononuclear cells ex vivo in stable Black and White male and female kidney transplant recipients

Kidney allograft survival remains poorer in Black compared to White recipients due to racial differences in calcineurin inhibitor (CNI) pharmacology. P-glycoprotein (P-gp), an ABC efflux transporter expressed in peripheral blood mononuclear cells (PBMCs), modulates CNI pharmacokinetics and intracellular pharmacology. This study investigated P-gp function in PBMC ex vivo at 0 (trough), 4, 8, and 12 h in stable Black and White male and female kidney transplant recipients (n = 67) receiving tacrolimus and mycophenolic acid. Tacrolimus doses were adjusted to troughs of 4-10 ng/ml. P-gp function was quantified with flow cytometric measurement of cyclosporine (CYA; 2.5 μM)-reversible efflux of P-gp substrate, 3,3'-Diethyloxacarbocyanine iodide by determining the percentage change of mean fluorescent intensity (MFI) with CYA (% ΔMFI). The composite parameter of area under the concentration versus time (AUC)0-12h % ΔMFI estimated P-gp function. Data analysis examined race, sex, and race-sex associations to P-gp function. A secondary aim analyzed ABCB1 genotypes: 1236C>T (rs1128503), 2677G>T/A (rs2032582), 3435C>T (rs1045642), and P-gp function. P-gp function (% ΔMFI) was higher in White patients at troughs (p = 0.031) compared to Black counterparts with similar trends at 4 and 8 h. Reduced AUC0-12h % ΔMFI was noted in Black recipients (N = 32) compared with Whites (N = 35, p = 0.029) with notable pairwise adjusted differences between Black and White women (p = 0.021). Higher AUC0-12h % ΔMFI was associated with ABCB1 2677 TT compared to GG variants (p = 0.035). The AUC0-12h % ΔMFI was greater in White than Black subjects. P-gp function was higher at troughs in White subjects and differed between race-sex groups. P-gp function in PBMC may influence intracellular tacrolimus exposure and inter-relating pharmacodynamic responses which may support race and sex pharmacologic differences.

Simpson's paradox and the impact of donor-recipient race-matching on outcomes post living or deceased donor kidney transplantation in the United States

Background

Race is a prognostic indicator in kidney transplant (KT). However, the effect of donor-recipient race-matching on survival after KT remains unclear.

Methods

Using the United Network for Organ Sharing (UNOS) database, a retrospective study was conducted on 244,037 adults who received first-time, kidney-alone transplantation between 2000 and 2019. All patients were categorized into two groups according to donor-recipient race-matching, and the living and deceased donor KT (LDKT and DDKT) were analyzed in subgroups.

Results

Of the 244,037 patients, 149,600 (61%) were race-matched, including 107,351 (87%) Caucasian, 20,741 (31%) African Americans, 17,927 (47%) Hispanics, and 3,581 (25%) Asians. Compared with race-unmatching, race-matching showed a reduced risk of overall mortality and graft loss (unadjusted hazard ratio (HR) 0.86, 95% confidence interval (CI) 0.84-0.87; and unadjusted HR 0.79, 95% CI: 0.78-0.80, respectively). After propensity score-matching, donor-recipient race-matching was associated with a decreased risk of overall graft loss (P < 0.001) but not mortality. In subgroup analysis, race-matching was associated with higher crude mortality (HR 1.12, 95% CI: 1.06-1.20 in LDKT and HR 1.11, 95% CI: 1.09-1.14 in DDKT). However, race-matching was associated with a decreased risk of graft loss in DDKT (unadjusted HR 0.97, 95% CI: 0.96-0.99), but not in LDKT. After propensity score-matching, race-matching had better outcomes for LDKT (patient survival, P = 0.047; graft survival, P < 0.001; and death-censored graft survival, P < 0.001) and DDKT (death-censored graft survival, P = 0.018). Nonetheless, race-matching was associated with an increased adjusted mortality rate in the DDKT group (P < 0.001).

Conclusion

Race-matching provided modest survival advantages after KT but was not enough to influence organ offers. Cofounding factors at baseline led to a contorted crude conclusion in subgroups, which was reversed again to normal trends in the combined analysis due to Simpson's paradox caused by the LDKT/DDKT ratio.

Can the Area Under the Curve/Trough Level Ratio Be Used to Optimize Tacrolimus Individual Dose Adjustment?

BACKGROUND

The aim of this work was to evaluate, in a large data set of renal transplant recipients, the intraindividual variability of the area under the curve (AUC)/predose concentration (C0) ratio in comparison with that of AUC, C0, AUC/dose, and C0/dose.

METHODS

Patients with at least 2 tacrolimus AUC estimation requests were extracted from the Immunosuppressant Bayesian dose Adjustment website, and relative variations between 2 consecutive visits for the different metrics were calculated and compared.

RESULTS

Data from 1325 patients on tacrolimus (3827 measured C0 and estimated AUC) showed that the lowest mean relative variation between 2 consecutives visits was for the AUC/C0 ratio (95% confidence interval [CI] relative fold change = -43% to 44% for AUC/C0; 95% CI, -77% to 72% for AUC; 95% CI, -82% to 98% for AUC/dose; 95% CI, -81% to 80% for C0 and 95% CI, -94% to 117% for C0/dose. The correlation between 2 consecutive requests, whether close or far apart, was also best for the AUC/C0 ratio ( r  = 0.33 and r  = 0.34, respectively) in comparison with C0 ( r  = 0.21 and r  = 0.22, respectively) and AUC ( r  = 0.19 and 0.28, respectively). Regression analysis between AUC0-24 and C0 showed that for some patients, the usual C0 targets translated into some very unusual AUC values. As the AUC/C0 ratio is quite stable during large periods, individualized C0 targets can be derived from the AUC targets, and an algorithm that estimates the individualized C0 was developed for situations in which prior AUC estimates are available or not.

CONCLUSIONS

In this study, we confirmed in a large data set that the AUC/C0 ratio yields low intraindividual variability, whereas C0 shows the largest, and we propose to calculate individualized C0 targets based on this ratio.

Malnutrition and immune cell subsets in children undergoing kidney transplantation

BACKGROUND

Malnutrition, including obesity and undernutrition, among children is increasing in prevalence and is common among children on renal replacement therapy. The effect of malnutrition on the pre-transplant immune system and how the pediatric immune system responds to the insult of both immunosuppression and allotransplantation is unknown. We examined the relationship of nutritional status with post-transplant outcomes and characterized the peripheral immune cell phenotypes of children from the Immune Development of Pediatric Transplant (IMPACT) study.

METHODS

Ninety-eight patients from the IMPACT study were classified as having obesity, undernutrition, or normal nutrition-based pre-transplant measurements. Incidence of infectious and alloimmune outcomes at 1-year post-transplantation was compared between nutritional groups using Gray's test and Fine-Gray subdistribution hazards model. Event-free survival was estimated by Kaplan-Meier method and compared between groups. Differences in immune cell subsets between nutritional groups over time were determined using generalized estimating equations accounting for the correlation between repeated measurements.

RESULTS

We did not observe that nutritional status was associated with infectious or alloimmune events or event-free survival post-transplant. We demonstrated that children with obesity had distinct T-and B-cell signatures relative to those with undernutrition and normal nutrition, even when controlling for immunosuppression. Children with obesity had a lower frequency of CD8 Tnaive cells 9-month post-transplant (p < .001), a higher frequency of CD4 CD57 + PD1- T cells, and lower frequencies of CD57-PD1+ CD8 and CD57-PD1- CD8 T cells at 12-month transplant (p < .05 for all).

CONCLUSIONS

Children with obesity have distinct immunophenotypes that may influence the tailoring of immunosuppression.

Cannabis Use and Heart Transplantation: Disparities and Opportunities to Improve Outcomes

Heart transplantation (HT) remains the optimal therapy for many patients with advanced heart failure. Use of substances of potential abuse has historically been a contraindication to HT. Decriminalization of cannabis, increasing cannabis use, clinician biases, and lack of consensus for evaluating patients with heart failure who use cannabis all have the potential to exacerbate racial and ethnic and regional disparities in HT listing and organ allocation. Here' we review pertinent pre-HT and post-HT considerations related to cannabis use' and relative attitudes between opiates and cannabis are offered for context. We conclude with identifying unmet research needs pertaining to the use of cannabis in HT that can inform a standardized evaluation process.

Prospective population pharmacokinetic study of tacrolimus in adult recipients early after liver transplantation: A comparison of Michaelis-Menten and theory-based pharmacokinetic models

Background and Objective: Tacrolimus, a calcineurin inhibitor widely used as a potent immunosuppressant to prevent graft rejection, exhibits nonlinear kinetics in patients with kidney transplantation and nephrotic syndrome. However, whether nonlinear drug metabolism occurs in adult patients undergoing liver transplantation remains unclear, as do the main underlying mechanisms. Therefore, here we aimed to further confirm the characteristics of nonlinearity through a large sample size, and determine the potential influence of nonlinearity and its possible mechanisms.

Methods: In total, 906 trough concentrations from 176 adult patients (150 men/26 women; average age: 50.68 ± 9.71 years, average weight: 64.54 ± 11.85 kg after first liver transplantation) were included in this study. Population pharmacokinetic analysis was performed using NONMEM®. Two modeling strategies, theory-based linear compartmental and nonlinear Michaelis–Menten (MM) models, were evaluated and compared. Potential covariates were screened using a stepwise approach. Bootstrap, prediction-, and simulation-based diagnostics (prediction-corrected visual predictive checks) were performed to determine model stability and predictive performance. Finally, Monte Carlo simulations based on the superior model were conducted to design dosing regimens.

Results: Postoperative days (POD), Aspartate aminotransferase (AST), daily tacrolimus dose, triazole antifungal agent (TAF) co-therapy, and recipient CYP3A5*3 genotype constituted the main factors in the theory-based compartmental final model, whereas POD, Total serum bilirubin (TBIL), Haematocrit (HCT), TAF co-therapy, and recipient CYP3A5*3 genotype were important in the nonlinear MM model. The theory-based final model exhibited 234 L h−1 apparent plasma clearance and 11,000 L plasma distribution volume. The maximum dose rate (Vmax) of the nonlinear MM model was 6.62 mg day−1; the average concentration at steady state at half-Vmax (Km) was 6.46 ng ml−1. The nonlinear MM final model was superior to the theory-based final model and used to propose dosing regimens based on simulations.

Conclusion: Our findings demonstrate that saturated tacrolimus concentration-dependent binding to erythrocytes and the influence of daily tacrolimus dose on metabolism may partly contribute to nonlinearity. Further investigation is needed is need to explore the causes of nonlinear pharmacokinetic of tacrolimus. The nonlinear MM model can provide reliable support for tacrolimus dosing optimization and adjustment in adult patients undergoing liver transplantation.

Genomewide association study identifies a novel variant associated with tacrolimus trough concentration in Chinese renal transplant recipients

Tacrolimus (TAC) is an immunosuppressant widely used in kidney transplantation. TAC displays considerable interindividual variability in pharmacokinetics (PKs). Genetic and clinical factors play important roles in TAC PKs. We enrolled a total of 251 Chinese renal transplant recipients and conducted a genomewide association study (GWAS), linkage disequilibrium (LD), and one-way analysis of variance (ANOVA) to find genetic variants affecting log-transformed TAC trough blood concentration/dose ratio (log[C₀ /D]). In addition, we performed dual luciferase reporter gene assays and multivariate regression models to evaluate the effect of the genetic variants. The GWAS results showed that all 23 genomewide significant single-nucleotide polymorphisms (p < 5 × 10^-8 ) were located on chromosome 7, including CYP3A5*3. LD, conditional association analysis, and one-way ANOVA showed that rs75125371 T > C independently influenced TAC log(C₀ /D). Dual luciferase reporter gene assays indicated that rs75125371 minor allele (C) was significantly associated with increased normalized luciferase activity than the major allele (T) in the Huh7 cells (p = 1.2 × 10^-5 ) and HepaRG cells (p = 0.0097). A model inclusive of age, sex, hematocrit, CYP3A5*3, and rs75125371 explained 37.34% variance in TAC C₀ . These results suggest that rs75125371 T > C is a functional and population-specific variant affecting TAC C₀ in Chinese renal transplant recipients.

Controversial Interactions of Tacrolimus with Dietary Supplements, Herbs and Food

Tacrolimus is an immunosuppressive calcineurin inhibitor used to prevent rejection in allogeneic organ transplant recipients, such as kidney, liver, heart or lung. It is metabolized in the liver, involving the cytochrome P450 (CYP3A4) isoform CYP3A4, and is characterized by a narrow therapeutic window, dose-dependent toxicity and high inter-individual and intra-individual variability. In view of the abovementioned facts, the aim of the study is to present selected interactions between tacrolimus and the commonly used dietary supplements, herbs and food. The review was based on the available scientific literature found in the PubMed, Scopus and Cochrane databases. An increase in the serum concentration of tacrolimus can be caused by CYP3A4 inhibitors, such as grapefruit, pomelo, clementine, pomegranate, ginger and turmeric, revealing the side effects of this drug, particularly nephrotoxicity. In contrast, CYP3A4 inducers, such as St. John’s Wort, may result in a lack of therapeutic effect by reducing the drug concentration. Additionally, the use of Panax ginseng, green tea, Schisandra sphenanthera and melatonin in patients receiving tacrolimus is highly controversial. Therefore, since alternative medicine constitutes an attractive treatment option for patients, modern healthcare should emphasize the potential interactions between herbal medicines and synthetic drugs. In fact, each drug or herbal supplement should be reported by the patient to the physician (concordance) if it is taken in the course of immunosuppressive therapy, since it may affect the pharmacokinetic and pharmacodynamic parameters of other preparations.

A UPLC-MS/MS Method for Plasma Biological Monitoring of Nirmatrelvir and Ritonavir in the Context of SARS-CoV-2 Infection and Application to a Case

Nirmatrelvir/ritonavir association has been authorized for conditional use in the treatment of COVID-19, especially in solid-organ transplant recipients who did not respond to vaccine and are still at high risk of severe disease. This combination remains at risk of drug interactions with immunosuppressants, so monitoring drug levels seems necessary. After a simple protein precipitation of plasma sample, analytes were analyzed using an ultrahigh performance liquid chromatography system coupled with tandem mass spectrometry in a positive ionization mode. Validation procedures were based on the guidelines on bioanalytical methods issued by the European Medicine Agency. The analysis time was 4 min per run. The calibration curves were linear over the range from 10 to 1000 ng/mL for ritonavir and 40 to 4000 ng/mL for nirmatrelvir, with coefficients of correlation above 0.99 for all analytes. Intra-/interday imprecisions were below 10%. The analytical method also meets criteria of matrix effect, carryover, dilution integrity, and stability. In the context of a SARS-CoV-2 infection in a renal transplant recipient, we present a case of tacrolimus overdose with serious adverse events despite discontinuation of nirmatrelvir and ritonavir. The patient had still effective concentrations of nirmatrelvir and tacrolimus 4 days after drug discontinuation. This method was successfully applied for therapeutic drug monitoring in clinical practice.

Model-informed Estimation of Acutely Decreased Tacrolimus Clearance and Subsequent Dose Individualization in a Pediatric Renal Transplant Patient with Posterior Reversible Encephalopathy Syndrome

BACKGROUND

Considerable inter-patient and inter-occasion variability has been reported in tacrolimus pharmacokinetics (PK) in the pediatric renal transplant population. The present study investigated tacrolimus PK in a 2-year-old post-renal transplant patient and a known CYP3A5 expresser who developed posterior reversible encephalopathy syndrome (PRES) and had significantly elevated tacrolimus blood concentrations during tacrolimus treatment. A model-informed PK assessment was performed to assist with precision dosing. Tacrolimus clearance was evaluated both before and after the development of PRES on post-transplant day (PTD) 26.

METHODS

A retrospective chart review was conducted to gather dosing data and tacrolimus concentrations, as part of a clinical pharmacology consultation service. Individual PK parameters were estimated by Bayesian estimation using a published pediatric PK model. Oral clearance (CL/F) was estimated for three distinct time periods-before CNS symptoms (PTD 25), during the PRES event (PTD 27-30), and after oral tacrolimus was re-started (PTD 93).

RESULTS

Bayesian estimation showed an estimated CL/F of 15.0 L/h in the days preceding the PRES event, compared to a population mean of 16.3 L/h (95% confidence interval 14.9-17.7 L/h) for CYP3A5 expressers of the same age and weight. Samples collected on PTD 27-30 yielded an estimated CL/F of 3.6 L/h, a reduction of 76%, coinciding with clinical confirmation of PRES and therapy discontinuation. On PTD 93, an additional assessment showed a stable CL/F value of 14.5 L/h one month after re-initiating tacrolimus and was used to recommend a continued maintenance dose.

CONCLUSION

This is the first report to demonstrate acutely decreased tacrolimus clearance in PRES, likely caused by the downregulation of metabolizing enzymes in response to inflammatory cytokines. The results suggest the ability of model-informed Bayesian estimation to characterize an acute decline in oral tacrolimus clearance after the development of PRES, and the role that PK estimation may play in supporting dose selection and individualization.

Tacrolimus-Induced Diffuse Coronary Artery Spasm

Prinzmetal angina, also known as vasospastic angina, is defined as an intermittent focal or diffuse coronary artery narrowing, which is often associated with transient ST-segment elevation on an electrocardiogram. Also, it could be associated with an atherosclerotic lesion at the site of the spasm. Vasospastic angina might be induced by medications, most commonly with cocaine and other examples which include catecholamines such as epinephrine, norepinephrine, isoproterenol, dopamine, and dobutamine. Parasympathomimetic agents include acetylcholine, methacholine, and pilocarpine. It is rarely caused by tacrolimus. The clinical evaluation includes an electrocardiogram and echocardiogram. The confirmed diagnosis is done by coronary angiography. Cardiac catheterization is indicated in such cases to rule out coronary artery disease.

High intrapatient variability of tacrolimus exposure associated with poorer outcomes in liver transplantation

Tacrolimus (TAC) is a dose‐dependent immunosuppressor with considerable intrapatient variability (IPV) in its pharmacokinetics. The aim of this work is to ascertain the association between TAC IPV at 6 months after liver transplantation (LT) and patient outcome. This single‐center cohort study retrospectively analyzed adult patients who underwent transplantation from 2015 to 2019 who survived the first 6 months with a functioning graft. The primary end point was the patient’s probability of death and the secondary outcome was the loss of renal function between month 6 and the last follow‐up. TAC IPV was estimated by calculating the coefficient of variation (CV) of the dose‐corrected concentration (C₀/D) between the third and sixth months post‐LT. Of the 140 patients who underwent LT included in the study, the low‐variability group (C₀/D CV < 27%) comprised 105 patients and the high‐variability group (C₀/D CV ≥ 27%) 35 patients. One‐, 3‐, and 5‐year patient survival rates were 100%, 82%, and 72% in the high‐variability group versus 100%, 97%, and 93% in the low‐variability group, respectively (p = 0.005). Moreover, significant impaired renal function was observed in the high‐variability group at 1 year (69 ± 16 ml/min/1.73 m² vs. 78 ± 16 ml/min/1.73 m², p = 0.004) and at 2 years post‐LT (69 ± 17 ml/min/1.73 m² vs. 77 ± 15 ml/min/1.73 m², p = 0.03). High C₀/D CV 3–6 months remained independently associated with worse survival (hazard ratio = 3.57, 95% CI = 1.32–9.67, p = 0.012) and loss of renal function (odds ratio = 3.47, 95% CI = 1.30–9.20, p = 0.01). Therefore, high IPV between the third and sixth months appears to be an early and independent predictor of patients with poorer liver transplant outcomes.

Predicting model‐informed precision dosing: A test‐case in tacrolimus dose adaptation for kidney transplant recipients

Before investing resources into the development of a precision dosing (model‐informed precision dosing [MIPD]) tool for tacrolimus, the performance of the tool was evaluated in silico. A retrospective dataset of 315 de novo kidney transplant recipients was first used to identify a one‐compartment pharmacokinetic (PK) model with time‐dependent clearance. MIPD performance was subsequently evaluated by calculating errors to predict future concentrations, which is directly related to dosing precision and probability of target attainment (PTA). Based on the identified model residual error, the theoretical upper limit was 45% PTA for a target of 13.5 ng/ml and an acceptable range of 12–15 ng/ml. Using empirical Bayesian estimation, this limit was reached on day 5 post‐transplant and beyond. By incorporating correlated within‐patient variability when predicting future individual concentrations, PTA improved beyond the theoretical upper limit. This yielded a Bayesian feedback dosing algorithm accurately predicting future trough concentrations and adapting each dose to reach a target concentration. Simulated concentration‐time profiles were then used to quantify MIPD‐based improvement on three end points: average PTA increased from 28% to 39%, median time to three concentrations in target decreased from 10 to 7 days, and mean log‐squared distance to target decreased from 0.080 to 0.055. A study of 200 patients was predicted to have sufficient power to demonstrate these nuanced PK end points reliably. These simulations supported our decision to develop a precision dosing tool for tacrolimus and test it in a prospective trial.

Race and sex associations with tacrolimus pharmacokinetics in stable kidney transplant recipients

Study Objective

This study investigated race and sex differences in tacrolimus pharmacokinetics and pharmacodynamics in stable kidney transplant recipients.

Design and Setting

A cross‐sectional, open‐label, single center, 12‐h pharmacokinetic‐pharmacodynamic study was conducted. Tacrolimus pharmacokinetic parameters included area under the concentration‐time curve (AUC_0–12), AUC_0–4, 12‐h troughs (C_12 h), maximum concentrations (C_max), oral clearance (Cl), with dose‐normalized AUC_0–12, troughs, and C_max with standardized adverse effect scores. Statistical models were used to analyze end points with individual covariate‐adjustment including clinical factors, genotypic variants CYP3A5*3, CYP3A5*6, CYP3A5*7(CYP3A5*3*6*7) metabolic composite, and ATP binding cassette gene subfamily B member 1 (ABCB1) polymorphisms.

Patients

65 stable, female and male, Black and White kidney transplant recipients receiving tacrolimus and mycophenolic acid ≥6 months post‐transplant were evaluated.

Measurements and Main Results

Black recipients exhibited higher tacrolimus AUC_0–12 (Race: p = 0.005), lower AUC* (Race: p < 0.001; Race × Sex: p = 0.068), and higher Cl (Race: p < 0.001; Sex: p = 0.066). Greater cumulative (Sex: p < 0.001; Race × Sex: p = 0.014), neurologic (Sex: p = 0.021; Race × Sex: p = 0.005), and aesthetic (Sex: p = 0.002) adverse effects were found in females, with highest scores in Black women. In 84.8% of Black and 68.8% of White patients, the target AUC_0–12 was achieved (p = 0.027). In 31.3% of White and 9.1% of Black recipients, AUC_0–12 was <100 ng‧h/ml despite tacrolimus troughs in the target range (p = 0.027). The novel CYP3A5*3*6*7 metabolic composite was the significant covariate accounting for 15%–19% of tacrolimus variability in dose (p = 0.002); AUC_0–12 h* (p < 0.001), and Cl (p < 0.001).

Conclusions

Tacrolimus pharmacokinetics and adverse effects were different among stable kidney transplant recipient groups based upon race and sex with interpatient variability associated with the CYP3A5*3*6*7 metabolic composite. More cumulative, neurologic, and aesthetic adverse effects were noted among females. Tacrolimus regimens that consider race and sex may reduce adverse effects and enhance allograft outcomes by facilitating more patients to achieve the targeted AUC_0–12 h.

Drug-Drug Interactions in Vestibular Diseases, Clinical Problems, and Medico-Legal Implications

Peripheral vestibular disease can be treated with several approaches (e.g., maneuvers, surgery, or medical approach). Comorbidity is common in elderly patients, so polytherapy is used, but it can generate the development of drug-drug interactions (DDIs) that play a role in both adverse drug reactions and reduced adherence. For this reason, they need a complex kind of approach, considering all their individual characteristics. Physicians must be able to prescribe and deprescribe drugs based on a solid knowledge of pharmacokinetics, pharmacodynamics, and clinical indications. Moreover, full information is required to reach a real therapeutic alliance, to improve the safety of care and reduce possible malpractice claims related to drug-drug interactions. In this review, using PubMed, Embase, and Cochrane library, we searched articles published until 30 August 2021, and described both pharmacokinetic and pharmacodynamic DDIs in patients with vestibular disorders, focusing the interest on their clinical implications and on risk management strategies.

Tacrolimus Dose-Conversion Ratios Based on Switching of Formulations for Patients with Solid Organ Transplants

Background

Tacrolimus may be administered during hospitalization as an IV formulation or oral suspension. However, literature suggesting appropriate ratios for conversion from these formulations to capsules is limited.

Objective

To evaluate conversion ratios after a switch in formulation of tacrolimus for solid-organ transplant recipients.

Methods

This single-centre observational longitudinal study involved hospitalized patients who underwent a switch in formulation of tacrolimus according to 1 of 3 possible scenarios: IV to oral suspension, IV to capsule, or oral suspension to capsule. Data were collected from the earliest accessible electronic file (January 2009) to January 1, 2019. Conversion ratios were calculated for each of the 3 groups using data for blood concentrations and doses before and after the switch. The calculated ratios were then compared with recommended conversion ratios: 1:5 (i.e., 1 mg of IV tacrolimus is converted to 5 mg of oral tacrolimus, expressed as "5") for either of the switches involving an IV formulation and 1:1 (i.e., same amount, expressed as "1") for the switch from oral formulation to capsules.

Results

For the group who underwent switching from the IV formulation to oral suspension, the mean calculated conversion ratio was 3.04, which was significantly different from the recommended ratio of 5. For the group who underwent switching from the IV formulation to capsules, the calculated conversion ratio was 5.18, which was not significantly different from the recommended ratio of 5. For the group who underwent switching from oral suspension to capsules, the calculated conversion ratio was 1.17, which was not significantly different from the recommended ratio of 1.

Conclusion

In this small retrospective study of tacrolimus therapy, the calculated conversion ratio was significantly different from the recommended ratio for patients who were switched from IV administration to oral suspension, but not for those switched from IV administration or oral suspension to capsules. Therapeutic drug monitoring therefore appears indispensable, regardless of conversion ratios.

Influential Factors and Efficacy Analysis of Tacrolimus Concentration After Allogeneic Hematopoietic Stem Cell Transplantation in Children with β-Thalassemia Major

Purpose

To analyze factors influencing tacrolimus (TAC) trough concentration (C₀) in β-thalassemia major (β-TM) pediatric patients after allogeneic hematopoietic stem cell transplantation (Allo-HSCT) and to investigate the effects of genotype polymorphism and drug-drug interactions on TAC trough concentration in children with β-TM. Furthermore, to analyze the correlation between TAC C₀ and efficacy and adverse reactions.

Patients and Methods

Prospectively collection of demographic information and details of combined treatment of patients with β-TM receiving HSCT, and genotypes of CYP3A4, CYP3A5, and ABCB1 (rs1045642, rs1128503, rs2032582) were obtained for each patient. Univariate analysis and multiple linear regression analysis were used to investigate influencing factors on TAC C₀. The impact of different genotypes and the co-administration of azole antifungal drugs on β-TM patients receiving TAC were evaluated, together with the correlation between acute graft-versus-host disease (aGVHD), infection, and liver injury of TAC C₀.

Results

A total of 46 patients with 587 concentration data were included. The multiple linear regression results showed that the patient's sex, weight, postoperative time, hemoglobin, platelet count, serum cystatin C, and combined voriconazole were independent influencing factors of the infusion trough concentration/daily dose, C₀/D_iv. Age, body surface area, postoperative time, co-administration of voriconazole, and CYP3A4*18B are independent influencing factors of C₀/D_po. Group comparisons showed that voriconazole can affect TAC C₀ administered intravenously (IV) and orally in β-TM pediatric patients, while patient genotype can affect TAC C₀ during oral administration. TAC C₀ does not correlate with aGVHD or liver injury, but infection may be associated with TAC C₀.

Conclusion

The concentration of TAC should be closely monitored when co-administered with voriconazole. It is worth considering that the influence of genotype on the trough concentration of oral TAC and individualized drug administration warrant investigation. Finally, this study indicated that C₀ is not suitable as an indicator of the efficacy of TAC.

Therapeutic Drug Monitoring Strategies for Envarsus in De Novo Kidney Transplant Patients Using Population Modelling and Simulations

INTRODUCTION

Tacrolimus, the cornerstone of transplantation immunosuppression, is a narrow therapeutic index drug with a low and highly variable bioavailability. Therapeutic drug monitoring based on trough level assessment is mandatory in order to target a personalised exposure and avoid both rejection and toxicity. Population pharmacokinetic (POPPK) models might be a useful tool for improving early attainment of target range by guiding initial doses until steady state is reached and trough levels can be reliably used as surrogate marker of exposure. Here we present the first POPPK for predicting the initial doses of the once-daily prolonged release tacrolimus Envarsus (LCPT) in adult kidney recipients.

METHODS

The model was developed exploiting the data from a recent pharmacokinetic randomised clinical study, in which 69 de novo kidney recipients, 33 of whom treated with LCPT, underwent an intensive blood sampling strategy for tacrolimus including four complete pharmacokinetic profiles.

RESULTS

The complex and prolonged absorption of LCPT is well described by the three-phase model that incorporates body weight and CYP3A5 genotype as significant covariates accounting for a great proportion of the inter-patient variability: in particular, CYP3A5*1/*3 expressors had a 66% higher LCPT clearance. We have then generated by simulation a personalised dosing strategy based on the model that could improve the early attainment of therapeutic trough levels by almost doubling the proportion of patients within target range (69.3% compared to 36.1% with the standard body weight-based approach) on post-transplantation day 4 and significantly reduce the proportion of overexposed patients at risk of toxicity.

CONCLUSIONS

A POPPK model was successfully developed for LCPT in de novo kidney recipients. The model could guide a personalised dosing strategy early after transplantation. For the model to be translated into clinical practice, its beneficial impact of earlier attainment of therapeutic trough levels should be demonstrated on hard clinical outcomes in further studies.

Apixaban Level and Its Influence on Immunosuppression and Graft Outcome in Kidney Transplant Recipients With Atrial Fibrillation

BACKGROUND

Currently, there is limited information on the level of apixaban in kidney transplant (KT) patients with atrial fibrillation and the influence of apixaban therapy on the level of immunosuppression and graft function.

METHODS

This was a cross-sectional prospective study of 19 KT patients treated with apixaban. The levels of apixaban were measured using a chromogenic assay calibrated for apixaban and compared with those predicted by the manufacturer. Mean immunosuppression trough levels before and after apixaban treatment initiation were calculated using 3 consecutive measurements. Apixaban levels were compared with a historical control group comprising of 20 nontransplant patients with atrial fibrillation who were treated with the standard 5-mg bid apixaban dosage.

RESULTS

All KT patients should have been treated with the standard 5-mg bid apixaban dosage according to the clinical parameters; however, 7 were inappropriately treated with a reduced dosage (2.5-mg bid). There was no significant difference in apixaban level between KT patients treated with the 5-mg bid dosage and nontransplant patients. No KT patient administered the standard dose had out-of-range levels. Peak GM level was significantly lower in KT patients administered an inappropriately reduced dose (P = 0.05). Two patients had below-range peak levels. Apixaban treatment initiation had minimal influence on the level of immunosuppression. Furthermore, it had no adverse impact on graft function.

CONCLUSIONS

Similar to nontransplant patients, KT patients administered the standard 5-mg bid dosage had apixaban levels that were well within the recommended manufacturers' expected ranges. In addition, this dosage had minimal influence on immunosuppression and no effect on graft function.

Chemotherapy, targeted therapy and immunotherapy: Which drugs can be safely used in the solid organ transplant recipients?

In solid organ transplant recipients, cancer is associated with worse prognosis than in the general population. Among the causes of increased cancer‐associated mortality, are the limitations in selecting the optimal anticancer regimen in solid organ transplant recipients, because of the associated risks of graft toxicity and rejection, drug‐to‐drug interactions, reduced kidney or liver function, and patient frailty and comorbid conditions. The advent of immunotherapy has generated further challenges, mainly because checkpoint inhibitors increase the risk of rejection, which may have life‐threatening consequences in recipients of life‐saving organs. In general, there are no safe or unsafe anticancer drugs. Rather, the optimal choice of the anticancer regimen results from a careful risk/benefit assessment, from the awareness of potential pharmacokinetic and pharmacodynamic drug‐to‐drug interactions, and of the risk of drug overexposure in patients with kidney or liver dysfunction. In this review, we summarize general principles that may help the oncologists and transplant physicians in the multidisciplinary management of recipients of solid organ transplantation with cancer who are candidates for chemotherapy, targeted therapy, or immunotherapy.

Chronic Kidney Disease: Strategies to Retard Progression

Chronic kidney disease (CKD), defined as the presence of irreversible structural or functional kidney damages, increases the risk of poor outcomes due to its association with multiple complications, including altered mineral metabolism, anemia, metabolic acidosis, and increased cardiovascular events. The mainstay of treatments for CKD lies in the prevention of the development and progression of CKD as well as its complications. Due to the heterogeneous origins and the uncertainty in the pathogenesis of CKD, efficacious therapies for CKD remain challenging. In this review, we focus on the following four themes: first, a summary of the known factors that contribute to CKD development and progression, with an emphasis on avoiding acute kidney injury (AKI); second, an etiology-based treatment strategy for retarding CKD, including the approaches for the common and under-recognized ones; and third, the recommended approaches for ameliorating CKD complications, and the final section discusses the novel agents for counteracting CKD progression.

Wuzhi Capsule Dosage Affects Tacrolimus Elimination in Adult Kidney Transplant Recipients, as Determined by a Population Pharmacokinetics Analysis

Purpose

In this study, we aimed to establish a tacrolimus population pharmacokinetic model and better understand the drug-drug interaction between Wuzhi capsule and tacrolimus in Chinese renal transplant recipients.

Patients and Methods

We performed a population pharmacokinetic analysis using a non-linear mixed-effects model to determine the suitable Wuzhi capsule dose in combination with tacrolimus. Data on 1378 tacrolimus steady-state concentrations were obtained from 142 patients who received kidney transplant in Changhai Hospital and Huashan Hospital. Demographic characteristics, laboratory tests, genetic polymorphisms, and co-medications were evaluated.

Results

The one-compartment model best described data. Our final model identified creatinine clearance rate, hematocrit, Wuzhi capsule dose, CYP3A5*3 genetic polymorphisms, and tacrolimus daily dose as significant covariates for tacrolimus clearance, with the value of 14.4 L h^-1, and the between-subject variability (BSV) was 25.4%. The Wuzhi capsule showed a dose-dependent effect on tacrolimus pharmacokinetics, demonstrating a stronger inhibitory effect than inductive effect.

Conclusion

Our model can accurately describe population pharmacokinetics of tacrolimus when combined with different doses of Wuzhi capsule. Additionally, this model can be used for individualizing tacrolimus dose following kidney transplantation.

Usage of Tacrolimus and Mycophenolic Acid During Conception, Pregnancy, and Lactation, and Its Implications for Therapeutic Drug Monitoring: A Systematic Critical Review

BACKGROUND

Conception, pregnancy, and lactation following solid organ transplantation require appropriate management. The most frequently used immunosuppressive drug combination after solid organ transplantation consists of tacrolimus (Tac) plus mycophenolic acid (MPA). Here, the effects of Tac and MPA on fertility, pregnancy, and lactation are systematically reviewed, and their implications for therapeutic drug monitoring (TDM) are discussed.

METHODS

A systematic literature search was performed (August 19, 2019) using Ovid MEDLINE, EMBASE, the Cochrane Central Register of controlled trials, Google Scholar, and Web of Science, and 102 studies were included. Another 60 were included from the reference list of the published articles.

RESULTS

As MPA is teratogenic, women who are trying to conceive are strongly recommended to switch from MPA to azathioprine. MPA treatment in men during conception seems to have no adverse effect on pregnancy outcomes. Nevertheless, in 2015, the drug label was updated with additional risk minimization measures in a pregnancy prevention program. Data on MPA pharmacokinetics during pregnancy and lactation are limited. Tac treatment during conception, pregnancy, and lactation seems to be safe in terms of the health of the mother, (unborn) child, and allograft. However, Tac may increase the risk of hypertension, preeclampsia, preterm birth, and low birth weight. Infants will ingest very small amounts of Tac via breast milk from mothers treated with Tac. However, no adverse outcomes have been reported in children exposed to Tac during lactation. During pregnancy, changes in Tac pharmacokinetics result in increased unbound to whole-blood Tac concentration ratio. To maintain Tac concentrations within the target range, increased Tac dose and intensified TDM may be required. However, it is unclear if dose adjustments during pregnancy are necessary, considering the higher concentration of (active) unbound Tac.

CONCLUSIONS

Tac treatment during conception, pregnancy and lactation seems to be relatively safe. Due to pharmacokinetic changes during pregnancy, a higher Tac dose might be indicated to maintain target concentrations. However, more evidence is needed to make recommendations on both Tac dose adjustments and alternative matrices than whole-blood for TDM of Tac during pregnancy. MPA treatment in men during conception seems to have no adverse effect on pregnancy outcomes, whereas MPA use in women during conception and pregnancy is strongly discouraged.

Functional CYP3A variants affecting tacrolimus trough blood concentrations in Chinese renal transplant recipients

The aim of this study was to identify novel genetic variants affecting tacrolimus trough blood concentrations. We analyzed the association between 58 single nucleotide polymorphisms (SNPs) across the CYP3A gene cluster and the log-transformed tacrolimus concentration/dose ratio (log (C₀/D)) in 819 renal transplant recipients (Discovery cohort). Multivariate linear regression was used to test for associations between tacrolimus log (C₀/D) and clinical factors. Luciferase reporter gene assays were used to evaluate the functions of select SNPs. Associations of putative functional SNPs with log (C₀/D) were further tested in 631 renal transplant recipients (Replication cohort). Nine SNPs were significantly associated with tacrolimus log (C₀/D) after adjustment for CYP3A5*3 and clinical factors. Dual luciferase reporter assays indicated that the rs4646450 G allele and rs3823812 T allele were significantly associated with increased normalized luciferase activity ratios (p < 0.01). Moreover, CYP3A7*2 was associated with higher TAC log(C₀/D) in the group of CYP3A5 expressers. Age, serum creatinine and hematocrit were significantly associated with tacrolimus log (C₀/D). CYP3A7*2, rs4646450, and rs3823812 are proposed as functional SNPs affecting tacrolimus trough blood concentrations in Chinese renal transplant recipients. Clinical factors also significantly affect tacrolimus metabolism.

Frequency of ABCB1 C3435T and CYP3A5*3 Genetic Polymorphisms in the Lebanese Population

OBJECTIVES

CYP3A5 and ABCB1 are highly implicated in the pharmacokinetics and pharmacodynamics of immunosuppressive agents, such as calcineurin inhibitors and mammalian target of rapamycin inhibitors. The polymorphisms of their coding genes play important roles in the interindividual and intraindividual differences of bioavailability of these drugs. In this study, our objective was to investigate, in a Lebanese population,the frequency of ABCB1C3435T (rs1045642) and CYP3A5*3 (rs776746) polymorphisms and to compare the results to preexisting data from other populations.

MATERIALS AND METHODS

We determined the frequencies of the allelic variants of interest for 1824 Lebanese participants, and we compared these results with those from other major ethnic groups.

RESULTS

The allelic frequencies were 91.4% (C) and 8.6% (T) for CYP3A5*3 and 50.8% (T) and 49.2% (C) for ABCB1 C3435T. Our results were significantly different from most other world populations, except the European population.

CONCLUSIONS

The frequencies of gene variants of interest in our Lebanese population were similar to those found in European populations. Most of our study population were CYP3A5*3 carriers, and more than half may have a lower P-glycoprotein efflux pump. These characteristics might render Lebanese transplant recipients more prone to the development of drug toxicity and in need of lower drug doses.

BK Polyomavirus Nephropathy in Kidney Transplantation: Balancing Rejection and Infection

BK polyomavirus nephropathy (BKVN) and allograft rejection are two closely-associated diseases on opposite ends of the immune scale in kidney transplant recipients. The principle of balancing the immune system remains the mainstay of therapeutic strategy. While patient outcomes can be improved through screening, risk factors identification, and rapid reduction of immunosuppressants, a lack of standard curative therapy is the primary concern during clinical practice. Additionally, difficulty in pathological differential diagnosis and clinicopathology’s dissociation pose problems for a definite diagnosis. This article discusses the delicate evaluation needed to optimize immunosuppression and reviews recent advances in molecular diagnosis and immunological therapy for BKVN patients. New biomarkers for BKVN diagnosis are under development. For example, measurement of virus-specific T cell level may play a role in steering immunosuppressants. The development of cellular therapy may provide prevention, even a cure, for BKVN, a complex post-transplant complication.

Solid organ donor-recipient race-matching: analysis of the United Network for Organ Sharing database

Donor ethnicity is a prognosticator in organ transplant. However, the impact of donor/recipient race-matching is unclear. We hypothesized that there would be increased survival in donor-recipient race-matched organ recipients because of genetic and physiologic similarities. The UNOS database from 1999 to 2018 was queried for all solid organ transplantations including heart, lung, liver, kidney, and pancreas transplants. Data were sorted by donor and recipient race into matched and unmatched categories for Caucasian, African American, and Hispanic transplant recipients. After controlling for potential confounders via inverse propensity of treatment weighting, post-transplant patient and graft survival were compared between race-matched and -unmatched donor groups for each organ. Race-matched Caucasian recipients experienced 1-3% improvement in mortality across most time points in lung, liver, and pancreas transplants, while Hispanics did not benefit. Matched African American recipients experienced 4-6% improvement in patient and graft survival in liver transplant but had 7-9% worse survival rates at 5 years in lung and pancreas transplants. Race-matching does not influence patient outcomes enough to factor into organ transplant offers. African American liver transplant recipients benefited the most. Matching was detrimental to African American lung and pancreas transplant recipients indicating there may be other factors influencing the outcomes of these transplants.

Differential Effect of a Continental Breakfast on Tacrolimus Formulations With Different Release Characteristics

Food reduces tacrolimus bioavailability after immediate-release tacrolimus (IR-Tac) and after a new prolonged-release tacrolimus formulation (PR-Tac), when using a high-fat breakfast, but the effects of a continental breakfast on PR-Tac are unknown. In an open-label, 4-phase, randomized, 2-sequence, crossover pharmacokinetic trial, 36 healthy volunteers (18 females) received single 5-mg tacrolimus doses as PR-Tac and as IR-Tac fasted or with a standardized continental breakfast. Tacrolimus pharmacokinetics were analyzed using noncompartmental methods and mixed-model analysis of variance. The continental breakfast significantly decreased average tacrolimus exposure (area under the plasma concentration-time curve) with both preparations (IR-Tac, 67%; 90% confidence interval [CI], 59%-75%; P < .01; and PR-Tac, 79%; 90%CI, 70%-89%; P < .01) with a nonsignificant difference between both preparations (P = .10). The maximum concentration (C_max ) and the time to maximum concentration (t_max ) were significantly affected only after IR-Tac (C_max IR-Tac, 39%; 90%CI, 34%-45%; P < .01; and PR-Tac, 87%; 90%CI, 76%-101%; P = .11; t_max IR-Tac, 212%, 90%CI, 179%-252%; P < .01; and PR-Tac, 101%; 90%CI, 86%-120%; P = .89), which was significantly different between both preparations (P < .01). Considering switching from IR-Tac to PR-Tac, predicted dose requirements differed according to the timing of drug intake in relation to food. In conclusion, a continental breakfast decreased average tacrolimus exposure of both preparations to a similar extent. C_max and t_max were affected only after IR-Tac. The effect of a standardized continental breakfast on PR-Tac was considerably smaller than previously reported effects of a high-fat breakfast on PR-Tac.

Rapamycin Inhibitors for Eye Squamous Cell Carcinoma after Renal Transplantation: A Case Report

INTRODUCTION

The immunosuppressive efficiency obtained in the last decades in kidney transplantation significantly improved graft survival. However, there is still a high risk and incidence of cancer in transplant patients strongly and directly related to the type of immunosuppression. An increasing body of evidence suggests that the PI3K/Akt/mTOR pathway may play a pivotal role in the development and progression of several neoplastic diseases.

CASE PRESENTATION

We describe a 47-year-old male patient who received a cadaveric primary renal transplant in November 2008 developing a poorly differentiated infiltrating and ulcerated squamous cell carcinoma (SCC) at the eye level. In this patient, the modification of an immunosuppressive regimen with introduction of rapamycin (mTOR) inhibitors and withdrawal of calcineurin inhibitors (CNIs) led to the resolution of this severe condition.

CONCLUSION

The introduction of mTOR inhibitors and withdrawal of CNIs in kidney-transplanted patients with de novo eye SCC should be considered in this clinical setting.

Research Progress of Herbal Medicines on Drug Metabolizing Enzymes: Consideration Based on Toxicology

The clinical application of herbal medicines is increasing, but there is still a lack of comprehensive safety data and in-depth research into mechanisms of action. The composition of herbal medicines is complex, with each herb containing a variety of chemical components. Each of these components may affect the activity of metabolizing enzymes, which may lead to herb-drug interactions. It has been reported that the combined use of herbs and drugs can produce some unexpected interactions. Therefore, this study reviews the progress of research on safety issues caused by the effects of herbs on metabolizing enzymes with reference to six categories of drugs, including antithrombotic drugs, non-steroidal anti-inflammatory drugs, anti-diabetic drugs, statins lipid-lowering drugs, immunosuppressants, and antineoplastic drugs. Understanding the effects of herbs on the activity of metabolizing enzymes could help avoid the toxicity and adverse drug reactions resulting from the co-administration of herbs and drugs, and help doctors to reduce the risk of prescription incompatibility.