Hemoglobin and total bilirubin may affect tacrolimus clearance in liver transplant patient following the early postoperative period: a case report.

BACKGROUND: Tacrolimus is a potent calcineurin inhibitor (CNI) that is principally used as a first-line immunosuppressant for the prophylaxis of allograft rejection in liver transplantation (LT) patients. In clinical practice, prescribing the optimal tacrolimus dosage is complicated by its narrow therapeutic index and high pharmacokinetic variability. Thus, performing therapeutic drug monitoring (TDM) of only tacrolimus may not provide optimal drug levels. However, other influential clinical factors affecting tacrolimus levels, such as hemoglobin (Hb), hematocrit, and total bilirubin (TBIL), should be considered while adjusting tacrolimus levels. This case report aims to introduce clinicians and their teams to taking the pharmacokinetic prediction equation into consideration for a better understanding of tacrolimus dosage adjustment during the early postoperative LT. CASE PRESENTATION: In this case report, an 18-year-old male patient of Thai ethnicity was admitted for orthotropic liver transplantation, and tacrolimus was prescribed as a cornerstone immunosuppressive agent. In the immediate postoperative period, which is the most challenging period in liver transplantation, the population pharmacokinetics predictive equation was clinically used to assist in dosage adjustment of tacrolimus by considering the significant clinical factors in this case. Hemoglobin and total bilirubin levels were deemed significant clinical factors affecting the oral clearance (CL/F) of tacrolimus. First, a decrease in the Hb concentration increases the free drug concentration and therefore increases the CL/F of tacrolimus. Second, an elevated TBIL decreases the biliary excretion of tacrolimus, resulting in a decrease in the CL/F of tacrolimus. Thus, dose optimization of tacrolimus would be accurate when taking the pharmacokinetic prediction equation into consideration. Moreover, the results may contribute to a better understanding of tacrolimus pharmacokinetic variability in each transplant patient during the immediate postoperative course. CONCLUSIONS: Hemoglobin and total bilirubin were significant clinical factors influencing the oral clearance of tacrolimus early after liver transplantation. A decrease in the hemoglobin concentration would increase the free drug concentration and therefore increase the oral clearance of tacrolimus. An elevated total bilirubin decreases the biliary excretion of tacrolimus, resulting in a decrease in the oral clearance of tacrolimus.

Hyaluronic acid-coated polypeptide nanogel enhances specific distribution and therapy of tacrolimus in rheumatoid arthritis.

Rheumatoid arthritis (RA) involves chronic inflammation, oxidative stress, and complex immune cell interactions, leading to joint destruction. Traditional treatments are often limited by off-target effects and systemic toxicity. This study introduces a novel therapeutic approach using hyaluronic acid (HA)-conjugated, redox-responsive polyamino acid nanogels (HA-NG) to deliver tacrolimus (TAC) specifically to inflamed joints. The nanogels' disulfide bonds enable controlled TAC release in response to high intracellular glutathione (GSH) levels in activated macrophages, prevalent in RA-affected tissues. In vitro results demonstrated that HA-NG/TAC significantly reduced TAC toxicity to normal macrophages and showed high biocompatibility. In vivo, HA-NG/TAC accumulated more in inflamed joints compared to non-targeted NG/TAC, enhancing therapeutic efficacy and minimizing side effects. Therapeutic evaluation in collagen-induced arthritis (CIA) mice revealed HA-NG/TAC substantially reduced paw swelling, arthritis scores, synovial inflammation, and bone erosion while suppressing pro-inflammatory cytokine levels. These findings suggest that HA-NG/TAC represents a promising targeted drug delivery system for RA, offering potential for more effective and safer clinical applications.

Extreme phenotype sampling and next generation sequencing to identify genetic variants associated with tacrolimus in African American kidney transplant recipients.

African American (AA) kidney transplant recipients (KTRs) have poor outcomes, which may in-part be due to tacrolimus (TAC) sub-optimal immunosuppression. We previously determined the common genetic regulators of TAC pharmacokinetics in AAs which were CYP3A5 *3, *6, and *7. To identify low-frequency variants that impact TAC pharmacokinetics, we used extreme phenotype sampling and compared individuals with extreme high (n = 58) and low (n = 60) TAC troughs (N = 515 AA KTRs). Targeted next generation sequencing was conducted in these two groups. Median TAC troughs in the high group were 7.7 ng/ml compared with 6.3 ng/ml in the low group, despite lower daily doses of 5 versus 12 mg, respectively. Of 34,542 identified variants across 99 genes, 1406 variants were suggestively associated with TAC troughs in univariate models (p-value < 0.05), however none were significant after multiple testing correction. We suggest future studies investigate additional sources of TAC pharmacokinetic variability such as drug-drug-gene interactions and pharmacomicrobiome.

Pharmacogenetic analysis of interleukin-10 variants and tacrolimus metabolism in kidney transplant patients from Pakistani population.

BACKGROUND: End stage renal disease (ESRD) occurs when the kidneys are unable to filter the waste products and excessive fluids from the blood that results into the accumulation of toxins and fluid in the body. Tacrolimus is commonly used immunosuppressant while sirolimus and cyclosporin are rarely used drugs to stop solid organ transplant rejection. The host's immunological response following transplantation produces interleukin-10 (IL-10), which influences the varied CYP3A-dependent drug disposition of tacrolimus. The aim of this study was to determine the genetic polymorphisms of IL-10 (rs1800871, rs1800872 and rs1800896) gene associated with tacrolimus metabolism in kidney transplant patients from Lahore Punjab, Pakistan. METHODS: The study collected blood samples of 103 healthy individuals and 137 kidney transplant patients as control and treatment groups, respectively. We employed Tetra ARMS PCR for the genotype analysis of extracted DNA. The alleles were called on 2% agarose gel. Moreover, the study utilized SPSS software to analyze statistical significance of polymorphism. RESULTS: It was found that genotypic frequencies of IL-10 (rs1800871), IL-10 (rs1800872), and IL-10 (rs1800896) were (TT: 66.4%; TC: 31.4%; CC: 2.2%), (AA: 27.7%; AC: 54%; CC: 18.2%), (AA: 64.2%; GA: 17.5%; GG: 18.3%), respectively among kidney transplant patients. All parameters show significant association at different points after transplantation. Genetic analysis showed that TC and CC genotypes in rs1800871 (OR (95%CI) = 5.721 (3.231-10.131), P < 0.001; OR (95%CI) = 3.370 (0.642-17.672), P = 0.150), AC and CC genotypes in rs1800872 (OR (95%CI) = 1.294 (0.695-2.410), P = 0.415; OR (95%CI) = 1.453 (0.671-3.147), P = 0.342), GA and GG genotypes in rs1800896 (OR (95%CI) = 42.952 (17.566-105.021), P = 0.001; OR (95%CI) = 7.040 (2.563-19.333), P = 0.342) was associated with risk of renal rejection in kidney transplant patients. Besides, genetic models showed that TT in rs1800871, AA genotypes in rs1800872 and rs1800892 were associated with risk of renal rejection under dominant model when compared to controls (OR (95%CI) = 5.721 (3.231-10.131), P < 0.001; OR (95%CI) = 1.335 (0.735-9.290), P < 0.341; OR (95%CI) = 24.629 (10.599-57.230), P < 0.001), respectively. CONCLUSION: From the results, it is concluded that genetic polymorphism of IL-10 (rs1800871, rs1800872 and rs1800896) has a highly significant association with risk of renal rejection in Pakistani kidney transplant patients.

Machine-learning model to predict the tacrolimus concentration and suggest optimal dose in liver transplantation recipients: a multicenter retrospective cohort study.

Titrating tacrolimus concentration in liver transplantation recipients remains a challenge in the early post-transplant period. This multicenter retrospective cohort study aimed to develop and validate a machine-learning algorithm to predict tacrolimus concentration. Data from 443 patients undergoing liver transplantation between 2017 and 2020 at an academic hospital in South Korea were collected to train machine-learning models. Long short-term memory (LSTM) and gradient-boosted regression tree (GBRT) models were developed using time-series doses and concentrations of tacrolimus with covariates of age, sex, weight, height, liver enzymes, total bilirubin, international normalized ratio, albumin, serum creatinine, and hematocrit. We conducted performance comparisons with linear regression and populational pharmacokinetic models, followed by external validation using the eICU Collaborative Research Database collected in the United States between 2014 and 2015. In the external validation, the LSTM outperformed the GBRT, linear regression, and populational pharmacokinetic models with median performance error (8.8%, 25.3%, 13.9%, and - 11.4%, respectively; P < 0.001) and median absolute performance error (22.3%, 33.1%, 26.8%, and 23.4%, respectively; P < 0.001). Dosing based on the LSTM model's suggestions achieved therapeutic concentrations more frequently on the chi-square test (P < 0.001). Patients who received doses outside the suggested range were associated with longer ICU stays by an average of 2.5 days (P = 0.042). In conclusion, machine learning models showed excellent performance in predicting tacrolimus concentration in liver transplantation recipients and can be useful for concentration titration in these patients.

A descriptive study of the single-nucleotide polymorphisms known to affect the Tacrolimus trough concentration per dose, among a population of kidney failure patients in a tertiary hospital in Ghana.

BACKGROUND: The burden of chronic kidney disease (CKD) and kidney failure in Ghana is on the ascendency, with the prevalence of CKD estimated at 13.3%. Patients with CKD who progress to kidney failure require life sustaining kidney replacement therapy (KRT) which is almost exclusively available in Ghana as haemodialysis. Kidney transplantation is considered the best KRT option for patients with irreversible kidney failure due to its relative cost efficiency as well as its superiority in terms of survival and quality of life. However, because transplants may trigger an immune response with potential organ rejection, immunosuppressants such as tacrolimus dosing are required. OBJECTIVE: This study sought to determine single nucleotide polymorphisms in CYP3A5, CYP3A4 and MDR1 genes that affect the pharmacokinetics of Tacrolimus in a population of Ghanaian patients with kidney failure. METHOD: This cross-sectional study comprised of 82 kidney failure patients undergoing maintenance haemodialysis at the Renal and Dialysis unit of Korle-Bu Teaching Hospital (KBTH). Clinical and demographic data were collected and genomic DNA isolated. Samples were genotyped for specific SNPs using Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP). RESULTS: Participants, 58/82 (70.73%) harbored the wildtype CYP3A5*1/*1 AA genotype, 20/82 (24.39%) carried the heterozygous CYP3A5*1/*3 AG genotype, and 4/82 (4.88%) had the homozygous mutant CYP3A5*3/*3 GG genotype. Also, 6/82 (7.32%) carried the wildtype AA genotype, 11/82 (13.41%) had the heterozygous AG genotype, and 65/82 (79.27%) harbored the homozygous mutant GG genotype of CYP3A4*1B (-290 A>G). For MDR1_Ex21 (2677 G>T), 81/82 (98.78%) carried the wildtype GG genotype, while 1/82 (1.22%) had the heterozygous GT genotype. For MDR1_Ex26 (3435 C>T), 63/82 (76.83%) had the wildtype CC genotype, while 18/82 (21.95%) carried the heterozygous CT genotype, and 1/82 (1.22%) harbored the mutant TT genotype. CONCLUSION: SNPs in CYP3A4, CYP3A5, and MDR1 genes in a population of Ghanaian kidney failure patients were described. The varying SNPs of the featured genes suggest the need to consider the genetic status of Ghanaians kidney failure patients prior to transplantation and tacrolimus therapy.

Impact of donor CYP3A5 genotype on pharmacokinetics of tacrolimus in South African paediatric liver transplant patients.

BACKGROUND: In the paediatric liver transplant programme in Johannesburg, South Africa (SA), tacrolimus is the calcineurin inhibitor of choice, comprising an essential component of the immunosuppression regimen. It is characterised by a narrow therapeutic index and wide interpatient variability, necessitating therapeutic drug monitoring of whole-blood concentrations. Pharmacogenetic research, although not representative of SA population groups, suggests that single-nucleotide polymorphisms within the cytochrome P450 3A5 (CYP3A5) gene contribute to the variability in tacrolimus dosing requirements. The rs776746 polymorphism, CYP3A5*3, results in a splice defect and a non-functional enzyme. Clinically, to reach the same tacrolimus concentration-to-dose ratio (CDR), expressors (CYP3A5*1/*1 and *1/*3) require a higher tacrolimus dose than non-expressors (*3/*3). OBJECTIVES: To compare the pharmacokinetics of tacrolimus in paediatric liver transplant recipients with their donors' CYP3A5 genotypes, considering both donor and recipient characteristics. METHODS: Blood samples from 46 living liver donors were collected, their genomic DNA was extracted, and their CYP3A5 genotype was established (polymerase chain reaction and restriction fragment length polymorphism analysis, validated by Sanger sequencing). The relationship of donor and recipient characteristics with the mean tacrolimus CDR was analysed using a general linear model. Non- confounding significant variables were included in a multiple regression model. RESULTS: The study showed that all expressor donors genotyped as CYP3A5*1/*1 were of black African self-reported race and ethnicity. During the first 15 days post-transplant, we found that children who received grafts from donor CYP3A5 expressors (CYP3A5*1/*1 and *1/*3) had significantly lower mean tacrolimus CDRs compared with those who received grafts from donor CYP3A5 non-expressors (*3/*3); the recipients of CYP3A5 expressor grafts therefore require higher doses of oral tacrolimus to achieve the same therapeutic target range. In addition, graft-to-recipient weight ratio and the CYP3A5 donor genotypes were independent factors that significantly (p<0.05) affected mean tacrolimus CDRs in recipients. CONCLUSION: In this study, we showed that all CYP3A5*1 homozygote donors were of black African self-reported race and ethnicity, and tacrolimus CDRs in paediatric living-donor liver transplant recipients were significantly affected by donor graft size and donor CYP3A5 genotypes. Information from this study may inform the development of an Afrocentric tacrolimus precision-medicine algorithm to optimise recipient safety and graft outcomes.

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.

Tacrolimus Intrapatient Variability on Graft Outcomes in Adherent Renal Transplantation Patients: A Cross-Sectional Study.

INTRODUCTION: Tacrolimus is the mainstem of immunosuppressive therapy in kidney transplant patients. It has high intrapatient variability (Tac-IPV), which has been reported to affect graft function by predisposing patients to rejection or nephrotoxicity. We conducted this study with the aim of assessing the influence of Tac-IPV on 2-year graft function, biopsy-proven rejection, and infections in compliant renal recipients. METHODS: In this single-center retrospective analytic cross-sectional study, 250 patients who underwent transplantation from March 21, 2018, to March 20, 2020 and had at least three outpatient tacrolimus trough levels on the same daily dose 6 to 12 months after transplantation were recruited. Tac-IPV was defined as a coefficient variation of > 15%. Graft function, biopsy-proven rejection, cytomegalovirus (CMV) and BK virus viremia, and calcineurin inhibitor (CNI) toxicity were evaluated. RESULTS: Of 202 transplant recipients, 128 were included with a mean age of 45.48 ± 13.14 years. The median Tac-IPV was 13.28% with 43.75% of patients with Tac-IPV > 15%. There were no significant differences in graft function, rejection, CNI toxicity, and CMV viremia among the groups during the 24-month study (P > .05).  However, BK viremia was significantly higher among patients with Tac-IPV > 15% (13 vs. 2.9%, P = .042). The risk of antibody mediated rejection alone (22.7 vs. 2.9%) or any kind of rejection (22.7 vs. 11.8%) was significantly higher in patients with higher Tac-IPV, and in those who had mean trough levels below 7 ng/mL (P = .015, .032; respectively). CONCLUSION: Tac-IPV is low in adherent patients (with the median of 13.28%) and maintaining tacrolimus trough level above 7 ng/mL can overcome the adverse graft outcome of Tac-IPV in compliant kidney transplant recipients. DOI: 10.52547/ijkd.7815.

A joint population pharmacokinetic model to assess the high variability of whole-blood and intracellular tacrolimus in early adult renal transplant recipients.

Tacrolimus (TAC) has high pharmacokinetic (PK) variability during the early transplantation period. The relationships between whole-blood and intracellular TAC concentrations and clinical outcomes remain controversial. This study identifies the factors affecting the PK variability of TAC and characterizes the relationships between whole-blood and intracellular TAC concentrations. Data regarding whole-blood TAC concentrations of 1,787 samples from 215 renal transplant recipients (<90 days postoperative) across two centers and intracellular TAC concentrations (648 samples) digitized from previous studies were analyzed using nonlinear mixed-effects modeling. The effects of potential covariates were screened, and the distribution of whole-blood to intracellular TAC concentration ratios (RWB:IC) was estimated. The final model was evaluated using bootstrap, goodness of fit, and prediction-corrected visual predictive checks. The optimal dosing regimens and target ranges for each type of immune cell subsets were determined using Monte Carlo simulations. A two-compartment model adequately described the data, and the estimated mean TAC CL/F was 23.6 L·h-1 (relative standard error: 11.5 %). The hematocrit level, CYP3A5*3 carrier status, co-administration with Wuzhi capsules, and tapering prednisolone dose may contribute to the high variability of TAC PK variability during the early post-transplant period. The estimated RWB:IC of all TAC concentrations in peripheral blood mononuclear cells (PBMCs) was 4940, and inter-center variability of PBMCs was observed. The simulated TAC target range in PBMCs was 20.2-85.9 pg·million cells-1. Inter-center variability in intracellular concentrations should be taken into account in further analyses. TAC dosage adjustments can be guided based on PK/PD variability and simulated intracellular concentrations.

Factors associated with changes in tacrolimus blood concentration after food initiation in patients with ulcerative colitis.

The therapeutic effect of tacrolimus against ulcerative colitis (UC) is correlated with its trough blood concentration. Conventionally, oral tacrolimus for the treatment of UC is initiated under fasting conditions; once the symptoms improve, food intake is resumed. Tacrolimus blood concentration decreases with food intake compared with that under fasting conditions. The aim of this study was to explore the characteristics of patients with UC whose tacrolimus blood concentrations tended to decrease after food initiation. Medical data of 13 patients with UC and treated with tacrolimus were retrospectively obtained. The participant characteristics associated with the changes in tacrolimus blood concentrations after food initiation were analyzed using regression analysis based on the rate of decrease in the concentration/dose (C/D) ratio after food initiation. Single regression analysis showed that the number of days required from tacrolimus initiation to food resumption (P = 0.0071) and individual differences in the increase in tacrolimus blood concentration after administration (P = 0.0247) were significantly associated with the rate of decrease in the C/D ratio after food initiation. Furthermore, multiple regression analysis showed a significant effect of the number of days to food resumption (P = 0.0004) and individual differences in the increase in tacrolimus blood concentration after administration (P = 0.0012). The results suggest that the degree of change in blood tacrolimus concentration after food initiation may be related to the severity of the symptoms and pathology of UC. Early identification of participant characteristics may help control tacrolimus blood concentration fluctuations after food initiation.

Tacrolimus-loaded chitosan-based nanoparticles as an efficient topical therapeutic for the effective treatment of atopic dermatitis symptoms.

Atopic dermatitis (AD) is a chronic cutaneous disease with a complex underlying mechanism, and it cannot be completely cured. Thus, most treatment strategies for AD aim at relieving the symptoms. Although corticosteroids are topically applied to alleviate AD, adverse side effects frequently lead to the withdrawal of AD therapy. Tacrolimus (TAC), a calcineurin inhibitor, has been used to treat AD, but its high molecular weight and insolubility in water hinder its skin permeability. Herein, we developed and optimized TAC-loaded chitosan-based nanoparticles (TAC@CNPs) to improve the skin permeability of TAC by breaking the tight junctions in the skin. The prepared nanoparticles were highly loadable and efficient and exhibited appropriate characteristics for percutaneous drug delivery. TAC@CNP was stable for 4 weeks under physiological conditions. CNP released TAC in a controlled manner, with enhanced skin penetration observed. In vitro experiments showed that CNP was non-toxic to keratinocyte (HaCaT) cells, and TAC@CNP dispersed in an aqueous solution was as anti-proliferative as TAC solubilized in a good organic solvent. Importantly, an in vivo AD mouse model revealed that topical TAC@CNP containing ~1/10 of the dose of TAC found in commercially used Protopic® Ointment exhibited similar anti-inflammatory activity to that of the commercial product. TAC@CNP represents a potential therapeutic strategy for the management of AD.

Pharmacogenetic Testing or Therapeutic Drug Monitoring: A Quantitative Framework.

BACKGROUND: Pharmacogenetic profiling and therapeutic drug monitoring (TDM) have both been proposed to manage inter-individual variability (IIV) in drug exposure. However, determining the most effective approach for estimating exposure for a particular drug remains a challenge. This study aimed to quantitatively assess the circumstances in which pharmacogenetic profiling may outperform TDM in estimating drug exposure, under three sources of variability (IIV, inter-occasion variability [IOV], and residual unexplained variability [RUV]). METHODS: Pharmacokinetic models were selected from the literature corresponding to drugs for which pharmacogenetic profiling and TDM are both clinically considered approaches for dose individualization. The models were used to simulate relevant drug exposures (trough concentration or area under the curve [AUC]) under varying degrees of IIV, IOV, and RUV. RESULTS: Six drug cases were selected from the literature. Model-based simulations demonstrated that the percentage of patients for whom pharmacogenetic exposure prediction is superior to TDM differs for each drug case: tacrolimus (11.0%), tamoxifen (12.7%), efavirenz (49.2%), vincristine (49.6%), risperidone (48.1%), and 5-fluorouracil (5-FU) (100%). Generally, in the presence of higher unexplained IIV in combination with lower RUV and IOV, exposure was best estimated by TDM, whereas, under lower unexplained IIV in combination with higher IOV or RUV, pharmacogenetic profiling was preferred. CONCLUSIONS: For the drugs with relatively low RUV and IOV (e.g., tamoxifen and tacrolimus), TDM estimated true exposure the best. Conversely, for drugs with similar or lower unexplained IIV (e.g., efavirenz or 5-FU, respectively) combined with relatively high RUV, pharmacogenetic profiling provided the most accurate estimate for most patients. However, genotype prevalence and the relative influence of genotypes on the PK, as well as the ability of TDM to accurately estimate AUC with a limited number of samples, had an impact. The results could be used to support clinical decision making when considering other factors, such as the probability for severe side effects.

Development and validation of individualized tacrolimus dosing software for Chinese pediatric liver transplantation patients: a population pharmacokinetic approach.

OBJECTIVE: We aim to describe the population pharmacokinetics (PPK) of tacrolimus in Chinese pediatric patients under 4 years old after liver transplantation and to develop individualized tacrolimus dosing software. METHODS: A total of 663 blood concentrations from 85 patients aged 4.57 months to 3.97 years were collected in this study. PPK analysis was performed using a nonlinear mixed effects modeling approach with the software, Phoenix. Using C#, an individualized tacrolimus dosing software was created. The software was then used to predict the concentrations of another ten pediatric liver transplantation patients to verify the accuracy of said software. The predictive error (PE) and the absolute predictive error (APE) for each predicted time point were computed. RESULTS: A one-compartment model with first-order elimination best fitted the data. The apparent volume of distribution (V/F) and apparent clearance (CL/F) were 198.65 L and 2.41 L/h. Postoperative days (POD), total bilirubin (TBIL), and the use of voriconazole significantly influenced tacrolimus apparent clearance. The incorporation of an increasing number of actual blood drug concentrations into the prediction resulted in a decrease in both PE (72%, 17%, 7%) and APE (87%, 53%, 26%). CONCLUSIONS: A qualified PPK model of tacrolimus was developed in Chinese pediatric patients. The individualized tacrolimus dosing software could be used as a suitable tool for the personalization of tacrolimus dosing for pediatric patients after liver transplantation.

Physiologically-based pharmacokinetic modelling to investigate the effect of CYP3A4/3A5 maturation on tacrolimus pharmacokinetics in paediatric HSCT patients.

Tacrolimus (FK506) is a cornerstone of GVHD-prophylaxis treatment in paediatrics undergoing haematopoietic stem cell transplantation (HSCT). However, due to concerns about highly inter/intra-individual variability, precision dosing of FK506 is crucial. Cytochrome P450 (CYP) 3A4 and 3A5 are considered important sources of FK506 pharmacokinetic variability. Nevertheless, the impact of age-related maturation in hepatic and intestinal CYP3A4/3A5 enzymes remains unknown in paediatric HSCT patients. Physiologically-based pharmacokinetic (PBPK) models were developed and verified in adult volunteers and adult HSCT patients using GastroPlus™ (version 9.0), and then extrapolated to paediatric HSCT patients, taking into account the maturation of CYP3A4 and CYP3A5. Default CYP3A4 and CYP3A5 ontogeny profiles were updated based on the latest reports. The paediatric PBPK model was evaluated with independent data collected from Sun Yat-sen Memorial Hospital (86 paediatric HSCT patients, 1 to 16 -year-old). Simulations were performed to evaluate a reported FK506 dosing regimen in infants and children with different CYP3A5 genotypes. Extensive PBPK model validation indicated good predictability, with the predicted/observed (P/O) ratios within the range of 0.80-fold to 1.25-fold. Blood tacrolimus concentration-time curves were comparable between the real and virtual patients. Simulations showed that the higher levels of tacrolimus in 9-month-old to 3-year-old infants were mainly attributed to the CYP3A4/3A5 ontogeny profiles, which resulted in lower clearance and higher exposure relative to dose. The oral dosage of 0.1 mg/kg/day (q12 h) is considered appropriate for paediatric HSCT patients 9 months to 15 years of age with CYP3A5 *1/*1 genotypes. Lower doses were required for paediatric HSCT patients with CYP3A5 *1/*3 (0.08 mg/kg/day, q12h) or CYP3A5 *3/*3 genotypes (0.07 mg/kg/day, q12h), and analyses demonstrated 12.5-20 % decreases in ≤3-year-old patients. The study highlights the feasibility of PBPK modelling to explore age-related enzyme maturation in infants and children (≤3-year-old) undergoing HSCT and emphasizes the need to include hepatic and gut CYP3A4/3A5 maturation parameters.

Immune responsiveness in stable kidney transplantation patients: Complete inhibition of T-cell proliferation but residual T-cell activity during maintenance immunosuppressive treatment.

The recommended immunosuppressive treatment after kidney transplantation consists of tacrolimus, mycophenolate mofetil, and low-dose corticosteroids. Drug concentrations are monitored using therapeutic drug monitoring (TDM), which does not necessarily correlate with pharmacodynamic activity. To find the balance between optimal efficacy and minimal toxicity, it might be more informative to monitor patients' immunological status rather than drug concentrations. We selected a panel of T-cell-based immune assays, which were used for immunomonitoring of 14 stable kidney transplantation patients. Whole blood was incubated with a T-cell stimulus, after which T-cell proliferation, T-cell activation marker expression and cytokine production were measured to study residual immune activity in vitro (before drug intake; drug added to the incubation) and ex vivo (after drug intake). T-cell proliferation was completely suppressed in all patients over the full day, while IL-2, IFN-γ, CD71, and CD154 showed fluctuations over the day with a strong inhibition (75%-25%) at 2 h post-dose. The level of inhibition was variable between patients and could not be related to pharmacokinetic parameters or the presence of regulatory or senescence immune cells. Moreover, the level of inhibition did not correlate with the in vitro tacrolimus drug effect as studied by incubating pre-dose blood samples with additional tacrolimus. Overall, IL-2, IFN-γ, CD71, and CD154 seem to be good markers to monitor residual immune activity of transplantation patients. To evaluate the correlation between these pharmacodynamic biomarkers and clinical outcome, prospective observational studies are needed.

Evaluation of Published Population Pharmacokinetic Models to Inform Tacrolimus Therapy in Adult Lung Transplant Recipients.

BACKGROUND: The applicability of currently available tacrolimus population pharmacokinetic models in guiding dosing for lung transplant recipients is unclear. In this study, the predictive performance of relevant tacrolimus population pharmacokinetic models was evaluated for adult lung transplant recipients. METHODS: Data from 43 lung transplant recipients (1021 tacrolimus concentrations) administered an immediate-release oral formulation of tacrolimus were used to evaluate the predictive performance of 17 published population pharmacokinetic models for tacrolimus. Data were collected from immediately after transplantation up to 90 days after transplantation. Model performance was evaluated using (1) prediction-based assessments (bias and imprecision) of individual predicted tacrolimus concentrations at the fourth dosing based on 1 to 3 previous dosings and (2) simulation-based assessment (prediction-corrected visual predictive check; pcVPC). Both assessments were stratified based on concomitant azole antifungal use. Model performance was clinically acceptable if the bias was within ±20%, imprecision was ≤20%, and the 95% confidence interval of bias crossed zero. RESULTS: In the presence of concomitant antifungal therapy, no model showed acceptable performance in predicting tacrolimus concentrations at the fourth dosing (n = 33), and pcVPC plots displayed poor model fit to the data set. However, this fit slightly improved in the absence of azole antifungal use, where 4 models showed acceptable performance in predicting tacrolimus concentrations at the fourth dosing (n = 33). CONCLUSIONS: Although none of the evaluated models were appropriate in guiding tacrolimus dosing in lung transplant recipients receiving concomitant azole antifungal therapy, 4 of these models displayed potential applicability in guiding dosing in recipients not receiving concomitant azole antifungal therapy. However, further model refinement is required before the widespread implementation of such models in clinical practice.

Impact of Switching From Immediate- or Prolonged-Release to Once-Daily Extended-Release Tacrolimus (LCPT) on Tremor in Stable Kidney Transplant Recipients: The Observational ELIT Study.

Once-daily extended-release tacrolimus (LCPT) exhibits increased bioavailability versus immediate-release (IR-TAC) and prolonged release (PR-TAC) tacrolimus. Improvements in tremor were previously reported in a limited number of kidney transplant patients who switched to LCPT. We conducted a non-interventional, non-randomized, uncontrolled, longitudinal, prospective, multicenter study to assess the impact of switching to LCPT on tremor and quality of life (QoL) in a larger population of stable kidney transplant patients. The primary endpoint was change in The Essential Tremor Rating Assessment Scale (TETRAS) score; secondary endpoints included 12-item Short Form Survey (SF-12) scores, tacrolimus trough concentrations, neurologic symptoms, and safety assessments. Subgroup analyses were conducted to assess change in TETRAS score and tacrolimus trough concentration/dose (C0/D) ratio by prior tacrolimus formulation and tacrolimus metabolizer status. Among 221 patients, the mean decrease of TETRAS score after switch to LCPT was statistically significant (p < 0.0001 vs. baseline). There was no statistically significant difference in change in TETRAS score after switch to LCPT between patients who had received IR-TAC and those who had received PR-TAC before switch, or between fast and slow metabolizers of tacrolimus. The overall increase of C0/D ratio post-switch to LCPT was statistically significant (p < 0.0001) and from baseline to either M1 or M3 (both p < 0.0001) in the mITT population and in all subgroups. In the fast metabolizers group, the C0/D ratio crossed over the threshold of 1.05 ng/mL/mg after the switch to LCPT. Other neurologic symptoms tended to improve, and the SF-12 mental component summary score improved significantly. No new safety concerns were evident. In this observational study, all patients had a significant improvement of tremor, QoL and C0/D ratio post-switch to LCPT irrespective of the previous tacrolimus formulation administered (IR-TAC or PR-TAC) and irrespective from their metabolism status (fast or slow metabolizers).