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.

Pharmacokinetics of nirmatrelvir/ritonavir and the drug-drug interaction with calcineurin inhibitor in renal transplant recipients.

OBJECTIVES: To describe the pharmacokinetic (PK) characteristics of nirmatrelvir/ritonavir in renal transplant recipients and explore the potential factors that related to the PK variance of nirmatrelvir/ritonavir and its interaction with calcineurin inhibitor (CNI). METHODS: Renal transplant recipients treated with CNI and nirmatrelvir/ritonavir were prospectively enrolled. Steady-state plasma concentrations of nirmatrelvir/ritonavir were determined by high-performance liquid chromatography-tandem mass spectrometry, and the PK parameters were calculated using non-compartmental analysis. Spearman correlation analysis was used for exploring influencing factors. RESULTS: A total of eight recipients were enrolled; for nirmatrelvir and ritonavir, AUC/dose was 0.24179 ± 0.14495 and 0.06196 ± 0.03767 µg·h·mL-1·mg-1. Red blood cell (RBC), hematocrit (Ht), hemoglobins (Hb), and creatinine clearance (Ccr) were negatively correlated with AUC/dose of nirmatrelvir, while Ccr, CYP3A5 genotype, and CYP3A4 genotype were related to the AUC/dose of ritonavir. Ccr was negatively correlated with the C0/dose of tacrolimus (TAC) after termination of nirmatrelvir/ritonavir (rs = -0.943, p = 0.008). CONCLUSIONS: The PK characteristics of nirmatrelvir/ritonavir vary greatly among renal transplant recipients. Factors including Ccr and CYP3A5 genotype were related to the in vivo exposure of nirmatrelvir/ritonavir. During the whole process before and after nirmatrelvir/ritonavir therapy, it is recommended to adjust the CNI basing on renal function to avoid CNI toxicity exposure.

A longitudinal study of long-term renal outcome after pediatric liver transplantation in relation to CNI exposure.

BACKGROUND: Chronic kidney disease (CKD) is reported in 20%-30% of children after liver transplantation (LT). One of the proposed underlying causes is the long-term exposure to tacrolimus, a calcineurin inhibitor (CNI), which is the main immunosuppressive drug used after LT. Variation in tacrolimus absolute exposure and relative dose requirements are believed to be important risk factors for developing CNI-associated nephrotoxicity. AIM: To describe the long-term renal outcome of pediatric LT recipients and determine the effects of tacrolimus exposure on renal outcome parameters. METHODS: Retrospective single center study of renal function (GFR, proteinuria) and pharmacokinetic parameters (C0 , AUC0-12h ) obtained during annual follow-up in children after liver transplantation, between 1998 and 2019. Relevant pharmacogenetic variants for tacrolimus disposition (CYP3A5 and ABCB1) were determined in recipients and donors. The evolution of individual renal function and tacrolimus exposure was evaluated using linear mixed models for repeated measurements. RESULTS: Twenty-six children were included (mean follow-up: 10.4 years (range 2-18.9)). Mean estimated GFR was 109.3 (SE: 7.4), vs. measured: 91.3 mL/min/1.73 m2 (SE: 6.3), which remained stable during follow-up. CKD stage ≥2 was observed in 32.8% of the visits based on eGFR versus 50.0% on mGFR. CKD stage ≥3 was uncommon (4.1% and 6.2% resp.). Mean tacrolimus C0 was 5.3 ng/mL (SE: 2.5) with a AUC0-12h of 72.7 ng*h/mL (SE: 30.3), which demonstrated a small decrease during follow-up. There was a negative correlation between C0 and mGFR (rS = -0.3; p < .001). We found no correlation between GFR and tacrolimus dose requirements ((ng/mL)/(mg/kg)) or pharmacogenetic background. CONCLUSION: Renal function during long-term follow-up after pediatric LT remained stable for the majority of our cohort. However, mild CKD was relatively common, warranting follow-up into adulthood. Although absolute tacrolimus exposure has a small depressing effect on concurrent GFR, there is no progressive deterioration of GFR due to long-term exposure, dose requirements or genetic background under the current target levels. These findings should be confirmed in a larger sample set, ideally including data from multiple centers.

Factors Affecting Time-Varying Clearance of Cyclosporine in Adult Renal Transplant Recipients: A Population Pharmacokinetic Perspective.

AIM: The pharmacokinetic (PK) properties of cyclosporine (CsA) in renal transplant recipients are patient- and time-dependent. Knowledge of this time-related variability is necessary to maintain or achieve CsA target exposure. Here, we aimed to identify factors explaining variabilities in CsA PK properties and characterize time-varying clearance (CL/F) by performing a comprehensive analysis of CsA PK factors using population PK (popPK) modeling of long-term follow-up data from our institution. METHODS: In total, 3674 whole-blood CsA concentrations from 183 patients who underwent initial renal transplantation were analyzed using nonlinear mixed-effects modeling. The effects of potential covariates were selected according to a previous study and well-accepted theoretical mechanisms. Model-informed individualized therapeutic regimens were also evaluated. RESULTS: A two-compartment model adequately described the data and the estimated mean CsA CL/F was 32.6 L h-1 (relative standard error: 5%). Allometrically scaled body size, hematocrit (HCT) level, CGC haplotype carrier status, and postoperative time may contribute to CsA PK variability. The CsA bioavailability in patients receiving a prednisolone dose (PD) of 80 mg was 20.6% lower than that in patients receiving 20 mg. A significant decrease (52.6%) in CL/F was observed as the HCT increased from 10.5% to 60.5%. The CL/F of the non-CGC haplotype carrier was 14.4% lower than that of the CGC haplotype carrier at 3 months post operation. CONCLUSIONS: By monitoring body size, HCT, PD, and CGC haplotype, changes in CsA CL/F over time could be predicted. Such information could be used to optimize CsA therapy. CsA dose adjustments should be considered in different postoperative periods.

Lack of Improvement in Insulin Sensitivity After Pancreas Transplantation in Recipients With a High Level of Calcineurin Inhibitors.

OBJECTIVES: This study aimed to assess posttransplant changes in insulin sensitivity and ß-cell function of pancreas transplant recipients according to the type of diabetes mellitus (DM) and the pretransplant insulin sensitivity measured by the Matsuda Index (MI). METHODS: We analyzed 60 patients who underwent pancreas transplantation and oral glucose tolerance test pretransplant and at 1 month posttransplant. RESULTS: At 1 month posttransplant, insulin sensitivity did not show significant improvement; particularly, the MI was significantly lower after transplant in recipients with type 1 DM (T1DM) and those with pretransplant MI of 5 or greater. ß-cell function was significantly improved after transplant in all recipients regardless of the type of DM and pretransplant MI values. Glucose control was significantly improved in recipients with T1DM and in all recipients regardless of the pretransplant MI values. Additional oral glucose tolerance test at 1 year posttransplant revealed that insulin sensitivity remained unimproved and ß-cell function was higher compared with pretransplant. Glucose control had partially reverted to pretransplant levels in recipients with T1DM and those with pretransplant MI of 5 or greater. CONCLUSIONS: Unlike ß-cell function and glucose control, insulin sensitivity did not significantly improve until posttransplant 1 year after pancreas transplantation regardless of the type of DM or the degree of pretransplant insulin sensitivity.

Voclosporin: First Approval.

Voclosporin (Lupkynis™) is an oral calcineurin inhibitor immunosuppressant that is being developed by Aurinia Pharmaceuticals. In January 2021, based on positive results from the pivotal phases II and III trials, oral voclosporin received its first approval in the USA for use in combination with a background immunosuppressive therapy regimen for adults with active lupus nephritis. Voclosporin is also being explored for the novel coronavirus disease 2019 (COVID-19) in kidney transplant recipients. This article summarizes the milestones in the development of voclosporin leading to this first approval for lupus nephritis.

Sustained Inhibition of Calcineurin Activity With a Melt-Dose Once-daily Tacrolimus Formulation in Renal Transplant Recipients.

Tacrolimus (Tac) is the cornerstone calcineurin inhibitor in transplantation. Extended-release Meltdose formulation (Tac-LCP) offers better bioavailability compared with immediate-release formulation (Tac-IR). We postulated that the less fluctuating pharmacokinetic (PK) profile of Tac-LCP might maintain a sustained inhibition of calcineurin activity (CNA) between dose intervals. Higher concentrations (peak plasma concentration (Cmax )) after Tac-IR may not result in a more potent CNA inhibition due to a capacity-limited effect. This study was aimed at evaluating the pharmacodynamic (PD)/PK profiles of Tac-IR compared with Tac-LCP. An open-label, prospective, nonrandomized, investigator-driven study was conducted. Twenty-five kidney transplant recipients receiving Tac-IR were switched to Tac-LCP. Before and 28 days after conversion, intensive CNA-PD and PK sampling were conducted using ultra-high-performance liquid chromatography-tandem accurate mass spectrometry. PD nonlinear mixed effects model was performed in Phoenix-WinNonlin. Statistically significant higher Cmax (P < 0.001) after Tac-IR did not result in lower CNA as compared with after Tac-LCP (P = 0.860). Tac-LCP showed a statistically more maintained CNA inhibition between dose intervals (area under the effect-time curve from 0 to 24 hours (AUE0-24h )) compared with Tac-IR, in which CNA returned to predose levels after 4 hours of drug intake (373.8 vs. 290.5 pmol RII·h/min·mg prot, Tac-LCP vs. Tac-IR; P = 0.039). No correlation was achieved between any PD and PK parameters in any formulations. Moreover, Tac concentration to elicit a 50% of the maximum response (half-maximal inhibitory concentration) was 9.24 ng/mL. The higher Cmax after Tac-IR does not result in an additional CNA inhibition compared with Tac-LCP attributable to a capacity-limited effect. Tac-LCP may represent an improvement of the PD of Tac due to the more sustained CNA inhibition during dose intervals.

Bariatric Surgery Is Associated With Decreased Calcineurin Inhibitor Time in Therapeutic Range After Heart Transplantation.

Bariatric surgery (BSg) is an effective treatment for morbid obesity, but little is known about the outcomes of BSg patients who undergo orthotopic heart transplantation (OHT). The aim of this study was to determine if BSg alters calcineurin inhibitor (CNI) level variability after OHT. Data were collected from 58 consecutive patients who underwent OHT at a single center from 1/2018 to 4/2019: 4 with BSg prior to OHT (BSg + OHT) and 54 without prior BSg (OHT). CNI level, cardiac biopsy, and left ventricular ejection fraction (LVEF) data were collected during the first 6 months post-OHT. Comparisons were made for 3 measures of CNI variability: coefficient of variation, time in therapeutic range (TTR), and TTR by the Rosendaal method. A Pearson's correlation coefficient was calculated to assess the relationship between CNI TTR, episodes of rejection, and LVEF. The results show TTR was lower in BSg + OHT compared to OHT (12.5% vs 31.3%, P < .05). For the entire cohort, greater TTR correlated with fewer episodes of rejection (r = 0.31, P < .05). In conclusion, these findings suggest BSg + OHT patients may warrant closer monitoring of CNI levels post-OHT. Furthermore, episodes of rejection and LVEF were similar for BSg + OHT patients, indicating that BSg should not be a contraindication to transplant.

Evaluation of the performance of a prior tacrolimus population pharmacokinetic kidney transplant model among adult allogeneic hematopoietic stem cell transplant patients.

Tacrolimus is a calcineurin inhibitor used to prevent acute graft versus host disease in adult patients receiving allogeneic hematopoietic stem cell transplantation (HCT). Previous population pharmacokinetic (PK) models have been developed in solid organ transplant, yet none exists for patients receiving HCT. The primary objectives of this study were to (1) use a previously published population PK model in adult patients who underwent kidney transplant and apply it to allogeneic HCT; (2) evaluate model-predicted tacrolimus steady-state trough concentrations and simulations in patients receiving HCT; and (3) evaluate covariates that affect tacrolimus PK in allogeneic HCT. A total of 252 adult patients receiving allogeneic HCT were included in the study. They received oral tacrolimus twice daily (0.03 mg/kg) starting 3 days prior to transplant. Data for these analyses included baseline clinical and demographic data, genotype data for single nucleotide polymorphisms in CYP3A4/5 and ABCB1, and the first tacrolimus steady-state trough concentration. A dosing simulation strategy based on observed trough concentrations (rather than model-based predictions) resulted in 12% more patients successfully achieving tacrolimus trough concentrations within the institutional target range (5-10 ng/ml). Stepwise covariate analyses identified HLA match and conditioning regimen (myeloablative vs. reduced intensity) as significant covariates. Ultimately, a previously published tacrolimus population PK model in kidney transplant provided a platform to help establish a model-based dose adjustment strategy in patients receiving allogenic HCT, and identified HCT-specific covariates to be considered for future prospective studies. Study Highlights WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC? Tacrolimus is a cornerstone immunosuppressant used in patients who undergo organ transplantations. However, because of its narrow therapeutic index and wide interpatient pharmacokinetic (PK) variability, optimizing its dose is crucial to maximize efficacy and minimize tacrolimus-induced toxicities. Prior to this study, no tacrolimus population PK models have been developed for adult patients receiving allogeneic hematopoietic stem cell transplantation (HCT). Therefore, research effort was warranted to develop a population PK model that begins to propose more precision tacrolimus dosing and begins to address both a clinical and scientific gap in this patient population. WHAT QUESTION DID THIS STUDY ADDRESS? The study addressed whether there is value in utilizing the observed tacrolimus steady-state trough concentrations from patients receiving allogeneic HCT within the context of a pre-existing population PK model developed for kidney transplant. The study also addressed whether there are clinically relevant covariates specific to adult patients receiving allogeneic HCT. WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE? Inclusion of a single steady-state tacrolimus trough concentration is beneficial to model predictions. The dosing simulation strategy based on observed tacrolimus concentration, rather than the model-predicted concentration, resulted in more patients achieving the target range at first steady-state collection. Future studies should evaluate HLA matching and myeloablative conditioning versus reduced intensity conditioning regimens as covariates. These data and model-informed dose adjustments should be included in future prospective studies. This research could also serve as a template as to how to assess the utility of prior information for other disease settings. HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE? The M2 model fitting method and D2 dosing simulation method can be applied to other clinical pharmacology studies where only a single steady-state trough concentration is available per patient in the presence of a previously published population PK model.

Effects of Sofosbuvir-Based Hepatitis C Treatment Regimens on Calcineurin Inhibitor Dosing in Liver and Kidney Transplant Recipients.

OBJECTIVES: Available data have suggested that directacting antivirals for hepatitis C virus may decrease calcineurin inhibitor concentrations. In this study, our aim was to determine the effects of hepatitis C directacting antivirals on calcineurin inhibitor doses and trough levels. MATERIALS AND METHODS: This retrospective, singlecenter study included 52 abdominal transplant recipients treated with sofosbuvir-based regimens between 2014 and 2017. The primary outcome was percent change in calcineurin inhibitor troughs and total daily doses between the week before treatment with direct-acting antivirals, days 21 to 35 oftreatment, and days 21 to 35 aftertreatment. Secondary outcomes included sustained virologic response and biopsyproven acute rejection rates. RESULTS: The median percent difference in calcineurin inhibitor troughs from pretreatment to during treatment was -20.5% (interquartile range, -36.2% to 13.1%) and from pretreatment to posttreatment was -13.5% (interquartile range, -33.7% to 10.7%). Corresponding percent changes in calcineurin inhibitor doses were 0% (interquartile range, 0%-0%) and 0% (interquartile range, -10.5% to 33.3%), respectively. Patients on tacrolimus experienced statistically significant changes in troughs but not doses. During treatment, 65% of patients required no dose change, 23% underwent a dose increase, and 12% had a dose decrease. The sustained virologic response rate was 98%, and the biopsy-proven acute rejection rate was 0%. CONCLUSIONS: Hepatitis C direct-acting antiviraltherapy may decrease calcineurin inhibitor levels, but this was not associated with clinically different dosing requirements or rejection rates.

Inhibition effect of epigallocatechin-3-gallate on the pharmacokinetics of calcineurin inhibitors, tacrolimus, and cyclosporine A, in rats.

BACKGROUND: Epigallocatechin-3-gallate (EGCG) is the most biologically active catechin of green tea. Tacrolimus (TAC) and cyclosporine A (CsA) are immunosuppressive agents commonly used in clinical organ transplantation. The present study investigated the effect of EGCG on the pharmacokinetics of TAC and CsA in rats and its underlying mechanisms. RESEARCH DESIGN AND METHODS: Either TAC or CsA was administered to rats intravenously or orally with or without concomitant EGCG. Polymerase Chain Reaction and Western Blot were used to determine the effect of EGCG on drug-metabolizing enzymes (DMEs), drug transporters (DTs) and nuclear receptors (NRs). RESULTS: The Cmax and AUC of TAC were reduced, and V/F and CL/F of TAC were enhanced after co-administration of EGCG. EGCG increased the Cmax, AUC of CsA at 3 ~ 30 mg∙kg-1 dosages, while decreased those parameters at the dosage of 100 mg∙kg-1. EGCG inhibited the mRNA and protein expressions of DMEs and DTs, such as CYP3A1, A2, UGT1A1, Mdr1 and Mrp2, but upregulated the expressions of Car, Pxr and Fxr. CONCLUSIONS: These results revealed consumption of high dose EGCG may cause a significant alteration in pharmacokinetics of TAC and distribution/elimination profiles of CsA through the regulation of DMEs, DTs and NRs.

Pharmacokinetics and Biodistribution of Tacrolimus after Topical Administration: Implications for Vascularized Composite Allotransplantation.

AIM: The high doses of oral tacrolimus (TAC) (1,2) necessary to prevent acute rejection (AR) after vascularized composite allotransplantation (VCA) are associated with systemic adverse effects. The skin is the most antigenic tissue in VCA and the primary target of AR. However, the short-term use of topical TAC (Protopic®), as an off-label adjunct to oral TAC, to treat AR episodes pro re nata (PRN), has yielded inconsistent results. There is lack of data on the pharmacokinetics and tissue distribution of topical TAC in VCA, that hampers our understanding of the reasons for unreliable efficacy. Toward this goal, we evaluated the ability of topical TAC to achieve high local tissue concentrations at the site of application with low systemic concentrations. MATERIALS AND METHODS: We assessed the pharmacokinetics and tissue distribution of topical TAC (Protopic®, 0.03%) after single or repeated topical application in comparison to those after systemic delivery in rats. Animals received a single topical application of TAC ointment (Group 1) or an intravenous (IV) injection of TAC (Group 2) at a dose of 0.5 mg/kg. In another experiment, animals received daily topical application of TAC ointment (Group 3), or daily intraperitoneal (IP) injection of TAC (Group 4) at a dose of 0.5 mg/kg for 7 days. TAC concentrations in blood and tissues were analyzed by Liquid Chromatography-Mass Spectrometry (LC/MS-MS). RESULTS: Following single topical administration, TAC was absorbed slowly with a Tmax of 4 h and an absolute bioavailability of 11%. The concentrations of TAC in skin and muscle were several folds higher than whole blood concentrations. Systemic levels remained subtherapeutic (< 3 ng/ml) with repeated once daily applications. CONCLUSION: Topical application of TAC ointment (Protopic®, 0.03%) at a dose of 0.5 mg/kg/day provided high concentrations in the local tissues with low systemic exposure. Repeated topical administration of TAC is well tolerated with no local or systemic adverse effects. This study confirms the feasibility of topical application of TAC for site specific graft immunosuppression and enables future applications in VCA.

Recent Approaches on Novel Topical Delivery Systems for Atopic Dermatitis Treatment.

Atopic dermatitis is a chronic inflammatory disease of the skin, which is characterized by itching, erythema, and eczematous lacerations. It affects about 10 % of adults and approximately 15-20 % of children worldwide. As a result of genetic, immunologic, and environmental factors, the disease manifests itself with the impaired stratum corneum barrier and then immunological responses. Topical administration of corticosteroids and calcineurin inhibitors are currently used as the first strategy in the management of the disease. However, they have low skin bioavailability and some side effects. The nanocarriers as novel drug delivery systems could overcome limitations of conventional dosage forms, owing to increment of poorly soluble drug' solubility, then its thermodynamic activity and, consequently, its skin permeation. Also, side effects of the drug substances on the skin could be reduced by the nano-sized drug delivery systems due to encapsulation of the drug in the nanocarriers and targeted drug delivery of drug substances to the inflammated skin areas. Thereby, there have been available numerous research studies and patents regarding the use of nanocarriers in the management of atopic dermatitis. This review focuses on the mechanism of disease and development of nanocarrier based on novel drug release systems in the management of atopic dermatitis.

Maintenance Immunosuppression in Solid Organ Transplantation: Integrating Novel Pharmacodynamic Biomarkers to Inform Calcineurin Inhibitor Dose Selection.

Calcineurin inhibitors, the primary immunosuppressive therapy used to prevent alloreactivity of transplanted organs, have a narrow therapeutic index. Currently, treatment is individualized based on clinical assessment of the risk of rejection or toxicity guided by trough concentration monitoring. Advances in immune monitoring have identified potential markers that may have value in understanding calcineurin inhibitor pharmacodynamics. Integration of these markers has the potential to complement therapeutic drug monitoring. Existing pharmacokinetic-pharmacodynamic (PK-PD) data is largely limited to correlation between the biomarker and trough concentrations at single time points. Immune related gene expression currently has the most evidence supporting PK-PD integration. Novel biomarker-based approaches to pharmacodynamic monitoring including development of enhanced PK-PD models are proposed to realize the full clinical benefit.

The Many Faces of Calcineurin Inhibitor Toxicity-What the FK?

Calcineurin inhibitors (CNIs) are both the savior and Achilles' heel of kidney transplantation. Although CNIs have significantly reduced rates of acute rejection, their numerous toxicities can plague kidney transplant recipients. By 10 years, virtually all allografts will have evidence of CNI nephrotoxicity. CNIs have been strongly associated with hypertension, dyslipidemia, and new onset of diabetes after transplantation-significantly contributing to cardiovascular risk in the kidney transplant recipient. Multiple electrolyte derangements including hyperkalemia, hypomagnesemia, hypercalciuria, metabolic acidosis, and hyperuricemia may be challenging to manage for the clinician. Finally, CNI-associated tremor, gingival hyperplasia, and defects in hair growth can have a significant impact on the transplant recipient's quality of life. In this review, the authors briefly discuss the pharmacokinetics of CNI and discuss the numerous clinically relevant toxicities of commonly used CNIs, cyclosporine and tacrolimus.

Worsening of Kidney Transplant Function During 2-Year Follow-up Is Associated With the Genetic Variants of CYP3A4, MDR1, and UGT1A9.

BACKGROUND: Calcineurin inhibitors (CNIs), tacrolimus and cyclosporine, undergo pharmacokinetic processes. Enzymes and transport proteins found in various organs are involved. It is possible that genetic polymorphisms of these proteins influence CNIs pharmacokinetics and the generation of CNIs metabolites. CNIs may be nephrotoxic, and it is thought that some CNIs' metabolites may have a similar effect. The study was aimed at the assessment of the relationship between selected gene polymorphisms for enzymes and transport proteins and change of estimated glomerular filtration rate (eGFR) during a 2-year follow-up in kidney transplant (KTX) patients. METHODS: The study involved 366 patients after KTX (160 women; 43.7%) receiving tacrolimus (62.57%) and cyclosporine (37.43%). The mean age was 50.1 years, and the median time after KTX was 60.5 months. The study protocol conformed with the Declaration of Helsinki. The percent of difference between eGFR at baseline and at 24 months (ΔeGFR) was calculated. We evaluated selected genetic polymorphisms of CYP3A4, CYP3A5, MDR1, UGT1A9, UGT2B7, UGT1A8, and MRP2. RESULTS: In the tacrolimus group, there were no significant differences of ΔeGFR between groups distinguished based on analyzed genotypes. In the cyclosporine group, differences were found for CYP3A4∗22 C/C -12.3 (-26.8 to -1.8) versus C/T 13.2 (12.4 to 13.9), P = .034; MDR1 3435C>T C/T -18.2 (-31.5 to -5.7) versus C/C -1.8 (-17.1 to 6.9) vs T/T -8.1 (-18.4 to 12.4), P = .031; and UGT1A9 2152C>T C/C -9.0 (-25.5 to 2.8) versus C/T -26.8 (-31.9 to -24.1), P = .017. CONCLUSION: The study results suggest that in KTX metabolic transformations and transport, especially of cyclosporine, dependence on the genetic variability of CYP3A4, UGT1A9, and MDR1 may contribute to kidney damage.

Tacrolimus: 20 years of use in adult kidney transplantation. What we should know about its nephrotoxicity.

Tacrolimus (or FK506), a calcineurin inhibitor (CNI) introduced in field of transplantation in the 1990s, is the cornerstone of most immunosuppressive regimens in solid organ transplantation. Its use has revolutionized the future of kidney transplantation (KT) and has been associated with better graft survival, a lower incidence of rejection, and improved drug tolerance with fewer side effects compared to cyclosporine. However, its monitoring remains complicated and underexposure increases the risk of rejection, whereas overexposure increases the risk of adverse effects, primarily nephrotoxicity, neurotoxicity, infections, malignancies, diabetes, and gastrointestinal complaints. Tacrolimus nephrotoxicity can be nonreversible and can lead to kidney graft loss, and its diagnosis is therefore best made with reference to the clinical context and after exclusion of other causes of graft dysfunction. Many factors contribute to its development including: systemic levels of tacrolimus; local renal exposure to tacrolimus; exposure to metabolites of tacrolimus; local susceptibility factors for CNI nephrotoxicity independent of systemic or local tacrolimus levels, such as the age of a kidney; local renal P-glycoprotein, local intestinal and hepatic cytochrome P450A3, and renin angiotensin system activation. The aim of this review is to describe the pharmacokinetics, pharmacodynamics, and mechanisms of acute and chronic tacrolimus nephrotoxicity in adult KT.

Clinical Pharmacokinetics and Impact of Hematocrit on Monitoring and Dosing of Tacrolimus Early After Heart and Lung Transplantation.

The calcineurin inhibitor tacrolimus is an effective immunosuppressant and is extensively used in solid organ transplantation. In the first week after heart and lung transplantation, tacrolimus dosing is difficult due to considerable physiological changes because of clinical instability, and toxicity often occurs, even when tacrolimus concentrations are within the therapeutic range. The physiological and pharmacokinetic changes are outlined. Excessive variability in bioavailability may lead to higher interoccasion (dose-to-dose) variability than interindividual variability of pharmacokinetic parameters. Intravenous tacrolimus dosing may circumvent this high variability in bioavailability. Moreover, the interpretation of whole-blood concentrations is discussed. The unbound concentration is related to hematocrit, and changes in hematocrit may increase toxicity, even within the therapeutic range of whole-blood concentrations. Therefore, in clinically unstable patients with varying hematocrit, aiming at the lower therapeutic level is recommended and tacrolimus personalized dosing based on hematocrit-corrected whole-blood concentrations may be used to control the unbound tacrolimus plasma concentrations and subsequently reduce toxicity.

Assessment of rejection risk following subtherapeutic calcineurin inhibitor levels after pediatric heart transplantation.

CNIs are the mainstay of immunosuppressive therapy after pediatric HTx. While regular laboratory surveillance is performed to ensure blood levels are within targeted range, the risk of acute rejection associated with subtherapeutic CNI levels has never been quantified. This is a retrospective single-center review of 8413 CNI trough levels in 138 pediatric HTx recipients who survived >1 year after HTx. Subtherapeutic CNI levels were defined as <50% of the lower limit of target range. The risk of acute, late (>12 months post-transplant) rejection following recipients' subtherapeutic CNI levels was assessed using time-varying multivariable Cox proportional hazards analysis. We found that 79 of 138 recipients (57%) had at least one subtherapeutic CNI level on routine surveillance laboratories during a mean follow-up of 5.5 ± 3.6 years. Following an episode of subtherapeutic levels, 17 recipients (22%) had biopsy-proven rejection within the next 3 months; the majority (9/17) within the first 2 weeks. After presenting with subtherapeutic CNI levels, recipients incurred a 6.1 times increased risk of acute rejection in the following 3 months (HR = 6.11 [2.41, 15.51], P = <.001). Age at HTx, HLA sensitization, or positive crossmatch were not associated with acute late rejection, but rejection in the first post-transplant year was (HR 2.61 [1.27, 5.35], P = .009). Thus, maintaining therapeutic CNI levels is the most important factor in preventing acute rejection in recipients who are >12 months after pediatric HTx. Recipients who present with subtherapeutic CNI levels on surveillance monitoring are 6.1 times more likely to develop rejection in the following 3 months.