Treatment optimization of maintenance immunosuppressive agents in pediatric renal transplant recipients.

Introduction: Graft survival in pediatric kidney transplant patients has increased significantly within the last three decades, correlating with the discovery and utilization of new immunosuppressants as well as improvements in patient care. Despite these developments in graft survival for patients, there is still improvement needed, particularly in long-term care in pediatric patients receiving grafts from deceased donor patients. Maintenance immunosuppressive therapies have narrow therapeutic indices and are associated with high inter-individual and intra-individual variability.Areas covered: In this review, we examine the impact of pharmacokinetic variability on renal transplantation and its association with age, genetic polymorphisms, drug-drug interactions, drug-disease interactions, renal insufficiency, route of administration, and branded versus generic drug formulation. Pharmacodynamics are outlined in terms of the mechanism of action for each immunosuppressant, potential adverse effects, and the utility of pharmacodynamic biomarkers.Expert opinion: Acquiring abetter quantitative understanding of immunosuppressant pharmacokinetics and pharmacodynamic components should help clinicians implement treatment regimens to maintain the balance between therapeutic efficacy and drug-related toxicity.

Low-Dose Antithymocyte Globulin Has No Disadvantages to Standard Higher Dose in Pediatric Kidney Transplant Recipients: Report From the Pediatric Nephrology Research Consortium.

INTRODUCTION: Rabbit antithymocyte globulin (rATG) dosing strategies for induction in pediatric kidney transplantation vary between centers. It is not known whether a lower rATG induction dose provides safe and effective immunosuppression compared with a "standard" higher dose. METHODS: We performed a retrospective multicenter study of all isolated first-time kidney transplant recipients <21 years old who received rATG induction between 1 January 2010 and 31 December 2014 at 9 pediatric centers. An a priori cutoff of a 4.5-mg/kg cumulative rATG dose was used to identify low (≤ 4.5 mg/kg) and standard (> 4.5 mg/kg) exposure groups. Outcomes examined included 12 months posttransplant graft function (estimated glomerular filtration rate [eGFR]); the occurrence of acute rejection, donor-specific antibody (DSA), neutropenia, and viral infection (cytomegalovirus [CMV], Epstein-Barr virus [EBV], and BK virus); and 24-month outcomes of posttransplant lymphoproliferative disorder (PTLD) occurrence and patient and graft survival. RESULTS: Two hundred thirty-five patients were included. Baseline features of the low and standard rATG dose groups were similar. By 12 months, the rATG dose group had no significant impact on the occurrence of neutropenia, positive DSA, or viral polymerase chain reaction (PCR). Graft function was similar. Acute rejection rates were similar at 17% (low dose) versus 19% (standard dose) (P = 0.13). By 24 months, graft survival (96.4% vs. 94.6%) and patient survival (100% vs. 99.3%) were similar between the low- and standard-dose groups (P = 0.54 and 0.46), whereas the occurrence of PTLD trended higher in the standard-dose group (0% vs. 2.6%, P = 0.07). CONCLUSION: A low rATG induction dose ≤ 4.5 mg/kg provided safe and effective outcomes in this multicenter low immunologic risk pediatric cohort. Prospective studies are warranted to define the optimal rATG induction dose in pediatric kidney transplantation.

Bortezomib in the treatment of antibody-mediated rejection in pediatric kidney transplant recipients: A multicenter Midwest Pediatric Nephrology Consortium study.

Antibody-mediated rejection leads to allograft loss after kidney transplantation. Bortezomib has been used in adults for the reversal of antibody-mediated rejection; however, pediatric data are limited. This retrospective study was conducted in collaboration with the Midwest Pediatric Nephrology Consortium. Pediatric kidney transplant recipients who received bortezomib for biopsy-proven antibody-mediated rejection between 2008 and 2015 were included. The objective was to characterize the use of bortezomib in pediatric kidney transplant recipients. Thirty-three patients received bortezomib for antibody-mediated rejection at nine pediatric kidney transplant centers. Ninety percent of patients received intravenous immunoglobulin, 78% received plasmapheresis, and 78% received rituximab. After a median follow-up of 15 months, 65% of patients had a functioning graft. The estimated glomerular filtration rate improved or stabilized in 61% and 36% of patients at 3 and 12 months post-bortezomib, respectively. The estimated glomerular filtration rate at diagnosis significantly predicted estimated glomerular filtration rate at 12 months after adjusting for chronic histologic changes (P .001). Fifty-six percent of patients showed an at least 25% reduction in the mean fluorescence intensity of the immune-dominant donor-specific antibody, 1-3 months after the first dose of bortezomib. Non-life-threatening side effects were documented in 21 of 33 patients. Pediatric kidney transplant recipients tolerated bortezomib without life-threatening side effects. Bortezomib may stabilize estimated glomerular filtration rate for 3-6 months in pediatric kidney transplant recipients with antibody-mediated rejection.

Effects of unbound mycophenolic acid on inosine monophosphate dehydrogenase inhibition in pediatric kidney transplant patients.

BACKGROUND: Mycophenolic acid (MPA) is a key immunosuppressive drug that acts through inhibition of inosine monophosphate dehydrogenase (IMPDH). MPA is commonly measured, as part of therapeutic drug monitoring, as the total concentration in plasma. However, it has been postulated that the free (unbound) fraction of MPA (fMPA) is responsible for the immunosuppressive effects. In this study, a sensitive low volume high-performance liquid chromatography (HPLC) assay was developed to measure fMPA concentrations to explore the relationship between fMPA and IMPDH activity. METHODS: To obtain fMPA concentrations, plasma samples were filtrated using Centrifree ultrafiltration devices. The ultrafiltrate was analyzed by HPLC using a Kinetex C18 column (2.6 µm, 3.0 × 75 mm). fMPA concentrations were compared with the total MPA concentrations available in 28 pediatric kidney transplant patients at 3 consecutive occasions after transplantation. The relationship between fMPA and IMPDH activity was analyzed using an Emax model. RESULTS: The HPLC assay, using 25 µL of the ultrafiltrates, was validated over a range from 2.5 to 1000 µL with good accuracy, precision, and reproducibility. Total and free MPA concentrations were well correlated (R = 0.85, P < 0.0001), although large intraindividual and interindividual variability in the bound MPA fractions was observed. The overall relationship between fMPA concentrations and IMPDH inhibition using the Emax model was comparable with that of total MPA, as previously reported. The model estimated EC50 value (164.5 µL) is in good agreement with reported in vitro EC50 values. CONCLUSIONS: This study provides a simple HPLC method for the measurement of fMPA and a pharmacologically reasonable EC50 estimate. The good correlation between the total and free MPA concentrations suggests that routine measurement of fMPA to characterize mycophenolate pharmacokinetic and pharmacodynamic does not seem warranted, although the large variability in the bound fractions of MPA warrants further study.

UGT1A9, UGT2B7, and MRP2 genotypes can predict mycophenolic acid pharmacokinetic variability in pediatric kidney transplant recipients.

BACKGROUND: Mycophenolic acid (MPA) exposure in pediatric patients with kidney transplant receiving body surface area (BSA)-based dosing exhibits large variability. Several genetic variants in glucuronosyltransferases (UGTs) and of multidrug resistance-associated protein 2 (MRP2) have independently been suggested to predict MPA exposure in adult patients with varying results. Here, the combined contribution of these genetic variants to MPA pharmacokinetic variability was investigated in pediatric renal transplant recipients who were on mycophenolic mofetil maintenance therapy. METHODS: MPA and MPA-glucuronide concentrations from 32 patients were quantified by high-performance liquid chromatography. MPA exposure (AUC) was estimated using a 4-point abbreviated sampling strategy (predose/trough and 20 minutes, 1 hour, and 3 hours after dose) using a validated pediatric Bayesian estimator. Genotyping was performed for all of the following single nucleotide polymorphisms (SNPs): UGT1A8 830G>A(*3), UGT1A9 98T>C(*3), UGT1A9-440C>T, UGT1A9-2152C>T, UGT1A9-275T>A, UGT2B7-900A>G, and MRP2-24T>C. RESULTS: Recipients heterozygous for MRP2-24T>C who also had UGT1A9-440C>T or UGT2B7-900A>G (n = 4), and MRP2-24T>C-negative recipients having both UGT1A9-440C>T and UGT2B7-900A>G (n = 5) showed a 2.2 and 1.7 times higher dose-dependent and BSA-normalized MPA-AUC compared with carriers of no or only 1 UGT-SNP (P < 0.001 and P = 0.01, respectively) (n = 7). Dose-dependent and BSA-normalized predose MPA concentrations were 3.0 and 2.4 times higher, respectively (P < 0.001). Interindividual variability in peak concentrations could be explained by the presence of the UGT1A9-440C>T genotype (P < 0.05). CONCLUSION: Our preliminary study demonstrates that combined UGT1A9-440C>T, UGT2B7-900A>G, and MRP2-24T>C polymorphisms can be important predictors of interindividual variability in MPA exposure in the pediatric population.

Pharmacokinetics of olmesartan medoxomil in pediatric patients with hypertension.

BACKGROUND: The prevalence and importance of hypertension in younger patients is becoming increasingly recognized; however, only a limited number of clinical trials have been conducted in the pediatric population. OBJECTIVE: The aim of this study was to characterize the pharmacokinetics and short-term safety of olmesartan medoxomil in children and adolescents with hypertension. METHODS: An open-label, multicenter, single-dose study was conducted in children and adolescents aged 12 months-16 years who were receiving treatment for hypertension or, if not currently treated for hypertension, had either a systolic blood pressure (SBP) or diastolic blood pressure (DBP).≥95th percentile, or SBP or DBP ≥90th percentile if diabetic or with a family history of hypertension. Patients were stratified by age: 12-23 months (Group 1; none enrolled), 2-5 years (Group 2; n = 4), 6-12 years (Group 3; n = 10), and 13-16 years (Group 4; n = 10). All patients received a single oral dose of olmesartan medoxomil based on the individual's age and bodyweight. Patients aged <6 years received an oral suspension of olmesartan medoxomil at a dose of 0.3 mg/kg of bodyweight (not to exceed 20 mg), those aged ≥6 years who weighed ≥35 kg received olmesartan medoxomil 40 mg tablets, and those who weighed <35 kg received olmesartan medoxomil 20 mg tablets. RESULTS: In Groups 2, 3, and 4, the weight-adjusted apparent total body clearance (CL/F) of olmesartan medoxomil was 0.100 ± 0.034, 0.062 ± 0.020, and 0.072 ± 0.022 L/h/kg, respectively, and the weight-adjusted apparent volume of distribution (Vd/F) was 0.32 ± 0.16, 0.33 ± 0.14, and 0.49 ± 0.23 L/kg, respectively. CL/F and Vd/F in Groups 3 and 4 were not significantly different. Statistical comparisons between Groups 3 or 4 and Group 2 were not performed due to the small sample size of Group 2 (n = 4). Plasma elimination half-life and time to maximum plasma concentration were similar across the three groups. In Groups 3 and 4, considerable interindividual variability was seen in maximum plasma concentration (C(max)), area under the curve (AUC) from time zero to the last measurable concentration, and apparent clearance, with AUC and C(max) approximately 30% greater in Group 3. Four of 24 (16.7%) patients experienced treatment-emergent adverse events that were all mild in severity and considered not drug-related. No deaths, serious adverse events, or discontinuations due to adverse events occurred in the study. CONCLUSIONS: Olmesartan medoxomil was well tolerated and demonstrated a pharmacokinetic profile in pediatric patients similar to that of adults when adjusted for body size. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT00151814

Inosine monophosphate dehydrogenase (IMPDH) activity as a pharmacodynamic biomarker of mycophenolic acid effects in pediatric kidney transplant recipients.

Monitoring inosine monophosphate dehydrogenase (IMPDH) activity as a biomarker of mycophenolic acid (MPA)-induced immunosuppression may serve as a novel approach in pharmacokinetics (PK)/pharmacodynamics (PD)-guided therapy. The authors prospectively studied MPA pharmacokinetics and IMPDH inhibition in 28 pediatric de novo kidney transplant recipients. Pretransplant IMPDH activity and full PK/PD profiles were obtained at 3 different occasions: 1 to 3 days, 4 to 9 days, and approximately 6 months after transplant. Large intra- and interpatient variability was noted in MPA pharmacokinetics and exposure and IMPDH inhibition. MPA exposure (AUC(0-12 h)) was low early posttransplant and increased over time and stabilized at months 3 to 6. Mean pretransplant IMPDH activity (6.4 ± 4.6 nmol/h/mg protein) was lower than previously reported in adults. In most of the patients, IMPDH enzyme activity decreased with increasing MPA plasma concentration, with maximum inhibition coinciding with maximum MPA concentration. The overall relationship between MPA concentration and IMPDH activity was described by a direct inhibitory E(max) model (EC(50) = 0.97 mg/L). This study suggests the importance of early PK/PD monitoring to improve drug exposure. Because IMPDH inhibition is well correlated to MPA concentration, pretransplant IMPDH activity may serve as an early marker to guide the initial level of MPA exposure required in a pediatric population.

Collecting duct carcinoma arising in association with BK nephropathy post-transplantation in a pediatric patient. A case report with immunohistochemical and in situ hybridization study.

The development of malignancy in a renal transplant graft is an uncommon phenomenon. A renal neoplasm developing in the adult donor kidney of a pediatric transplant recipient has only rarely been reported. We report a case of collecting duct carcinoma arising in association with BK virus nephropathy in an adult living-related donor renal allograft to a pediatric recipient. Our case is the second report of neoplasia occurring in association with BK virus nephropathy post-transplantation, suggesting that BK virus may play a role in oncogenesis. It has been proposed that the T-Ag protein encoded by the polyomavirus family of viruses disrupts chromosomal integrity, creating oncogenes, and inactivating tumor suppressor genes. In our study, immunohistochemical staining with antibody directed against BK virus large T antigen showed nuclear staining within urothelium, tubular epithelium, tubular intraepithelial neoplasia, and invasive carcinoma. In situ hybridization did not identify BK virus DNA within neoplastic cells. T-Ag protein expression has been shown to be tumor-specific in bladder, gastric, and colorectal cancers. The finding of T-Ag protein expression in both intraepithelial and invasive neoplastic tissues in our case raises the possibility of BK virus as a causative agent in oncogenesis.

Modifications in cyclosporine (CsA) microemulsion blood concentrations by olestra.

OBJECTIVE: Determine whether olestra alters the absorption of cyclosporine microemulsion in pediatric renal transplant recipients. DESIGN: Prospective, open-label, crossover pharmacokinetic study. SETTING: General clinical research center in a university medical setting providing tertiary care. PARTICIPANTS: Seven pediatric-adolescent renal transplant recipients, ages 9 to 18, 5 to 24 months post-transplant with mean serum creatinine of 0.9 mg/dL (range, 0.7-1.6 mg/dL). METHODOLOGY: Patients participated in 2 study periods: 1. Patients were given their usual dose of Neoral (Novartis Pharmaceuticals Corporation, East Hanover, NJ) without olestra, 2. patients were given their usual dose of Neoral combined with 0.35 g/kg (maximum of 16 g of olestra or approximately 2 ounces of Lays WOW [Frito Lay, Plano, TX] potato chips). The 2 study periods were separated by a minimum 7-day washout period. CsA blood concentrations were obtained at 1, 2, 3, 4, 6, 8, and 12 hours after drug administration. RESULTS: Each patient in the study had a consistent decrease in area under the curve (AUC) when given olestra along with their usual dose of Neoral, compared with giving Neoral alone (5,018 ng*hr/mL versus 4,086 ng*hr/mL; P <.001). There also was a decrease in maximum concentration (Cmax) when Neoral was given with olestra compared with giving Neoral alone (1,202 ng/mL versus 876 ng/mL; P =.015). There was no statistical difference in the mean elimination rate or the trough values for both regimens (half-life 4.767 hours versus 4.771 hours and trough levels of 143 ng/mL versus 124 ng/mL). CONCLUSION: Olestra decreases total CsA exposure in pediatric renal transplant recipients. The noted decrease in AUC was not adequately predicted by CsA trough values which could lead to rejection episodes in the clinical setting.

Recurrent hemolytic uremic syndrome.

Hemolytic uremic syndrome (HUS) in children follows a diarrheal prodrome (D+) approximately 90% of the time, and recurrence due to enteric reinfection with Shiga toxin producing E. coli (e.g., O157:H7) can occur but is rare. It is not well recognized that nondiarrheal (D-) recurrences can also follow an episode of D+ HUS; we report 2 unrelated females who experienced multiple D- episodes following an initial episode of D+ HUS. We also present an HUS classification system that includes recurrence risk. It illustrates that recurrence is seen most frequently with familial HUS but can also occur in cases that are secondary to drugs, cancer, and pregnancy.