Hospital admissions associated with dehydration in childhood kidney transplantation.

BACKGROUND: Paediatric kidney transplant recipients may be at a particular risk of dehydration due to poor kidney concentrating capacity and illness associated with poor fluid intake or losses. In this population, creatinine rise may be more likely with relatively mild dehydration, which may trigger hospital admission. This study describes hospital admissions in the first 12 months after transplantation with diagnosis of graft dysfunction associated with dehydration due to illness or poor fluid intake. We assess risk factors for these admissions. METHODS: Data was extracted from medical records of patients transplanted in two tertiary children hospitals. Following descriptive analysis, multiple failure regression analyses were used to identify factors associated with admission for acute kidney allograft dysfunction associated with dehydration. RESULTS: Of 92 children, 42% had at least 1 dehydration admission in the 12 months following transplantation. Almost half of the dehydration admissions were due to poor fluid intake, which accounted for 1/5 of all unplanned hospital admissions. Target fluid intake at first discharge of > 100 ml/kg/day was associated with dehydration admissions of all types (hazard ratio (HR) 2.04 (95% CI 1.13-3.68)). Teen age was associated with poor fluid intake dehydration admissions (HR 4.87 (95% CI 1.19-19.86)), which were more frequent in mid-summer. Use of enteric feeding tube, which correlated with age under 4, associated with contributing illness dehydration admissions (HR 2.18 (95% CI 1.08-4.41)). CONCLUSIONS: Dehydration admissions in the 12 months following childhood kidney transplantation are common. Highlighted admission risk factors should prompt further study into optimal fluid intake prescription and hydration advice given to children, teenagers, and their carers following kidney transplantation. Use of an enteric feeding tube may not protect patients from admission with dehydration associated with contributing illness. A highger resolution version of the Graphical abstract is available as Supplementary information.

Ravulizumab facilitates reduced burden of vascular access, a major benefit in paediatric atypical haemolytic uraemic syndrome.

BACKGROUND: Atypical haemolytic uraemic syndrome (aHUS) is a rare thrombotic microangiopathy resulting from dysregulation of the alternative complement pathway, leading to multi-organ dysfunction and chronic kidney disease. Eculizumab is an anti-C5 monoclonal antibody therapy that has significantly improved aHUS disease control and patient outcomes, however it requires fortnightly intravenous dosing. This often necessitates long term central access and a high hospital attendance burden. Ravulizumab is a novel, next-generation anti-C5 monoclonal antibody engineered from eculizumab to reduce endosomal degradation of the antibody, increasing the dosing interval up to 8 weeks. CASE SERIES: In this retrospective case series we present the transition of three children with aHUS from eculizumab to ravulizumab from a single tertiary paediatric nephrology service. All patients underwent genomic and immunological work up for aHUS, with no cause found. After stabilisation with eculizumab, two patients developed macrovascular thrombotic complications associated with indwelling central vascular catheters, ultimately leading to central access failure. All patients were transitioned from eculizumab to ravulizumab without relapse of aHUS. One patient successfully underwent deceased donor kidney transplantation with ravulizumab for complement inhibition. All patients have transitioned to peripheral access for infusions given the reduced frequency of dosing, maintaining good control of aHUS for 2-4 years. CONCLUSION: Ravulizumab permits sufficiently reduced frequency of infusion to allow for administration by peripheral cannulation - removing the risks of long term central vascular access often required to deliver eculizumab to paediatric patients.

Paediatric deceased donor kidney transplant in Australia: A 30-year review-What have paediatric bonuses achieved and where to from here?

BACKGROUND: In this 30-year national review, we describe trends in DD transplantation for paediatric recipients, assess the impact of paediatric allocation bonuses and identify outstanding areas of need for this population. METHODS: A retrospective review of all DD kidney only transplants to paediatric recipients (<18 years old) in Australia between 1989 and 2018 was conducted using deidentified extracts from the ANZDATA. RESULTS: Of the 1011 kidney only transplants performed in paediatric recipients during the study period, 426 (42%) were from deceased donors. Paediatric candidates on the DD waiting list had consistently higher rates of transplantation and shorter time from dialysis initiation to transplantation compared with adult candidates (median 372 vs 832 days in 2018, for example). Donor characteristics remained more favourable for paediatric recipients, despite a decline in the overall quality of the donor pool. The mean number of HLA antigen mismatches for paediatric recipients of DD transplants increased each decade (2.86 [1989-1998], 3.85 [1999-2008], 4.01 [2009-2018]). Both patient and graft survival have improved for paediatric DD transplant recipients in the most recent era (5-year graft and patient survival 85% vs 65% and 99% vs 94%, respectively, for 2009-2018 vs 1999-2008). CONCLUSIONS: The current DD kidney allocation system in Australia provides rapid access to high-quality organs for paediatric recipients, and early graft loss has decreased significantly in recent years; however, additional targeted interventions to address HLA matching may improve long-term outcomes in this population.

Altered in utero kidney development in newborns with congenital heart disease.

BACKGROUND: It is known that the heart is not the only organ affected in congenital heart disease (CHD); there is growth restriction of both the brain and the whole body. The protective mechanism of "the brain-sparing phenomenon" re-directs blood flow toward the growing brain in fetuses with CHD. We hypothesized that these changes would result in impaired fetal kidney growth. METHODS: The preoperative ultrasound measurements of kidney length were obtained retrospectively from 452 neonates requiring surgery for CHD. Percentiles were generated based on regression analysis of normative kidney length from three datasets according to both corrected gestational age and to birthweight. RESULTS: As a cohort, neonates with CHD have significantly enlarged kidneys, with a mean percentile ranging from 54.1-72.7 (p < 0.001), depending on the three normal population datasets used for comparison. The kidneys of neonates with left heart obstruction were consistently demonstrated to be greater than normal, unlike those with cyanotic heart disease which were shown to have either normal or enlarged kidneys, depending on the reference population used. CONCLUSIONS: The kidneys of newborns with CHD are not reduced in size, and on average are larger than normal. The nature of this size discrepancy and its subsequent clinical significance is unknown.

Lifetime risk of end-stage kidney disease in living donors for paediatric kidney transplant recipients in Australia and New Zealand - a retrospective study.

Living kidney donors (LKD) for paediatric kidney transplant recipients (KTR) have a heightened motivation to donate for emotional reasons and the clear health benefits to the KTR. We hypothesized that the cohort of LKD for paediatric KTR (LKD-P) includes motivated young parents with a higher lifetime end-stage kidney disease (ESKD) risk compared to adult KTR (LKD-A). Data from the Australia and New Zealand Dialysis and Transplant LKD Registry (2004-2015) was analysed to compare baseline characteristics and predonation ESKD risk in LKD-P (n = 315) versus LKD-A (n = 3448). LKD-P were younger (median age 42 vs. 50 years; P < 0.001) and had a marginally higher lifetime ESKD risk (median 0.44% vs. 0.40%; P < 0.01), with a similar proportion of LKD exceeding 1% risk threshold (5.4% vs. 5.6%; P = NS). Compared to grandparents as LKD-P, parents (median age 41 vs. 59 years; P < 0.001) had a higher lifetime ESKD (0.44% vs. 0.25%; P < 0.001). Although unique benefits to paediatric KTR justify the minor increase in lifetime ESKD risk in young parents, carefully selected grandparents are an alternative LKD-P option, allowing parents to donate for subsequent transplants.

Consensus opinion on diagnosis and management of thrombotic microangiopathy in Australia and New Zealand.

Thrombotic microangiopathy (TMA) arises in a variety of clinical circumstances with the potential to cause significant dysfunction of the kidneys, brain, gastrointestinal tract and heart. TMA should be considered in all patients with thrombocytopenia and anaemia, with an immediate request to the haematology laboratory to look for red cell fragments on a blood film. Although TMA of any aetiology generally demands prompt treatment, this is especially so in thrombotic thrombocytopenic purpura (TTP) and atypical haemolytic uraemic syndrome (aHUS), where organ failure may be precipitous, irreversible and fatal. In all adults, urgent, empirical plasma exchange (PE) should be started within 4-8 h of presentation for a possible diagnosis of TTP, pending a result for ADAMTS13 (a disintegrin and metalloprotease thrombospondin, number 13) activity. A sodium citrate plasma sample should be collected for ADAMTS13 testing prior to any plasma therapy. In children, Shiga toxin-associated haemolytic uraemic syndrome due to infection with Escherichia coli (STEC-HUS) is the commonest cause of TMA, and is managed supportively. If TTP and STEC-HUS have been excluded, a diagnosis of aHUS should be considered, for which treatment is with the monoclonal complement C5 inhibitor, eculizumab. Although early confirmation of aHUS is often not possible, except in the minority of patients in whom auto-antibodies against factor H are identified, genetic testing ultimately reveals a complement-related mutation in a significant proportion of aHUS cases. The presence of other TMA-associated conditions (e.g. infection, pregnancy/postpartum and malignant hypertension) does not exclude TTP or aHUS as the underlying cause of TMA.

Consensus opinion on diagnosis and management of thrombotic microangiopathy in Australia and New Zealand.

Thrombotic microangiopathy (TMA) arises in a variety of clinical circumstances with the potential to cause significant dysfunction of the kidneys, brain, gastrointestinal tract and heart. TMA should be considered in all patients with thrombocytopenia and anaemia, with an immediate request to the haematology laboratory to look for red cell fragments on a blood film. While TMA of any aetiology generally demands prompt treatment, this is especially so in thrombotic thrombocytopenic purpura (TTP) and atypical haemolytic uraemic syndrome (aHUS), where organ failure may be precipitous, irreversible and fatal. In all adults, urgent, empirical plasma exchange (PE) should be started within 4-8 h of presentation for a possible diagnosis of TTP, pending a result for ADAMTS13 activity (a disintegrin and metalloprotease thrombospondin, number 13). A sodium citrate plasma sample should be collected for ADAMTS13 testing prior to any plasma therapy. In children, Shiga toxin-associated haemolytic uraemic syndrome due to infection with Escherichia coli (STEC-HUS) is the commonest cause of TMA, and is managed supportively. If TTP and STEC-HUS have been excluded, a diagnosis of aHUS should be considered, for which treatment is with the monoclonal complement C5 inhibitor, eculizumab. While early confirmation of aHUS is often not possible, except in the minority of patients in whom autoantibodies against factor H are identified, genetic testing ultimately reveals a complement-related mutation in a significant proportion of aHUS cases. The presence of other TMA-associated conditions (e.g. infection, pregnancy/postpartum and malignant hypertension) does not exclude TTP or aHUS as the underlying cause of TMA.

HLA epitope matching in pediatric renal transplantation.

Chronic graft loss due to antibody-mediated rejection (AMR) and the difficulty of re-transplanting highly sensitized patients are two of the major long-term challenges in pediatric renal transplantation. Treatments for AMR are often ineffective and desensitization protocols can be a high risk, making prevention a highly appealing strategy. Insights into the structural determinants of humoral alloantigenicity present an exciting opportunity to reassess our current paradigm of tissue matching and potentially preventing these complications. We review the theory behind human leukocyte antigen (HLA) B cell epitopes and the various systems that have been proposed to define them, including eplets. There is a growing body of clinical evidence suggesting that epitope-based tissue matching may be superior to traditional HLA antigen matching at predicting a range of clinical outcomes. However, additional studies are required to better understand the biological relevance of these systems of defining epitopes and their role in pediatric transplantation.

Application of an epitope-based allocation system in pediatric kidney transplantation.

Donor-recipient HLA mismatch remains a leading cause for sensitization and graft loss in kidney transplantation. HLA compatibility at an epitope level is emerging as an improved method of matching compared with current HLA antigen allocation. A novel epitope-based allocation approach to prospectively exclude donors with high-level mismatches was implemented for pediatric KTRs on the DD waiting list. Nineteen consecutive transplants were followed for 12 months, including eight DD KTRs listed with eplet exclusions, as well as three DD KTRs and eight LD KTRs without exclusions. KTRs with eplet exclusions had estimated GFR of 78.5 mL/min/1.73 m2 , no episodes of rejection, and time to transplant 6.55 months. HLA-A, HLA-B, HLA-DR antigen mismatches were similar between all groups. KTRs with exclusions had significantly lower class II eplet mismatches (20.4) than the contemporary DD KTRs without exclusions (63.7) and DD KTRs transplanted in the preceding decade (46.9). dnDSAs were identified in two of eight DD KTRs with exclusions, two of three DD KTRs without exclusions and five of eight LD KTRs. Epitope-based allocation achieved timely access to transplantation, low class II eplet mismatches, and low rates of dnDSAs in the first year. This strategy requires longer follow-up and larger numbers, but has the potential to reduce anti-HLA sensitization and improve both graft survival and opportunities for future retransplantation.

Paediatric nephrology: the last 50 years.

In 1965, the specialty of paediatric nephrology was in its infancy. Following the development of a landmark collaborative research study, the International Study of Kidney Disease in Childhood in the mid-1960s, the first specialist societies were formed: the European Society of Pediatric Nephrology in 1967 and the American Society of Pediatric Nephrology in 1969. The extraordinary improvements in care delivered to children with kidney disease over the past 50 years are too broad to cover in any one paper. They traverse the spectrum of diagnosis, classification, therapeutics, social well-being and transition to adult care. We have selected four case scenarios to highlight these changes in key areas of paediatric nephrology: post-streptococcal glomerulonephritis, nephrotic syndrome, haemolytic uraemic syndrome and neonatal dialysis and childhood transplantation.

Complicated Henoch-Schönlein purpura.

We present a case of Henoch Schonlein pupura in a 6-year-old boy demonstrating some of the diagnostic pitfalls, complications and management challenges of this common paediatric condition.

Deletion of bone-marrow-derived receptor for AGEs (RAGE) improves renal function in an experimental mouse model of diabetes.

AIMS/HYPOTHESIS: The AGEs and the receptor for AGEs (RAGE) are known contributors to diabetic complications. RAGE also has a physiological role in innate and adaptive immunity and is expressed on immune cells. The aim of this study was to determine whether deletion of RAGE from bone-marrow-derived cells influences the pathogenesis of experimental diabetic nephropathy. METHODS: Groups (n = 8/group) of lethally irradiated 8 week old wild-type (WT) mice were reconstituted with bone marrow from WT (WT → WT) or RAGE-deficient (RG) mice (RG → WT). Diabetes was induced using multiple low doses of streptozotocin after 8 weeks of bone marrow reconstitution and mice were followed for a further 24 weeks. RESULTS: Compared with diabetic WT mice reconstituted with WT bone marrow, diabetic WT mice reconstituted with RG bone marrow had lower urinary albumin excretion and podocyte loss, more normal creatinine clearance and less tubulo-interstitial injury and fibrosis. However, glomerular collagen IV deposition, glomerulosclerosis and cortical levels of TGF-ß were not different among diabetic mouse groups. The renal tubulo-interstitium of diabetic RG → WT mice also contained fewer infiltrating CD68(+) macrophages that were activated. Diabetic RG → WT mice had lower renal cortical concentrations of CC chemokine ligand 2 (CCL2), macrophage inhibitory factor (MIF) and IL-6 than diabetic WT → WT mice. Renal cortical RAGE ligands S100 calgranulin (S100A)8/9 and AGEs, but not high mobility box protein B-1 (HMGB-1) were also decreased in diabetic RG → WT compared with diabetic WT → WT mice. In vitro, bone-marrow-derived macrophages from WT but not RG mice stimulated collagen IV production in cultured proximal tubule cells. CONCLUSIONS/INTERPRETATION: These studies suggest that RAGE expression on haemopoietically derived immune cells contributes to the functional changes seen in diabetic nephropathy by promoting macrophage infiltration and renal tubulo-interstitial damage.

Renal dendritic cells adopt a pro-inflammatory phenotype in obstructive uropathy to activate T cells but do not directly contribute to fibrosis.

Unilateral ureteral obstruction (UUO) is a well-characterized murine model of renal inflammation leading to fibrosis. Renal dendritic cells (DCs) constitute a significant portion of kidney leukocytes and may participate in local inflammation and have critical roles in antigen presentation. The heterogeneity in renal DC populations and surface marker overlap with monocytes/macrophages has made studying renal DCs difficult. These studies used CD11c-promoter driven reporter/depletion mice to study DCs in vivo. Studying early local inflammatory events (day 3 of UUO), in vivo multiphoton imaging of the intact kidney of CD11c reporter mice revealed more dendrite extensions and increased activity of renal DCs in real time. Phenotypic analysis suggested resident DC maturation in obstructed kidneys with increased CD11b and less F4/80 expressed. CD11b(hi) Gr-1(+) inflammatory DCs were also present in obstructed kidneys. T-cell receptor transgenic mice revealed enhanced antigen-presenting capacity of renal DCs after UUO, with increased antigen-specific T-cell proliferation in vivo and ex vivo. However, conditional DC ablation at days 0, 2, or 4 did not attenuate fibrosis or apoptosis 7 days after UUO, and depletion at 7 days did not alter outcomes at day 14. Therefore, after UUO, renal DCs exhibit inflammatory morphological and functional characteristics and are more effective antigen-presenting cells, but they do not directly contribute to tubulointerstitial damage and fibrosis.

The Introduction of cPRA and Its Impact on Access to Deceased Donor Kidney Transplantation for Highly Sensitized Patients in Australia.

BACKGROUND: In March 2016, Australia's deceased donor kidney allocation program introduced calculated panel reactive antibody (cPRA) based on antibody exclusions using multiplex assays to define sensitization for waitlisted candidates. We aimed to assess the impact of this change and review access to transplantation for highly sensitized patients under the current allocation rules. METHODS: Registry data were used to reconstruct changes in panel reactive antibody (PRA)/cPRA for all patients active on the waiting list between 2013 and 2018. A multilevel, mixed-effects negative binomial regression model was used to determine the association between sensitization and transplantation rate in the cPRA era. RESULTS: Following the introduction of cPRA, there was an increase in the percentage of the waiting list classified as highly sensitized (PRA/cPRA ≥80%) from 7.2% to 27.8% and very highly sensitized (PRA/cPRA ≥99%) from 2.7% to 15.3%. Any degree of sensitization was associated with a decreased rate of transplantation with a marked reduction for those with cPRA 95%-98% (adjusted incidence rate ratio, 0.36 [95% confidence interval, 0.28-0.47], P < 0.001) and cPRA ≥99% (adjusted incidence rate ratio, 0.09 [95% confidence interval, 0.07-0.12], P < 0.001). CONCLUSIONS: The proportion of the waiting list classified as highly sensitized increased substantially following the introduction of cPRA, and despite current prioritization, very highly sensitized patients have markedly reduced access to deceased donor transplantation.

Successful Implementation of an Increased Viral Risk Donor Waiting List for Preconsented Kidney Transplant Candidates in Victoria, Australia.

Increased viral risk donors (IVRDs) with increased risk behaviors for blood-borne virus infection and negative nucleic acid testing have a low absolute risk of "window period" infection. Utilization and allocation of IVRD organs differ between jurisdictions. METHODS: We examined the characteristics and utilization of deceased donor IVRD kidneys and recipient outcomes within a 2-y period (July 31, 2018-July 31, 2020) postimplementation of a new opt-in allocation pathway for preconsented recipients in Victoria, Australia. RESULTS: Fifty-six kidneys from 31 IVRDs were utilized, comprising 13% of donors. Preconsent rate to accept IVRD kidneys increased to 41% of the waitlist in the 2 y postimplementation, and IVRDs having no kidneys utilized reduced to 0%. Compared with non-IVRD kidneys, kidney offer declines >10 per donor were less likely from IVRDs (3% vs 19%; P < 0.05). IVRDs were younger (median age 36 [IQR 30-44] vs 51 [35-60] y; P < 0.0001), with lower kidney donor profile index (25% [13-40%] vs 57% [29-75%]; P < 0.0001), and less hypertension (0% vs 22%; P < 0.01). Estimated glomerular filtration rate 3 mo post-transplant was superior (P < 0.01). Injecting drug use (61%) was the most common increased risk behavior. 29% of IVRDs were hepatitis C antibody positive but nucleic acid testing negative. No active infection was detected in any recipient post-transplant. CONCLUSIONS: The described opt-in system permits efficient allocation and utilization of kidneys from IVRDs, with superior quality and graft function. Education is crucial to facilitate informed consent and equity of access to this donor pool.

Th1 and Th17 cells induce proliferative glomerulonephritis.

Th1 effector CD4+ cells contribute to the pathogenesis of proliferative and crescentic glomerulonephritis, but whether effector Th17 cells also contribute is unknown. We compared the involvement of Th1 and Th17 cells in a mouse model of antigen-specific glomerulonephritis in which effector CD4+ cells are the only components of adaptive immunity that induce injury. We planted the antigen ovalbumin on the glomerular basement membrane of Rag1(-/-) mice using an ovalbumin-conjugated non-nephritogenic IgG1 monoclonal antibody against alpha3(IV) collagen. Subsequent injection of either Th1- or Th17-polarized ovalbumin-specific CD4+ effector cells induced proliferative glomerulonephritis. Mice injected with Th1 cells developed progressive albuminuria over 21 d, histologic injury including 5.5 +/- 0.9% crescent formation/segmental necrosis, elevated urinary nitrate, and increased renal NOS2, CCL2, and CCL5 mRNA. Mice injected with Th17 cells developed albuminuria by 3 d; compared with Th1-injected mice, their glomeruli contained more neutrophils and greater expression of renal CXCL1 mRNA. In conclusion, Th1 and Th17 effector cells can induce glomerular injury. Understanding how these two subsets mediate proliferative forms of glomerulonephritis may lead to targeted therapies.

Intrarenal antigens activate CD4+ cells via co-stimulatory signals from dendritic cells.

Dendritic cells in the kidney take up antigens, but little is known about their role in providing co-stimulatory signals for the activation of CD4(+) cells. This study examined the phenotype of dendritic cells in the renal interstitium and in the lymph node draining the kidney before and after intrarenal ovalbumin injection. After intrarenal injection of the antigen, expression of the co-stimulatory molecules CD86 and programmed cell death ligand 1 (PD-L1) increased on renal dendritic cells, whereas expression of only CD86 increased on dendritic cells of the draining lymph node. The activation and proliferation of antigen-specific CD4(+) cells in the lymph node were assessed by transfer of naïve, fluorescently labeled ovalbumin-specific T cell receptor transgenic cells to mice before antigen administration. Blocking both CD86 and CD80 profoundly inhibited CD4(+) cell proliferation, but CD86 was the dominant CD28 ligand in the early proliferative response of CD4(+) cells. Conversely, activation of PD-1, the receptor expressed on CD4(+) cells that binds PD-L1 and PD-L2, reduced the proliferation of CD4(+) cells in the draining lymph node. Comparing subcutaneous and intrarenal administration of antigen, it was found that CD4(+) cell activation was slower and the effects of combined CD80 and CD86 blockade were more profound when antigen was presented via the kidney compared with the skin. In summary, renal dendritic cells take up antigen and participate in the control of antigen-specific CD4(+) cell proliferation by upregulating co-stimulatory molecules such as CD86 that stimulate CD4(+) cell proliferation and by signaling through PD-1, which prevents an inappropriately exuberant immune response.

Optimizing Mycophenolic Acid Exposure in Kidney Transplant Recipients: Time for Target Concentration Intervention.

The immunosuppressive agent mycophenolate is used extensively in kidney transplantation, yet dosing strategy applied varies markedly from fixed dosing ("one-dose-fits-all"), to mycophenolic acid (MPA) trough concentration monitoring, to dose optimization to an MPA exposure target (as area under the concentration-time curve [MPA AUC0-12]). This relates in part to inconsistent results in prospective trials of concentration-controlled dosing (CCD). In this review, the totality of evidence supporting mycophenolate CCD is examined: pharmacological characteristics, observational data linking exposure to efficacy and toxicities, and randomized controlled trials of CCD, with attention to dose optimization method and exposure achieved. Fixed dosing of mycophenolate consistently leads to underexposure associated with rejection, as well as overexposure associated with toxicities. When CCD is driven by pharmacokinetic calculation to a target concentration (target concentration intervention), MPA exposure is successfully controlled and clinical benefits are seen. There remains a need for consensus on practical aspects of mycophenolate target concentration intervention in contemporary tacrolimus-containing regimens and future research to define maintenance phase exposure targets. However, given ongoing consequences of both overimmunosuppression and underimmunosuppression in kidney transplantation, impacting short- and long-term outcomes, these should be a priority. The imprecise "one-dose-fits-all" approach should be replaced by the clinically proven MPA target concentration strategy.

Standard dosing of tacrolimus leads to overexposure in pediatric renal transplantation recipients.

Tacrolimus dosage in pediatric RTRs is empirically based on weight. There is evidence that adolescents are at greater risk of toxicity than young children on this dosing regimen. We investigated the rate of tacrolimus overexposure within the first three wk post-transplantation in pediatric RTRs receiving tacrolimus 0.15 mg/kg twice daily. Of 63 RTRs studied, 41 (65.1%) experienced a tacrolimus level above the therapeutic range (supratherapeutic), the majority (48.8%) on days two to four post-transplant. Patients with supratherapeutic levels were older (14.2 vs. 9.9 yr, p = 0.016), taller (146.7 vs. 126.5 cm, p = 0.029), larger (1.36 vs. 1.01 m(2), p = 0.039) and heavier (44.1 vs. 29.3 kg, p = 0.043) and by day 12 were receiving much lower tacrolimus doses than those without supratherapeutic levels (0.425 vs. 0.198 mg/kg/day, p = 0.0002). Supratherapeutic levels were more common among white (British) children than other ethnic groups (74 vs. 45%, p = 0.02). There were no observed differences in rates of patient or graft survival, or acute rejection during the three-yr study period. Adolescent patients appear to be at greater risk of excessive tacrolimus dosing on a standard regimen. We therefore outline a regimen restricting tacrolimus dosage given to larger/older patients, but emphasize the need for a prospective randomized trial to define optimal dosing.