Zinc Supplementation Trial in Pediatric Chronic Kidney Disease: Effects on Circulating FGF-23 and Klotho.

Background: Zinc status, its role in bone metabolism and efficacy of deficiency correction has not been well studied in children with chronic kidney disease (CKD). Objectives: The primary objective was to investigate whether 3 months of oral zinc supplementation corrects zinc deficiency in children with CKD who have native or transplanted kidneys. The secondary objective was to compare circulating intact FGF-23 (iFGF-23), c-terminal FGF-23 (cFGF-23), and Klotho between zinc-sufficient and zinc-deficient children with CKD and to assess the relationship between circulating zinc, iFGF-23, cFGF-23, Klotho, bone biomarkers, copper, and phosphate excretion pre-supplementation and post-supplementation of zinc. Methods: Forty-one children (25 male and 16 female, age 12.94 ± 4.13 years) with CKD in native or transplanted kidneys were recruited through 2 pediatric nephrology divisions in Ontario, Canada. Of those, 14 patients (9 native CKD, 5 transplant CKD) with identified zinc deficiency (64% enrollment rate) received zinc citrate supplement for 3 months: 10 mg orally once (4-8 years) or twice (9-18 years) daily. Results: Zinc deficiency (plasma concentration < 11.5 µmol/L) was found in 22 patients (53.7%). A linear regression model suggested that zinc concentration reduced by 0.026 µmol/L (P = .04) for every 1-unit of estimated glomerular filtration rate (eGFR) drop. Zinc deficiency status was associated with higher serum iFGF-23; however, this was predominantly determined by the falling GFR. Zinc deficient and sufficient children had similar circulating c-FGF-23 and alpha-Klotho. Normalization of plasma zinc concentration was achieved in 8 (5 native CKD and 3 transplant CKD) out of 14 treated patients rising from 10.04 ± 1.42 to 12.29 ± 3.77 µmol/L (P = .0038). There were no significant changes in other biochemical measures in all treated patients. A statistically significant (P = .0078) rise in c-FGF-23 was observed only in a subgroup of 11 children treated with zinc but not receiving calcitriol. Conclusions: Zinc status is related to kidney function and possibly connected to bone metabolism in patients with CKD. However, it plays a minor role in fine-tuning various metabolic processes. In this exploratory non-randomized study, 3 months supplementation with zinc corrected deficiency in just over half of patients and only modestly affected bone metabolism in asymptomatic CKD patients.

Contexte: Le statut du zinc, son rôle dans le métabolisme osseux et l'efficacité de la correction d'une carence n'ont pas encore été bien étudiés chez les enfants atteints d'insuffisance rénale chronique (IRC). Objectifs: L'objectif principal était d'examiner si une supplémentation orale en zinc pendant trois mois pouvait corriger une carence chez les enfants atteints d'IRC avec des reins natifs ou transplantés. Les objectifs secondaires étaient de comparer les taux circulants de FGF-23 intact (iFGF-23), de FGF-23 c-terminal (cFGF-23) et de Klotho d'enfants atteints d'IRC et ayant des niveaux corrects ou déficients en zinc, puis d'évaluer la relation entre le zinc circulant, l'iFGF-23, le cFGF-23, le Klotho, les biomarqueurs osseux et l'excrétion de cuivre et de phosphate avant et après la supplémentation en zinc. Méthodologie: Un total de 41 enfants (25 garçons et 16 filles, âgés de 12,94 ±4,13 ans) atteints d'IRC avec reins natifs ou transplantés ont été recrutés par deux divisions de néphrologie pédiatrique en Ontario, au Canada. De ceux-ci, 14 patients (9 avec reins natifs; 5 avec reins transplantés) qui présentaient une carence en zinc (taux d'inclusion de 64 %) ont reçu un supplément de citrate de zinc pendant trois mois à raison de 10 mg par voie orale une fois (4 à 8 ans) ou deux fois (9 à 18 ans) par jour. Résultats: Une carence en zinc (concentration plasmatique < 11,5 µmol/L) a été constatée chez 22 patients (53,7 %). Un modèle de régression linéaire a suggéré que la concentration de zinc diminue de 0,026 µmol/L (P = 0,04) pour chaque chute d'une unité de DFGe. Le statut de carence en zinc était associé à un taux sérique d'iFGF-23 plus élevé; cependant, cela était principalement déterminé par la baisse du DFG. Tous les enfants, avec ou sans carence en zinc, avaient des taux circulants similaires de c-FGF-23 et d'alpha-Klotho. La normalisation de la concentration plasmatique de zinc a été obtenue chez 8 patients (5 avec reins natifs; 3 avec reins transplantés) sur les 14 qui ont été traités, passant de 10,04 ±1,42 à 12,29 ±3,77 µmol/L (P = 0,003 8). Aucun changement significatif n'a été observé dans les autres mesures biochimiques chez les patients traités. Une augmentation statistiquement significative (P = 0,007 8) du taux de c-FGF-23 a été observée uniquement dans un sous-groupe de 11 enfants traités avec du zinc, mais ne recevant pas de calcitriol. Conclusion: Le statut du zinc est lié à la fonction rénale et peut être lié au métabolisme osseux chez les patients atteints d'IRC. Il joue toutefois un rôle mineur dans le réglage fin de divers processus métaboliques. Dans cet essai exploratoire non randomisé, une supplémentation en zinc pendant trois mois a permis de corriger la carence chez un peu plus de la moitié des patients et n'a eu qu'un effet modeste sur le métabolisme osseux chez les patients asymptomatiques atteints d'IRC.

Eculizumab Dosing in Infants.

Eculizumab is the therapy of choice for patients with atypical hemolytic uremic syndrome (aHUS). Dosing recommendations stem from two trials: one retrospective trial (19 children and 5 infants) and one prospective trial (22 patients and 5 infants). This case report highlights the need for more precise dosing recommendations in children, particularly in infants, and for smaller vials of the medication to facilitate more precise dosing. Such changes would ensure that adverse events are minimized and that the children with aHUS who are treated with eculizumab experience an optimal clinical response.

Successful Treatment of Multiple Angiomyolipomas with Sirolimus in a Child.

Tuberous sclerosis complex frequently results in the formation of renal angiomyolipomas (AMLs). Sirolimus (SIR) or everolimus can be used to treat large AMLs, although this treatment has rarely been described in children, particularly for multiple renal AMLs. A 15-year-old girl presented with bilateral severe chronic flank pain coinciding with increased renal size and hundreds of renal AMLs. We opted to treat her with SIR over the course of 3.5 years. Following her treatment, her renal size had substantially decreased and the AMLs had shrunk. The patient's pain subsided as well. Our case, which has never been described in published literature, demonstrates that a child with multiple renal AMLs can be treated with SIR, and suggests that this treatment may be a viable option for preventing the development of secondary morbidities such as chronic pain.

Skeletal findings in the first 12 months following initiation of glucocorticoid therapy for pediatric nephrotic syndrome.

UNLABELLED: Incident vertebral fractures and lumbar spine bone mineral density (BMD) were assessed in the 12 months following glucocorticoid initiation in 65 children with nephrotic syndrome. The incidence of vertebral fractures was low at 12 months (6 %) and most patients demonstrated recovery in BMD Z-scores by this time point. INTRODUCTION: Vertebral fracture (VF) incidence following glucocorticoid (GC) initiation has not been previously reported in pediatric nephrotic syndrome. METHODS: VF was assessed on radiographs (Genant method); lumbar spine bone mineral density (LS BMD) was evaluated by dual-energy X-ray absorptiometry. RESULTS: Sixty-five children were followed to 12 months post-GC initiation (median age, 5.4 years; range, 2.3-17.9). Three of 54 children with radiographs (6 %; 95 % confidence interval (CI), 2-15 %) had incident VF at 1 year. The mean LS BMD Z-score was below the healthy average at baseline (mean ± standard deviation (SD), -0.5 ± 1.1; p = 0.001) and at 3 months (-0.6 ± 1.1; p < 0.001), but not at 6 months (-0.3 ± 1.3; p = 0.066) or 12 months (-0.3 ± 1.2; p = 0.066). Mixed effect modeling showed a significant increase in LS BMD Z-scores between 3 and 12 months (0.22 SD; 95 % CI, 0.08 to 0.36; p = 0.003). A subgroup (N = 16; 25 %) had LS BMD Z-scores that were ≤-1.0 at 12 months. In these children, each additional 1,000 mg/m(2) of GC received in the first 3 months was associated with a decrease in LS BMD Z-score by 0.39 at 12 months (95 % CI, -0.71 to -0.07; p = 0.017). CONCLUSIONS: The incidence of VF at 1 year was low and LS BMD Z-scores improved by 12 months in the majority. Twenty-five percent of children had LS BMD Z-scores ≤-1.0 at 12 months. In these children, LS BMD Z-scores were inversely associated with early GC exposure, despite similar GC exposure compared to the rest of the cohort.

Antibody mediated rejection associated with complement factor h-related protein 3/1 deficiency successfully treated with eculizumab.

Antibody mediated rejection (AMR) activates the classical complement pathway and can be detrimental to graft survival. AMR can be accompanied by thrombotic microangiopathy (TMA). Eculizumab, a monoclonal C5 antibody prevents induction of the terminal complement cascade (TCC) and has recently emerged as a therapeutic option for AMR. We present a highly sensitized 13-year-old female with end-stage kidney disease secondary to spina bifida-associated reflux nephropathy, who developed severe steroid-, ATG- and plasmapheresis-resistant AMR with TMA 1 week post second kidney transplant despite previous desensitization therapy with immunoglobulin infusions. Eculizumab rescue therapy resulted in a dramatic improvement in biochemical (C3; creatinine) and hematological (platelets) parameters within 6 days. The patient was proven to be deficient in complement Factor H-related protein 3/1 (CFHR3/1), a plasma protein that regulates the complement cascade at the level of C5 conversion and has been involved in the pathogenesis of atypical hemolytic uremic syndrome caused by CFH autoantibodies (DEAP-HUS). CFHR1 deficiency may have worsened the severe clinical progression of AMR and possibly contributed to the development of donor-specific antibodies. Thus, screening for CFHR3/1 deficiency should be considered in patients with severe AMR associated with TMA.

Muscle force and power in obese and overweight children.

The study investigated differences in skeletal muscle function between obese and non-obese children using a force platform. Forty obese children and adolescents (age range 8 to 18 years; 21 girls) and 40 age- and sex-matched controls performed two tests: (1) single two-legged jump, a countermovement jump for maximal height; (2) multiple one-legged hopping on the forefoot, a test of maximal force. In the single two-legged jump, obese subjects had higher absolute peak force (1.62 kN vs 1.09 kN) and peak power (2.46 kW vs 2.06 kW), but lower body weight-related peak force (2.10 vs 2.33) and lower peak power per body mass (30.9 W/kg vs 41.6 W/kg). Jump height (29.3 cm vs 37.5 cm) and maximal vertical velocity (1.92 ms(-1) vs 2.31 ms(-1)) were reduced in obese children. In multiple one-legged hopping, obese subjects had 72% and 84% higher absolute peak force on the left and right foot, respectively. However, forces relative to body weight were 24% and 23% lower in the obese group than in the control group. In conclusion, obese children and adolescents have increased muscle force and power. This partly compensates for the effect of high body weight on muscle performance.

Skeletal findings in children recently initiating glucocorticoids for the treatment of nephrotic syndrome.

SUMMARY: Eighty children with nephrotic syndrome underwent lumbar spine densitometry and vertebral morphometry soon after glucocorticoid initiation. We found an inverse relationship between glucocorticoid exposure and spine areal bone mineral density (BMD) Z-score and a low rate of vertebral deformities (8%). INTRODUCTION: Vertebral fractures are an under-recognized complication of childhood glucocorticoid-treated illnesses. Our goal was to study the relationships among glucocorticoid exposure, lumbar spine areal BMD (LS BMD), and vertebral shape in glucocorticoid-treated children with new-onset nephrotic syndrome. METHODS: Lateral thoracolumbar spine radiography and LS BMD were performed in 80 children with nephrotic syndrome (median age 4.4 years; 46 boys) within the first 37 days of glucocorticoid therapy. Genant semiquantitative grading was used as the primary method for vertebral morphometry; the algorithm-based qualitative (ABQ) method was used for secondary vertebral deformity analysis. RESULTS: Six of the 78 children with usable radiographs (8%; 95% confidence interval 4 to 16%) manifested a single Genant grade 1 deformity each. All deformities were mild anterior wedging (two at each of T6, T7, and T8). Four of the 78 children (5%; 95% confidence interval 2 to 13%) showed one ABQ sign of fracture each (loss of endplate parallelism; two children at T6 and two at T8). Two of the children with ABQ signs also had a Genant grade 1 deformity in the same vertebral body. None of the children with a Genant or ABQ deformity reported back pain. An inverse relationship was identified between LS BMD Z-score and glucocorticoid exposure. CONCLUSIONS: Although we identified an inverse relationship between steroid exposure and LS BMD soon after glucocorticoid initiation for childhood nephrotic syndrome, there was only a low rate of vertebral deformities. The clinical significance of these findings requires further study.

Optimization of immunosuppressive drug monitoring in children.

BACKGROUND: The metabolism of drugs in children differs from adults, although pediatric pharmacokinetic (PK) studies remain scarce. Many of the drugs are metabolized by polymorphically expressed enzymes (cytochrome P450 [CYP450]; glucuronyl transferase [GT]) and/or transported by drug transporters (ABC and SLC families). In children, there is added complexity because of the age dependency of drug metabolism. This review addresses the age dependency of drug metabolism in childhood on the basis of routine PK monitoring. METHODS: Standard pharmacokinetic studies in pediatric renal transplant recipients were analyzed to study drug-drug interactions between mycophenolic acid and cyclosporine on the one hand, and tacrolimus and sirolimus on the other hand. The exposure was compared with age. We also studied sirolimus metabolites, both by mass spectrometry as well as using human liver microsomes. RESULTS: We demonstrated age dependency for MPA exposure. Independent of the concomitant medication, infants required approximately twice as much drug for the same exposure. The drug-drug interaction between sirolimus and tacrolimus demonstrated age dependency. Sirolimus metabolites showed a remarkably different pattern in children. Whereas 39-O-desmethyl sirolimus is the most prevalent metabolite in adults, we found 77.5% hydroxylated metabolites in children. Similarly, pediatric human liver microsomes produced 86.1% hydroxylated metabolites. CONCLUSIONS: Our long-term objective is to develop evidence-based guidelines for age-appropriate drug dosing of all drugs commonly used during childhood and adolescence, based on pharmacokinetically/pharmacogenetically determined drug exposure to maximize therapeutic yield while minimizing toxicity. The potential need for lifelong medications warrants efforts to minimize toxicity in chronically ill pediatric patients.

Value of therapeutic drug monitoring of MMF therapy in pediatric transplantation.

Therapeutic drug monitoring (TDM) is desirable whenever the desired drug effect cannot be predicted from a given dose, or when it is necessary to find a balance between the efficacy and toxicity of the drug. Children and adolescents particularly benefit from TDM, because dosing requirements are often not studied in the same detail as in adults. Also, drug-drug interactions are frequent. The gold standard for assessment of drug exposure is the area-under-the-curve (AUC) for a full pharmacokinetic profile. TDM for mycophenolic acid (MPA) is less well established. Monitoring of trough levels does not suffice because of enterohepatic recirculation of MPA after formation of its main metabolite, a glucoronide termed MPA-G. However, abbreviated sampling schemes specific to mycophenolate mofetil (MMF) correlate well with the AUC for MPA. Cyclosporine interacts with MPA by inhibiting the multidrug resistance-associated protein 2 (MRP2). Higher MPA concentrations result in a decreased two h concentration of cyclosporine, while higher cyclosporine exposure results in a lower MPA exposure. There are no drug interactions between tacrolimus and MPA, and lower doses of MMF are required in combination with tacrolimus. Steroids may induce the clearance of MPA, which could account in part for the increasing MPA exposure following transplantation. TDM has allowed for dosing recommendations of MMF in children, which could lead to improved efficacy and minimization of toxicities. It is important that these provisional target levels are validated in prospective studies. The above points clearly indicate that there is a role for TDM of MPA in pediatric transplant recipients.

Prevalence of complications in children with chronic kidney disease according to KDOQI.

The Kidney Disease Outcome and Quality Initiative (KDOQI) Group recommended guidelines for the monitoring and treatment of chronic kidney disease (CKD) in 2002. These recommendations were based on the prevalence of known complications as seen in adults. In children, the exact prevalence of these complications is unknown. We therefore conducted a cross-sectional study of 366 patients with CKD in a single center to analyze the prevalence of these complications across all stages of kidney disease. Patients were categorized to their KDOQI stage of CKD according to their estimated renal function as determined from serum cystatin C. Fifty seven percent of patients had CKD stage 1, 29.0% stage 2, 10.4% stage 3 and 4.1% stages 4+5. Uropathies (31%) were the most prevalent causes of CKD. Glomerular disease accounted for 27%. The overall prevalence of complications was as follows: hypertension 70.2%, anemia 36.6%, proteinuria 11.5%, and metabolic bone disease 16.9%. Metabolic bone disease and anemia occurred frequently, even with a glomerular filtration rate >60 ml/min/1.73 m2. Growth failure (11.5%) was also common and is not a component of the KDOQI guidelines for CKD in children. The prevalence of all complications increased with worsening stage of kidney disease (all P-values significant). In summary, this study supports the KDOQI guidelines in defining and staging CKD in children. This study also highlights the differences in the causes and complications that occur in CKD between adults and pediatrics. We recommend modification of the KDOQI guidelines for children to reflect the differences described in this paper.

Age-dependency of mycophenolate mofetil dosing in combination with tacrolimus after pediatric renal transplantation.

BACKGROUND: Dosing of mycophenolate mofetil (MMF) must be lower in combination therapy with Tacrolimus (Tac) than with Cyclosporine. One study with mostly adolescent recipients recommended an MMF dose of 250 mg/m2 BID. Because this dose resulted in low area-under-the-curve (AUC) in our infant population, we retrospectively analyzed all available pharmacokinetic (PK) profiles in pediatric renal transplant patients on MMF plus Tac therapy to propose appropriate MMF dosing in pediatric patients of all ages. PATIENTS AND METHODS: Forty-four PK profiles were performed in 27 patients (median age, 11.6 years; range, 1.8-20.7 years). The investigations were performed at a median of 299 days (range, 24-3424) after transplantation. Ten patients were converted to Tac plus MMF, all others received this as primary therapy. For patients with repeated measurements, we calculated the average AUC and doses. We used first-order PK modeling to calculate the doses for a mycophenolic acid (MPA) AUC of 60 ug*h/mL and a Tac AUC of 150 ng*h/mL. RESULTS: The mean Tac dose was 2.6 +/- 1.2 mg/m2/d or 0.086 +/- 0.038 mg/kg/d, resulting in an average AUC of 120.6 +/- 30.4 ng*h/mL. The MMF dose was not normally distributed; the median dose was 549 mg/m2/d (range, 146-1413) and the median MPA AUC was 49.8 ug*h/mL (range, 26.7-156.0). The mean dose for a Tac AUC of 150 ng*h/mL was 3.50 +/- 1.77 mg/m2/d (0.117 +/- 0.058 mg/kg) and was independent of age or time after transplantation. By contrast, we found a negative relationship between the dose per m2 (r2 = 0.29; P = 0.0038) or per kg (r2 = 0.58; P < .0001) required for an MPA AUC of 60 ug*h/mL and patient age. Converted and primary patients behaved identically. The dosing requirement decreased from 500 mg/m2 BID in 2-year-old patients to 250 mg/m2 in adolescents. There was substantial interpatient variability of 44%. CONCLUSIONS: Higher MMF doses are required for young children. Our data suggest a starting dose for infants of 500 mg/m2 BID, with PK monitoring of MPA due to substantial interpatient variability.

Resolution of severe, adolescent-onset hypophosphatemic rickets following resection of an FGF-23-producing tumour of the distal ulna.

Oncogenic hypophosphatemic osteomalacia (OHO) is an uncommon hypophosphatemic syndrome characterized by bone pain, proximal muscle weakness and rickets. It has been postulated that OHO results from overproduction of a humoral phosphaturic factor by an occult tumour. Recently, some OHO tumours have been shown to elaborate fibroblast growth factor-23 (FGF-23), which causes renal phosphate wasting when administered to mice. The purpose of this study was to undertake detailed investigations to confirm the diagnosis of OHO in a pediatric patient and to document the biochemical, radiographic and bone histological phenotype before and after tumour removal. We describe an 11-year-old, previously healthy girl with significant pain and functional disability associated with hypophosphatemic rickets. Circulating 1,25-(OH)(2) vitamin D was very low (14 pM; N: 40-140) while the FGF-23 serum level was markedly elevated [359.5 reference units (RU)/ml, N: 33-105]. An iliac bone biopsy revealed severe osteomalacia, but periosteocytic lesions, as are typical for X-linked hypophosphatemic rickets, were not seen. Sequence analyses of the PHEX and FGF23 genes were normal. A radiographic skeletal survey revealed a small exostosis of the left, distal ulnar metaphysis. A tumour was subsequently removed from this site and the pathology was consistent with benign, fibro-osseous tissue. Serum FGF-23 was normal when measured at 7 h post-operatively, while serum phosphate reached the low-normal range at 16 days following surgery. An iliac bone biopsy taken 5 months after the operation showed improvement, but not yet resolution, of the osteomalacia. Biochemical parameters of bone and mineral metabolism suggested that complete resolution of the osteomalacia was not achieved until 12 months following surgery. One year after tumour removal, the patient was pain-free and had resumed a normal level of activity. The rapid normalization of FGF-23 levels following removal of a benign tumour and the subsequent improvement in the biochemical and histological parameters of bone and mineral metabolism suggest that FGF-23 played a key role in this girl's disease.

Early dialysis in a neonate with intrauterine lisinopril exposure.

In general, angiotensin converting enzyme (ACE) inhibitors should be discontinued in pregnancy, as they can induce an ACE fetopathy. For the treatment of the latter, early peritoneal dialysis is recommended for in utero exposure to captopril and enalapril, although the outcome is poor. Early peritoneal dialysis has not previously been reported for lisinopril induced multiorgan failure. A case is reported in which treatment was given on postnatal day 3. The patient recovered from oligoanuria to almost normal renal function, and heart, brain, and musculoskeletal injury was reversible. This is despite relatively poor clearance of the drug through peritoneal dialysis. Analysis of the pharmacokinetic data suggests that haemodialysis or haemofiltration would be more efficacious for removal of the drug, and these treatments should be performed if available.

Tissue HHV6 and 7 determination in pediatric solid organ recipients--a pilot study.

Herpes virus infections remain a major challenge in solid organ transplantation. HHV6 and 7 blood viral load was associated with pathology after renal transplantation. Little is known about the significance of tissue HHV6 and 7 infections. A total of 18 tissue biopsies (13 kidney, three GI and two BAL) from nine pediatric transplant patients (five kidney, two liver, one combined liver and kidney and one bone marrow transplant) were subjected to blood HHV6 IgG and IgM testing. In addition, tissue HHV6 and 7 semi-quantitative PCR analysis with subsequent detection by ELISA and quantitative methods were applied to the same samples. We also studied four native kidney biopsies of children with other kidney disease. The results of the biopsies were correlated with clinical data. Of the transplant patients, 78% were HHV6 IgG positive. Six of nine had a positive IgM on at least one occasion, however, only two of nine transplant patients were symptomatic with a mixed CMV/EBV septic picture of multi-organ failure. Only these two patients had a significant tissue viral load for HHV6. Additionally, a very significant tissue viral load for HHV6 was detected in an immunocompromised patient 3 wk after a roseola-like febrile illness. The HHV6 copies were 31, 88 and 206 per 10 microL of DNA, respectively. In the patient who also had the fourth positive ELISA for HHV6 PCR product, the Multiplex PCR and restriction enzyme assay on its PCR product revealed a significant contribution by HHV7, while the HHV6-B signal was rather weak. Significant tissue HHV6 loads can be found in tissue biopsies from organ recipients with significant illness and also in native kidneys after primary infection. This may explain the high prevalence of HHV6 in transplanted kidneys. Further studies on HHV6 and 7 using molecular techniques should be supported.

Universal approach to pharmacokinetic monitoring of immunosuppressive agents in children.

Current data indicate that pharmacokinetic (PK) monitoring of cyclosporin microemulsion (CsA) should be performed using the 2-h concentration (C2), that tacrolimus (Tac) is commonly monitored using the trough level, and mycophenolate mofetil (MMF) should be monitored using the 1-h (C1), 2-h (C2) and 6-h (C6) concentrations. The three differing time-point requirements are cumbersome, and we aimed to develop universal guidelines for all three drugs using a large number of full PK profiles in children. One-hundred and twenty two stable pediatric patients, receiving either CsA (165 PK profiles, 69 patients, 24 with concomitant MMF) or Tac (122 PK profiles, 53 patients, 18 with MMF) were analyzed retrospectively. Pearson r for the CsA C2 was 0.90 [95% confidence interval(CI): 0.86-0.92], for Tac C2 r was 0.86 (95% CI: 0.80-0.90), and for MPA C2 r was 0.77 (95% CI: 0.68-0.83), respectively. For MPA, at least three time-points are required to accurately estimate the area under the concentration-time curve (AUC), and C1, C2 and C6 serve as best markers. Excellent AUC estimations could be obtained from a limited sampling strategy from C1, C2 and C6 or C0, C1, C2 and C4 with clinically acceptable errors for all three drugs. The AUC can be estimated with great precision by using an identical approach for all three drugs. Target AUCs for a given time-point after transplantation remain to be established.