Does kL/PCr estimate GFR, or does GFR determine k?

Optimizing dosing of the cycloserine pro-drug terizidone in children with rifampicin-resistant tuberculosis

There are no pharmacokinetic data in children on terizidone, a pro-drug of cycloserine and a World Health Organization (WHO)-recommended group B drug for rifampicin-resistant tuberculosis (RR-TB) treatment. We collected pharmacokinetic data in children <15 years routinely receiving 15-20 mg/kg of daily terizidone for RR-TB treatment. We developed a population pharmacokinetic model of cycloserine assuming a 2-to-1 molecular ratio between terizidone and cycloserine. We included 107 children with median (interquartile range) age and weight of 3.33 (1.55, 5.07) years and 13.0 (10.1, 17.0) kg, respectively. The pharmacokinetics of cycloserine was described with a one-compartment model with first-order elimination and parallel transit compartment absorption. Allometric scaling using fat-free mass best accounted for the effect of body size, and clearance displayed maturation with age. The clearance in a typical 13 kg child was estimated at 0.474 L/h. The mean absorption transit time when capsules were opened and administered as powder was significantly faster compared to when capsules were swallowed whole (10.1 vs 72.6 min) but with no effect on bioavailability. Lower bioavailability (-16%) was observed in children with weight-for-age z-score below -2. Compared to adults given 500 mg daily terizidone, 2022 WHO-recommended pediatric doses result in lower exposures in weight bands 3-10 kg and 36-46 kg. We developed a population pharmacokinetic model in children for cycloserine dosed as terizidone and characterized the effects of body size, age, formulation manipulation, and underweight-for-age. With current terizidone dosing, pediatric cycloserine exposures are lower than adult values for several weight groups. New optimized dosing is suggested for prospective evaluation.

Pharmacokinetics and optimized dosing of dispersible and non-dispersible levofloxacin formulations in young children

BACKGROUND

Levofloxacin is used for treatment and prevention of rifampicin-resistant (RR)-TB in children. Recent data showed higher exposures with 100 mg dispersible compared with non-dispersible tablet formulations with potentially important dosing implications in children. We aimed to verify and better characterize this finding.

METHODS

We conducted a crossover pharmacokinetic trial in children aged ≤5 years receiving levofloxacin RR-TB preventive therapy. Pharmacokinetic sampling was done after 15-20 mg/kg doses of levofloxacin with 100 mg dispersible and crushed 250 mg non-dispersible levofloxacin formulations. A population pharmacokinetic model was developed.

RESULTS

Twenty-five children were included, median (IQR) weight and age 12.2 (10.7-15.0) kg and 2.56 (1.58-4.03) years, respectively. A two-compartment model with first-order elimination and transit compartment absorption best described levofloxacin pharmacokinetics. Allometric scaling adjusted for body size, and maturation of clearance with age was characterized. Typical clearance in a 12 kg child was estimated at 4.17 L/h. Non-dispersible tablets had 21.5% reduced bioavailability compared with the dispersible formulation, with no significant differences in other absorption parameters.Dosing simulations showed that current recommended dosing for both formulations result in median exposures below adult-equivalent exposures at a 750 mg daily dose, mainly in children >6 months. Higher levofloxacin doses of 16-30 mg/kg for dispersible and 20-38 mg/kg for crushed non-dispersible tablets may be required in children >6 months.

CONCLUSIONS

The dispersible paediatric levofloxacin formulation has improved bioavailability compared with the crushed non-dispersible adult formulation, but exposures remain below those in adults. We propose optimized age- and weight-based dosing for levofloxacin, which require further evaluation.

Population Pharmacokinetic Model for Unbound Concentrations of Daptomycin in Patients with MRSA Including Patients Undergoing Hemodialysis

BACKGROUND AND OBJECTIVE

Unbound daptomycin concentrations are responsible for pharmacologically beneficial and adverse effects, although most previous reports have been limited to the use of total concentrations. We developed a population pharmacokinetic model to predict both total and unbound daptomycin concentrations.

METHODS

Clinical data were collected from 58 patients with methicillin-resistant Staphylococcus aureus including patients undergoing hemodialysis. A total of 339 serum total and 329 unbound daptomycin concentrations were used for model construction.

RESULTS

Total and unbound daptomycin concentration was explained by a model that assumed first-order distribution with two compartments, and first-order elimination. Normal fat body mass was identified as covariates. Renal function was incorporated as a linear function of renal clearance and independent non-renal clearance. The unbound fraction was estimated to be 0.066 with a standard albumin of 45 g/L and standard creatinine clearance of 100 mL/min. Simulated unbound daptomycin concentration was compared with minimum inhibitory concentration as a measure of clinical effectiveness and exposure-level-related induction of creatine phosphokinase elevation. The recommended doses were 4 mg/kg for patients with severe renal function [creatinine clearance (CLcr) ≤ 30 mL/min] and 6 mg/kg for patients with mild to moderate renal function (CLcr > 30 and ≤ 60 mL/min). A simulation indicated that dose adjusted by body weight and renal function improved target attainment.

CONCLUSIONS

This population pharmacokinetics model for unbound daptomycin could help clinicians to select the appropriate dose regimen for patients undergoing daptomycin treatment and reduce associated adverse effects.

Consistent methods for fat-free mass, creatinine clearance, and glomerular filtration rate to describe renal function from neonates to adults

Quantifying the effect of kidney disease on glomerular filtration rate (GFR) is important when describing variability in the clearance of drugs eliminated by the kidney. We aimed to develop a continuous model for renal function (RF) from prematurity to adulthood based on consistent models for fat-free mass (FFM), creatinine production rate (CPR), and GFR. A model for fractional FFM in premature neonates to adults was developed using pooled data from 4462 subjects and 2847 FFM observations. It was found that girls have an FFM higher than that predicted from adult women based on height, total body mass, and sex, and boys have an FFM lower than adult men until around the onset of puberty, when it approaches adult male values. Data from 108 subjects with measurements of serum creatinine (Scr) and GFR were used to construct a model for CPR. Creatinine clearance was predicted using a model for CPR (based on FFM, postmenstrual age, and sex) and Scr that avoids discontinuous predictions between neonates, children, and adults. Individual CPR may then be used with individual Scr to predict the estimated GFR (eGFR; eGFR = CPR/Scr). A previously published model for human GFR based on 1153 GFR observations in 923 subjects without known kidney disease was updated using the model for fractional FFM to predict individual size and age-consistent values for the expected normal GFR (nGFR). Individual renal function was then calculated using RF = eGFR/nGFR.

Pharmacokinetics and Dose Optimization Strategies of Para-Aminosalicylic Acid in Children with Rifampicin-Resistant Tuberculosis

Treatment options for children with Rifampicin-resistant tuberculosis (RR-TB) remain limited, and para-aminosalicylic acid (PAS) is still a relevant component of treatment regimens. Prevention of resistance to companion drugs by PAS is dose related, and at higher concentrations, PAS may exhibit significant bactericidal activity in addition to its bacteriostatic properties. The optimal dosing of PAS in children is uncertain, specifically for delayed-release granule preparations, which are the most used. A population pharmacokinetic model was developed describing PAS pharmacokinetics in children receiving routine RR-TB treatment. Model-based simulations evaluated current World Health Organization (WHO) weight-band doses against the adult pharmacokinetic target of 50 to 100 mg/liter for peak concentrations. Of 27 children included, the median (range) age and weight were 3.87 (0.58 to 13.7) years and 13.3 (7.15 to 30.5) kg, respectively; 4 (14.8%) were HIV positive. PAS followed one-compartment kinetics with first-order elimination and transit compartment absorption. The typical clearance in a 13-kg child was 9.79 liters/h. Increased PAS clearance was observed in both pharmacokinetic profiles from the only patient receiving efavirenz. No effect of renal function, sex, ethnicity, nutritional status, HIV status, antiretrovirals (lamivudine, abacavir, and lopinavir-ritonavir), or RR-TB drugs was detected. In simulations, target concentrations were achieved only using the higher WHO dose range of 300 mg/kg once daily. A transit compartment adequately describes absorption for the slow-release PAS formulation. Children should be dosed at the higher range of current WHO-recommended PAS doses and in a once-daily dose to optimize treatment.

Estimation of Total Creatinine Clearance is Unreliable in Children on Peritoneal Dialysis

Objective

To test the reliability of creatinine clearance in children on peritoneal dialysis (PD).

Design

Longitudinal, case-controlled.

Setting

Routine clinic visits at the pediatric dialysis unit of the Universitätskinderklinik of Vienna. Patients: Eleven children (2 -13 years, 10 -55 kg) with end-stage renal disease on PD.

Interventions

Creatinine clearance (CCr) was determined by measuring creatinine excretion (ECr) over 24 hours in both dialysate and urine. Each child had three to five separate measurements of their CCr. At the same time we also calculated the schwartz formula clearance from the patient's height and serum creatinine, using a modified correlate.

Main Outcome Measures

Reliability of CCr was assessed by two approaches. First, we compared each serial measurement with the mean value for each patient and thereby assessed the “intramethodical” variability. Second, we compared each CCr with the simultaneous formula clearance and assessed the “intermethodical” disagreement.

Results

Twenty-seven percent of the measurements of CCr were classified as unreliable based on a comparison with the mean value for each patient. Reliability was closely correlated with residual renal function (p < 0.01); only 12% of the measurements in the an uric patients were classified as unreliable (vs 31% in the patients with residual renal function). The simultaneous formula clearance was less variable than the CCr. The formula clearance had a sensitivity of 93% and a specificity of 60% for detecting unreliable values of CCr.

Conclusion

Estimation of total CCr is unreliable in pediatric patients on PD. A simultaneous formula clearance can be used to detect which values are unreliable.

Can We Improve Stavudine's Safety Profile in Children? Pharmacokinetics of Intracellular Stavudine Triphosphate with Reduced Dosing

Stavudine remains a useful replacement option for treatment for HIV⁺ children. WHO reduced the adult dose to 30 mg twice daily, which maintains efficacy and lowers mitochondrial toxicity. We explored intracellular stavudine triphosphate levels in children receiving a reduced dose of 0.5 to 0.75 mg/kg of body weight twice daily to investigate whether a similar dose optimization can safely be made. A population pharmacokinetic model was developed to describe the pharmacokinetics of intracellular stavudine triphosphate in 23 HIV⁺ children and 24 HIV⁺ adults who received stavudine at 0.5 mg/kg and 20 mg twice daily for 7 days, respectively. Simulations were employed to optimize the pediatric dosing regimen to match exposures in adults receiving the current WHO-recommended dose of 30 mg twice daily. A biphasic disposition model with first-order appearance and disappearance described the pharmacokinetics of stavudine triphosphate. The use of allometric scaling with fat-free mass characterized well the pharmacokinetics in both adults and children, and no other significant effect could be detected. Simulations of 30 mg twice daily in adults predicted median (interquartile range [IQR]) stavudine triphosphate minimum drug concentration (C _min) and maximum drug concentration (C _max) values of 13 (10 to 19) and 45 (38 to 53) fmol/10⁶ cells, respectively. Targeting this exposure, simulations in HIV⁺ children were used to identify a suitable weight-band dosing approach (0.5 to 0.75 mg/kg), which was predicted to achieve median (IQR) C _min and C _max values of 13 (9 to 18) and 49 (40 to 58) fmol/10⁶ cells, respectively. Weight-band dosing using a stavudine dose of 0.5 to 0.75 mg/kg is proposed, and it shows comparable exposures to adults receiving the current WHO-recommended dose of 30 mg twice daily. Our pharmacokinetic results suggest that the decreased stavudine dose in children >2 years would have a reduced toxic effect while retaining antiretroviral efficacy.

Drugs pharmacokinetics during veno-venous extracorporeal membrane oxygenation in pediatrics

Data evaluating pharmacokinetic/pharmacodynamic (PK/PD) aspect in the pediatric population are scarce especially regarding the pediatric intensive care unit. Dosing of frequently used drugs (sedatives, analgesics, antibiotics and cardiovascular drugs) are mainly based on non "pediatric intensive care unit (PICU)" patients, and sometimes are translated from adult patients. Among PICU patients, the most complex patients are the ones who are critically ill and are receiving mechanical circulatory/respiratory support for cardiac and/or respiratory failure. The use of extracorporeal membrane oxygenation is associated with major PK and PD changes, especially in neonates and children. The objective of this review is to assess the current literature for pediatric PK data in patients receiving extracorporeal membrane oxygenation (ECMO).

Pharmacokinetic variability due to environmental differences

This tutorial describes sources of pharmacokinetic variability that are not obviously linked to genetic differences. The sources of variability are therefore described as environmental. The major quantitative sources of environmental variability are body size (including body composition), maturation and organ function. Size should be considered in all patients. Maturation is mainly relevant to neonates and infants less than 2 years of age. Renal function is the most important predictable source of variability due to differences in organ function.

Estimating glomerular filtration rate (GFR) in children. The average between a cystatin C- and a creatinine-based equation improves estimation of GFR in both children and adults and enables diagnosing Shrunken Pore Syndrome

Estimating glomerular filtration rate (GFR) in adults by using the average of values obtained by a cystatin C- (eGFR_{cystatin C}) and a creatinine-based (eGFR_creatinine) equation shows at least the same diagnostic performance as GFR estimates obtained by equations using only one of these analytes or by complex equations using both analytes. Comparison of eGFR_{cystatin C} and eGFR_creatinine plays a pivotal role in the diagnosis of Shrunken Pore Syndrome, where low eGFR_{cystatin C} compared to eGFR_creatinine has been associated with higher mortality in adults. The present study was undertaken to elucidate if this concept can also be applied in children. Using iohexol and inulin clearance as gold standard in 702 children, we studied the diagnostic performance of 10 creatinine-based, 5 cystatin C-based and 3 combined cystatin C-creatinine eGFR equations and compared them to the result of the average of 9 pairs of a eGFR_{cystatin C} and a eGFR_creatinine estimate. While creatinine-based GFR estimations are unsuitable in children unless calibrated in a pediatric or mixed pediatric-adult population, cystatin C-based estimations in general performed well in children. The average of a suitable creatinine-based and a cystatin C-based equation generally displayed a better diagnostic performance than estimates obtained by equations using only one of these analytes or by complex equations using both analytes. Comparing eGFR_cystatin and eGFR_creatinine may help identify pediatric patients with Shrunken Pore Syndrome.

Paediatric pharmacokinetics: key considerations

A number of anatomical and physiological factors determine the pharmacokinetic profile of a drug. Differences in physiology in paediatric populations compared with adults can influence the concentration of drug within the plasma or tissue. Healthcare professionals need to be aware of anatomical and physiological changes that affect pharmacokinetic profiles of drugs to understand consequences of dose adjustments in infants and children. Pharmacokinetic clinical trials in children are complicated owing to the limitations on blood sample volumes and perception of pain in children resulting from blood sampling. There are alternative sampling techniques that can minimize the invasive nature of such trials. Population based models can also limit the sampling required from each individual by increasing the overall sample size to generate robust pharmacokinetic data. This review details key considerations in the design and development of paediatric pharmacokinetic clinical trials.

Clinical and ultrasonographical characterization of childhood cystic kidney diseases in Egypt

BACKGROUND

Renal cystic disorders (RCD) constitute an important and leading cause of end-stage renal disease (ESRD) in children. It can be acquired or inherited; isolated or associated with extrarenal manifestations. The precise diagnosis represents a difficult clinical challenge.

METHODS

The aim of this study was to define the pattern of clinical phenotypes of children with renal cystic diseases in Pediatric Nephrology Center, Cairo University. We have studied the clinical phenotypes of 105 children with RCD [45 (43%) of them had extrarenal manifestations].

RESULTS

The most common disorders were the presumably inherited renal cystic diseases (65.7%) mainly nephronophthisis and related ciliopathies (36.2%), as well as polycystic kidney diseases (29.5%). Moreover, multicystic dysplastic kidneys accounted for 18% of study cases. Interestingly, eight syndromic cases are described, yet unclassified as none had been previously reported in the literature.

CONCLUSION

RCD in this study had an expanded and complex spectrum and were largely due to presumably inherited/genetic disorders (65.7%). Moreover, we propose a modified algorithm for clinical and diagnostic approach to patients with RCD.

Understanding dosing: children are small adults, neonates are immature children

Paediatric dose cannot be scaled down directly from an adult using weight (eg, mg/kg). This results in a dose too small in infants and children because elimination does not change in direct proportion to weight, and a dose too large in neonates whose drug elimination pathways are immature. The goal of treatment is a desired response (the target effect). An understanding of the concentration-response relationship (pharmacodynamics) can be used to predict the target concentration required to achieve this target effect. Pharmacokinetic knowledge then determines the target dose that will achieve the target concentration. Variability associated with both pharmacokinetics and pharmacodynamics can be reduced by demographic information (covariates), which can be used to help predict the target dose in a specific child. The covariates of size, maturation and organ function are the three principle contributors to pharmacokinetic variability. Children (2 years postnatal age or older) are essentially similar to adults (ie, mature) and differ only in size. Maturation processes are only important in neonates and infants, therefore, this cohort can be viewed as immature children. Paediatric pharmacodynamic studies are fewer than pharmacokinetic studies, but are required to elucidate the target concentration and consequent dose. The lack of pharmacodynamic studies is a serious challenge for rational dosing.

A pharmacokinetic standard for babies and adults

The pharmacokinetic behavior of medicines used in humans follows largely predictable patterns across the human age range from premature babies to elderly adults. Most of the differences associated with age are in fact due to differences in size. Additional considerations are required to describe the processes of maturation of clearance processes and postnatal changes in body composition. Application of standard approaches to reporting pharmacokinetic parameters is essential for comparative human pharmacokinetic studies from babies to adults. A standardized comparison of pharmacokinetic parameters obtained in children and adults is shown for 46 drugs. Appropriate size scaling shows that children (over 2 years old) are similar to adults. Maturation changes are generally completed within the first 2 years of postnatal life; consequently babies may be considered as immature children, whereas children are just small adults.

Novel multidrug therapy for children with cyclosporine-resistant or -intolerant nephrotic syndrome

An effective treatment for children with refractory nephrotic syndrome (NS), especially in those with cyclosporine (CsA)-resistant or CsA-intolerant NS, has yet to be established. Recently, the efficacy of multidrug therapy consisting of tacrolimus (Tac), mycophenolate mofetil (MMF) in combination with prednisolone (PDN) in adult patients with refractory NS has been reported. We successfully treated 14 consecutive children with refractory CsA-resistant or CsA-intolerant NS using combination therapy consisting of relatively low-dose Tac, mizoribine (MZR), which has a mechanism of action very similar to that of MMF, and PDN. There were no serious clinical toxicities. Of the 14 children, 9 with a mean age of 13.0 years had steroid-dependent NS (SDNS) and 5 with a mean age of 9.6 years had steroid-resistant NS (SRNS). All SDNS patients had minimal change disease (MCD), 4 with SRNS had focal segmental glomerulosclerosis (FSGS), and the remaining child had MCD on renal biopsy. All patients were in a prospective cohort, but were evaluated retrospectively. The mean follow-up from the initiation of multidrug therapy was 18.4 months in SDNS and 18.6 months in SRNS patients. At the last observation point, the calculated relapse rate and minimum dose of PDN required for maintenance of clinical remission after the start of multidrug therapy were significantly decreased compared with those prior to this therapy, while on CsA, in SDNS patients (0.4 ± 0.5 times/year vs 2.9 ± 1.5 times/year, P = 0.0077, and 0.3 ± 0.2 mg/kg on alternate days vs 0.5 ± 0.2 mg/kg on alternate days, P = 0.0184 respectively). All SDNS and two SRNS patients (40%) achieved complete remission, allowing further decreases in the minimal doses of PDN required for maintenance of clinical remission in most our patients. However, one patient with FSGS remained refractory to multidrug therapy and subsequently developed end-stage renal disease. These clinical observations, although preliminary and involving a small number of patients, suggest that multidrug therapy consisting of relatively low-dose Tac, MZR, and PDN might be effective and safe for treating children with refractory CsA-resistant or CsA-intolerant NS. However, further studies involving larger numbers of patients are needed.

Effects of valproic acid on organic acid metabolism in children: a metabolic profiling study

Young children are at increased risk for valproic acid (VPA) hepatotoxicity. Urinary organic acid profiles, as a measure of mitochondrial function, were obtained in children 3.5 to 17.3 years old treated for seizure disorders with valproic acid (VPA; n=52). Age-matched patients treated with carbamazepine (CBZ; n=50) and untreated healthy children (n=22) served as controls. Age-related changes in organic acid profiles were observed in all three groups. Although untreated and CBZ control subjects were not distinguished by the principal component analysis (PCA) scores plot, a distinct boundary was apparent between the VPA and control/CBZ groups. Inter-individual variability in VPA-induced alterations in endogenous pathways reflecting branched chain amino acid metabolism and oxidative stress was observed. The data suggest that more detailed metabolomic analysis may provide novel insights into biological mechanisms and predictive biomarkers for children at highest risk for serious toxicity.

Benefits of once-daily administration of cyclosporine a for children with steroid-dependent, relapsing nephrotic syndrome

Cyclosporine A (CsA) is an effective steroid-sparing agent for patients with steroid-dependent, relapsing nephrotic syndrome (SDRNS). The efficacy and safety of single-daily dose administration (SDD protocol) of CsA in selected patients with SDRNS has been reported. However, the efficacy of initial CsA treatment for children with SDRNS using the SDD protocol remains to be elucidated. The SDD protocol might be associated with lower clinical toxicity, compared to the conventional twice-daily dose administration (TDD protocol). Here we evaluated the efficacy and safety of the SDD protocol versus the TDD protocol in patients with SDRNS. The data from 19 patients (9.9 +/- 4.2 years old) were retrospectively collected and analyzed. Ten patients treated according to the SDD protocol for a mean of 27 months (SDD group), while 9 patients treated with the TDD protocol for a mean of 35 months (TDD group) as an initial CsA treatment. Although the mean daily CsA dose was significantly lower in the SDD group (1.5 +/- 0.4 mg/kg/day vs. 3.7 +/- 0.7 mg/kg/day, P < 0.01), there were no differences between the two groups in the mean minimum dose of prednisolone required for maintenance of clinical remission nor in the calculated relapse rate. One patient in the TDD group developed biopsy-proven mild CsA nephrotoxicity, whereas no patient in the SDD group showed nephrotoxicity. Despite a small number of patients, this study may support that the SDD protocol is at least as effective as the conventional TDD protocol, and is more cost-effective for selected children with SDRNS.

Effect of malnutrition on serum creatinine and cystatin C levels

The concentration of cystatin C has been shown to be independent of age, gender and height, but the effect of malnutrition has not been studied. Levels of serum creatinine and cystatin C were estimated in 77 malnourished and 77 normally nourished boys between 2 years and 6 years of age without evidence of renal disease. The mean (95% confidence interval) serum creatinine level in the malnourished boys was significantly lower than that in the normally nourished boys [0.42 (0.38-0.45) mg/dl and 0.51 (0.48-0.55)] mg/dl, respectively, (P < 0.01)]. The mean level of serum cystatin C was 1.05 (0.94-1.17) mg/l and 1.12 (1.01-1.24) mg/l, respectively, in normally nourished and malnourished boys (P = 0.35). Mean glomerular filtration rate (GFR) estimated by the Schwartz equation in the malnourished boys was significantly higher than that in normally nourished children [141.8 (123.3-160.2) ml/min per 1.73 m(2) body surface area and 119.4 (109.3-129.5) ml/min per 1.73 m(2) body surface area], respectively (P = 0.04). However, the mean cystatin C-derived GFR was similar in the malnourished and normally nourished boys [99.70 (85.8-113.5) ml/min per 1.73 m(2) and 109.2 (94.4-124.0) ml/min per 1.73 m(2)], respectively (P = 0.35). The mean bias between GFR estimates using Bland and Altman analysis was greater in the malnourished children than in the normally nourished children (32.3% and 17.6%, respectively) (P = 0.15). Serum creatinine levels are lower in malnourished children and lead to overestimation of GFR, while cystatin C levels are unaffected.

Intérêt de la cystatine C pour l’adaptation de posologie des médicaments anticancéreux à élimination rénale

Cystatin C is a protein freely filtered in the renal glomerulus, then reabsorbed and completely metabolised within the tubular cells. The possibility to predict the clearance of compounds eliminated by the kidneys (and then to control their interindividual variability) was evaluated for two cytotoxic drugs (carboplatin and topotecan) in adults and EDTA (ethylene diamine tetraacetic acid), a compound used to determine the glomerular filtration rate in children. The population pharmacokinetic approach based on NONMEM program was used. For each of the three compounds, the cystatin C serum level was better predictive of clearance than that of creatinine. Moreover, for carboplatin and EDTA, the best equation between clearance and patients' characteristics included both cystatin C and creatinine level. A generalisation of cystatin C assay would contribute to standardise the clinical practices in Oncology.

Glomerular filtration rate via plasma iohexol disappearance: pilot study for chronic kidney disease in children

To guide the design of a nation-wide cohort study of chronic kidney disease in children, we determined how iohexol plasma disappearance curves could be used in children to measure glomerular filtration rate (GFR). Iohexol (5 ml) was administered intravenously and blood samples were obtained at 10, 20, 30, 60, 120, 240, 300, and 360 min after injection (N=29) and assayed by high performance liquid chromatography. Four urines were also collected following the injection. Intra-assay coefficient of variation (CV) in serum was 1.3% at 100 mg/l, 2.6% at 15 mg/l, and 3.4% for duplicate unknowns. GFR(9) was computed from iohexol dose and area under the nine-point blood disappearance curve, using double exponential modeling. Only 2.8% of 254 data points deviated by >3 CV from the curves. GFR(4) calculated from 10, 30, 120, and 300 min points correlated well with GFR(9) (r=0.999) and showed no bias (means+/-s.d. of GFR(9) and GFR(4)=59.3+/-36.3 and 59.4+/-36.0 ml/min per 1.73 m(2)). Relationship of GFR(9) and one-compartment GFR followed quadratic equation as previously reported by Brochner-Mortensen, allowing GFR to be calculated from 120 and 300 min points. This GFR(2) correlated well with GFR(9) (r=0.986). Estimated GFR from Schwartz height/creatinine formula correlated with GFR(9)(r=0.934) but overestimated GFR by 12.2 ml/min per 1.73 m(2). Urine iohexol clearance was poorly correlated (r=0.770) with GFR(9) owing to variability in urine collections (median CV=24%). GFR can be measured accurately using four-point iohexol plasma disappearance (in most cases, two points suffice); estimated GFR and urinary clearances are less useful.

GFR is better estimated by considering both serum cystatin C and creatinine levels

Serum cystatin C (cysC) is a potential marker of the glomerular filtration rate (GFR) that has generated conflicting reports in children. A prospective study was conducted to assess the benefit of considering cysC together with serum creatinine (SCr) and demographic and morphologic characteristics to better estimate the 51Cr-ethylenediaminetetraacetate (EDTA) clearance (CL), i.e., the GFR. Plasma 51Cr-EDTA data from 100 children or young adults (range: 1.4-22.8 years old) were analyzed according to the population pharmacokinetic approach by using the nonlinear mixed effects model (NONMEM) program. The actual CL was compared to the CL predicted according to different covariate equations. The best covariate equation (+/-95% confidence interval) was: GFR (ml/min)=63.2(+/-3.4) . [(SCr (microM)/96)(-0.35 (+/-0.20))] . [(cysC (mg/l)/1.2)(-0.56 (+/-0.19))] . [(body weight (kg)/45)(0.30 (+/-0.17))] . [age (years)/14)(0.40 (+/-0.16))]. This equation was associated with a less biased and more precise estimation than the Schwartz equation. CysC improves the estimation of the GFR in children if considered with other covariates within the mathematical formula.

Independent risk factors for chronic cyclosporine induced nephropathy in children with nephrotic syndrome

BACKGROUND

Cyclosporine A (CsA) has been widely used in children with steroid dependent and steroid resistant nephrotic syndrome (NS) because of its efficacy in relieving these patients from systemic side effects of steroids. However, its long term use is controversial, since chronic CsA induced nephropathy (CsAN) may develop in a considerable number of patients.

AIMS AND METHODS

In order to clarify the risk factors for the development of CsAN, the clinical characteristics of children with steroid dependent or steroid resistant NS taking CsA (target blood trough levels 50-150 ng/ml) for more than six months, managed at a single centre, were retrospectively analysed.

RESULTS

Thirteen of 30 children (24 boys and 6 girls) taking CsA (mean duration 43 months, range 6-144) had CsAN defined as the presence of CsA associated arteriopathy with or without striped tubulointerstitial lesions. The multivariate analysis revealed that CsA treatment for more than 36 months and an age younger than 5 years at the start of CsA treatment were independent risk factors for the development of CsAN. The univariate analysis also showed that patients with CsAN had more frequent relapses during CsA treatment than those without CsAN.

CONCLUSION

An alternative treatment should be seriously considered after a 36 month administration of CsA in order to prevent CsAN. Data also suggest that CsA treatment in children younger than 5 years should be avoided if possible.

Renal biopsy findings in children receiving long-term treatment with cyclosporine a given as a single daily dose

Long-term treatment of childhood nephrotic syndrome (NS) and rheumatic diseases with cyclosporine A (CsA) given as a single daily dose may yield better results and allow safer use of the drug than the conventional twice-daily dosing. However, the safety of such long-term treatment from the histological standpoint remains to be established. Posttreatment renal biopsy was conducted in a total of eight children (5 with minimal change NS, 2 with focal segmental glomerulosclerosis and 1 with X-linked immune dysregulation, polyendocrinopathy and enteropathy) receiving CsA as a single daily dose, after a mean treatment duration of 20 months (9-36 months). The initial daily dose of CsA (Neoral) was 2.0 mg/kg, given as a single daily dose before breakfast. The dose was subsequently adjusted to achieve a peak (between 1 and 2 hrs post-dosing, C1-C2) blood level of around 800 ng/ml. The mean daily CsA dose, mean C1-C2 blood level, and mean trough blood level in the subjects were 1.9 +/- 0.6 mg/kg, 803.8 +/- 117.2 ng/ml and 36.1 +/- 12.7 ng/ml, respectively. The result revealed no evidence of CsA-related nephrotoxicity, including arteriopathy, striped interstitial fibrosis or tubular atrophy, in any of the study participants. Also, no significant changes were observed in the mean estimated glomerular filtration rate as compared to the pretreatment values (127.6 +/- 14.9 ml/min/1.73 m(2) vs 115.6 +/- 22.8 ml/min/1.73 m(2), and except for mild hypertrichosis, no significant adverse effects of CsA were observed. These findings lend further support to the safety of long-term low-dose CsA treatment (median treatment duration in this study, 20 months), with the drug administered as a single daily dose while maintaining a peak (C1-C2) blood level of around 800 ng/ml.

Estimation of the glomerular filtration rate in children: which algorithm should be used?

Glomerular filtration rate (GFR) in children can be estimated by the formula GFR=k x BH/Pcr (where BH is body height in centimetres and Pcr is the plasma creatinine concentration in micromoles per litre). For k, several values have been reported: k=38 (Counahan), k=40 (Morris) and k=48.7 (Schwartz). In this study the predictive performance of these formulae was compared with that of newly developed formulae. GFR measurements based on inulin concentration time curves were divided into an index (n=58) and a validation data set (n=48). In the index data set a value for k was derived by application of nonlinear mixed-effect modelling. This approach was also used to develop a formula that better explained the relationship between patient factors and GFR. Bias and precision of all formulae were calculated for the validation data set. In the index data set a value of 41.2 was found for k, which was close to the value k=40 (Morris). Both formulae estimated GFR well (bias <5%; precision 25%). Further modelling of the relationship between patient factors and GFR did not improve the predictive performance. In our hospital GFR was best estimated by the formula with k=40 and k=41.2. It is recommended that the optimal value for k be assessed locally.

Comparison of two formulae for estimation of glomerular filtration rate in children

Glomerular filtration rate (GFR) was measured in 216 studies in 151 children using the cimetidine protocol. This was compared with the GFR calculated using Léger's pharmacokinetic equation and with that calculated using k*L/[Cr](s )(constant x length in centimeters divided by serum creatinine concentration). The GFR calculated using the equation GFR=k*L/[Cr](s) yielded a closer approximation to the measured GFR than that using Léger's pharmacokinetic equation. Currently there is focus on screening children for decreased GFR to identify those with asymptomatic chronic kidney disease at a time when intervention may delay progression to chronic renal failure. This study showed close approximation of the calculated GFR with the measured GFR using the equation GFR=k*L/[Cr](s), when the values for k were determined in the laboratory in which creatinine was measured.

The ratio of urinary cystatin C to urinary creatinine for detecting decreased GFR

Glomerular filtration rate (GFR) and urine and serum concentrations of cystatin C and creatinine were measured in 40 boys and 42 girls. The fractional excretion of cystatin C (FE Cyst C) increased in proportion to the decrease in GFR. Since serum creatinine concentration (S-Creatinine) in the numerator of the fractional excretion equation and serum cystatin C concentration (S-Cystatin C) in the denominator have similar numerical values, they cancel out. The result is an equation in which the FE Cyst C is equal to the ratio of urinary cystatin C to urinary creatinine (u[cystatin-C/Cr]). The ratio of u[cystatin C/Cr] was compared with GFR. Using a receiving operating characteristic (ROC) plot, the data showed that a ratio of u[cystatin C/Cr]*100 that is > or =0.100 has a sensitivity of 90.0% for identification of children with GFR < or =60 ml/min per 1.73 m(2). The false-positive rate is 16.1%. The u[cystatin C/Cr] ratio is a reliable screening tool for detecting decreased GFR that does not require a serum sample.

Predicting GFR in children and adults: a comparison of the Cockcroft-Gault, Schwartz, and modification of diet in renal disease formulas

BACKGROUND

A rapid prediction of glomerular filtration rate (GFR) is often needed in clinics. Formulas based on plasma creatinine level are being increasingly used, Schwartz for children, supposed to give GFR; Cockcroft-Gault for adults, supposed to indicate the creatinine clearance; and a recent formula introduced by the Modification of Diet in Renal Disease (MDRD) group. Our objective was to test whether one single formula could suffice and which one gives the best estimation of GFR.

METHODS

In 198 children (with two kidneys, single kidney, or renal transplant) and 116 adults (single kidney and transplanted), we measured inulin clearance and creatinine clearance and calculated Cockcroft-Gault, MDRD and, in children only, Schwartz. Data were compared with analysis of variance (ANOVA), regression statistics, and concordance studies.

RESULTS

In patients over 12 years of age, Cockcroft-Gault was almost similar to GFR corrected for body surface and creatinine clearance exceeded GFR by more than 20%; Schwartz was above creatinine clearance excepted for transplanted children. In younger children, no prediction approached GFR. Predictions were well correlated with GFR, but concordance studies showed Schwartz with dispersed results and GFR overestimated (20 mL/min/1.73 m2); Cockcroft-Gault was close to GFR and results were dispersed; MDRD in children gave a large overestimation and badly dispersed results; in transplanted adults its prediction was good.

CONCLUSION

Cockcroft-Gault prediction could be used for children over 12 years of age and adults; it should not be considered as creatinine clearance but as GFR corrected for body surface, it is merely a prediction, 95% of the results are between +/-40 mL/min/1.73 m(2) in children and +/-30 mL/min/1.72 m(2) in adults. In younger children no formula is satisfying.

Simple estimation of the glomerular filtration rate in sick Thai children

The objective of this study was to establish an appropriate formula for the estimation of creatinine clearance (CCr) in sick Thai children, and to evaluate the accuracy of using the Schwartz formula. Children aged between 0 and 19 years with various diseases and varying levels of renal function (but remained stable) were studied. Height in centimetres (L) and weight in kilograms (W), time of urine collection and urine volume were measured to provide urine flow (mL/min (V)) measurements. Body surface area (m2; SA) was also assessed. Quantitative urinary and plasma creatinine concentration (UCr and PCr, respectively) were determined. Creatinine clearance was calculated by using the following formula: UCr x V x 1.73/(PCr x SA). The linear association between CCr and L/PCr derived from these data was compared with the Schwartz formula by using bootstrap statistics. One-hundred and sixty children were studied. A least squares straight-line regression through the origin of CCr against L/PCr provided a good fit to the data. Our dataset revealed no evidence of an age or sex affect on the relationship. Creatinine clearance was estimated by using the following formula: 0.465 x (L/PCr), in which the calculated 95% confidence interval of the coefficient was 0.44-0.49. A comparison of this coefficient with that for the Schwartz formula for children aged > or =1 year (0.55), using 1000 bootstrapped resamples, showed an incompatibility between the two coefficients (P < 0.00005). In conclusion, we suggest estimating CCr in sick Thai children of either sex by using a modification of the Schwartz formula in which the coefficient equals 0.465.

Urate-oxidase in the prevention and treatment of metabolic complications in patients with B-cell lymphoma and leukemia, treated in the Société Française d'Oncologie Pédiatrique LMB89 protocol

PURPOSE

To evaluate the frequency of metabolic complications and dialysis due to tumor lysis syndrome in patients with B-cell advanced-stage non-Hodgkin's lymphoma (NHL) and L3 leukemia at initiation of chemotherapy including the use of urate-oxidase.

PATIENTS AND METHODS

Retrospective review of the clinical records of 410 patients with stage III and IV B-cell NHL and L3 leukemia treated in France and prospectively registered in the LMB89 protocol.

RESULTS

During the first week of chemotherapy, only 34 of 410 patients recorded metabolic problems that included hypocalcemia (< 70 mg/dl) in 24 patients, hyperphosphatemia (> 6.5 mg/dl) in 28 and elevation of creatinine > or = 2 SD in 16. Six patients underwent dialysis for life-threatening problems and a seventh as a preventive measure. In the other 27 cases, metabolic problems were successfully resolved using urate-oxidase in combination with alkaline hyperhydration. Among the 410 patients, one case of hemolysis was reported and there was no severe allergic reaction to urate-oxidase.

CONCLUSIONS

Only 1.7% of patients in our study receiving urate-oxidase during their induction chemotherapy needed renal dialysis. Urate-oxidase was well tolerated, and used as prophylaxis and/or treatment of hyperuricemia and tumor lysis syndrome consistently gave a lower rate of renal and metabolic complications than in other series of similar patients.

An infant case of bilateral small kidneys with both proximal and distal tubular dysfunction

A male infant with bilateral small kidneys associated with both proximal and distal tubular dysfunction, who showed chronic renal failure soon after birth, is reported. He was also noted to have both proximal and distal type of renal tubular acidosis. The small kidneys were thought to be due to renal hypodysplasia associated with bilateral severe vesicoureteral reflux, by radiological findings. An alkalization therapy with chemoprophylaxis seemed to be of benefit in slowing the progression of renal failure in this case.

Randomised multicentre study of a low-protein diet on the progression of chronic renal failure in children. European Study Group of Nutritional Treatment of Chronic Renal Failure in Childhood

BACKGROUND

Some studies have suggested that a low-protein diet slows the deterioration of renal function in patients with chronic renal failure (CRF). The effects of a low-protein diet on renal function and growth, have not been assessed in a large, prospective randomised trial in children with CRF.

METHODS

A 2-year prospective, stratified, and randomised multicentre study recruited 191 patients aged 2-18 years. After a run-in period of at least 6 months, patients were stratified into either a progressive or non-progressive category based on the change in creatinine clearance in this period. The patients were also stratified into three renal-disease categories and then randomly assigned to a control or diet group. In the diet group, the protein intake was the lowest, safe WHO recommendation--i.e., 0.8-1.1 g/kg daily adjusted for age. All patients were advised to have a calorie intake of at least 70% of the WHO recommendations. Glomerular filtration rate (GFR) was measured every 2 months by creatinine clearance; dietary compliance was checked by urinary urea-nitrogen excretion and dietary diaries (weighing method). 112 patients completed an optional third year of the study.

FINDINGS

The low-protein diet did not affect growth. However, there was no effect of diet on the mean decline in creatinine clearance over 2 years (diet vs control: progressive group -9.7 [SD 8.0] vs -10.7 [11.8] mL/min per 1.73 m2; non-progressive group -2.5 [7.5] vs -4.3 [10.0] mL/min per 1.73 m2). Patients classified as having progressive disease were older and had a lower creatinine clearance and a higher blood pressure at randomisation, and had a greater decrease in creatinine clearance than non-progressive patients. On multivariate regression analysis proteinuria (partial R2 = 0.259) and systolic blood pressure (partial R2 = 0.087) were independent predictors of the change in GFR. Similar results were found after the study was extended for a third year.

INTERPRETATION

A low-protein diet for 3 years did not affect the decrease in renal function in children with CRF. Proteinuria and blood pressure explain a large part of the variability of, and may be causally related to the decline in the GFR.

Validity of random urines to quantitate proteinuria in children with human immunodeficiency virus nephropathy

Accurate assessment of proteinuria in pediatric patients infected with the human immunodeficiency virus (HIV) is limited by constraints imposed by timed urine collections and low creatinine excretion in very ill patients with low muscle mass. We therefore sought to validate the use of random urine specimens to quantitate total protein and creatinine excretion in a population of 236 HIV-positive children. A mathematical derivation for estimating urine volume (V) was constructed. The accuracy of the final calculation [V = 832 (kL/Ucr)BSA] (where k = constant, L body length, UCr urine creatinine and BSA body surface area) was tested by regression analysis comparing the calculated and measured volume of 31 urines from ambulatory HIV-negative patients. The correlation coefficient was highly significant (r = 0.77, P < or = 0.0001). The relationship was also applied to 23 timed urine specimens from HIV-positive patients with similar significance (r = 0.87, P < 0.0001). A regression analysis of measured proteinuria against the urine protein: creatinine ratio (Upr/Ucr) in these same urines from the HIV-positive patients yielded a significant relationship both in the linear (r = 0.95, y = 0.4x) and the logarithmic regression (r = 0.97, y = x + 0.4). These data support the use of random Upr/Ucr ratios to estimate daily proteinuria in HIV-infected pediatric patients despite low creatinine excretion rates. The previously accepted values continue to apply, with Upr/Ucr < or = 2.0 considered normal and > 2.0 representative of nephrotic proteinuria.

Evaluation of clinical and laboratory parameters during 2 years of growth hormone treatment in prepubertal children with chronic renal failure

Twelve prepubertal children with chronic renal failure (CRF) were treated with human growth hormone (GH) (1.2 IU/kg/week) for 2 years. High doses of GH clearly increased growth velocity, from 3.8 +/- 1.3 to 9.6 +/- 1.5 (P = 0.0001) and 6.9 +/0 0.8 cm/year (P = 0.0001) after the 1st and 2nd year of treatment, respectively, leading to a mean height gain of 1.4 SD. During the 1st year of treatment the height increment, expressed in SDS, correlated negatively with chronological age (P = 0.003). Basal insulin-like growth factor 1 (IGF 1) levels were normal or elevated (7/12 patients) and correlated positively with the overnight integrated GH concentration (r = 0.68, P < 0.001). Basal insulin-like growth factor binding protein 3 (IGF-BP3) levels were elevated in 8/12 patients. GH induced a significant increase in IGF 1 and IGF-BP3 levels; IGF 1 peaked after 6 months (when growth velocity was optimal) and IGF-BP3 peaked after 12 months. The mean glomerula filtration rate, measured by inulin clearance and corrected for body surface area, fell after the 1st year of treatment, and significantly so at the end of the 2nd year (P = 0.02).

CONCLUSION

Early initiation of GH therapy during CRF may prevent severe growth retardation and allow these children to attain normal height before dialysis and transplantation.

Nephrocalcinosis and nephrolithiasis in infants with congestive heart failure treated with furosemide

Nephrocalcinosis and nephrolithiasis developed in five children after furosemide therapy for congestive heart failure. In four children renal calcifications were detected by ultrasonography and in one by autopsy. Discontinuation of the loop diuretic in three children resulted in resolution of the calcifications in two of the patients. Residual renal morbidity included reduced creatinine clearance, microscopic hematuria, and hypercalciuria. The phenomenon of renal calcifications associated with furosemide treatment is more frequent than previously recognized.