Sevelamer controls parathyroid hormone-induced bone disease as efficiently as calcium carbonate without increasing serum calcium levels during therapy with active vitamin D sterols

Diagnosis and management of mineral and bone disorders in infants with CKD: clinical practice points from the ESPN CKD-MBD and Dialysis working groups and the Pediatric Renal Nutrition Taskforce

BACKGROUND

Infants with chronic kidney disease (CKD) form a vulnerable population who are highly prone to mineral and bone disorders (MBD) including biochemical abnormalities, growth retardation, bone deformities, and fractures. We present a position paper on the diagnosis and management of CKD-MBD in infants based on available evidence and the opinion of experts from the European Society for Paediatric Nephrology (ESPN) CKD-MBD and Dialysis working groups and the Pediatric Renal Nutrition Taskforce.

METHODS

PICO (Patient, Intervention, Comparator, Outcomes) questions were generated, and relevant literature searches performed covering a population of infants below 2 years of age with CKD stages 2-5 or on dialysis. Clinical practice points (CPPs) were developed and leveled using the American Academy of Pediatrics grading matrix. A Delphi consensus approach was followed.

RESULTS

We present 34 CPPs for diagnosis and management of CKD-MBD in infants, including dietary control of calcium and phosphate, and medications to prevent and treat CKD-MBD (native and active vitamin D, calcium supplementation, phosphate binders).

CONCLUSION

As there are few high-quality studies in this field, the strength of most statements is weak to moderate, and may need to be adapted to individual patient needs by the treating physician. Research recommendations to study key outcome measures in this unique population are suggested. A higher resolution version of the Graphical abstract is available as Supplementary information.

Idiopathic infantile hypercalcemia in children with chronic kidney disease due to kidney hypodysplasia

BACKGROUND

Idiopathic infantile hypercalcemia (IIH) etiologies include pathogenic variants in CYP24A1, leading to increased 1,25(OH)₂ D, hypercalciuria and suppressed parathyroid hormone (PTH), and in SLC34A1 and SLC34A3, leading to the same metabolic profile via increased phosphaturia. IIH has not been previously described in CKD due to kidney hypodysplasia (KHD).

METHODS

Retrospective study of children with bilateral KHD and simultaneously tested PTH and 1,25(OH)₂D, followed in a tertiary care center between 2015 and 2021.

RESULTS

Of 295 screened patients, 139 had KHD, of them 16 (11.5%) had IIH (study group), 26 with normal PTH and any 1,25(OH)₂D were controls. There were no differences between groups' gender, obstructive uropathy rate and baseline eGFR. Study patients were younger [median (IQR) age: 5.2 (3.2-11.3) vs. 61 (13.9-158.3) months, p < 0.001], had higher 1,25(OH)₂D (259.1 ± 91.7 vs. 156.5 ± 46.4 pmol/l, p < 0.001), total calcium (11.1 ± 0.4 vs. 10.7 ± 0.3 mg/dl, p < 0.001), and lower phosphate standard deviation score (P-SDS) [median (IQR): - 1.4 (- 1.9, - 0.4) vs. - 0.3 (- 0.8, - 0.1), p = 0.03]. During 12 months of follow-up, PTH increased among the study group (8.8 ± 2.8 to 22.7 ± 12.4 pg/ml, p < 0.001), calcium decreased (11 ± 0.5 to 10.3 ± 0.6 mg/dl, p = 0.004), 1,25(OH)₂D decreased (259.5 ± 91.7 to 188.2 ± 42.6 pmol/l, p = 0.1), P-SDS increased [median (IQR): - 1.4 (- 1.9, - 0.4) vs. - 0.3 (- 0.9, 0.4), p = 0.04], while eGFR increased. Five of 9 study group patients with available urine calcium had hypercalciuria. Five patients had nephrocalcinosis/lithiasis. Genetic analysis for pathogenic variants in CYP24A1, SLC34A1 and SLC34A3 had not been performed.

CONCLUSIONS

Transient IIH was observed in infants with KHD, in association with hypophosphatemia, resembling SLC34A1 and SLC34A3 pathogenic variants' metabolic profile. A higher resolution version of the Graphical abstract is available as Supplementary information.

Renal association commentary on the KDIGO (2017) clinical practice guideline update for the diagnosis, evaluation, prevention, and treatment of CKD-MBD

This report comments on the relevance and utility of the recently published (2017) KDIGO Clinical Practice Guideline Update for the diagnosis, evaluation, prevention and treatment of mineral bone disease in patients with chronic kidney disease (CKD-MBD) with respect to UK clinical practice. This document replaces all previously published Renal Association guidelines on the topic.

Phosphate binders for preventing and treating chronic kidney disease-mineral and bone disorder (CKD-MBD)

BACKGROUND

Phosphate binders are used to reduce positive phosphate balance and to lower serum phosphate levels for people with chronic kidney disease (CKD) with the aim to prevent progression of chronic kidney disease-mineral and bone disorder (CKD-MBD). This is an update of a review first published in 2011.

OBJECTIVES

The aim of this review was to assess the benefits and harms of phosphate binders for people with CKD with particular reference to relevant biochemical end-points, musculoskeletal and cardiovascular morbidity, hospitalisation, and death.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 12 July 2018 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) or quasi-RCTs of adults with CKD of any GFR category comparing a phosphate binder to another phosphate binder, placebo or usual care to lower serum phosphate. Outcomes included all-cause and cardiovascular death, myocardial infarction, stroke, adverse events, vascular calcification and bone fracture, and surrogates for such outcomes including serum phosphate, parathyroid hormone (PTH), and FGF23.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion and extracted study data. We applied the Cochrane 'Risk of Bias' tool and used the GRADE process to assess evidence certainty. We estimated treatment effects using random-effects meta-analysis. Results were expressed as risk ratios (RR) for dichotomous outcomes together with 95% confidence intervals (CI) or mean differences (MD) or standardised MD (SMD) for continuous outcomes.

MAIN RESULTS

We included 104 studies involving 13,744 adults. Sixty-nine new studies were added to this 2018 update.Most placebo or usual care controlled studies were among participants with CKD G2 to G5 not requiring dialysis (15/25 studies involving 1467 participants) while most head to head studies involved participants with CKD G5D treated with dialysis (74/81 studies involving 10,364 participants). Overall, seven studies compared sevelamer with placebo or usual care (667 participants), seven compared lanthanum to placebo or usual care (515 participants), three compared iron to placebo or usual care (422 participants), and four compared calcium to placebo or usual care (278 participants). Thirty studies compared sevelamer to calcium (5424 participants), and fourteen studies compared lanthanum to calcium (1690 participants). No study compared iron-based binders to calcium. The remaining studies evaluated comparisons between sevelamer (hydrochloride or carbonate), sevelamer plus calcium, lanthanum, iron (ferric citrate, sucroferric oxyhydroxide, stabilised polynuclear iron(III)-oxyhydroxide), calcium (acetate, ketoglutarate, carbonate), bixalomer, colestilan, magnesium (carbonate), magnesium plus calcium, aluminium hydroxide, sucralfate, the inhibitor of phosphate absorption nicotinamide, placebo, or usual care without binder. In 82 studies, treatment was evaluated among adults with CKD G5D treated with haemodialysis or peritoneal dialysis, while in 22 studies, treatment was evaluated among participants with CKD G2 to G5. The duration of study follow-up ranged from 8 weeks to 36 months (median 3.7 months). The sample size ranged from 8 to 2103 participants (median 69). The mean age ranged between 42.6 and 68.9 years.Random sequence generation and allocation concealment were low risk in 25 and 15 studies, respectively. Twenty-seven studies reported low risk methods for blinding of participants, investigators, and outcome assessors. Thirty-one studies were at low risk of attrition bias and 69 studies were at low risk of selective reporting bias.In CKD G2 to G5, compared with placebo or usual care, sevelamer, lanthanum, iron and calcium-based phosphate binders had uncertain or inestimable effects on death (all causes), cardiovascular death, myocardial infarction, stroke, fracture, or coronary artery calcification. Sevelamer may lead to constipation (RR 6.92, CI 2.24 to 21.4; low certainty) and lanthanum (RR 2.98, CI 1.21 to 7.30, moderate certainty) and iron-based binders (RR 2.66, CI 1.15 to 6.12, moderate certainty) probably increased constipation compared with placebo or usual care. Lanthanum may result in vomiting (RR 3.72, CI 1.36 to 10.18, low certainty). Iron-based binders probably result in diarrhoea (RR 2.81, CI 1.18 to 6.68, high certainty), while the risks of other adverse events for all binders were uncertain.In CKD G5D sevelamer may lead to lower death (all causes) (RR 0.53, CI 0.30 to 0.91, low certainty) and induce less hypercalcaemia (RR 0.30, CI 0.20 to 0.43, low certainty) when compared with calcium-based binders, and has uncertain or inestimable effects on cardiovascular death, myocardial infarction, stroke, fracture, or coronary artery calcification. The finding of lower death with sevelamer compared with calcium was present when the analysis was restricted to studies at low risk of bias (RR 0.50, CI 0.32 to 0.77). In absolute terms, sevelamer may lower risk of death (all causes) from 210 per 1000 to 105 per 1000 over a follow-up of up to 36 months, compared to calcium-based binders. Compared with calcium-based binders, lanthanum had uncertain effects with respect to all-cause or cardiovascular death, myocardial infarction, stroke, fracture, or coronary artery calcification and probably had reduced risks of treatment-related hypercalcaemia (RR 0.16, CI 0.06 to 0.43, low certainty). There were no head-to-head studies of iron-based binders compared with calcium. The paucity of placebo-controlled studies in CKD G5D has led to uncertainty about the effects of phosphate binders on patient-important outcomes compared with placebo.It is uncertain whether the effects of binders on clinically-relevant outcomes were different for patients who were and were not treated with dialysis in subgroup analyses.

AUTHORS' CONCLUSIONS

In studies of adults with CKD G5D treated with dialysis, sevelamer may lower death (all causes) compared to calcium-based binders and incur less treatment-related hypercalcaemia, while we found no clinically important benefits of any phosphate binder on cardiovascular death, myocardial infarction, stroke, fracture or coronary artery calcification. The effects of binders on patient-important outcomes compared to placebo are uncertain. In patients with CKD G2 to G5, the effects of sevelamer, lanthanum, and iron-based phosphate binders on cardiovascular, vascular calcification, and bone outcomes compared to placebo or usual care, are also uncertain and they may incur constipation, while iron-based binders may lead to diarrhoea.

Clinical practice recommendations for treatment with active vitamin D analogues in children with chronic kidney disease Stages 2-5 and on dialysis

In patients with chronic kidney disease (CKD), renal synthesis of active vitamin D [1,25-dihydroxyvitamin D (1,25(OH)2D)] declines and is associated with hypocalcaemia, secondary hyperparathyroidism and the spectrum of CKD-mineral and bone disorder (MBD). In advanced CKD, active vitamin D analogues, including alfacalcidol, calcitriol and paricalcitol, are routinely administered. There are few studies on the use of vitamin D analogues in children with CKD and on dialysis. It is difficult to define bone-specific outcomes that can guide treatment with active vitamin D analogues in children with CKD-MBD. A core working group (WG) of the European Society for Paediatric Nephrology (ESPN) CKD-MBD and Dialysis WGs has developed recommendations for the use of active vitamin D therapy in children with CKD and on dialysis. A second document in parallel with this one covers treatment recommendations for native vitamin D therapy. The WGs have performed an extensive literature review to include systematic reviews and randomized controlled trials in adults and children with CKD and prospective observational studies in children with CKD. The Grading of Recommendation, Assessment, Development and Evaluation (GRADE) system was used to develop and grade the recommendations. In the absence of applicable study data, the opinion of experts from the ESPN CKD-MBD and Dialysis WGs is provided, but clearly GRADE-ed as such and must be carefully considered by the treating physician and adapted to individual patient needs as appropriate.

Phosphate Binding with Sevelamer Preserves Mechanical Competence of Bone Despite Acidosis in Advanced Experimental Renal Insufficiency

Introduction

Phosphate binding with sevelamer can ameliorate detrimental histomorphometric changes of bone in chronic renal insufficiency (CRI). Here we explored the effects of sevelamer-HCl treatment on bone strength and structure in experimental CRI.

Methods

Forty-eight 8-week-old rats were assigned to surgical 5/6 nephrectomy (CRI) or renal decapsulation (Sham). After 14 weeks of disease progression, the rats were allocated to untreated and sevelamer-treated (3% in chow) groups for 9 weeks. Then the animals were sacrificed, plasma samples collected, and femora excised for structural analysis (biomechanical testing, quantitative computed tomography).

Results

Sevelamer-HCl significantly reduced blood pH, and final creatinine clearance in the CRI groups ranged 30%-50% of that in the Sham group. Final plasma phosphate increased 2.4- to 2.9-fold, and parathyroid hormone 13- to 21-fold in CRI rats, with no difference between sevelamer-treated and untreated animals. In the femoral midshaft, CRI reduced cortical bone mineral density (-3%) and breaking load (-15%) (p<0.05 for all versus Sham), while sevelamer increased bone mineral density (+2%) and prevented the deleterious changes in bone. In the femoral neck, CRI reduced bone mineral density (-11%) and breaking load (-10%), while sevelamer prevented the decrease in bone mineral density (+6%) so that breaking load did not differ from controls.

Conclusions

In this model of stage 3–4 CRI, sevelamer-HCl treatment ameliorated the decreases in femoral midshaft and neck mineral density, and restored bone strength despite prevailing acidosis. Therefore, treatment with sevelamer can efficiently preserve mechanical competence of bone in CRI.

Reduction of Dialysate Calcium Level Reduces Progression of Coronary Artery Calcification and Improves Low Bone Turnover in Patients on Hemodialysis

Exposure to high Ca concentrations may influence the development of low-turnover bone disease and coronary artery calcification (CAC) in patients on hemodialysis (HD). In this randomized, controlled study, we investigated the effects of lowering dialysate Ca level on progression of CAC and histologic bone abnormalities in patients on HD. Patients on HD with intact parathyroid hormone levels ≤300 pg/ml receiving dialysate containing 1.75 or 1.50 mmol/L Ca (n=425) were randomized to the 1.25-mmol/L Ca (1.25 Ca; n=212) or the 1.75-mmol/L Ca (1.75 Ca; n=213) dialysate arm. Primary outcome was a change in CAC score measured by multislice computerized tomography; main secondary outcome was a change in bone histomorphometric parameters determined by analysis of bone biopsy specimens. CAC scores increased from 452±869 (mean±SD) in the 1.25 Ca group and 500±909 in the 1.75 Ca group (P=0.68) at baseline to 616±1086 and 803±1412, respectively, at 24 months (P=0.25). Progression rate was significantly lower in the 1.25 Ca group than in the 1.75 Ca group (P=0.03). The prevalence of histologically diagnosed low bone turnover decreased from 85.0% to 41.8% in the 1.25 Ca group (P=0.001) and did not change in the 1.75 Ca group. At 24 months, bone formation rate, trabecular thickness, and bone volume were higher in the 1.25 Ca group than in the 1.75 Ca group. Thus, lowering dialysate Ca levels slowed the progression of CAC and improved bone turnover in patients on HD with baseline intact parathyroid hormone levels ≤300 pg/ml.

Interventions for metabolic bone disease in children with chronic kidney disease

BACKGROUND

Bone disease is common in children with chronic kidney disease (CKD) and when untreated may result in bone deformities, bone pain, fractures and reduced growth rates. This is an update of a review first published in 2010.

OBJECTIVES

This review aimed to examine the benefits (improved growth rates, reduced risk of bone fractures and deformities, reduction in PTH levels) and harms (hypercalcaemia, blood vessel calcification, deterioration in kidney function) of interventions (including vitamin D preparations and phosphate binders) for the prevention and treatment of metabolic bone disease in children with CKD.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Specialised Register to 8 September 2015 through contact with the Trial's Search Co-ordinator using search terms relevant for this review.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing different interventions used to prevent or treat bone disease in children with CKD stages 2 to 5D.

DATA COLLECTION AND ANALYSIS

Data were assessed for study eligibility, risk of bias and extracted independently by two authors. Results were reported as risk ratios (RR) or risk differences (RD) with 95% confidence intervals (CI) for dichotomous outcomes. For continuous outcomes the mean difference (MD) or standardised mean difference (SMD) with 95% confidence intervals (CI) was used. Statistical analyses were performed using the random-effects model.

MAIN RESULTS

This review included 18 studies (576 children); three new studies were added for this update. Adequate sequence generation and allocation concealment were reported in 12 and 11 studies respectively. Only four studies reported blinding of children, investigators or outcome assessors. Nine studies were at low risk of attrition bias and 12 studies were at low risk of selective reporting bias.Eight different interventions were compared. Two studies compared intraperitoneal (IP) with oral calcitriol. PTH levels were significantly lower with IP compared with oral calcitriol (1 study: MD -501.00 pg/mL, 95% CI -721.54 to -280.46) but the number of children with abnormal bone histology did not differ between treatments. Three studies compared intermittent with daily oral calcitriol. The change in mean height SDS (1 study: MD 0.13, 95% CI -0.22 to 0.48) and the percentage fall in parathyroid hormone (PTH) levels at eight weeks (1 study: MD -5.50%, 95% CI -32.37 to 21.37) and 12 months (1 study: MD -6.00% 95% CI -25.27 to 13.27) did not differ between treatments.Four studies compared active vitamin D preparations (calcitriol, paricalcitol, 1α-hydroxyvitamin D) with placebo or no specific treatment. One study reported vitamin D preparations significantly reduced PTH levels (-55.00 pmol/L, 95% CI -83.03 to -26.97). There was no significant difference in hypercalcaemia risk with vitamin D preparations compared with placebo or no specific treatment (4 studies, 103 children: RD 0.08 mg/dL, 95% CI -0.08 to 0.24). However, there was heterogeneity (I(2) = 55%) with one study showing a significantly greater risk of hypercalcaemia with intravenous (IV) calcitriol administration. Two studies (97 children) compared calcitriol with other vitamin D preparations and both found no significant differences in growth between preparations.Two studies compared ergocalciferol in patients with CKD and vitamin D deficiency. Elevated PTH levels developed significantly later in ergocalciferol treated children (1 study: hazard ratio 0.30, 95% CI 0.09 to 0.93) though the number with elevated PTH levels did not differ between groups (1 study, 40 children: RR 0.33, 95% CI 0.11 to 1.05).Two studies compared calcium carbonate with aluminium hydroxide as phosphate binders. One study (17 children: MD -0.86 SDS, 95% CI -2.24 to 0.52) reported no significant difference in mean final height SDS between treatments. Three studies compared sevelamer with calcium-containing phosphate binders. There were no significant differences in the final calcium, phosphorus or PTH levels between binders. More episodes of hypercalcaemia occurred with calcium-containing binders. One study reported no significant differences between calcitriol and doxercalciferol in bone histology or biochemical parameters.

AUTHORS' CONCLUSIONS

Bone disease, assessed by changes in PTH levels, is improved by all vitamin D preparations. However, no consistent differences between routes of administration, frequencies of dosing or vitamin D preparations were demonstrated. Although fewer episodes of high calcium levels occurred with the non-calcium-containing phosphate binder, sevelamer, compared with calcium-containing binders, there were no differences in serum phosphorus and calcium overall and phosphorus values were reduced to similar extents. All studies were small with few data available on patient-centred outcomes (growth, bone deformities) and limited data on biochemical parameters or bone histology resulting in considerable imprecision of results thus limiting the applicability to the care of children with CKD.

Pre-treatment considerations in childhood hypertension due to chronic kidney disease

Hypertension (HTN) develops very early in childhood chronic kidney disease (CKD). It is linked with rapid progression of kidney disease, increased morbidity and mortality hence the imperative to start anti-hypertensive medication when blood pressure (BP) is persistently > 90^th percentile for age, gender, and height in non-dialyzing hypertensive children with CKD. HTN pathomechanism in CKD is multifactorial and complexly interwoven. The patient with CKD-associated HTN needs to be carefully evaluated for co-morbidities that frequently alter the course of the disease as successful treatment of HTN in CKD goes beyond life style modification and anti-hypertensive therapy alone. Chronic anaemia, volume overload, endothelial dysfunction, arterial media calcification, and metabolic derangements like secondary hyperparathyroidism, hyperphosphataemia, and calcitriol deficiency are a few co-morbidities that may cause or worsen HTN in CKD. It is important to know if the HTN is caused or made worse by the toxic effects of medications like erythropoietin, cyclosporine, tacrolimus, corticosteroids and non-steroidal anti-inflammatory drugs. Poor treatment response may be due to any of these co-morbidities and medications. A satisfactory hypertensive CKD outcome, therefore, depends very much on identifying and managing these co-morbid conditions and HTN promoting medications promptly and appropriately. This review attempts to point attention to factors that may affect successful treatment of the hypertensive CKD child and how to attain the desired therapeutic BP target.

The demise of calcium-based phosphate binders-is this appropriate for children?

In children with chronic kidney disease (CKD) optimal control of mineral and bone disorder (MBD) is essential not only for the prevention of debilitating skeletal complications and for achieving adequate growth, but also for preserving long-term cardiovascular health. The growing skeleton is particularly vulnerable to the effects of CKD, and bone pain, fractures and deformities are common in children on dialysis. Defective bone mineralisation has been linked with ectopic calcification, which in turn leads to significant morbidity and mortality. Despite national and international guidelines for the management of CKD-MBD, the management of mineral dysregulation in CKD can be extremely challenging, and a significant proportion of patients have calcium, phosphate or parathyroid hormone levels outside the normal ranges. Clinical and experimental studies have shown that, in the setting of CKD, low serum calcium levels are associated with poor bone mineralisation, whereas high serum calcium levels can lead to arterial calcification, even in children. The role of calcium in CKD-MBD is the focus of this review.

Effects of vitamin D on parathyroid hormone and clinical outcomes in peritoneal dialysis: a narrative review

Vitamin D deficiency is very prevalent in dialysis and peritoneal dialysis (PD) patients show lower levels of cholecalciferol (25(OH)D3) than hemodialysis patients. We conducted a systematic narrative review to assess the effects of vitamin D therapy on control of secondary hyperparathyroidism and clinical outcomes induced by vitamin D pleiotropic effects. Medline database was searched for cohort and intervention studies reporting data on vitamin D (all sterols including synthetic analogs) and peritoneal dialysis without language restriction. Two authors independently extracted data. Twenty-nine observational and eleven interventional studies were identified for inclusion (1,036 subjects). PTH levels decreased in twenty-nine studies, increased in one study and remained stable in ten studies. Thirty-three studies analyzed the oral route for vitamin D administration, ten the intraperitoneal, one the subcutaneous and one the intravenous. A significant decrease of peritonitis risk was observed in two studies. Proteinuria decreased in four studies and remained stable in one study. Peritoneal protein loss decreased in one study and was stable in two studies. Studies on the therapeutic effects of vitamin D in PD are limited and describe small population samples. Moreover, vitamin D compounds do not consistently reduce PTH levels. The administration of active vitamin D in PD may have interesting pleiotropic effects such as decreasing proteinuria and peritoneal protein loss. According to these effects, vitamin D could help to preserve residual renal function and ensure efficient peritoneal membrane dialysance.

Clinical and economic aspects of sevelamer therapy in end-stage renal disease patients

Phosphate control is still a great challenge in chronic kidney disease (CKD), and in spite of the great improvements in dialysis techniques, achievement of the goals for mineral metabolism control is still far from ideal. Aluminum hydroxide has been largely abandoned due to the high risk of aluminum toxicity, while the use of calcium-based phosphate binders may cause hypercalcemia, overzealous parathyroid suppression, and extraskeletal calcification. Sevelamer hydrochloride has been introduced as an efficient medication for phosphate control, with a lower risk of hypercalcemia and parathyroid suppression. Various clinical trials have compared the risk of vascular calcification between sevelamer and calcium salts with inconsistent results. In spite of these inconsistencies, the Kidney Disease Outcomes Quality Initiative (KDOQI) suggests non-calcium phosphate binders as the preferred phosphate binder in dialysis patients with severe vascular and/or other soft-tissue calcifications and in those with hypercalcemia or parathyroid hormone (PTH) <150 mg/dL. The Kidney Disease Improving Global Outcome (KDIGO) limits the use of non-calcium phosphate binders to patients with hypercalcemia. Regarding the effect on mortality, the results of clinical trials are again inconsistent. The other important aspect of using sevelamer is the issue of price, which is substantially higher than calcium-based phosphate binders. Reviewing the studies on economic aspects shows that sevelamer increases quality-adjusted life-years (QALY) and possibly life years, with a higher cost compared to calcium-based phosphate binders. In conclusion, sevelamer is a very useful drug for phosphate control, reduction of hypercalcemia, and lessening the risk of adynamic bone disease, with probable reduction in vascular calcification and possible reduction in mortality rate. It has a higher economic burden on health care systems compared to calcium-based phosphate binders. This may affect its extensive use according to guideline recommendations, and will be influenced by local health care budgets and the decision of health care strategists.

Optimal use of phosphate binders in chronic kidney disease

INTRODUCTION

Hyperphosphatemia is one of the major factors associated with the development of vascular calcification in patients with chronic kidney disease (CKD). Since phosphate is retained in such patients, pharmacological treatment and other measures are necessary to control hyperphosphatemia. Several phosphate binders (calcium salts, magnesium salts, non-calcium-based binders and aluminium) are available for the treatment of hyperphosphatemia. Nevertheless, none of the above mentioned agents has shown an overall superiority over others, while potency and side effects are quite variable among them creating difficulties in choosing the optimal drug for each patient.

AREAS COVERED

The authors discuss the disturbed phosphate metabolism, the available phosphate binders, as well as the general therapeutic principles of treating hyperphosphatemia in CKD patients. The literature used for this review had been retrieved from PubMed and covers a large number of original and retrospective studies as well as prospective cohort studies, meta-analyses and international clinical guidelines.

EXPERT OPINION

Lowering serum phosphate levels in CKD patients may potentially have a positive impact on cardiovascular morbidity and mortality. Factors that should be taken into consideration when selecting a specific drug include CKD stage, cardiovascular disease, severity of secondary hyperparathyroidism, concomitant medications, life expectancy and patient compliance. Therefore, when selecting a specific phosphate binder, individualisation is mandatory.

Chronic kidney disease: mineral and bone disorder in children

Childhood and adolescence are crucial times for the development of a healthy skeletal and cardiovascular system. Disordered mineral and bone metabolism accompany chronic kidney disease (CKD) and present significant obstacles to optimal bone strength, final adult height, and cardiovascular health. Early increases in bone and plasma fibroblast growth factor 23 (FGF23) are associated with early defects in skeletal mineralization. Later in the course of CKD, secondary hyperparathyroidism--caused by a combination of declining calcitriol values and phosphate retention--results in high-turnover renal osteodystrophy whereas increased levels of both phosphate and FGF23 contribute to cardiovascular disease. Treatment of hyperphosphatemia and secondary hyperparathyroidism improves high-turnover bone disease but fails to correct defects in skeletal mineralization. Because overtreatment may result in adynamic bone disease, growth failure, hypercalcemia, and progression of cardiovascular calcifications, therapy therefore must be titrated carefully to maintain optimal serum biochemical parameters according to stage of CKD. Newer therapeutic agents and new treatment paradigms may suppress serum PTH levels effectively while limiting intestinal calcium absorption and skeletal FGF23 stimulation and may provide future therapeutic alternatives for children with CKD.

Ferric citrate hydrate, a new phosphate binder, prevents the complications of secondary hyperparathyroidism and vascular calcification

BACKGROUND/AIMS

Ferric citrate hydrate (JTT-751) is being developed as a treatment for hyperphosphatemia in chronic kidney disease patients, and shows serum phosphorus-reducing effects on hyperphosphatemia in hemodialysis patients. We examined whether JTT-751 could reduce phosphorus absorption in normal rats and prevent the progression of ectopic calcification, secondary hyperparathyroidism and bone abnormalities in chronic renal failure (CRF) rats.

METHODS

Normal rats were fed a diet containing 0.3, 1 or 3% JTT-751 for 7 days. The effects of JTT-751 on phosphorus absorption were evaluated with fecal and urinary phosphorus excretion. Next, a CRF model simulating hyperphosphatemia was induced by feeding rats a 0.75% adenine diet. After 21 days of starting the adenine diet feeding, 1 or 3% JTT-751 was administered for 35 days by dietary admixture. The serum phosphorus levels and mineral parameters were measured. Calcification in the aorta was examined biochemically and histopathologically. Hyperparathyroidism and bone abnormalities were evaluated by histopathological analysis of the parathyroid and femur, respectively.

RESULTS

In normal rats, JTT-751 increased fecal phosphorus excretion and reduced phosphorus absorption and urinary phosphorus excretion. In CRF rats, JTT-751 reduced serum phosphorus levels, the calcium-phosphorus product and calcium content in the aorta. Serum intact parathyroid hormone levels and the incidence and severity of parathyroid hyperplasia were also decreased. JTT-751 reduced femoral bone fibrosis, porosity and osteoid formation.

CONCLUSIONS

JTT-751 could bind with phosphate in the gastrointestinal tract, increase fecal phosphorus excretion and reduce phosphorus absorption. JTT-751 could prevent the progression of ectopic calcification, secondary hyperparathyroidism and bone abnormalities in rats.

The consequences of chronic kidney disease on bone metabolism and growth in children

Growth retardation, decreased final height and renal osteodystrophy (ROD) are common complications of childhood chronic kidney disease (CKD), resulting from a combination of abnormalities in the growth hormone (GH) axis, vitamin D deficiency, hyperparathyroidism, hypogonadism, inadequate nutrition, cachexia and drug toxicity. The impact of CKD-associated bone and mineral disorders (CKD-MBD) may be immediate (serum phosphate/calcium disequilibrium) or delayed (poor growth, ROD, fractures, vascular calcifications, increased morbidity and mortality). In 2012, the clinical management of CKD-MBD in children needs to focus on three main objectives: (i) to provide an optimal growth in order to maximize the final height with an early management with recombinant GH therapy when required, (ii) to equilibrate calcium/phosphate metabolism so as to obtain acceptable bone quality and cardiovascular status and (iii) to correct all metabolic and clinical abnormalities that can worsen bone disease, growth and cardiovascular disease, i.e. metabolic acidosis, anaemia, malnutrition and 25(OH)vitamin D deficiency. The aim of this review is to provide an overview of the mineral, bone and vascular abnormalities associated with CKD in children in terms of pathophysiology, diagnosis and clinical management.

Non-calcium-containing phosphate binders: comparing efficacy, safety, and other clinical effects

Phosphate-binder therapy for hyperphosphataemia is key to the treatment of patients with chronic kidney disease (CKD)-mineral and bone disorder (MBD). Calcium-free phosphate binders are increasingly favoured since calcium-based agents potentially cause harmful calcium overload and vascular calcification that confound the benefits of reducing serum phosphorus. Several calcium-free phosphate binders are available, including the non-absorbed agent sevelamer and the absorbed agents, e.g. lanthanum and magnesium salts. Randomised controlled studies consistently show that sevelamer and lanthanum carbonate offer equivalent lowering of serum phosphorus and often effectively achieve phosphorus targets versus calcium salts, with sevelamer having a positive effect on bone disease, vascular calcification, and patient-level outcomes in dialysis patients in several trials. There is also evidence that lanthanum carbonate can improve bone health, but data are limited to its effects to vascular calcification or patient-level outcomes. Magnesium salts have also been shown to reduce serum phosphorus levels, but clear evidence is lacking on bone, vascular, or clinical outcomes. It also remains to be established whether long-term systemic accumulation of lanthanum and magnesium, in tissues including bone, has clinically relevant toxic effects. This review summarises the evidence of efficacy and safety for newer calcium-free phosphate binders in CKD-MBD management.

Mineral and bone disorders in children with chronic kidney disease

As children with chronic kidney disease (CKD) have a long lifespan, optimal control of bone and mineral homeostasis is essential not only for the prevention of debilitating skeletal complications and for achieving adequate growth but also for preserving long-term cardiovascular health. As the growing skeleton is highly dynamic and at particular risk of deterioration, close control of bone and mineral homeostasis is required in children with CKD. However, assessment of bone disease is hampered by the limited validity of biochemical parameters-major controversy exists on key issues such as parathyroid hormone target ranges and the lack of useful imaging techniques. The role of newly discovered factors in bone and mineral homeostasis, such as fibroblast growth factor 23, is not yet established. Even though scientific evidence is limited in children with CKD, ergocalciferol or cholecalciferol supplementation and the use of calcium-free phosphate binders is recommended. The new drug cinacalcet is highly promising; however, pediatric experience is still limited to observational data and the effect of cinacalcet on longitudinal growth and pubertal development is unknown. Randomized, controlled trials are underway, including studies of cinacalcet pharmacokinetics and pharmacodynamics in infants.

Uraemic vasculopathy in children with chronic kidney disease: prevention or damage limitation?

Since the inception of pediatric dialysis programmes nearly 50 years ago, there have been vast improvements in both the technology and expertise in the care of children with chronic kidney disease (CKD). Nevertheless, children on dialysis continue to have a significantly higher mortality than their healthy peers and cardiovascular disease (CVD) is the most common cause of death in this group. Chronic kidney disease is described as the "perfect storm" of risk factors for CVD development, and vascular calcification is a highly regulated cell-mediated process with several promoters and inhibitors of calcification. CVD begins early in the course of CKD and there is an independent and graded association between cardiovascular morbidity and renal decline. Also, it is shown that once vascular damage and calcification begin, they progress inexorably in the uraemic milieu and may only be partially reversed after successful transplantation. Thus, preventing the development of CVD is key, and early identification and management of specific CVD-related risk factors should begin from the early stages of CKD. While the vasculopathy of childhood CKD is clearly multifactorial, clinical, epidemiological and cell biology studies provide converging evidence pointing to the role of dysregulated mineral metabolism as an important modifiable risk factor in the development of vascular calcification. In this review we focus on the role of calcium, phosphate, parathyroid hormone and vitamin D in ectopic vascular calcification, and discuss the role of screening, early intervention and management of established vascular calcification.

Derangements in phosphate metabolism in chronic kidney diseases/endstage renal disease: therapeutic considerations

The changes in phosphate (PO(4)) metabolism across the spectrum of chronic kidney disease (CKD) and specific strategies to address these abnormalities by reducing PO(4) loads are discussed in this review. This review also addresses briefly the evidence for specific PO(4) serum targets in CKD and endstage renal disease (ESRD) and the potential for other biomarkers such as fibroblast growth factor-23 (FGF-23) to define disease and monitor the effectiveness of therapy. As renal function declines, single nephron excretion of PO(4) must increase to maintain PO(4) balance. Abnormalities in PO(4) metabolism occur early in CKD. Compensatory changes in renal PO(4) handling are sufficient to maintain a normal serum PO(4) level in early stages of CKD, but in more advanced CKD, these processes no longer suffice and overt hyperphosphatemia develops. The resulting increased PO(4) burden contributes directly to development of secondary hyperparathyroidism. The FGF-23 increases early in CKD, likely in response to abnormal PO(4) metabolism, and mediates processes that help restore serum PO(4) levels to normal in CKD stage 3 and in early stage 4. The increased PO(4) burden and subsequent overt hyperphosphatemia are associated with increased mortality and morbidity. Dietary PO(4) restriction, modification of dialysis prescriptions, and administration of oral PO(4) binders can restore PO(4) balance. As CKD progresses, population-based studies demonstrate that diet alone is typically not able to prevent or treat hyperphosphatemia. Dialysis modalities that are currently used often fail to remove sufficient PO(4) to prevent hyperphosphatemia in patients with an inadequately controlled dietary PO(4) load. This is particularly likely among patients without significant residual renal function. Thus, in the majority of ESRD patients, PO(4) binders remain the mainstay of therapy for hyperphosphatemia. All currently available PO(4) binders can restore serum PO(4) to the required level when administered appropriately and in conjunction with dietary PO(4) restrictions. PO(4) binders differ regarding their potential side-effects and impact on long-term patient-centered outcomes. Which of the PO(4) binders might result in the most favorable survival and cardiovascular morbidity profiles and which remain uncertain, remains a subject of considerable clinical investigation. Compelling observational and more limited randomized controlled trial (RCT) evidence support the view that PO(4) binders might differ in their effects on mortality and/or morbidity. The limited evidence from RCTs is mostly congruent with the findings from large observational studies. In particular, evidences from both epidemiologic and RCT support the view that excess calcium administration may independently increase the risk of cardiovascular disease in individuals with normal renal function and in patients with CKD and ESRD. Additional RCT evidence might help determine the degree at which any increased risk from oral calcium exposure can be mitigated with the use of noncalcium-based PO(4) binders. Judicious control of PO(4) early in CKD, possibly monitored by measures of FGF-23, could potentially reduce the risk of development of renal secondary hyperparathyroidism and all of the adverse clinical consequences of poorly controlled CKD-mineral and bone disorder. The mainstays of therapy are likely to include a balance of dietary restriction and PO(4) binders to reduce PO(4) input, and in ESRD patients, dialysis modalities to augment PO(4) output.

Value of the new bone classification system in pediatric renal osteodystrophy

BACKGROUND AND OBJECTIVES

Although lesions of renal osteodystrophy have traditionally been defined by bone turnover, alterations in skeletal mineralization and volume are also prevalent and may contribute to significant morbidity in patients with chronic kidney disease (CKD). The study presented here was undertaken to compare the traditional spectrum of renal osteodystrophy defined by bone turnover to a new classification system that includes T (turnover), M (mineralization), and V (volume) and to determine the value of biochemical parameters as predictors of specific TMV lesions.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Pediatric patients (n = 161) treated with peritoneal dialysis were enrolled into the study.

RESULTS

Increased bone turnover and abnormal mineralization were prevalent (57% and 48%, respectively); bone volume was normal or increased in all subjects. Predictive algorithms for different skeletal diagnoses were established by Classification and regression tree analysis. Serum parathyroid hormone (PTH) less than 400 pg/ml in combination with alkaline phosphatase values less than 400 IU/L provided the highest correct prediction rate for patients with both normal bone turnover and normal mineralization. Levels of PTH were higher and serum calcium levels were lower in patients with defective mineralization, irrespective of bone turnover.

CONCLUSIONS

Although no single biochemical marker is able to provide a complete assessment of renal osteodystrophy, a combination of serum calcium, alkaline phosphatase, and PTH levels may lead to a more precise noninvasive assessment of turnover and mineralization abnormalities in this population.

Calcitriol and doxercalciferol are equivalent in controlling bone turnover, suppressing parathyroid hormone, and increasing fibroblast growth factor-23 in secondary hyperparathyroidism

We compared the effects of calcitriol and doxercalciferol, in combination with either calcium carbonate or sevelamer, on bone, mineral, and fibroblast growth factor-23 (FGF-23) metabolism in patients with secondary hyperparathyroidism. A total of 60 pediatric patients treated with peritoneal dialysis were randomized to 8 months of therapy with either oral calcitriol or doxercalciferol, combined with either calcium carbonate or sevelamer. Bone formation rates decreased during therapy and final values were within the normal range in 72% of patients. A greater improvement in eroded surface was found in patients treated with doxercalciferol than in those given calcitriol. On initial bone biopsy, a mineralization defect was identified in the majority of patients which did not normalize with therapy. Serum phosphate concentrations were controlled equally well by both binders, but serum calcium levels increased during treatment with calcium carbonate, and serum parathyroid hormone levels were decreased by 35% in all groups. Baseline plasma FGF-23 values were significantly elevated and rose over fourfold with calcitriol and doxercalciferol, irrespective of phosphate binder. Thus, doxercalciferol is as effective as calcitriol in controlling serum parathyroid hormone levels and suppressing the bone formation rate. Sevelamer allows the use of higher doses of vitamin D. Implications of these changes on bone and cardiovascular biology remain to be established.

Ironing out the phosphorus problem

Control of serum phosphorus remains a vexing problem in chronic kidney disease. Although novel dialysis regimens may provide excellent phosphorus control, phosphate binders remain necessary for most dialysis patients. Block et al. present a phase I clinical trial examining the safety and efficacy of SBR759, a novel non-calcium, iron-based phosphate binder. Although the risks of iron accumulation and hypocalcemia must be addressed, this phosphate binder appears to be well tolerated and effective and offers a powder-based formulation.

Ten-year experience with sevelamer and calcium salts as phosphate binders

Most patients with chronic kidney disease experience abnormalities in serum calcium, phosphorus, parathyroid hormone, and vitamin D metabolism. These can lead to vascular calcification (VC), which has been associated with increased risk for cardiovascular disease and mortality. Although hyperphosphatemia is believed to be a risk factor for mortality and VC, no randomized trial was ever designed to demonstrate that lowering phosphate reduces mortality. Nonetheless, binders have been used extensively, and the preponderance of evidence shows that sevelamer slows the development of VC whereas calcium salts do not. Four studies have demonstrated a slower progression of VC with sevelamer than with calcium-containing binders, although a fifth study showed nonsuperiority. Conversely, the results on mortality with sevelamer have been variable, and data on calcium-based binders are nonexistent. Improved survival with sevelamer was demonstrated in a small randomized clinical trial, whereas a larger randomized trial failed to show a benefit. In addition, preclinical models of renal failure and preliminary clinical data on hemodialysis patients suggest a potential benefit for bone with sevelamer. Meanwhile, several randomized and observational studies suggested no improvement in bone density and fracture rate, and a few noted an increase in total and cardiovascular mortality in the general population given calcium supplements. Although additional studies are needed, there are at least indications that sevelamer may improve vascular and bone health and, perhaps, mortality in hemodialysis patients, whereas data on calcium-based binders are lacking.

New therapies: calcimimetics, phosphate binders and vitamin D receptor activators

At present, new compounds are available to treat secondary hyperparathyroidism, namely calcimimetics, novel phosphorus binders and also novel vitamin D receptor activators. Calcimimetics increase the sensitivity of the parathyroid gland to calcium through spatial configurational changes of the calcium-sensing receptor. In addition, experimental studies have demonstrated that calcimimetics also upregulate both the calcium-sensing receptor and the vitamin D receptor. They are efficacious in children, though the experience in paediatric chronic kidney disease is still limited. Sevelamer, lanthanum carbonate and magnesium iron hydroxycarbonate are novel phosphorus binders available on the market. Several studies have demonstrated their efficacy and safety up to 6 years, though costs are the main limitation for a wider use. Since almost all the experience available on the new phosphorus binders comes from its use in adults, studies on children are needed in order to confirm the efficacy and safety of these products. Other new salts and polymers are also being developed. New vitamin D receptor activators, such as paricalcitol, are as effective at suppressing parathyroid hormone (PTH) as the traditional vitamin D receptor activators used for the past two decades, but they have a better and safer profile, showing fewer calcaemic and phosphoraemic effects while preserving the desirable effects of the vitamin D receptor activators on the cardiovascular system, hypertension, inflammation and fibrosis. Their use in children with chronic kidney disease has revealed similar responses to those of adults. The novel compounds discussed in this review should facilitate and improve the management of mineral and bone disorders in children with chronic kidney disease.

Phosphate binders in CKD: chalking out the differences

Plasma phosphate levels are important in the evolution of hyperparathyroidism and ectopic calcification in chronic kidney disease (CKD). Although dietary management may be adequate to control plasma phosphate in its early stages, most patients develop hyperphosphataemia by CKD stages 3-4 and require the addition of a phosphate binder. Calcium-containing phosphate binders are the most used and cheapest binders but have fallen out of favour because of the potential for positive calcium balance and calcium toxicity. This problem may be attenuated by newer phosphate binders such as sevelamer hydrochloride and lanthanum carbonate. In this review, the role of phosphate as a uraemic toxin and the advantages and disadvantages of the currently available phosphate binders are discussed.

Interventions for bone disease in children with chronic kidney disease

BACKGROUND

Bone disease is common in children with chronic kidney disease (CKD) and when untreated may result in bone deformities, bone pain, fractures and reduced growth rates.

OBJECTIVES

To investigate the benefits and harms of interventions for preventing and treating bone disease in children with CKD.

SEARCH STRATEGY

The Cochrane Renal Group's specialised register, the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, reference lists and abstracts were searched without language restriction.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing different interventions used to prevent or treat bone disease in children with CKD stages 2-5D compared with placebo, no treatment or other agents were included. Studies examining different routes or frequency of treatment were also included.

DATA COLLECTION AND ANALYSIS

Data were extracted by two authors. The random-effects model was used and results were reported as risk ratios or risk differences for dichotomous outcomes and mean differences for continuous outcomes with 95% confidence intervals.

MAIN RESULTS

Fifteen RCTs (369 children) were identified. Compared with oral calcitriol, intraperitoneal calcitriol significantly reduced the level of serum parathyroid hormone (PTH) but there were no significant differences in bone histology or other biochemical measures (2 RCTs). There were no significant differences detected in growth, PTH, serum calcium or phosphorus between daily versus intermittent calcitriol (3 RCTs). Vitamin D therapy significantly reduced PTH levels compared with placebo or no treatment. The number of children with hypercalcaemia did not differ significantly between groups (4 RCTs). No significant differences were detected in growth rates, bone histology or biochemical parameters between calcitriol and either dihydrotachysterol or ergocalciferol (2 RCTs). Though fewer episodes of hypercalcaemia were reported with sevelamer, no significant differences were detected in serum calcium, phosphorus and PTH levels between calcium-containing phosphate binders and either aluminium hydroxide or sevelamer (4 RCTs).

AUTHORS' CONCLUSIONS

Bone disease, assessed by changes in PTH levels, is improved by all vitamin D preparations. However no consistent differences between routes of administration, frequencies of dosing or vitamin D preparations have been demonstrated. Though fewer episodes of high calcium levels occurred with the non calcium-containing binder, sevelamer, compared with calcium-containing binders, there were no differences in serum phosphorus and calcium overall and phosphorus values were reduced to similar extents. All RCTs were small with few data available on patient-centred outcomes (growth, bone deformities) and limited data on biochemical parameters resulting in considerable imprecision of results thus limiting the applicability to care of children with CKD.

Sevelamer carbonate increases serum bicarbonate in pediatric dialysis patients

Sevelamer hydrochloride (HCl), a calcium-free phosphate binder, is increasingly used due to concerns related to calcium exposure and the development of vascular calcifications. However, a common side effect of sevelamer HCl, metabolic acidosis, is particularly concerning in children, as it can contribute to poor growth. Sevelamer carbonate is now available and has been shown to increase serum bicarbonate in adult patients. We conducted a prospective single-center study of pediatric dialysis patients comparing serum bicarbonate before and 3 months after a switch from sevelamer HCl to sevelamer carbonate. Inclusion criteria were a minimum of 3 months of dialysis therapy and either a serum bicarbonate <20 mmol/L or the need for sodium bicarbonate supplementation. Ten hemodialysis and 14 peritoneal dialysis patients, aged 16 +/- 3 years, were enrolled. Whereas serum calcium and phosphorus remained unchanged, serum bicarbonate increased from 20 (17.2-22.0) to 24.5 (20.75-26) mmol/L (p < 0.001) after 3 months of sevelamer carbonate therapy. Sodium bicarbonate supplementation was stopped in all patients (n = 10), reducing the mean daily sodium intake by an average of 2.3 g per patient. These results demonstrate that sevelamer carbonate is an effective phosphate binder that improves acid-base status in pediatric dialysis patients.

Effect of sevelamer hydrochloride on bone in experimental uremic rats

Hyperphosphatemia in dialysis patients is known to cause secondary hyperparathyroidism and high-turnover bone disease. Sevelamer hydrochloride (sevelamer) is a nonabsorbed, calcium-free phosphate-binder. We determined the effect of sevelamer on parathyroid hormone (PTH)-induced high bone turnover. Rats were sham-operated or 5/6-nephrectomized (Nx) and fed a phosphate loading diet for 16 weeks or 5/6-nephrectomized and fed a phosphate loading diet for 8 weeks and then fed the same diet containing 3% sevelamer for the subsequent 8 weeks (Nx-S). Sevelamer significantly reduced serum PTH. The relative osteoid volume (OV/BV), osteoid surface (OS/BS), eroded surface (ES/BS), mineral appositional rate (MAR), volume-referent bone formation rate (BFR/TV), and bone-referent bone formation rate (BFR/BV) were measured for vertebral bone histomorphometric analysis. All parameters were statistically higher in the Nx rats than in the sham-operated control rats. The administration of sevelamer attenuated increases in OV/BV, ES/BS, BFR/TV, and BFR/BV. For femur histomorphometric analysis, the porosity area (%) (PoAr/CtAr), osteoid surface on the periosteal surface, osteoid surface on the endocortical surface (OS/Es), mineral appositional rate on the periosteal surface, mineral appositional rate on the endocortical surface, bone formation rate on the periosteal surface, and bone formation rate on the endocortical surface (Es BFR) were calculated. All parameters were higher in the Nx group than in the control group. Sevelamer inhibited the elevation of PoAr/CtAr, OS/Es, and Es BFR. Our findings suggest that the decrease in PTH by sevelamer may be beneficial in the treatment of high PTH-induced bone disease.

Relationship between plasma fibroblast growth factor-23 concentration and bone mineralization in children with renal failure on peritoneal dialysis

CONTEXT

Fibroblast growth factor (FGF)-23 is produced in bone, and circulating levels are markedly elevated in patients with end-stage kidney disease, but the relationship between plasma levels of FGF-23 and bone histology in dialysis patients with secondary hyperparathyroidism is unknown.

OBJECTIVE

The aim of the study was to evaluate the correlation between plasma levels of FGF-23 and bone histology in pediatric patients with end-stage kidney disease who display biochemical evidence of secondary hyperparathyroidism.

DESIGN

We performed a cross-sectional analysis of the relationship between plasma FGF-23 levels and bone histomorphometry.

SETTING

The study was conducted in a referral center.

STUDY PARTICIPANTS

Participants consisted of forty-nine pediatric patients who were treated with maintenance peritoneal dialysis and who had serum PTH levels (1st generation Nichols assay) greater than 400 pg/ml.

INTERVENTION

There were no interventions.

MAIN OUTCOME MEASURE

Plasma FGF-23 levels and bone histomorphometry were measured.

RESULTS

No correlation existed between values of PTH and FGF-23. Bone formation rates correlated with PTH (r = 0.44; P < 0.01), but not with FGF-23. Higher FGF-23 concentrations were associated with decreased osteoid thickness (r = -0.49; P < 0.01) and shorter osteoid maturation time (r = -0.48; P < 0.01).

CONCLUSIONS

High levels of FGF-23 are associated with improved indices of skeletal mineralization in dialyzed pediatric patients with high turnover renal osteodystrophy. Together with other biomarkers, FGF-23 measurements may indicate skeletal mineralization status in this patient population.

Response of different PTH assays to therapy with sevelamer or CaCO3 and active vitamin D sterols

Amino-terminally truncated parathyroid hormone (PTH) fragments are detected to differing degrees by first- and second-generation immunometric PTH assays (PTH-IMAs), and acute changes in serum calcium affect the proportion of these fragments in circulation. However, the effect of chronic calcium changes and different vitamin D doses on these PTH measurements remains to be defined. In this study, 60 pediatric dialysis patients, aged 13.9 +/- 0.7 years, with secondary hyperparathyroidism were randomized to 8 months of therapy with oral vitamin D combined with either calcium carbonate (CaCO(3)) or sevelamer. Serum phosphorus levels did not differ between groups. Serum calcium levels rose from 9.3 +/- 0.1 to 9.7 +/- 0.1 mg/dl during CaCO(3) therapy (p < 0.01 from baseline) but remained unchanged during sevelamer therapy. In the CaCO(3) and sevelamer groups, baseline serum PTH levels (1st PTH-IMA; Nichols Institute Diagnostics, San Clemente, CA) were 964 +/- 75 and 932 +/- 89 pg/ml, and levels declined to 491 +/- 55 and 543 +/- 59 pg/ml, respectively (nonsignificant between groups). Patients treated with sevelamer received higher doses of vitamin D than those treated with CaCO(3). The PTH values obtained by first- and second-generation PTH-IMAs correlated closely throughout therapy and the response of PTH was similar to both PTH-IMAs, despite differences in serum calcium levels.

Phosphate binders in chronic kidney disease and end-stage renal disease: a patient-centered approach

Disorders of calcium and phosphorus metabolism are associated with significant morbidity and mortality in patients with advanced chronic kidney disease. These patients typically require oral phosphate binders to maintain phosphorus homeostasis, but the choice of which among several agents to use has been actively investigated and debated. Recent debate has been polarized between those who favor calcium-based binders for their proven efficacy and relatively low cost and those who favor sevelamer for its putative beneficial effects on inflammatory biomarkers and vascular calcification. This review summarizes the current state of the art of prescribing phosphate binders, ranging from large-scale clinical trials to focused mechanistic studies, and proposes that the available evidence does not conclusively prove the relative superiority of any one binder.

Sevelamer hydrochloride improves hyperphosphatemia in hemodialysis patients with low bone turnover rate and low intact parathyroid hormone levels

Sevelamer improves hyperphosphatemia without increasing the calcium load. However, it remains unknown whether sevelamer restores bone metabolism in hemodialysis patients with low bone turnover osteodystrophy and hypoparathyroidism. We investigated the changes in serum intact parathyroid hormone (iPTH) and bone metabolic marker levels after replacing calcium carbonate with sevelamer in these patients. We also conducted stratified analysis based on patient background and multivariate analysis to determine the factors affecting these parameters. During sevelamer replacement therapy, serum calcium and phosphate concentrations, and the calcium phosphate product were measured at 0, 1, 3, and 6 months. Serum iPTH, bone alkaline phosphatase and osteocalcin concentrations were measured at 0 and 6 months. In hemodialysis patients (71 men and 46 women, 63 +/- 12 years old) serum calcium levels and the calcium phosphate product decreased significantly at 1 month. Serum iPTH, bone alkaline phosphatase and osteocalcin levels increased significantly at 6 months. Increases in serum iPTH concentrations were observed in all stratified groups. Significant increases in serum bone alkaline phosphatase and osteocalcin concentrations were found only in the relative hypoparathyroidism group (iPTH levels > or =51.5 pg/mL, the median pretreatment level). Multivariate analysis showed that the factors affecting change in serum iPTH level are baseline serum iPTH, baseline calcium level (> or =9.5 mg/dL), and dialysis duration of 10 years or longer. Sevelamer appears useful for the treatment of hyperphosphatemia in these patients. Particularly, in the relative hypoparathyroidism group, the iPTH secretory response is probably enhanced and bone turnover may have been improved as a result of reducing the calcium load.

Management of Renal Osteodystrophy: THe Heart and Bone of Pediatric Dialysis

Control of mineral homeostasis is a particularly challenging task in children and adolescents on dialysis. Treatment efforts must not only ensure patient survival and the absence of debilitating complications of bone disease, but in view of a potentially long lifespan, must also consider how to best promote long-term cardiovascular health and successful psychosocial transition into adult life. In that context, avoidance of cardiovascular calcifications and accomplishment of adequate statural growth and a normal final height are major objectives of uremic bone disease management in children. Unfortunately, current pediatric management guidelines operate on a small evidence base, and major controversy surrounds key issues such as optimal target ranges for serum parathyroid hormone, calcium, and phosphorus in the individual childhood phases, and individual risk–benefit ratios for the use of phosphate binders, vitamin D analogs, and calcimimetics in children. The present review summarizes the current state of knowledge and outlines future research requirements in bone disease associated with pediatric end-stage renal disease.

Vascular Calcification in Peritoneal Dialysis Patients

Vascular calcification (VC) is being recognized as a common complication at all stages of chronic kidney disease, particularly in patients on dialysis. Traditional and nontraditional cardiovascular risk factors both appear to be involved in the development of VC in this population. Although few studies focusing exclusively on peritoneal dialysis (PD) patients are available, some data support the view that VC constitutes an independent prognostic marker of morbidity and mortality in the PD population. In this review, we discuss the potential pathophysiologic pathways of VC in PD patients, and we examine the relevant clinical data.