Calcium acetate, an effective phosphorus binder in patients with renal failure

Calcium Acetate Drug Produced from Rapana venosa Invasive Gastropod Shells: Green Process Control Assisted by Raman Technology

The highly demanded calcium acetate (Ca(CH3COO)2) for biomedicine and various industries constantly requires green and low-cost methods of synthesis. In the present work, a sustainable approach to produce Ca(CH3COO)2 is reported as a proof of concept, processing for the first time as a starting material the worldwide highly abundant Rapana venosa shells, which is a neglected biogenic waste with high economical potential due to the rich mineral and organic pigmentary content. A green synthesis involving an eco-friendly acetic acid has been optimized at room temperature, without any additional energy consumption, and the resulting saturated Ca(CH3COO)2 solution was further slowly evaporated in three stages to obtain white Ca(CH3COO)2 crystalline powder, without impurity traces. Raman spectroscopy provided efficient structural information for every step of the process control, during demineralization as well as end product validation. Yields as high as 87.5% of highly pure Ca(CH3COO)2 mass have been achieved from raw R. venosa shells, proving the uniqueness and economic viability of the method. X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDX), and Fourier-Transform IR spectroscopy (FTIR) analyses validated the final product identity, hydration status, crystalline morphology, and composition. The purity of the resulting product suggests a high valorization potential of the abundant R. venosa shell in the context of the blue bioeconomy and offers a cleaner and efficient method of Ca(CH3COO)2 production with important applications in relevant industries.

Rabbits (Oryctolagus cuniculus) increase caecal calcium absorption at increasing dietary calcium levels

Hindgut fermenting herbivores from different vertebrate taxa, including tortoises, and among mammals some afrotheria, perissodactyla incl. equids, several rodents as well as lagomorphs absorb more calcium (Ca) from the digesta than they require, and excrete the surplus via urine. Both proximate and ultimate causes are elusive. It was suggested that this mechanism might ensure phosphorus availability for the hindgut microbiome by removing potentially complex-building Ca from the digesta. Here we use Ussing chamber experiments to show that rabbits (Oryctolagus cuniculus) maintained on four different diets (six animals/diet) increase active Ca absorption at increasing Ca levels. This contradicts the common assumption that at higher dietary levels, where passive uptake should be more prevalent, active transport can relax and hence supports the deliberate removal hypothesis. In the rabbits, this absorption was distinctively higher in the caecum than in the duodenum, which is unexpected in mammals. Additional quantification of the presence of two proteins involved in active Ca absorption (calbindin-D9K CB; vitamin D receptor, VDR) showed higher presence with higher dietary Ca. However, their detailed distribution across the intestinal tract and the diet groups suggests that other factors not investigated in this study must play major roles in Ca absorption in rabbits. Investigating strategies of herbivores to mitigate potential negative effects of Ca in the digesta on microbial activity and growth might represent a promising area of future research.

Small Intestinal Phosphate Absorption: Novel Therapeutic Implications

BACKGROUND

Chronic kidney disease (CKD) affects approximately 15% of adults in the USA. As CKD progresses, urinary phosphate excretion decreases and results in phosphate retention and, eventually, hyperphosphatemia. As hyperphosphatemia is associated with numerous adverse outcomes, including increased cardiovascular mortality, reduction in phosphorus concentrations is a guideline-recommended, established clinical practice. Dietary phosphate restriction, dialysis, and phosphate binders are currently the only options for phosphate management. However, many patients with hyperphosphatemia have phosphorus concentrations >5.5 mg/dL, despite treatment.

SUMMARY

This review pre-sents recent advances in the understanding of intestinal phosphate absorption and therapeutic implications. Dietary phosphate is absorbed in the intestine through two distinct pathways, paracellular absorption and transcellular transport. Recent evidence indicates that the paracellular route accounts for 65-80% of total phosphate absorbed. Thus, the paracellular pathway is the dominant mechanism of phosphate absorption. Tenapanor is a first-in-class, non-phosphate binder that inhibits the sodium-hydrogen exchanger 3 or solute carrier family 9 member 3 (SLC9A3) encoded by the SLC9A3 gene, and blocks paracellular phosphate absorption. Key Messages: Targeted inhibition of sodium-hydrogen exchanger 3 effectively reduces paracellular permeability of phosphate. Novel therapies that target the paracellular pathway may improve phosphate control in chronic kidney disease.

Phosphate Balance and CKD-Mineral Bone Disease

Chronic kidney disease-mineral bone disorder (CKD-MBD) is a common comorbidity in patients with CKD. Characterized by laboratory abnormalities, bone abnormality, and vascular calcification, CKD-MBD encompasses a group of mineral and hormone disturbances that are strongly associated with increased cardiovascular (CV) morbidity and mortality. Abnormal serum phosphate concentrations are an independent risk factor for CV morbidity and mortality, and overall mortality. Phosphate retention plays a central role in initiating and driving many other disturbances in CKD-MBD (e.g., increased parathyroid hormone and fibroblast growth factor 23 concentrations, hypocalcemia, low vitamin D) that are also linked to increased CV risk. Thus, effective phosphate control is a logical therapeutic target for CKD-MBD treatment. Current phosphate management strategies (dietary restrictions, dialysis, phosphate binders) are insufficient to consistently achieve and maintain target phosphate concentrations in patients on dialysis. Phosphate binders reduce available phosphate for intestinal absorption but do not impair the dominant phosphate absorption pathway. Novel therapies that consider new mechanistic understandings of intestinal phosphate absorption are needed. One such therapy is tenapanor, a targeted sodium-hydrogen exchanger isoform 3 inhibitor that has been shown to reduce serum phosphate concentrations in multiple clinical trials. Tenapanor has a novel mechanism of action that reduces intestinal phosphate absorption in the primary paracellular phosphate absorption pathway.

Revising Dietary Phosphorus Advice in Chronic Kidney Disease G3-5D

We summarize how practicing dietitians combined available evidence with clinical experience, to define revised dietary recommendations for phosphorus in chronic kidney disease G3-5D. As well as a review of the evidence base, 4 priority topics were reviewed. These were translated into 3 nutrient level recommendations: the introduction of some plant protein where phosphorus is largely bound by phytate; consideration of protein intake in terms of phosphorus load and the phosphorus to protein ratio; and an increased focus on avoiding phosphate additives. This review summarizes and interprets the available evidence in order to support the development of practical food-based advice for patients with chronic kidney disease.

Low Calcium Dialysate and Hyperparathyroidism

A low calcium dialysate reduces hypercalcemia from calcium-containing phosphate binders and makes phosphate control possible without the use of aluminum salts. We asked whether this might, however, lead to hyperparathyroidism. We prospectively studied serum concentrations of parathyroid hormone levels (by an immunoreactive intact molecule assay) in 173 patients on continuous ambulatory peritoneal dialysis (CAPD) who were started on a low calcium dialysate (Ca2+ 1.25 or 1.00 mmol/L) because of hypercalcemia. Median follow-up was 13.2 months (range 1 -28). Initial serum parathyroid hormone was [median (range)]: 70 (5 -1043) ng/L pre low calcium dialysate, and this rose to 130(5 -914) ng/LatO 6 months; 130 (5 -1030) ng/Lat 6 -12 months; 170 (170 1400) ng/L at 12 -18 months; and 130 (5 -1200) ng/L at 18 24 months (p = 0.0006). Twenty-two patients required a parathyroidectomy because of a sustained rise in parathyroid hormone that was not responsive to alfacalcidol and hypercalcemia. Initial serum parathyroid hormone was significantly higher in these patients at 359 (5 1073) ng/L as compared to a level of 69.5 (6 1147) ng/L in patients who did not have a parathyroidectomy (p = 0.0009). There was a significant sustained fall in mean serum corrected calcium from 2.77 (2.37 3.51) mmol/L to 2.53 (1.39 3.20) mmol/L at three months (p = 0.0006), a nonsignificant rise in mean serum alkaline phosphate from 179 (47 -1858) mmol/L to 191 (55 -1821) mmol/L (p = 0.15), and a fall in mean serum phosphate levels from 1.87 (0.59–3.18) mmol/L to 1.68 (0.45–3.6) mmol/L (p = 0.76). Our data suggest that the benefits of a low calcium dialysate in CAPD patients are balanced by an increased risk of hyperparathyroidism, and that this risk is higher in patients with an initially high serum parathyroid hormone level.

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.

Long-Term Complications in Patients With Hypoparathyroidism Evaluated by Biochemical Findings: A Case-Control Study

Hypoparathyroidism (HypoPT) is associated with an increased risk of various complications, but only few data are available on risk factors. Using a case-control design, we assessed associations between biochemical findings and risk of different complications within a subpopulation of our previously identified Danish patients. We retrieved all biochemical data available on 431 (81% women) patients from the Central Region of Denmark, covering approximately 20% of the Danish population. Average age of patients was 41 years at time of diagnosis. Most patients (88%) had HypoPT due to surgery, mainly due to atoxic goiter and more than 95% were on treatment with calcium supplements and activated vitamin D. On average, time-weighted (tw) plasma levels of ionized calcium (Ca²⁺_tw ) was 1.17 mmol/L (interquartile range [IQR], 1.14 to 1.21 mmol/L) and the calcium-phosphate (CaxP_tw ) product was 2.80 mmol² /L² (IQR, 2.51 to 3.03 mmol² /L² ). High phosphate_tw levels were associated with increased mortality and risk of any infections, including infections in the upper airways. A high CaxP_tw product was associated with an increased mortality and risk of renal disease. Compared to levels around the lower part of the reference interval, lower Ca²⁺_tw levels were associated with an increased risk of cardiovascular diseases. Mortality and risk of infections, cardiovascular diseases, and renal diseases increased with number of episodes of hypercalcemia and with increased disease duration. Treatment with a relatively high dose of active vitamin D was associated with a decreased mortality and risk of renal diseases and infections. In conclusion, risk of complications in HypoPT is closely associated with disturbances in calcium-phosphate homeostasis. © 2018 American Society for Bone and Mineral Research.

Effect of additive calcium administration on FGF23 levels in patients with mild chronic kidney disease treated with calcitriol: a randomized, open-labeled clinical trial

BACKGROUND

The purpose of the present study was to determine the effect of additional calcium carbonate treatment on fibroblast growth factor 23 (FGF23) levels in patients treated with calcitriol.

METHODS

In this randomized, open-labeled, and parallel-group study, a total of 30 patients with early chronic kidney disease (CKD) and vitamin D deficiency were randomly assigned to two groups and received interventions for 8 weeks: 1) a combination of calcium carbonate and calcitriol group; and 2) calcitriol only group. The primary outcome was the difference in percentage change of serum FGF23 levels from baseline between the two groups. Secondary end points included the changes in serum levels of calcium, phosphate, parathyroid hormone (PTH), and 25-hydroxyvitamin D₃ (25(OH)D) from baseline.

RESULTS

Serum FGF23 levels were more elevated in the combination group than in the calcitriol-alone group. However, both mean change and percentage change in the serum FGF23 levels during the 8-week period were not significantly different between the two groups. Serum calcium level was increased significantly only in the combination treatment group. There was no significant difference in percentage change of serum calcium levels between the two groups. In addition, changes in serum levels of phosphate, 25(OH)D, or PTH were not significantly different between the two groups. In correlation analysis, changes in serum FGF23 levels were positively correlated with changes in serum calcium and phosphate levels, but not with changes in 25(OH)D or PTH levels. No serious adverse events were observed, however, there was one case of mild gastrointestinal discomfort.

CONCLUSION

This study revealed that additional calcium carbonate treatment significantly increased serum FGF23 levels in patients treated with calcitriol, with their synergistic effect in promoting intestinal calcium absorption. This suggests that serum FGF23 levels should be monitored regularly, especially in those who use combination of vitamin D and calcium carbonate from the early stages of CKD.

Calcium Bioavailability and Kinetics of Calcium Ascorbate and Calcium Acetate in Rats

The objective was to investigate the bioavailability and mechanism of calcium absorption of calcium ascorbate (ASC) and calcium acetate (AC). A series of studies was performed in adult Sprague-Dawley male rats. In the first study, each group of rats (n = 10/group) was assigned to one of the five test meals labeled with 45Ca: (i) 25 mg calcium as heated ASC or (ii) unheated ASC, (iii) 25 mg calcium as unheated AC, (iv) 3.6 mg Ca as unheated ASC, or (v) unheated AC. Femur uptake indicated better calcium bioavailability from ASC than AC t both calcium loads. A 5-min heat treatment partly reduced bioavailability of ASC. Kinetic studies were performed to further investigate the mechanism of superior calcium bioavailability from ASC. Two groups of rats (n = 10/group) received oral doses of 25 mg Ca as ASC or AC. Each dose contained 20 μCi 45Ca. Two additional groups of rats (n = 10/group) received an intravenous injection (iv) of 10 μCi 45Ca after receiving an unlabeled oral dose of 25 mg calcium as ASC or AC. Sequential blood samples were collected over 48 hrs. Urine and fecal samples were collected every 12 hrs for 48 hrs and were analyzed for total calcium and 45Ca content. Total calcium and 45Ca from serum, urine, and feces were fitted by a compartment kinetics model with saturable and nonsaturable absorption pathways by WinSAAM (Windows-based Simulation Analysis and Modeling). The difference in calcium bioavailability between the two salts was due to differences in saturable rather than passive intestinal absorption and not to endogenous secretion or calcium deposition rate. The higher bioavailability of calcium ascorbate was due to a longer transit time in the small intestine compared with ASC.

Effect of Patiromer on Urinary Ion Excretion in Healthy Adults

BACKGROUND AND OBJECTIVES

Patiromer is a nonabsorbed potassium-binding polymer that uses calcium as the counterexchange ion. The calcium released with potassium binding has the potential to be absorbed or bind phosphate. Because binding is not specific for potassium, patiromer can bind other cations. Here, we evaluate the effect of patiromer on urine ion excretion in healthy adults, which reflects gastrointestinal ion absorption.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We analyzed the effect of patiromer on urine potassium, sodium, magnesium, calcium, and phosphate in two studies. Healthy adults on controlled diets in a clinical research unit were given patiromer up to 50.4 g/d divided three times a day for 8 days (dose-finding study) or 25.2 g/d in a crossover design as daily or divided (two or three times a day) doses for 18 days (dosing regimen study). On the basis of 24-hour collections, urinary ion excretion during the baseline period (days 5-11) was compared with that during the treatment period (days 13-19; dose-finding study), and the last 4 days of each period were compared across regimens (dosing regimen study).

RESULTS

In the dose-finding study, patiromer induced a dose-dependent decrease in urine potassium, urine magnesium, and urine sodium (P<0.01 for each). Patiromer at 25.2 g/d decreased urine potassium (mean±SD) by 1140±316 mg/d, urine magnesium by 45±1 mg/d, and urine sodium by 225±145 mg/d. Urine calcium increased in a dose-dependent manner, and urine phosphate decreased in parallel (both P<0.01). Patiromer at 25.2 g/d increased urine calcium by 73±23 mg/d and decreased urine phosphate by 64±40 mg/d. Urine potassium, urine sodium, and urine magnesium were unaffected by dosing regimen, whereas the increase in urine calcium was significantly lower with daily compared with three times a day dosing (P=0.01). Urine phosphate also decreased less with daily compared with two or three times a day dosing (P<0.05).

CONCLUSIONS

In healthy adults, patiromer reduces urine potassium, urine sodium, urine magnesium, and urine phosphate, while modestly increasing urine calcium. Compared with divided dosing, administration of patiromer once daily provides equivalent reductions in urine potassium, urine sodium, and urine magnesium, with less effect on urine calcium and urine phosphate.

Review: Therapy for the altered mineral metabolism of chronic kidney disease: implications for vascular calcification

The development of chronic kidney disease (CKD) is associated with poor outcomes largely due an increased likelihood of adverse cardiovascular events. Many factors are playing a role in cardiovascular disease in CKD including the development of vascular calcification (VC). Studies have indeed shown that the presence of VC is associated with decreased survival among patients with CKD. The pathogenesis of VC is itself multi-factorial. LikeLy playing a significant role is the altered mineral metabolism of CKD. Management of the altered mineral metabolism in CKD is quite difficult and may also play a role in the pathogenesis of VC. In this manuscript, we will review the pathogenesis of the altered mineral metabolism of CKD, its management, and how both may play a role in the development of VC.

Managing hyperphosphatemia in patients with chronic kidney disease on dialysis with ferric citrate: latest evidence and clinical usefulness

Ferric citrate is a novel phosphate binder that allows the simultaneous treatment of hyperphosphatemia and iron deficiency in patients being treated for end-stage renal disease with hemodialysis (HD). Multiple clinical trials in HD patients have uniformly and consistently demonstrated the efficacy of the drug in controlling hyperphosphatemia with a good safety profile, leading the US Food and Drug Administration in 2014 to approve its use for that indication. A concurrent beneficial effect, while using ferric citrate as a phosphate binder, is its salutary effect in HD patients with iron deficiency being treated with an erythropoietin-stimulating agent (ESA) in restoring iron that becomes available for reversing chronic kidney disease (CKD)-related anemia. Ferric citrate has also been shown in several studies to diminish the need for intravenous iron treatment and to reduce the requirement for ESA. Ferric citrate is thus a preferred phosphate binder that helps resolve CKD-related mineral bone disease and iron-deficiency anemia.

Use of magnesium as a drug in chronic kidney disease

From chronic kidney disease (CKD) Stage 4 onwards, phosphate binders are needed in many patients to prevent the development of hyperphosphataemia, which can result in disturbed bone and mineral metabolism, cardiovascular disease and secondary hyperparathyroidism. In this review, we re-examine the use of magnesium-containing phosphate binders for patients with CKD, particularly as their use circumvents problems such as calcium loading, aluminum toxicity and the high costs associated with other agents of this class. The use of magnesium hydroxide in the 1980s has been superseded by magnesium carbonate, as the hydroxide salt was associated with poor gastrointestinal tolerability, whereas studies with magnesium carbonate show much better gastrointestinal profiles. The use of combined magnesium- and calcium-based phosphate binder regimens allows a reduction in the calcium load, and magnesium and calcium regimen comparisons show that magnesium may be as effective a phosphate binder as calcium. A large well-designed trial has recently shown that a drug combining calcium acetate and magnesium carbonate was non-inferior in terms of lowering serum phosphate to sevelamer-HCl and had an equally good tolerability profile. Because of the high cost of sevelamer and lanthanum carbonate, the use of magnesium carbonate could be advantageous and drug acquisition cost savings would compensate for the cost of introducing routine magnesium monitoring, if this is thought to be necessary and not performed anyway. Moreover, given the potential cost savings, it may be time to re-investigate magnesium-containing phosphate binders for CKD patients with further well-designed clinical research using vascular end points.

Calcium acetate or calcium carbonate for hyperphosphatemia of hemodialysis patients: a meta-analysis

BACKGROUND

High levels of serum phosphorus both at baseline and during follow-up are associated with increased mortality in dialysis patients, and administration of phosphate binders was independently associated with improved survival among hemodialysis population. Calcium-based phosphate binders are the most commonly used phosphate binders in developing countries for their relatively low costs.

OBJECTIVES

To compare the efficacy and safety between calcium carbonate and calcium acetate in the treatment of hyperphosphatemia in hemodialysis patients.

METHODS

PubMed, EMBASE, Cochrane Library, Google scholar and Chinese databases (Wanfang, Weipu, National Knowledge Infrastructure of China) were searched for relevant studies published before March 2014. Reference lists of nephrology textbooks and review articles were checked. A meta-analysis of randomized controlled trials (RCTs) and quasi-RCTs that assessed the effects and adverse events of calcium acetate and calcium carbonate in adult patients with MHD was performed using Review Manager 5.0.

RESULTS

A total of ten studies (625 participants) were included in this meta-analysis. There was insufficient data in all-cause mortality and cardiovascular events for meta-analysis. Compared with calcium carbonate group, the serum phosphorus was significantly lower in calcium acetate group after4 weeks' administration (MD -0.15 mmol/L, 95% CI -0.28 to -0.01) and after 8 weeks' administration (MD -0.25 mmol/L, 95% CI -0.40 to -0.11). There was no difference in serum calcium levels or the incidence of hypercalcemia between two groups at 4 weeks and 8 weeks. No statistical difference was found in parathyroid hormone (PTH) levels or serum calcium by phosphorus (Ca x P) product. There was significantly higher risk of intolerance with calcium acetate treatment (RR 3.46, 95% CI 1.48 to 8.26).

CONCLUSIONS

For hyperphosphatemia treatment, calcium acetate showed better efficacy and with a higher incidence of intolerance compared with calcium carbonate. There are insufficient data to establish the comparative superiority of the two calcium-based phosphate binders on all-cause mortality and cardiovascular end-points in hemodialysis patients.

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.

Dietary phosphate restriction in dialysis patients: a new approach for the treatment of hyperphosphataemia

BACKGROUND AND AIM

Elevated serum phosphate and calcium-phosphate levels play an important role in the pathogenesis of vascular calcifications in uraemic patients and appear to be associated with increased cardiovascular mortality. We aimed to evaluate the effects of a partial replacement of food protein with a low-phosphorus and low-potassium whey protein concentrate on phosphate levels of dialysis patients with hyperphosphataemia.

METHODS AND RESULTS

Twenty-seven patients undergoing chronic haemodialysis were studied for a 3-month period. In the intervention group (n = 15), food protein were replaced by 30 or 40 g of low-phosphorus and low-potassium protein concentrate aimed at limiting the phosphate intake. In the control group (n = 12) no changes were made to their usual diet. Anthropometric measurements, biochemical markers and dietary interviews were registered at baseline and during the follow-up period. From baseline to the end of the study, in the intervention group, serum phosphate and circulating intact parathyroid hormone levels lessened significantly (8.3 ± 1.2 mg/dL vs 5.7 ± 1.4 mg/dL and 488 ± 205 pg/ml vs 177 ± 100 pg/ml respectively; p < 0.05) with decreasing of phosphate and potassium intake. No significant differences were found in the control group. No significant changes were observed in serum albumin, calcium, potassium, Kt/V, body weight and body composition in both the intervention and control groups.

CONCLUSION

Dietary intake of phosphate mainly comes from protein sources, so dietary phosphorus restriction may lead to a protein/energy malnutrition in a dialysis patient. A phosphorus-controlled diet plan including a nutritional substitute resulted in serum phosphate and intact parathyroid hormone decrease without nutritional status modifications in dialysis patients.

Phosphate binding therapy in dialysis patients: focus on lanthanum carbonate

Hyperphosphatemia is an inevitable consequence of end stage chronic kidney disease and is present in the majority of dialysis patients. Recent observational data has associated hyperphosphatemia with increased cardiovascular mortality among dialysis patients. Dietary restriction of phosphate and current dialysis prescription practices are not enough to maintain serum phosphate levels within the recommended range so that the majority of dialysis patients require oral phosphate binders. Unfortunately, conventional phosphate binders are not reliably effective and are associated with a range of limitations and side effects. Aluminium-containing agents are highly efficient but no longer widely used because of well established and proven toxicity. Calcium based salts are inexpensive, effective and most widely used but there is now concern about their association with hypercalcemia and vascular calcification. Sevelamer hydrochloride is associated with fewer adverse effects, but a large pill burden and high cost are limiting factors to its wider use. In addition, the efficacy of sevelamer as a monotherapy in lowering phosphate to target levels in severe hyperphosphatemia remains debatable. Lanthanum carbonate is a promising new non-aluminium, calcium-free phosphate binder. Preclinical and clinical studies have demonstrated a good safety profile, and it appears well tolerated and effective in reducing phosphate levels in dialysis patients. Its identified adverse events are apparently mild to moderate in severity and mostly GI related. It appears to be effective as a monotherapy, with a reduced pill burden, but like sevelamer, it is significantly more expensive than calcium-based binders. Data on its safety profile over 6 years of treatment are now available.

The phosphate binder equivalent dose

Phosphate binders include calcium acetate or carbonate, sevelamer hydrochloride or carbonate, magnesium and lanthanum carbonate, and aluminum carbonate or hydroxide. Their relative phosphate-binding capacity has been assessed in human, in vivo studies that have measured phosphate recovery from stool and/or changes in urinary phosphate excretion or that have compared pairs of different binders where dose of binder in each group was titrated to a target level of serum phosphate. The relative phosphate-binding coefficient (RPBC) based on weight of each binder can be estimated relative to calcium carbonate, the latter being set to 1.0. A systematic review of these studies gave the following estimated RPBC: for elemental lanthanum, 2.0, for sevelamer hydrochloride or carbonate 0.75, for calcium acetate 1.0, for anhydrous magnesium carbonate 1.7, and for "heavy" or hydrated, magnesium carbonate 1.3. Estimated RPBC for aluminum-containing binders were 1.5 for aluminum hydroxide and 1.9 for aluminum carbonate. The phosphate-binding equivalent dose was then defined as the dose of each binder in g × its RPBC, which would be the binding ability of an equivalent weight of calcium carbonate. The phosphate-binding equivalent dose may be useful in comparing changes in phosphate binder prescription over time when multiple binders are being prescribed, when estimating an initial binder prescription, and also in phosphate kinetic modeling.

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.

Evaluation of morbidity and mortality data related to cardiovascular calcification from calcium-containing phosphate binder use in patients undergoing hemodialysis

Cardiovascular disease is the leading cause of death among patients with stage 5 chronic kidney disease. Several mechanisms are thought to contribute to vascular calcification and subsequent cardiovascular disease in patients who require hemodialysis. One of these mechanisms is the use of calcium-containing phosphate binders to treat hyperphosphatemia. Although most phosphate binding occurs in the gastrointestinal tract, some calcium is inevitably absorbed and has the potential to perpetuate the calcium-phosphorus product and the development of vascular and soft tissue calcification. Some phosphate binders such as sevelamer hydrochloride do not contain calcium and therefore may not carry the same risks. We examined the cardiovascular calcification effect and morbidity and mortality data with calcium-containing phosphate binders compared with sevelamer hydrochloride when given to patients with stage 5 chronic kidney disease for the treatment of hyperphosphatemia. A literature search using the MEDLINE and PubMed databases identified relevant articles from 1989-2009; nine studies compared vascular calcification between a calcium-containing phosphate binder and sevelamer hydrochloride. Three mortality studies were also identified. Seven of the nine studies reported a statistically significant increase in vascular calcification in patients taking calcium-containing phosphate binders as measured by coronary artery calcification scores and aortic calcification scores. In two trials, lower mortality rates were observed in the patients receiving sevelamer hydrochloride compared with calcium-containing phosphate binders. No significant difference in the mortality rate was observed in the third trial. Based on the current literature, it appears that calcium-containing phosphate binders promote the progression of vascular calcification to a greater extent than does sevelamer hydrochloride. In addition, some evidence suggests that sevelamer hydrochloride may reduce all-cause mortality rates in patients undergoing hemodialysis, particularly those aged 65 years or older. Thus, although sevelamer hydrochloride appears to be the more appropriate choice of phosphate binder for patients undergoing hemodialysis in whom cardiovascular calcification is a concern, more clinical trials are needed to further guide practitioners on the selection of phosphate binders.

Management of hyperphosphatemia in patients with end-stage renal disease: focus on lanthanum carbonate

Elevated serum phosphate levels as a consequence of chronic kidney disease (CKD) contribute to the increased cardiovascular risk observed in dialysis patients. Protein restriction and dialysis fail to adequately prevent hyperphosphatemia, and in general treatment with oral phosphate binding agents is necessary in patients with advanced CKD. Phosphate plays a pivotal role in the development of vascular calcification, one of the factors contributing to increased cardiovascular risk in CKD patients. Treatment of hyperphosphatemia with standard calcium-based phosphate binders and vitamin D compounds can induce hypercalcemic episodes, increase the Ca × PO₄ product and thus add to the risk of ectopic mineralization. In this review, recent clinical as well as experimental data on lanthanum carbonate, a novel, non-calcium, non-resin phosphate binding agent are summarized. Although lanthanum is a metal cation no aluminium-like toxicity is observed since the bioavailability of lanthanum is extremely low and its metabolism differs from that of aluminium. Clinical studies now document the absence of toxic effects of lanthanum for up to 6 years of follow-up. The effects of lanthanum on bone, vasculature and brain are discussed and put in perspective with lanthanum pharmacokinetics.

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.

Current Approaches in the Treatment of Chronic Kidney Disease Mineral and Bone Disorder

Patients with chronic kidney disease (CKD) develop mineral and bone disorder (MBD), a common and important complication, as a result of impaired phosphorus excretion and reduced vitamin D activation. Altered mineral metabolism is now recognized as an independent cardiovascular risk factor in end-stage renal disease patients and contributes to the risk for accelerating vascular calcification. CKD patients are at high risk for cardiovascular disease and vascular calcification which account for the high morbidity and mortality in this patient population. Pharmacotherapeutic interventions are necessary to manage and treat the condition. Multiple classes of agents including phosphorus binders, vitamin D analogs, and calcimimetics are now available to treat CKD-MBD. Recent data have shown that treatment with sevelamer and vitamin D analogs are associated with a reduction in calcification and cardiovascular mortality and improved survival. This article provides an overview of the strategies and considerations for the management of CKD-MBD, as well as their implications on clinical outcomes.

Does a change in angiotensin II formation caused by antihypertensive drugs affect the risk of stroke?

BACKGROUND

Stroke prevention by antihypertensive therapy is believed to be related to the fall in blood pressure (BP). Experimental data have documented that activation of non-AT1 receptors of angiotensin II may exert anti-ischaemic mechanisms in the brain. The present meta-analysis of various randomized clinical trials attempts to relate stroke risk to angiotensin II formation during antihypertensive therapy.

METHODS

Primary and secondary stroke prevention was examined in 26 prospective, randomized clinical trials including 206,632 patients without heart failure, in whom a total of 7,108 strokes occurred. The trials were selected because a difference in angiotensin II generation was expected between the two treatment arms on the basis of the drugs' pharmacodynamic effects, and allowed 36 evaluations of the relative risk of stroke.

FINDINGS

In placebo-controlled trials, stroke risk was significantly higher with angiotensin II-decreasing than increasing drugs, but systolic BP decreased less in the former. Compared with an active therapy having a neutral effect on angiotensin II formation, stroke risk was also higher with angiotensin-decreasing drugs than with angiotensin-increasing drugs, whereas BP decrease was comparable with both drug classes. When angiotensin II-decreasing drugs were directly compared with angiotensin II-increasing drugs in the same trials, stroke risk was significantly increased. On-treatment systolic BP was minimally and significantly higher with angiotensin II-decreasing drugs, but not large enough to explain the excess in stroke risk.

CONCLUSION

Within the limitations of the methodology, our meta-analysis supports the hypothesis that angiotensin II-decreasing drugs are less stroke protective than angiotensin II-increasing drugs, although this difference is not entirely explained by their smaller BP-lowering effect.

PHOSPHORUS METABOLISM AND MANAGEMENT IN CHRONIC KIDNEY DISEASE: Phosphate Metabolism in the Setting of Chronic Kidney Disease: Significance and Recommendations for Treatment

Phosphorus is an essential mineral that plays a crucial role in cell structure and metabolism. In living organisms, phosphorus exists surrounded by four oxygen atoms to form phosphate (PO(4)). Within cells, PO(4) regulates enzymatic activity and serves as an essential component of nucleic acids, adenosine triphosphate, and phospholipid membranes. Outside cells, PO(4) primarily resides in bone and teeth as hydroxyapatite. A small amount of inorganic PO(4) circulates in serum, with levels balanced by gastrointestinal intake, renal excretion, and a set of specific hormones. Under normal conditions, PO(4) is excreted through the kidneys. Among patients with end stage renal disease (ESRD) receiving chronic dialysis, circulating PO(4) levels typically rise to levels well above the normal laboratory range. Higher serum PO(4) levels are strongly associated with arterial calcification and mortality in this setting. Among predialysis patients with chronic kidney disease (CKD), phosphaturic hormones enhance renal PO(4) excretion to maintain serum PO(4) levels within the high-normal laboratory range. Recently, high-normal serum PO(4) levels have been associated with cardiovascular (CV) events and mortality among individuals who have CKD and among those who have normal kidney function. This review discusses PO(4) metabolism in the context of CKD, examines associations of PO(4) levels with adverse outcomes in the CKD setting, and suggests treatment strategies for moderating serum PO(4) levels.

Comment atteindre et maintenir les recommandations K/DOQITM sur le métabolisme phosphocalcique chez les patients dialysés: une stratégie efficace

INTRODUCTION

Recent publications have indicated that alterations in bone and mineral metabolism are known to participate to a high mortality rate in patients undergoing haemodialysis. A new therapeutic strategy is progressively undertaken in the dialysis unit over a 36 months period covering years 2002 to 2004.

METHODS

This new strategy includes the prescription of non-calcium, non-aluminium phosphate binder, sevelamer hydrochloride, an increase in vitamin D analogues prescription and a moderation in calcium carbonate administration. Sixty patients participated to the entire study and are evaluated three times a year on the four K/DOQI parameters. Other indicators such as haemoglobin, bicarbonate, total cholesterol and HDL cholesterol levels were studied.

RESULTS

At the beginning of the study, 7% of the patients achieved the four K/DOQI parameters. This proportion seemed identical to those observed in the major studies. But progressively with the new therapeutic strategy 13%, then 21%, and at the end of the study 35% reached the four criteria. Therapeutic calcium intakes decreased from 100 g per patient/month to 28 g per patient-month. Prescription of vitamin D analogues increased from 3.3 microg per patient-month to 18.3 microg per patient/month. At the end of the study 60% of the patients received sevelamer hydrochloride at the mean dosage of 4800 mg per day. Haemoglobin remains stable. Bicarbonate level decreased due to a minor prescription in calcium carbonate. Under statins the ratio total cholesterol/HDL cholesterol decreased to 3.3.

CONCLUSION

A modification in the therapeutic strategy offer to patients undergoing haemodialysis, the possibility to achieve the K/DOQI recommendations with the hope to obtain a beneficial effect on patient outcomes.

Medical therapy of secondary hyperparathyroidism in chronic kidney disease: old and new drugs

Secondary hyperparathyroidism (SHPT), a common complication of chronic kidney disease, is characterised by elevated serum levels of parathyroid hormone, parathyroid hyperplasia, excessive bone resorption and increased risk for cardiovascular morbidity. The stringent metabolic targets proposed by the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) for patients with SHPT are difficult to achieve using conventional treatment regimens. Several new agents, including new vitamin D sterols and phosphate binders, as well as a novel class of compounds--the calcimimetics--have been developed in recent years. This review examines new and traditional therapies for SHPT and how these can best be utilised in order to achieve the new K/DOQI targets.

Emerging strategies for lowering serum phosphorous in patients with end-stage renal disease

Hyperphosphataemia is a major problem in patients with chronic kidney disease as it has been associated with increased morbidity and mortality. Over the last four decades, different modalities have been applied to treat hyperphosphataemia with varying degrees of success. Unfortunately, treatment strategies have led to unforeseen complications. These have prompted the development of new classes of medications with potentially better efficacy and few short-term and long-term side effects. This article reviews the causes, mechanism and management of hyperphosphataemia.

The safety of phosphate binders

Disturbances of mineral metabolism occur during the early stages of chronic kidney disease. As renal function worsens, excess dietary phosphorus accumulates and blood levels increase, that can be clearly seen when the glomerular filtration rate has fallen below 30 ml/min/1.73 m2. In patients with end stage renal disease, standard dialysis (three times/week) falls far short of removing adequate amounts of absorbed phosphorus; therefore, hyperphosphataemia is found in the majority of these patients. Hyperphosphataemia has long been associated with progression of secondary hyperparathyroidism and renal osteodystrophy, it can also lead to soft-tissue and vascular calcification. Recent observational data have associated hyperphosphataemia with increased cardiovascular mortality among dialysis patients. Adequate control of serum phosphorus remains a cornerstone in the clinical management and, despite the growing amount of available therapeutic options, achievement of NFK/KDOQI targets for mineral metabolism remain poor. Several reasons may explain the failure to adequately treat hyperphosphataemia: poor compliance with diet and phosphate binder prescriptions are common causes. Also, factors related with cost, tolerance, palatability, safety and efficacy are important. In this article, the authors review the advantages and drawbacks of conventional and emerging therapies in phosphorous binding.

Control of Hyperphosphatemia among Patients with ESRD

Derangements of mineral metabolism occur during the early stages of chronic kidney disease (CKD). Hyperphosphatemia develops in the majority of patients with ESRD and has long been associated with progression of secondary hyperparathyroidism and renal osteodystrophy. More recent observational data have associated hyperphosphatemia with increased cardiovascular mortality among dialysis patients. Adequate control of serum phosphorus remains a cornerstone in the clinical management of patients with CKD not only to attenuate the progression of secondary hyperparathyroidism but also possibly to reduce the risk for vascular calcification and cardiovascular mortality. These measures include dietary phosphorus restriction, dialysis, and oral phosphate binders. Dietary restriction is limited in advanced stages of CKD. Phosphate binders are necessary to limit dietary absorption of phosphorus. Aluminum hydroxide is an efficient binder; however, its use has been nearly eliminated because of concerns of toxicity. Calcium salts are inexpensive and have been used effectively worldwide as an alternative to aluminum. Concerns of calcium overload have led to the investigation of alternatives. Currently, only two Food and Drug Administration-approved noncalcium, nonaluminum binders are available. Sevelamer hydrochloride is an exchange resin and was not as effective as calcium acetate in meeting new guideline recommendations in one double-blind clinical trial. Lanthanum carbonate is a rare earth element and has been studied less extensively. Concerns of long-term administration and toxicity exist. Furthermore, these agents are significantly more expensive than calcium salts, which may contribute to patient noncompliance.

Viewpoint: How Do Calcimimetics Fit Into the Management of Parathyroid Hormone, Calcium, and Phosphate Disturbances in Dialysis Patients?

As suggested by its American brand name (Sensipar), the calcimimetic cinacalcet sensitizes the parathyroid cells to the extracellular calcium signal, suppressing parathyroid hormone (PTH) release and synthesis and preventing parathyroid cell proliferation. This primary PTH suppression decreases the release of calcium and phosphate from bone without increasing intestinal absorption of calcium and phosphate. Therefore cinacalcet decreases the risk of hypercalcemia and hyperphosphatemia in contrast to 1alpha-OH vitamin D derivatives. Compared with calcium-containing oral phosphate binder (OPB), it increases the risk of hypocalcemia and may decrease the PTH-mediated phosphaturia in predialysis patients. This justifies its combined use with calcium-containing OPB in order to prevent hypocalcemia and enhance the hypophosphatemic effect of the latter, while improving PTH suppression. The National Kidney Foundation (NKF) Kidney Disease Outcomes Quality Initiative (K/DOQI) has recommended restriction of supplemental elemental calcium to 1.5 g/day, a recommendation that we believe should be revised. No pathophysiologic or randomized trial data have yet evidenced the absolute necessity for systematically using 1alpha-OH vitamin D derivatives and noncalcium-containing OPB rather than higher doses of calcium-containing OPB alone in uremic patients without vitamin D insufficiency. In patients with hyperparathyroidism as severe as in the "Treat to Goal Study," the Durham study showed that a calcium carbonate dose more than three times the K/DOQI limit could decrease PTH into the recommended range, with the advantage of a lower calcium-phosphate product compared with the combination of calcitriol and noncalcium OPB. Besides the efficient PTH suppression associated with lower calcium-phosphate product and a good gastrointestinal tolerance, long-term data suggest that cinacalcet may decrease the risk of parathyroidectomy and fracture, while high bone turnover lesions are improved. However, no long-term data on bone mineral density and cardiovascular calcification and complications are yet available. Such studies, along with those comparing cinacalcet and 1alpha-OH vitamin D-based approaches to hyperparathyroidism, are needed.

Complications of chronic kidney disease: anemia, mineral metabolism, and cardiovascular disease

This article focuses on the importance of three major complications of chronic kidney disease: (1) anemia, (2) calcium-phosphorus regulation and bone disease, and (3) cardiovascular risk profiling and treatment. The arguments for early and effective intervention have been amply made with respect to these three complications. Substantive trial data are sorely need to provide the definitive evidence that effective treatment of these complications results in better outcomes.

A comparison of clinically useful phosphorus binders for patients with chronic kidney failure

A comparison of clinically useful phosphorus binders for patients with chronic kidney failure. Over the past 30 years it has become apparent that hyperphosphatemia plays a major causative role across the entire spectrum of morbidity associated with advancing kidney dysfunction and failure. A large fraction (60% to 70%) of dietary phosphorus is absorbed and normally excreted by the kidneys. Ideally, as kidney function deteriorates, the net quantity of phosphorus absorbed from the GI tract should be proportionally reduced to match the decrease in kidney function. After initiation of chronic dialysis therapy, the absorbed phosphorus load should match the amount of phosphorus removed via dialysis plus any excreted by residual kidney function. Because it is very difficult to reduce dietary phosphorus to these levels, a variety of oral phosphorus binders have been employed. Currently available binders include alkaline aluminum, magnesium, and calcium salts (primarily calcium carbonate and calcium acetate), various iron salts, and the binding resin sevelamer hydrochloride. Lanthanum carbonate is the newest agent and will probably be released shortly. This review compares the theoretic and in vitro chemistry of these drugs with in vivo data obtained in both normal patients, and in patients with kidney failure. The clinical potency and potential toxicity of the binding agents are compared, and optimal drug administration strategies are also reviewed.

Hyperphosphataemia in renal failure: causes, consequences and current management

Hyperphosphataemia is prevalent among chronic renal failure and dialysis patients. It is known to stimulate parathyroid hormone and suppress vitamin D3 production, thereby inducing hyperparathyroid bone disease. In addition, it may independently contribute to cardiac causes of death through increased myocardial calcification and enhanced vascular calcification. Hyperphosphataemia is also associated with cardiac microcirculatory abnormalities. Therefore, phosphate control is of prime importance. It is important to control phosphate levels early in the course of chronic renal failure in order to avoid and treat secondary hyperparathyroidism, and cardiovascular and soft tissue calcifications. Dietetic restrictions are often difficult to follow long term. Because of its large sphere of hydration and the complex kinetics of phosphate elimination, phosphate is not easily removed by dialysis. Long, slow dialysis may be effective, but this needs logistics and acceptance by patients. Thus, oral phosphate binders are generally required to control serum levels. None of the existing phosphate binding agents is truly satisfactory. Aluminium-containing agents are highly efficient but many clinicians have abandoned their use because of the potential toxicity. Despite of the wide use of calcium-containing agents, there was a link with hypercalcaemia and soft tissue calcifications. Novel phosphate binders in the form of polyallylamine hydrochloride, polyuronic acid derivatives and lanthanum carbonate appear promising. In this review, we discuss causes of hyperphosphataemia, pathological consequences and modalities of treatment.

Treatment of hyperphosphatemia with sevelamer hydrochloride in hemodialysis patients: a comparison with calcium acetate

BACKGROUND

Sevelamer hydrochloride is a recently approved calcium- and aluminium-free phosphate binder. A randomized study comparing sevelamer and calcium acetate was performed to assess the control of hyperphosphatemia in hemodialysis patients.

METHODS

Administration of phosphate binders was discontinued during a two-week washout period. The patients were then randomized to receive sevelamer or calcium acetate. The laboratory tests were performed monthly for 34 weeks.

RESULTS

There was a statistically significant decrease of serum phosphorus in both sevelamer and calcium acetate treatments. In addition, sevelamer improved the lipid profile.

CONCLUSION

This study confirms that sevelamer is effective at lowering serum phosphorus in hemodialysis patients and that it has several striking properties that could be beneficial in atherosclerosis in dialysis patients.