Sevelamer, a phosphate-binding polymer, is a non-absorbed compound

Repurposing of sevelamer as a novel antidote against aluminum phosphide poisoning: An in vivo evaluation

Aluminum phosphide (AlP) is widely used for protecting grains from pests. AlP releases toxic phosphine gas (PH₃) while exposed to humidity. Poisoning with these tablets is dangerous and can cause death or serious injuries. Up to now, no definite antidote has been introduced for specific treatment of this poisoning. Sevelamer carbonate or sevelamer hydrochloride (Renagel) is a polymeric pharmaceutical prescribed for treating hyperphosphatemia in patients with chronic kidney disease. Sevelamer can bind with phosphate groups and act as an anion exchanger. Herein, sevelamer is repurposed as a potent antidote agent in phosphine gas poisoning. In vivo evaluation was conducted on male Sprague Dawley rats. The evaluation was conducted on three groups of animals: control, AlP-poisoned, and AlP-poisoned treated with sevelamer. Survival percentage, serum biomarkers level of organ injury, and ATP level were recorded. The results indicate a high survival rate in sevelamer-treated animals compared with the AlP-poisoned group (75% vs. 0% respectively, 48 h after poisoning). The analysis of serum markers of organ injury also showed that sevelamer could reduce toxicity and organ injury in poisoned animals. ATP level of separate organs showed that sevelamer treated groups were recovered. The results showed that sevelamer could be a potent antidote for managing aluminum phosphide poisoning. Moreover, a mechanism is suggested for the interaction of sevelamer with phosphine gas.

Phosphate Frustration: Treatment Options to Complement Current Therapies

Hyperphosphatemia eventually develops in almost all patients with advanced chronic kidney disease and is associated with negative clinical outcomes. Thus, guidelines recommend targeting treatment to normal phosphate levels in patients with chronic kidney disease. Despite low phosphorus diets, clearance by dialysis, and phosphate binder use, many patients with chronic kidney disease on dialysis are unable to consistently achieve and maintain serum phosphate concentrations <5.5 mg/dL. A chart audit of patients on dialysis receiving phosphate binders showed that 74 to 86% were unable to consistently achieve serum phosphate ≤5.5 mg/dL over 6 months. Furthermore, although there is evidence that serum phosphate concentrations <4.5 mg/dL are associated with improved survival and cardiovascular outcomes, real-world phosphate control data suggest achieving and maintaining this goal for most patients would be extremely challenging, if not near impossible, using current therapies. As phosphate binders can only remove approximately 300 mg of the 2,500 mg or more daily dietary phosphate intake, therapeutic innovations are necessary to improve phosphate management. We present treatment options to complement current therapies including tenapanor, a novel sodium/hydrogen exchanger isoform 3 inhibitor that blocks the dominant paracellular phosphate absorption pathway and has been shown to reduce phosphate levels in several clinical trials.

Predict drug permeability to blood-brain-barrier from clinical phenotypes: drug side effects and drug indications

Motivation

Blood-Brain-Barrier (BBB) is a rigorous permeability barrier for maintaining homeostasis of Central Nervous System (CNS). Determination of compound's permeability to BBB is prerequisite in CNS drug discovery. Existing computational methods usually predict drug BBB permeability from chemical structure and they generally apply to small compounds passing BBB through passive diffusion. As abundant information on drug side effects and indications has been recorded over time through extensive clinical usage, we aim to explore BBB permeability prediction from a new angle and introduce a novel approach to predict BBB permeability from drug clinical phenotypes (drug side effects and drug indications). This method can apply to both small compounds and macro-molecules penetrating BBB through various mechanisms besides passive diffusion.

Results

We composed a training dataset of 213 drugs with known brain and blood steady-state concentrations ratio and extracted their side effects and indications as features. Next, we trained SVM models with polynomial kernel and obtained accuracy of 76.0%, AUC 0.739, and F 1 score (macro weighted) 0.760 with Monte Carlo cross validation. The independent test accuracy was 68.3%, AUC 0.692, F 1 score 0.676. When both chemical features and clinical phenotypes were available, combining the two types of features achieved significantly better performance than chemical feature based approach (accuracy 85.5% versus 72.9%, AUC 0.854 versus 0.733, F 1 score 0.854 versus 0.725; P  < e -90 ). We also conducted de novo prediction and identified 110 drugs in SIDER database having the potential to penetrate BBB, which could serve as start point for CNS drug repositioning research.

Availability and Implementation

https://github.com/bioinformatics-gao/CASE-BBB-prediction-Data.

Contact

rxx@case.edu.

Supplementary information

Supplementary data are available at Bioinformatics online.

Sevelamer carbonate: a review in hyperphosphataemia in adults with chronic kidney disease

Sevelamer carbonate (Renvela(®)), a buffered form of sevelamer hydrochloride (Renagel(®)), is an orally administered non-absorbed phosphate-binding anion exchange resin used in the treatment of hyperphosphataemia in chronic kidney disease (CKD). In the EU, sevelamer carbonate is approved in adult CKD patients who require dialysis and in those who do not require dialysis with serum phosphate levels ≥ 1.78 mmol/L, whereas in the USA sevelamer carbonate is approved in adult CKD patients who require dialysis. Sevelamer carbonate and sevelamer hydrochloride achieved similar reductions in serum phosphate levels in randomized comparative trials in patients with CKD receiving haemodialysis; sevelamer carbonate also reduced serum phosphate levels in noncomparative studies in CKD patients not requiring dialysis. The most common adverse events with sevelamer carbonate are gastrointestinal in nature. Sevelamer has pleiotropic effects, such as improving the serum lipid profile and attenuating endothelial and cardiovascular risk factors in CKD. All formulations of sevelamer have markedly higher acquisition costs than calcium-based phosphate binders. Cost-effectiveness analyses focusing specifically on sevelamer carbonate have not been conducted, and those based on clinical trial data with sevelamer hydrochloride have provided both favourable and unfavourable results compared with calcium-based phosphate binders, reflecting heterogeneity between modelled analyses in terms of data sources, assumptions, comparators, geographical regions, type of costs included and other factors. Although well-designed studies evaluating the impact of phosphate binders on hard clinical endpoints appear to be warranted, sevelamer carbonate may be particularly useful for the treatment of patients at risk of metabolic acidosis (offering advantages over sevelamer hydrochloride in this regard) and for individuals requiring treatment with a phosphate binding agent that does not contain aluminium or calcium.

Practical use of sevelamer in chronic kidney disease patients on dialysis in People's Republic of China

Hyperphosphatemia is a common complication of dialysis patients. Only 38.5% of Chinese dialysis patients met the Kidney Disease Outcomes Quality Initiative defined targets for serum phosphate. Sevelamer is a high molecular weight cationic hydrogel polymer that prevents absorption of dietary phosphate by binding it in the gastrointestinal tract. In Chinese trials, it was confirmed that sevelamer had better efficacy than calcium carbonate in terms of reducing the serum level of phosphorus and calcium-phosphate product. Sevelamer can also reduce the levels of lipid parameters and improve the micro-inflammatory state. When sevelamer was combined with other treatments, it elicited superior effects on calcium phosphorus metabolism, secondary hyperparathyroidism, and renal osteodystrophy. Combination treatment of sevelamer and traditional Chinese medicine has the unique advantage. However, sevelamer is associated with a high incidence of gastrointestinal adverse effects in Chinese patients. Although more effective, the practical use of sevelamer is not very common because it is expensive and not paid by medical insurance. This article provides a comprehensive review of the practical use of sevelamer in chronic kidney disease patients on dialysis in People's Republic of China.

Sevelamer in a diabetologist's perspective: a phosphate-binding resin with glucose-lowering potential

Sevelamer is a calcium-free and metal-free phosphate-binding oral drug used in the management of hyperphosphataemia in chronic kidney disease. Preclinical and clinical trials have shown glucose and lipid-lowering effects of sevelamer, thereby giving rise to a potential role of the drug in the treatment of patients with type 2 diabetes. These 'novel' effects are most probably derived from the bile acid-binding properties of sevelamer. The proposed potential is supported by the approval of the bile acid sequestrant colesevelam in the United States for the treatment of type 2 diabetes and hypercholesterolaemia. This article offers a brief review on the effects of sevelamer and a perspective on the potential mechanisms behind the glucose-lowering effect of the drug.

Non-systemic drugs: a critical review

Non-systemic drugs act within the intestinal lumen without reaching the systemic circulation. The first generation included polymeric resins that sequester phosphate ions, potassium ions, or bile acids for the treatment of electrolyte imbalances or hypercholesteremia. The field has evolved towards non-absorbable small molecules or peptides targeting luminal enzymes or transporters for the treatment of mineral metabolism disorders, diabetes, gastrointestinal (GI) disorders, and enteric infections. From a drug design and development perspective, non-systemic agents offer novel opportunities to address unmet medical needs while minimizing toxicity risks, but also present new challenges, including developing a better understanding and control of non-transcellular leakage pathways into the systemic circulation. The pharmacokinetic-pharmacodynamic relationship of drugs acting in the GI tract can be complex due to the variability of intestinal transit, interaction with chyme, and the complex environment of the surface epithelia. We review the main classes of nonabsorbable agents at various stages of development, and their therapeutic potential and limitations. The rapid progress in the identification of intestinal receptors and transporters, their functional characterization and role in metabolic and inflammatory disorders, will undoubtedly renew interest in the development of novel, safe, non-systemic therapeutics.

The copolymer P(HEMA-co-SS) binds gluten and reduces immune response in gluten-sensitized mice and human tissues

BACKGROUND & AIMS

Copolymers of hydroxyethyl methacrylate and styrene sulfonate complex with isolated gliadin (the toxic fraction of gluten) and prevent damage to the intestinal barrier in HLA-HCD4/DQ8 mice. We studied the activity toward gluten and hordein digestion and biologic effects of poly(hydroxyethyl methacrylate-co-styrene sulfonate (P(HEMA-co-SS)). We also investigated the effect of gliadin complex formation in intestinal biopsy specimens from patients with celiac disease.

METHODS

We studied the ability of P(HEMA-co-SS) to reduce digestion of wheat gluten and barley hordein into immunotoxic peptides using liquid chromatography-mass spectrometry. The biodistribution and pharmacokinetic profile of orally administered P(HEMA-co-SS) was established in rodents using tritium-labeled polymer. We assessed the capacity of P(HEMA-co-SS) to prevent the immunologic and intestinal effects induced by a gluten-food mixture in gluten-sensitized HLA-HCD4/DQ8 mice after short-term and long-term administration. We measured the effects of gliadin complex formation on cytokine release ex vivo using intestinal biopsy specimens from patients with celiac disease.

RESULTS

P(HEMA-co-SS) reduced digestion of wheat gluten and barley hordein in vitro, thereby decreasing formation of toxic peptides associated with celiac disease. After oral administration to rodents, P(HEMA-co-SS) was predominantly excreted in feces, even in the presence of low-grade mucosal inflammation and increased intestinal permeability. In gluten-sensitized mice, P(HEMA-co-SS) reduced paracellular permeability, normalized anti-gliadin immunoglobulin A in intestinal washes, and modulated the systemic immune response to gluten in a food mixture. Furthermore, incubation of P(HEMA-co-SS) with mucosal biopsy specimens from patients with celiac disease showed that secretion of tumor necrosis factor-α was reduced in the presence of partially digested gliadin.

CONCLUSIONS

The copolymer P(HEMA-co-SS) reduced digestion of wheat gluten and barley hordein and attenuated the immune response to gluten in a food mixture in rodents. It might be developed to prevent or reduce gluten-induced disorders in humans.

Sevelamer carbonate for the treatment of hyperphosphatemia in patients with kidney failure (CKD III - V)

IMPORTANCE OF THE FIELD

Altered mineral metabolism in chronic kidney disease (CKD) is associated with increased morbidity, mortality, hospitalization, cost of care and reduced quality of life. Phosphorus control, one component of CKD metabolic derangements, is potentially related to impaired outcomes and has significant room for improvement.

AREAS COVERED IN THIS REVIEW

Historical, present and future aspects of treatment of hyperphosphatemia focusing on sevelamer hydrochloride and sevelamer carbonate.

WHAT THE READER WILL GAIN

Comprehensive insight into the background and controversies regarding phosphate binders.

TAKE HOME MESSAGE

While calcium-free phosphate binders with a sevelamer backbone may offer therapeutic advantages for CKD patients at risk, more studies comprising significant patient numbers are warranted to answer compelling clinical questions.

Prevention measures and exploratory pharmacological treatments of celiac disease

Increasing prevalence, protean clinical manifestations, and lack of pharmacological therapy make celiac disease (CD) a complex and highly relevant illness in gastroenterology. This chronic inflammatory disorder of the small intestine is caused by the ingestion of gluten containing cereals in genetically susceptible individuals, leading to a variety of gastrointestinal (GI) and non-GI manifestations. Awareness among physicians is growing due to accessible and highly accurate diagnostic and screening methods. Recent evidence suggests a possible rising incidence of CD. Environmental factors such as early life gluten exposure, intestinal infections, short duration of breast-feeding, and changes in intestinal microbiota have been proposed to have a role in CD pathogenesis. Thus, prevention approaches to diminish the rising prevalence of CD are currently being evaluated. Still, the cornerstone treatment of CD remains a strict gluten-free diet. This nutritional regime is demanding, and non-adherence is common because of social isolation, financial issues, or restriction of food diversity. Allowing patients to occasionally consume small amounts of gluten would greatly improve their quality of life. Owing to recent advances in the understanding of the pathogenesis of CD, different targets have been identified and have motivated the development of several experimental therapeutic strategies. The main goal of this review is to discuss the mechanisms that can be exploited therapeutically to prevent or delay CD, disease associations and its complications. Current treatments for complications of CD, including refractory CD and malignancy, are beyond the scope of this review.

The effect of sevelamer carbonate and lanthanum carbonate on the pharmacokinetics of oral calcitriol

Background. Lanthanum carbonate and sevelamer carbonate are non-calcium-based phosphate binders used to manage hyperphosphataemia in patients with chronic kidney disease (CKD). Patients with CKD may require intravenous or oral active vitamin D. We investigated the effects of lanthanum carbonate and sevelamer carbonate on the bioavailability of oral calcitriol.

Methods. This was a three-period, crossover study in healthy volunteers. Forty-one individuals were randomized to one of six possible sequences, each consisting of three treatment periods separated by washouts. The treatments were calcitriol (1 μg at lunch), calcitriol with lanthanum carbonate (3000 mg/day) and calcitriol with sevelamer carbonate (7200 mg/day). Serum calcitriol levels were assessed at baseline and throughout the study.

Results. Co-administration of lanthanum carbonate with calcitriol had no significant effect on area under the curve over 48 h (AUC_0–48) for serum exogenous calcitriol [least-squares (LS) mean, calcitriol with lanthanum carbonate vs calcitriol alone: 429 pg h/mL vs 318 pg h/mL, respectively; P = 0.171]. Similarly, there was no significant effect on maximum concentration (C_max). In contrast, co-administration with sevelamer was associated with a significant reduction in bioavailability parameters for calcitriol (calcitriol with sevelamer carbonate vs calcitriol alone, LS mean AUC_0–48: 137 pg h/mL vs 318 pg h/mL, respectively; P = 0.024; LS mean C_max: 40.1 pg/mL vs 49.7 pg/mL, respectively; P < 0.001).

Conclusions. Sevelamer carbonate significantly reduces serum concentrations of exogenous calcitriol when administered concomitantly with oral calcitriol, whereas lanthanum carbonate has no significant effect. This should be considered when treating CKD patients who require phosphate binders and oral vitamin D.

Update and critical appraisal of sevelamer in the management of chronic renal failure

Sevelamer (Renagel and Renvela), is an orally administered weakly basic anion exchange resin that binds dietary phosphate in the gastrointestinal tract, and is approved for use in the US, Europe and many other countries for the treatment of hyperphosphatemia in adult patients on hemodialysis or peritoneal dialysis. Clinical evidence shows that sevelamer is at least as effective as calcium-based oral phosphate binders in controlling serum phosphate, but with a lower incidence of hypercalcemia. Whilst sevelamer hydrochloride is associated with mild acidosis, sevelamer carbonate does not have this drawback. Use of sevelamer and avoidance of calcium-based binders may slow the progression of vascular calcification in hemodialysis patients, and it also reduces serum low-density lipoprotein-cholesterol levels. There was no between-group difference in all-cause mortality between sevelamer and calcium-based phosphate binder therapy in the primary efficacy analysis of the large (n >2100), 3-year DCOR trial. In the smaller (n = 109) nonblind RIND trial in patients new to hemodialysis, data suggest there may be an overall survival benefit with sevelamer versus calcium-based phosphate binder treatment but the evidence on the efficacy of sevelamer in reducing mortality and hospitalization is not strong. The balance of evidence, however, does not strongly support the use of sevelamer over the much less costly calcium-based binders except in patients at risk of hypercalcemic episodes. Further research into cardiovascular and all-cause mortality over a longer time period would be needed to settle this issue, and the relative survival benefits and cost effectiveness of all phosphate binder therapies remains to be fully determined. Despite the relative paucity of data available, sevelamer has established itself as the most widely used binder in the United States and the most widely used noncalcium-based binder worldwide. However, affordability is a major issue for most health economies and in the light of recent economic events is likely to become more prominent.

Does concomitant administration of sevelamer and calcium carbonate modify the control of phosphatemia?

There is no guideline regarding the concomitant or distant administration of sevelamer and calcium carbonate. Our aim was to determine whether serum phosphate varied when sevelamer and calcium carbonate were administered concomitantly in comparison to administration at separate meals. Fourteen chronic hemodialysis patients were enrolled in this cross-over, randomized trial. Each subject underwent two four-week study periods. During the "concomitant" period, subjects were instructed to take both sevelamer and calcium carbonate together at each meal, whereas in the "separate" period, they were required to take them at separate meals. The order of the "concomitant" and "separate" periods was randomized. Phosphate-binding agents were stopped for a one-week washout period before each study period. The total dose of sevelamer and calcium carbonate for each subject remained the same for the whole duration of the study and had been determined according to their usual dose of phosphate binders. Patients were instructed to keep their usual eating habits constant and a nutritionist evaluated the daily phosphate intake three times per week. Dialysis parameters were kept constant. Pre-dialysis serum phosphate, calcium, bicarbonate, and albumin were measured at the end of each week. The average daily dietary phosphate intake remained unchanged throughout the study. At the end of the two study periods there was no significant difference in serum phosphate (1.50 +/- 0.46 mmol/L in the "concomitant" period vs. 1.51 +/- 0.31 mmol/L in the "separate" period, P = 0.97), calcium (2.26 +/- 0.19 mmol/L in the "concomitant" period vs. 2.27 +/- 0.15 mmol/L in the "separate" period, P = 0.64), calcium x phosphate product (3.36 +/- 0.94 mmol(2)/L(2) in the "concomitant" period vs. 3.41 +/- 0.71 mmol(2)/L(2) in the "separate" period, P = 0.84) and bicarbonate levels (21.5 +/- 3.3 mmol/L for the "concomitant" period vs. 21.6 +/- 3.1 mmol/L for the "separate" period, P = 0.81). Our results show that simultaneous administration of calcium carbonate and sevelamer does not decrease phosphate-binding capacity. Hence, patients can choose to take their phosphate binders concomitantly or at separate meals, according to their preference.

Endotoxin-binding affinity of sevelamer: a potential novel anti-inflammatory mechanism

Chronic inflammation is highly prevalent in patients with chronic kidney disease (CKD), and is associated with increased cardiovascular morbidity and mortality. There are numerous causes of inflammation in CKD, including the potential exposure to bacterial lipopolysaccharide (LPS) in the bloodstream from the intestinal tract as a result of uremia-related increases in intestinal permeability. Sevelamer, a commonly prescribed non-calcium, non-metal-based phosphate binder in CKD, also possesses putative anti-inflammatory properties, as its use has been associated with a reduction in systemic markers of inflammation. Emerging studies have provided direct evidence that sevelamer shows in vitro LPS-binding properties. Indirect clinical evidence suggests that sevelamer might also limit translocation of LPS from the intestinal lumen into the bloodstream. This review focuses on bacterial LPS as a source of chronic inflammation in CKD, and proposes that sevelamer might possess novel anti-inflammatory properties as a result of LPS binding in the intestinal tract. The proposed hypothesis that intestinal LPS-binding by sevelamer may lower circulating LPS, and in turn systemic inflammation, requires further evaluation in a clinical trial.

Sevelamer Carbonate

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical efficacy, safety data, and place in therapy of sevelamer carbonate for the treatment of hyperphosphatemia in patients with chronic kidney disease (CKD).

DATA SOURCES

A literature search of MEDLINE and MEDLINE In-Process & Other Non-Indexed Citations Databases (1966-August 2009) was conducted using the key words chronic kidney disease, hyperphosphatemia, and sevelamer carbonate. All published articles regarding sevelamer carbonate were included. References of selected articles, data from multiple presentations, and abstract publications were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Available English-language data from reviews, abstracts, presentations, and clinical trials of sevelamer carbonate in humans were reviewed; relevant clinical data were selected and included.

DATA SYNTHESIS

Sevelamer carbonate is approved to control serum phosphorus levels and treat hyperphosphatemia in patients with CKD who are on dialysis. In clinical trials, sevelamer carbonate has been shown to lower serum phosphorus levels and calcium-phosphorus product to a similar extent as sevelamer hydrochloride. Significantly fewer patients receiving treatment with sevelamer carbonate were likely to report any gastrointestinal adverse event compared with those on sevelamer hydrochloride treatment. Further, sevelamer carbonate is associated with significant effects on decreasing low-density lipoprotein cholesterol levels and may cause less metabolic acidosis than sevelamer hydrochloride. Additionally, sevelamer hydrochloride was removed from the market in October 2009; sevelamer carbonate is now the only available formulation.

CONCLUSIONS

Sevelamer carbonate is a treatment option for hyperphosphatemia in patients with CKD who are on dialysis. Clinical data indicate that sevelamer carbonate effectively lowers serum phosphorus levels while having minimal effect on serum calcium or serum chloride levels. The role of sevelamer carbonate in the treatment of hyperphosphatemia relative to other phosphate-binding drugs, including calcium salts and lanthanum, has not yet been established.

Absorption and excretion of colestilan in healthy subjects

Colestilan, an anion-exchange resin binding both phosphate and bile-acid anions, is under development for the treatment of hyperphosphataemia and dyslipidaemia, which occur in the majority of end-stage renal disease patients. This study using 14C-colestilan was conducted to investigate the absorption and excretion of colestilan in humans. Following a 28-day run-in period with administration of colestilan 3 g three times daily, 12 subjects received a single oral dose of 14C-colestilan 100 mg (approximately 4.0 MBq) and colestilan 3 g under fasted conditions on the morning of day 1. A total of 9 g of colestilan was administered three times daily on days 1-4. Total radioactivity levels in whole blood (at 4, 8, 12 and 24 hours and then at 24-hour intervals) and in the urine and faeces (from 0 to 24 hours and then at 24-hour intervals) were monitored up to 216 hours postdose (day 10). Total radioactivity measured in all whole-blood samples was below the lower limit of quantification (0.025 microg equivalent of 14C-labelled colestilan/mL of whole blood). Total radioactivity assessed in all urine samples was also below the lower limit of quantification (0.003 microg equivalent/mL for urine), except at 0-24 hours postdose, when 0.01% of the radioactive dose was excreted by all subjects. This level was below the predetermined water soluble impurity level of 0.04%. The mean cumulative excretion of total radioactivity in the faeces was 99.66% by 216 hours postdose, excluding one subject with incomplete collection of faecal samples. These results demonstrate that colestilan is not absorbed from the gastrointestinal tract and is completely excreted in the faeces.

Functional polymers as therapeutic agents: concept to market place

Biologically active synthetic polymers have received considerable scientific interest and attention in recent years for their potential as promising novel therapeutic agents to treat human diseases. Although a significant amount of research has been carried out involving polymer-linked drugs as targeted and sustained release drug delivery systems and prodrugs, examples on bioactive polymers that exhibit intrinsic therapeutic properties are relatively less. Several appealing characteristics of synthetic polymers including high molecular weight, molecular architecture, and controlled polydispersity can all be utilized to discover a new generation of therapies. For example, high molecular weight bioactive polymers can be restricted to gastrointestinal tract, where they can selectively recognize, bind, and remove target disease causing substances from the body. The appealing features of GI tract restriction and stability in biological environment render these polymeric drugs to be devoid of systemic toxicity that are generally associated with small molecule systemic drugs. The present article highlights recent developments in the rational design and synthesis of appropriate functional polymers that have resulted in a number of promising polymer based therapies and biomaterials, including some marketed products.

Sevelamer hydrochloride: a review of its use for hyperphosphataemia in patients with end-stage renal disease on haemodialysis

Sevelamer (Renagel), an orally administered metal-free cationic hydrogel polymer/resin that binds dietary phosphate in the gastrointestinal (GI) tract, is approved for use in the US, Europe and several other countries for the treatment of hyperphosphataemia in adult patients with end-stage renal disease (ESRD) on haemodialysis or peritoneal dialysis.Clinical evidence shows that sevelamer was at least as effective as calcium acetate and calcium carbonate at controlling serum phosphorus, calcium-phosphorus product (Ca x P) and intact parathyroid hormone (iPTH) levels, but generally reduced serum calcium levels to a greater extent and was associated with a lower risk of hypercalcaemic episodes than calcium-based phosphate binders. Sevelamer appeared to slow the progression of cardiovascular calcification in patients with ESRD and also had a beneficial effect on serum low-density lipoprotein-cholesterol (LDL-C) levels. In patients receiving chronic haemodialysis, there was no between-group difference in all-cause mortality between sevelamer and calcium-based phosphate binder therapy in the primary efficacy analysis in the large (n >2100), 3-year DCOR trial; in the smaller (n = 109) nonblind RIND trial in patients new to dialysis, data suggest there is an overall survival benefit with sevelamer versus calcium-based phosphate binder treatment. The relative survival benefits and cost effectiveness of these phosphate binder therapies remains to be fully determined. Sevelamer treatment was generally as well tolerated as calcium acetate or calcium carbonate treatment. Overall, sevelamer is a valuable option for the management of hyperphosphataemia in patients with ESRD on haemodialysis.

Lanthanum carbonate as a first-line phosphate binder: the "cons"

Controlling serum phosphorus levels in patients with renal failure is critical. The use of oral phosphate-binding agents is universal for patients with end-stage kidney disease to reduce phosphate absorption. The therapeutic goal is to reduce serum phosphorus levels without disturbing calcium homeostasis or promoting accumulation of potentially toxic elements from the medication. Aluminum hydroxide effectively reduces serum phosphorus, but has largely been abandoned as a first-line phosphate binder because of hazards associated with metal absorption and tissue accumulation. Traditional calcium-based phosphate binders tend to promote hypercalcemia and calcium overloading, and are linked to accelerated cardiovascular calcification. Interest in aluminum-free, calcium-free phosphate-binding agents continues to grow. Sevelamer hydrochloride, a metal-free, calcium-free hydrogel, is not absorbed, has been proven safe and efficacious in controlling serum phosphorus, and is associated with attenuated progression of cardiovascular calcification. Lanthanum carbonate is a newer aluminum-free, calcium-free phosphate-binding agent. Lanthanum is a rare-earth trace metal with industrial and agricultural applications. As a therapeutic, this metal-based binder appears effective in reducing serum phosphorus, yet concerns remain about lanthanum accumulation in tissues during long-term oral administration. Similar to the metal aluminum, lanthanum is absorbed in the intestine and accumulates in body tissues, especially in the liver, bone, muscle, kidney, and brain. Moreover, the rate of intestinal absorption of lanthanum is enhanced in chronic renal failure. Our experience with aluminum hydroxide suggests caution regarding the long-term use of another metal-based agent that displays enhanced absorption in the uremic state and progressive tissue accumulation.

Systemic lanthanum is excreted in the bile of rats

Lanthanum carbonate is a non-calcium-based oral phosphate binder for the control of hyperphosphataemia in patients with chronic kidney disease Stage 5. As part of its pre-clinical safety evaluation, studies were conducted in rats to determine the extent of absorption and routes of excretion. Following oral gavage of a single 1500 mg/kg dose, the peak plasma lanthanum concentration was 1.04+/-0.31 ng/mL, 8 h post-dose. Lanthanum was almost completely bound to plasma proteins (>99.7%). Within 24h of administration of a single oral dose, 97.8+/-2.84% of the lanthanum was recovered in the faeces of rats. Comparing plasma exposure after oral and intravenous administration of lanthanum yielded an absolute oral bioavailability of 0.0007%. Following intravenous administration of lanthanum chloride (0.3 mg/kg), 74.1+/-5.82% of the dose (96.9+/-0.50% of recovered lanthanum) was excreted in faeces in 42 days, and in bile-duct cannulated rats, 10.0+/-2.46% of the dose (85.6+/-2.97% of recovered lanthanum) was excreted in bile in 5 days. Renal excretion was negligible, with <2% of the intravenous dose recovered in urine. These studies demonstrate that lanthanum undergoes extremely low intestinal absorption and that absorbed drug is predominantly excreted in the bile.

Results of a randomized crossover study comparing once-daily and thrice-daily sevelamer dosing

BACKGROUND

Patients with renal failure require complex regimens of renal replacement therapies and medications, including ingestion of phosphate-binding agents 3 times daily. Previous studies suggested that sevelamer may provide extended phosphate binding and be effective with once-daily dosing, thus simplifying the phosphate-binder regimen.

METHODS

Twenty-four patients were enrolled in this study, 21 of whom were randomly assigned to sevelamer administration at their previously prescribed dose, either once daily with the largest meal or thrice daily with meals, with crossover to the other regimen after 4 weeks. Eighteen patients completed both treatment periods. The primary efficacy measure for which the study was powered is comparison of the effect of once-daily versus standard thrice-daily sevelamer dosing on serum phosphorus level control, determined by using equivalence testing. Secondary efficacy measures are the effects of the 2 regimens on serum calcium level corrected for albumin level; calcium x phosphorus product; albumin; intact parathyroid hormone; total, low-density lipoprotein, high-density lipoprotein, and non-high-density lipoprotein cholesterol; and triglyceride levels.

RESULTS

Once-daily sevelamer was as effective as thrice-daily dosing of sevelamer in controlling serum phosphorus, calcium, calcium x phosphorus product, serum albumin, and serum lipid levels. Bioequivalence was not shown for intact parathyroid hormone, likely because of high variability. Mean serum phosphorus levels were 4.6 +/- 0.3 mg/dL (1.49 +/- 0.10 mmol/L) during thrice-daily dosing and 5.0 +/- 0.3 mg/dL (1.61 +/- 0.10 mmol/L) during once-daily dosing. The average prescribed dose of sevelamer during both treatment regimens was 6.7 +/- 2.4 g. Routine laboratory measures were similar in the 2 groups. Both regimens were well-tolerated.

CONCLUSION

Despite concerted patient-directed educational efforts, phosphorus level control in patients with renal failure is suboptimal and contributes to increased mortality risk. Once-daily sevelamer could simplify these regimens and encourage medication compliance, perhaps improving hyperphosphatemia management.

Novel Dosage Forms and Regimens for Sevelamer-Based Phosphate Binders

Sevelamer, a nonabsorbed, calcium- and metal-free dietary phosphate binder, consists of a polyallylamine polymer backbone with a cationic charge that shows a high capacity for binding anionically charged compounds such as phosphate. The currently licensed form of sevelamer, Renagel, exists as sevelamer hydrochloride, which disassociates in the acidic environment of the stomach and early gastrointestinal tract, exchanging the chloride ions attached to the polymer backbone for phosphate ions. The resulting absorption of these chloride ions has been reported to be accompanied by a reduction in serum levels of bicarbonate in some patients. To minimize the possibility of this effect, a new salt form of sevelamer has been developed in which carbonate replaces the chloride counter ion, thereby providing a source of buffer. The majority of phosphate binders exist only in tablet form and are dosed three times per day with meals. Genzyme has developed sevelamer carbonate in tablet form and also as a powder formulation that can be taken after mixing with water. This allows for an alternate and potentially more palatable way of dosing. Preliminary data exist suggesting that once daily dosing with sevelamer hydrochloride tablets provides similar phosphate control to three times daily dosing. By providing novel dosage forms and regimens for sevelamer-based phosphate binders, Genzyme will be providing patients and health care providers additional choices and flexibility in controlling phosphorus levels in chronic kidney disease. This should translate to increased compliance and improved rates of phosphate control.

Decrease in thoracic vertebral bone attenuation with calcium-based phosphate binders in hemodialysis

We performed a post hoc analysis of a 52-week randomized trial conducted in adult hemodialysis patients that compared the effects of calcium-based phosphate binders and sevelamer, a nonabsorbable polymer, on parameters of mineral metabolism and vascular calcification by electron beam tomography. In this analysis, we evaluated the relative effects of calcium and sevelamer on thoracic vertebral attenuation by CT and markers of bone turnover. Subjects randomized to calcium salts experienced a significant reduction in trabecular bone attenuation and a trend toward reduction in cortical bone attenuation, in association with higher concentrations of serum calcium, lower concentrations of PTH, and reduced total and bone-specific alkaline phosphatase.

INTRODUCTION

In patients with chronic kidney disease, hyperphosphatemia is associated with osteodystrophy, vascular and soft tissue calcification, and mortality. Calcium-based phosphate binders are commonly prescribed to reduce intestinal phosphate absorption and to attenuate secondary hyperparathyroidism. Clinicians and investigators have presumed that, in hemodialysis patients, calcium exerts beneficial effects on bone.

MATERIALS AND METHODS

We performed a post hoc analysis of a 52-week randomized trial conducted in adult hemodialysis patients that compared the effects of calcium-based phosphate binders and sevelamer, a nonabsorbable polymer, on parameters of mineral metabolism and vascular calcification by electron beam tomography. In this analysis, we evaluated the relative effects of calcium and sevelamer on thoracic vertebral attenuation by CT and markers of bone turnover.

RESULTS AND CONCLUSIONS

The average serum phosphorus and calcium x phosphorus products were similar for both groups, although the average serum calcium concentration was significantly higher in the calcium-treated group. Compared with sevelamer-treated subjects, calcium-treated subjects showed a decrease in thoracic vertebral trabecular bone attenuation (p = 0.01) and a trend toward decreased cortical bone attenuation. More than 30% of calcium-treated subjects experienced a 10% or more decrease in trabecular and cortical bone attenuation. On study, sevelamer-treated subjects had higher concentrations of total and bone-specific alkaline phosphatase, osteocalcin, and PTH (p < 0.001). When used to correct hyperphosphatemia, calcium salts lead to a reduction in thoracic trabecular and cortical bone attenuation. Calcium salts may paradoxically decrease BMD in hemodialysis patients.

Accumulation of Metals and Minerals from Phosphate Binders

Metals and minerals that depend on renal clearance may accumulate to toxic levels in patients with marginal kidney function. Toxicities of aluminum-based phosphate binders became apparent approximately 25 years ago. Nephrologists now recognize cardiovascular calcification may follow use of calcium-based phosphate binders. Five lessons can be learned: (1)safety must not be assumed in absence of data; (2) all evidence for causal linkage of toxicities from therapeutics must be considered, including animal data; (3) clinical trials are unlikely to reveal the spectrum of problems from long-term drug exposure; (4) complications can remain unrecognized until late in post-introduction surveillance; (5) minerals important for normal function can be toxic with excess accumulation. Introduction of new agents necessitates caution - it is difficult to change practice once a therapeutic is commonplace. Lessons learned about hazards of past phosphate binders must be applied judiciously when evaluating long-term risks/safety of novel metal-based binders such as lanthanum carbonate.

Calcium Loading, Calcium Accumulation, and Associated Cardiovascular Risks in Dialysis Patients

Calcium and phosphate imbalances are important mutable risk factors for cardiovascular disease in chronic kidney disease (CKD). Nearly all dialysis patients require phosphate binders. These include traditional calcium-based compounds and, more recently, the calcium-free, metal-free, non-absorbed agent, sevelamer hydrochloride. Both binder types reduce serum phosphorus, but differ with respect to calcium load and metabolism. Absorption from calcium-based agents very likely promotes positive total calcium balance in many patients. Positive calcium balance is inappropriate in adults and may promote or accelerate soft-tissue and vascular calcification even in the absence of hypercalcemia. Calcium accumulation in heart and vascular tissues contributes to rapidly progressive cardiovascular calcification - a strong predictor of cardiovascular and all-cause mortality in stage 5 CKD. More than two-thirds of stage 5 CKD patients have calcification scores above the 75th percentile for matched controls -- scores associated with extremely high risk of cardiovascular events and death.

Efficacy and side-effect profile of sevelamer hydrochloride used in combination with conventional phosphate binders

BACKGROUND

Poor phosphate control is common among patients with end-stage renal disease. Sevelamer hydrochloride has been demonstrated to be a safe and effective phosphate binder when used as a monotherapy. However, cost limits its usefulness in many countries. Data assessing its effectiveness and safety in combination with conventional phosphate binders are lacking.

METHODS

Dialysis patients meeting the following inclusion criteria participated in this study: (i) hyperphosphataemia >1.8 mmol/L (5.6 mg/dL); and (ii) an inability to tolerate currently available binders. The trial was conducted in three phases each lasting 3 months: (i) an observation phase (patients continued on their regular phosphate binders); (ii) a titration phase (sevelamer was added at a dose of 403 mg three times daily with meals, titrated to a maximum of 1209 mg three times daily); and (iii) a maintenance phase.

RESULTS

Twenty-five patients were recruited into the study. Eighteen patients completed all three trial phases. Mean serum phosphate dropped from 2.11 +/- 0.06 mmol/L (6.6 +/- 0.2 mg/dL) during the observation period to 1.91 +/- 0.01 mmol/L (5.9 +/- 0.003 mg/dL) during the maintenance phase (P=0.02). Calcium x phosphate product fell from 5.49 +/- 0.17 mmol2/L2 (68.64 +/- 2.11 mg2 dL2) to 4.89 +/- 0.27 mmol2/L2 (61.36 +/- 3.35 mg2 dL2) (P=0.02). There was no significant change in serum calcium or parathyroid hormone. Total serum cholesterol fell from 3.8 mmol/L (3.4-4.37) 147 mg/dL (131-169) to 3.55 mmol/L (2.97-4.2) 137 mg/dL (115-162) (P=0.02). Serum low-density lipoprotein cholesterol also fell significantly from 1.67 +/- 0.10 mmol/L (65 +/- 4 mg/dL) to 1.52 +/- 0.11 mmol/L (59 +/- 4 mg/dL) (P=0.04). The average prescribed dose of sevelamer was 2.4 g/day. Elemental calcium dropped from 3.4 g/day (1.4 to 4.6) to 1.2 g/day (0.6-2.4) (P=0.04). Seventy-two per cent of patients reported mild flatulence, nausea and indigestion. Three patients discontinued treatment because of adverse effects.

CONCLUSIONS

Sevelamer in combination with conventional phosphate binders is effective in lowering serum phosphate and calcium-phosphate product in patients with refractory hyperphosphataemia. Beneficial effects on lipid profile were also observed. Mild gastrointestinal upset is common.

The effect of sevelamer on the pharmacokinetics of cyclosporin A and mycophenolate mofetil after renal transplantation

BACKGROUND

After renal transplantation, patients with insufficient graft function may require phosphate binders. It is still unknown if sevelamer, a new calcium-free phosphate binder, interferes with the uptake of immunosuppressants. We studied its effects on the pharmacokinetics of cyclosporin A (CsA) and mycophenolate mofetil.

METHODS

We examined 10 adults and eight children with stable renal graft function and stable CsA trough levels. A 12 h pharmacokinetic profile (10 observation points) was conducted without sevelamer, after a single dose and after 4 days of treatment with it. CsA levels were measured with both a monoclonal antibody assay (CEDIA) and a polyclonal antibody assay (FPIA), mycophenolic acid (MPA) levels by EMIT assay and CsA metabolites AM1, AM9 and AM4N by a modified HPLC method.

RESULTS

Sevelamer had no significant effect on CsA kinetics [area under the curve (AUC), peak concentration (C(max)), time of C(max)]. The AUC of AM1 was decreased by 30% and C(max) by 25% after 4 days of sevelamer intake. MPA levels were significantly reduced by a mean of 25% of the AUC (P<0.05) and by 30% of the C(max) after a single dose of sevelamer.

CONCLUSIONS

A single sevelamer dose reduces the C(max) and the AUC of MPA. Its intake for several days does not significantly influence CsA kinetics.

Effects of sevelamer hydrochloride and calcium acetate on the oral bioavailability of ciprofloxacin

BACKGROUND

The oral bioavailability of ciprofloxacin is significantly decreased when administered with calcium carbonate. Sevelamer hydrochloride is a phosphate-binding cationic polymer that is devoid of calcium. The authors conducted a 3-way, randomized, crossover study to determine the effects of sevelamer hydrochloride and calcium acetate on the relative oral bioavailability of ciprofloxacin.

METHODS

Fifteen healthy volunteers were assigned randomly to receive each of the following oral regimens: ciprofloxacin 750 mg, alone (Arm A); ciprofloxacin 750 mg plus 7 sevelamer hydrochloride 403 mg capsules (Arm B); ciprofloxacin 750 mg plus 4 calcium acetate 667 mg tablets (Arm C). Serial blood and urine samples were obtained over 24 hours, and ciprofloxacin concentrations were determined by high-performance liquid chromatography. Pharmacokinetic data were analyzed using noncompartmental methods, and maximum serum concentration (Cmax) and area under the serum concentration time curve from 0 to infinity (AUC(0- infinity )) were tested for bioequivalence after log transformation of the data. The relative oral bioavailability of ciprofloxacin was calculated as AUC(0- infinity ), Arm B or Arm C/AUC(0- infinity ), Arm A.

RESULTS

The Cmax and AUC(0- infinity ) of ciprofloxacin were significantly decreased when administered concomitantly with sevelamer hydrochloride or calcium acetate (P < 0.05), and bioequivalence was not achieved for either parameter. The relative oral bioavailability of ciprofloxacin was decreased by 48% with sevelamer hydrochloride and 51% with calcium acetate (P < 0.05).

CONCLUSION

The relative oral bioavailability of ciprofloxacin is significantly decreased when administered with sevelamer hydrochloride or calcium acetate. Concomitant administration of these drugs may decrease clinical efficacy and promote bacterial resistance to ciprofloxacin.

Nephrogenic fibrosing dermopathy in pediatric patients

Nephrogenic fibrosing dermopathy (NFD) is a rare and recently recognized sclerosing skin disorder of unknown etiology. Reported cases have occurred in patients with chronic renal failure, with or without renal replacement therapy. All previous cases have been reported in older adult patients. We describe two pediatric patients who recently developed this condition and review the existing literature for NFD. Our patients included an 8-year-old boy on peritoneal dialysis with no prior renal transplant and a 19-year-old boy on hemodialysis with a history of previous failed renal transplants. We speculate that the recent emergence of this condition and occurrence in patients with chronic renal failure suggest an association with some newer pharmacological agent that has recently come into wide use. Since both our patients also had previously experienced large vessel thrombosis, hypercoagulable states may also be implicated.

Management of Hyperphosphataemia in Dialysis Patients

Phosphorus control remains a relevant clinical problem in dialysis patients. With age, however, serum phosphorus level decreases significantly because of a spontaneous decrease in protein intake. Older patients usually need lower doses of phosphorus binders. Nevertheless, hyperphosphataemia is observed in a quarter of patients aged >65 years. Phosphorus retention is related to an imbalance between phosphorus intake and removal by dialysis, and is usually aggravated when vitamin D analogues are employed. Hyperphosphataemia induces secondary hyperparathyroidism and the development of osteitis fibrosa. Recent publications describe an association between phosphorus retention and increased calcium and phosphorus product (Ca2+ x P), with significant progression of tissue calcification and higher mortality risk. Dietary intervention, phosphorus removal during dialysis and phosphorus binders are current methods for the management of hyperphosphataemia. However, the phosphorus removed by standard haemodialysis is insufficient to achieve a neutral phosphorus balance when protein intake is >50 g/day. Additional protein restriction may impose the risk of a negative protein balance. More frequent dialysis may help to control resistant hyperphosphataemia. Phosphorus binders constitute the mainstay of serum phosphorus level control in end-stage renal disease patients. Aluminium-based phosphorus binders, associated with toxic effects, have largely been substituted by calcium-based phosphorus binders. However, widespread use of calcium-based phosphorus binders has evidenced the frequent appearance of hypercalcaemia and long-term progressive cardiovascular calcification. Sevelamer, a relatively new phosphorus binder, has proved efficacious in lowering serum phosphorus and parathyroid hormone (PTH) levels without inducing hypercalcaemia. Furthermore, several investigators have reported that sevelamer may prevent progression of coronary calcification. However, its efficacy in severe cases of hyperphosphataemia remains to be confirmed in large series. There are no specific guidelines for phosphorus control in the elderly. Until more information is available, levels of mineral metabolites should be targeted in the same range as those recommended for the general population on dialysis (calcium 8.7-10.2 mg/dL, phosphorus 3.5-5.5 mg/dL and Ca2+ x P 50-55 mg2/dL2). PTH values over 120 ng/L help to avoid adynamic bone disease. Since elderly patients have a higher incidence of adynamic bone (which buffers less calcium) and vascular calcification, sevelamer should be the phosphorus binder of choice in this population; but sevelamer is costly and its long-term efficacy has not been definitively validated. Patients with low normal levels of calcium may receive calcium-based phosphorus binders with little risk. Patients with low values of PTH and high normal calcium should receive sevelamer. Tailored combinations of calcium-based phosphorus binders and sevelamer should be considered, and calcium dialysate concentration adjusted accordingly.

Pharmacological and clinical trial data on a novel phosphate-binding polymer (sevelamer hydrochloride), a medicine for hyperphosphatemia in hemodialysis patients

Hyperphosphatemia is one of the major complications of hemodialysis patients and plays a key role in the pathogenesis of cardiovascular calcification and secondary hyperparathyroidism. Dietary phosphate restriction and removal of phosphate by dialysis are insufficient to control hyperphosphatemia. Therefore, almost all patients undergoing hemodialysis should take oral phosphate binders. Sevelamer hydrochloride (sevelamer) is a novel phosphate-binding polymer that contains neither aluminum nor calcium, and it is not absorbed from the gastrointestinal tract. In rat models with progressive chronic renal insufficiency, in addition to lowering effects on serum levels of phosphorus, calcium x phosphorus product, and parathyroid hormone, dietary treatment of sevelamer can prevent parathyroid hyperplasia, vascular calcification, high turnover bone lesion, and renal functional deterioration. In clinical studies with hemodialysis patients, sevelamer lowers serum phosphorus and calcium x phosphorus product without any incidence of hypercalcemia. Switching calcium-containing phosphate binders to sevelamer can decrease the percentage of hypoparathyroidism and hyperparathyroidism by negative calcium balance and increased dosage of vitamin D, respectively. Sevelamer also decreases serum low-density lipoprotein cholesterol levels by its bile acid-binding capacity. A long-term clinical study has demonstrated that the progression of coronary and aortic calcification in hemodialysis patients is attenuated by sevelamer. Thus, sevelamer offers the promise of impacting cardiac calcification and thereby reducing morbidity and mortality of hemodialysis patients.

Safety of New Phosphate Binders for Chronic Renal Failure

Phosphate (Pi) retention is a common problem in patients with chronic kidney disease, particularly in those who have reached end-stage renal disease (ESRD). In addition to causing secondary hyperparathyroidism and renal osteodystrophy, recent evidence suggests that, in ESRD patients, high serum phosphorus concentration and increased calcium and phosphorous (Ca x P) product are associated with vascular and cardiac calcifications and increased mortality. Dietary phosphorus restriction and Pi removal by dialysis are not sufficient to restore Pi homeostasis. Reduction of intestinal Pi absorption with the use of Pi binders is currently the primary treatment for Pi retention in patients with ESRD. The use of large doses of calcium-containing Pi binders along with calcitriol administration may contribute to over-suppression of parathyroid hormone secretion and adynamic bone disease as well as to a high incidence of vascular calcifications. When used in patients with impaired renal function, aluminium salts were found to accumulate in bone and other tissues, resulting in osteomalacia and encephalopathy.Sevelamer, an aluminium- and calcium-free Pi binder can reduce serum phosphorus concentration and is associated with a significantly lower incidence of hypercalcaemia, while maintaining the ability to suppress parathyroid hormone production. An additional benefit of sevelamer is its ability to lower low density lipoprotein-cholesterol and total cholesterol levels. Sevelamer attenuates the progression of vascular calcifications in haemodialysis patients, which may lead to lower mortality. The use of sevelamer in non-dialysed patients might aggravate metabolic acidosis, common in these patients. Several other calcium-free Pi binders are in development. Lanthanum carbonate has shown significant promise in clinical trials in ESRD patients. Magnesium salts do not offer a significant advantage over currently available Pi binders. Their use is restricted to patients receiving dialysis since excess magnesium must be removed by dialysis. Iron-based compounds have shown variable efficacy in short-term clinical trials in small numbers of haemodialysis patients. Mixed metal hydroxyl carbonate compounds have shown efficacy in animals but have not been studied in humans. Major safety issues include absorption of the metal component with possible tissue accumulation and toxicity.