Efficacy and side effects of intermittent intravenous and oral doxercalciferol (1α-Hydroxyvitamin D2) in dialysis patients with secondary hyperparathyroidism: A sequential comparison

The American Association of Endocrine Surgeons Guidelines for the Definitive Surgical Management of Secondary and Tertiary Renal Hyperparathyroidism

OBJECTIVE

To develop evidence-based recommendations for safe, effective, and appropriate treatment of secondary (SHPT) and tertiary (THPT) renal hyperparathyroidism.

BACKGROUND

Hyperparathyroidism is common among patients with chronic kidney disease, end-stage kidney disease, and kidney transplant. The surgical management of SHPT and THPT is nuanced and requires a multidisciplinary approach. There are currently no clinical practice guidelines that address the surgical treatment of SHPT and THPT.

METHODS

Medical literature was reviewed from January 1, 1985 to present January 1, 2021 by a panel of 10 experts in SHPT and THPT. Recommendations using the best available evidence was constructed. The American College of Physicians grading system was used to determine levels of evidence. Recommendations were discussed to consensus. The American Association of Endocrine Surgeons membership reviewed and commented on preliminary drafts of the content.

RESULTS

These clinical guidelines present the epidemiology and pathophysiology of SHPT and THPT and provide recommendations for work-up and management of SHPT and THPT for all involved clinicians. It outlines the preoperative, intraoperative, and postoperative management of SHPT and THPT, as well as related definitions, operative techniques, morbidity, and outcomes. Specific topics include Pathogenesis and Epidemiology, Initial Evaluation, Imaging, Preoperative and Perioperative Care, Surgical Planning and Parathyroidectomy, Adjuncts and Approaches, Outcomes, and Reoperation.

CONCLUSIONS

Evidence-based guidelines were created to assist clinicians in the optimal management of secondary and tertiary renal hyperparathyroidism.

[Utilization of alfacalcidol and active vitamin D analogs in chronic kidney disease]

Secondary hyperparathyroidism (SHPT) is one of the most frequent and deleterious complication of chronic kidney disease (CKD). SHPT is also one of the principal components of the now called CKD-mineral and bone disorders (MBD) syndrome. It is usually prevented and treated by vitamin D derivatives. However, the rationale for the prescription of vitamin D sterols in those patients is still a matter of hotly debates, mainly because of unsatisfactory results from numerous observational and not well-controlled studies. Scanty clinical data on head-to-head comparisons between the multiple vitamin D sterols are currently available. Moreover, there is crescent expectations on nutritional vitamin D, as well as vitamin D receptor activators (VDRA), regarding their putative pleiotropic effects even in CKD patients, and the promising effects of VDRA against proteinuria and myocardial hypertrophy in diabetic CKD cohorts. Nevertheless, additional randomized controlled trials (RCT) are needed to answer to many open questions and incertitude considering the effect of nutritional vitamin D and VDRA on hard end points including the risk of skeletal fractures and of mortality in CKD patients. RCT comparing VDRA to calcimimetics in the control of SHPT are also needed in dialysis patients. The present review will visit these open questions that nephrologists should ask before starting a treatment by nutritional vitamin D or VDRA.

Vitamin D Receptor Activators

The fields for clinical employment of vitamin D analogs are growing and under active evaluation in different medical specialties, ranging from dermatology to immunology and oncology. In this review we provide a brief description of the drugs that have been developed more specifically for the treatment of secondary hyperparathyroidism (SH) associated with uremia.

The Use of Vitamin D Metabolites and Analogues in the Treatment of Chronic Kidney Disease

Chronic kidney disease (CKD) and end-stage renal disease (ESRD) are associated with abnormalities in bone and mineral metabolism, known as CKD-bone mineral disorder. CKD and ESRD cause skeletal abnormalities characterized by hyperparathyroidism, mixed uremic osteodystrophy, osteomalacia, adynamic bone disease, and frequently enhanced vascular and ectopic calcification. Hyperparathyroidism and mixed uremic osteodystrophy are the most common manifestations due to phosphate retention, reduced concentrations of 1,25-dihydroxyvitamin D, intestinal calcium absorption, and negative calcium balance. Treatment with 1-hydroxylated vitamin D analogues is useful.

Pharmacological Management of Secondary Hyperparathyroidism in Patients with Chronic Kidney Disease

Secondary hyperparathyroidism (SHPT) is a common complication of chronic kidney disease (CKD) and is part of the CKD-mineral bone disorder (CKD-MBD). SHPT is associated with increased risk of fracture and mortality; thus, SHPT control is recommended as kidney function declines. Effective SHPT management becomes more difficult once skeletal and cardiovascular adverse effects associated with severe SHPT have become established. However, interventional studies to lower parathyroid hormone (PTH) have so far shown inconsistent results in improving patient-centred outcomes such as mortality, cardiovascular events and fracture. Pharmacological treatment effect on PTH level is also inconsistent between pre-dialysis CKD and dialysis patients, which adds to the complexity of SHPT management. This review aims to give an overview on the pathophysiology, pharmacological and non-pharmacological treatment for SHPT in CKD including some of the limitations of current therapeutic options.

Secondary Hyperparathyroidism in Chronic Kidney Disease: Focus on Clinical Consequences and Vitamin D Therapies

Objective:

To assess vitamin D–based treatment approaches for secondary hyperparathyroidism and its complications.

Data Sources:

A literature search was performed using MEDLINE (1990–February 28, 2006). Key words used were chronic kidney disease and vitamin D to identify relevant papers published in English.

Study Selection and Data Extraction:

From the database of articles generated, 48 papers were identified. Titles and abstracts were examined to identify those directly related to the objective. Discussion was expanded through the bibliographies of cited articles.

Data Synthesis:

The increasing prevalence of chronic kidney disease (CKD) in the US indicates an urgent need for treatment strategies to delay or prevent disease progression. Abnormalities in phosphorus and calcium homeostasis, vitamin D levels, and the subsequent development of secondary hyperparathyroidism (SHPT) are secondary complications of CKD associated with increased morbidity and mortality. Management options include dietary phosphorus restriction, phosphate binders and/or calcium supplementation, vitamin D supplementation, and calcimimetics. Vitamin D supplementation has received increased attention given the prevalence of vitamin D deficiency in patients with CKD and the beneficial effect of correcting this deficiency.

Conclusions:

Early identification and intervention appropriate to the stage of CKD are likely to improve patient outcomes. Improved knowledge of interactions between vitamin D and vitamin D receptors has led to the development of vitamin D analogs and calcimimetics, which offer benefits in the management of SHPT. Integrating available treatment options into practice to achieve optimal therapeutic goals of SHPT based on the stage of CKD is a significant challenge for pharmacists managing patients with CKD.

Medical and Surgical Treatment for Secondary and Tertiary Hyperparathyroidism

Prevention and treatment of secondary hyperparathyroidism (SHPT) in patients on chronic maintenance hemodialysis and of tertiary hyperparathyroidism (THPT) in patients after kidney transplantation is a challenge for the nephrologist and for the surgeon. Indication and results of medical and surgical therapy for SHPT and THPT have remained under discussion during the last decades. This review resumes the current medical and surgical strategies for patients with SHPT and THPT.

Vitamin D: Metabolism, Molecular Mechanism of Action, and Pleiotropic Effects

1,25-Dihydroxvitamin D3 [1,25(OH)2D3] is the hormonally active form of vitamin D. The genomic mechanism of 1,25(OH)2D3 action involves the direct binding of the 1,25(OH)2D3 activated vitamin D receptor/retinoic X receptor (VDR/RXR) heterodimeric complex to specific DNA sequences. Numerous VDR co-regulatory proteins have been identified, and genome-wide studies have shown that the actions of 1,25(OH)2D3 involve regulation of gene activity at a range of locations many kilobases from the transcription start site. The structure of the liganded VDR/RXR complex was recently characterized using cryoelectron microscopy, X-ray scattering, and hydrogen deuterium exchange. These recent technological advances will result in a more complete understanding of VDR coactivator interactions, thus facilitating cell and gene specific clinical applications. Although the identification of mechanisms mediating VDR-regulated transcription has been one focus of recent research in the field, other topics of fundamental importance include the identification and functional significance of proteins involved in the metabolism of vitamin D. CYP2R1 has been identified as the most important 25-hydroxylase, and a critical role for CYP24A1 in humans was noted in studies showing that inactivating mutations in CYP24A1 are a probable cause of idiopathic infantile hypercalcemia. In addition, studies using knockout and transgenic mice have provided new insight on the physiological role of vitamin D in classical target tissues as well as evidence of extraskeletal effects of 1,25(OH)2D3 including inhibition of cancer progression, effects on the cardiovascular system, and immunomodulatory effects in certain autoimmune diseases. Some of the mechanistic findings in mouse models have also been observed in humans. The identification of similar pathways in humans could lead to the development of new therapies to prevent and treat disease.

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

Pharmacotherapy of chronic kidney disease and mineral bone disorder

INTRODUCTION

Disturbances of the bone and mineral metabolism are a common complication of chronic kidney disease (CKD); these disturbances are known as CKD-mineral bone disorder (CKD-MBD). A better understanding of the pathophysiological mechanisms of CKD-MBD, along with its negative impact on other organs and systems, as well as on survival, has led to a shift in the treatment paradigm of this disorder. The use of phosphate binders changed dramatically over the last decade when noncalcium-containing phosphate binders, such as sevelamer and lanthanum carbonate, became possible alternative treatments to avoid calcium overload. Vitamin D receptor activators, such as paricalcitol and doxercalciferol, with fewer calcemic and phosphatemic effects, have also been introduced to control parathormone production and the interest in native vitamin D supplementation has grown. Furthermore, a new drug class, the calcimimetics, has recently been introduced into the therapeutic arsenal for treating secondary hyperparathyroidism.

AREAS COVERED

This review discusses the advantages and disadvantages of the above pharmacological options to treat CKD-MBD.

EXPERT OPINION

The individual-based use of phosphate binders, vitamin D and calcimimetics, separately or in combination, constitute a reasonable approach to treat CKD-MBD. These treatments aim to achieve a rigorous control of phosphorus and parathormone levels, while avoiding calcium overload.

Simultaneous control of PTH and CaxP Is sustained over three years of treatment with cinacalcet HCl

BACKGROUND & OBJECTIVES

Chronic kidney disease (CKD) is commonly complicated by secondary hyperparathyroidism (SHPT), leading to increased risk of morbidity and mortality. SHPT is a progressive disease often requiring long-term therapy to control parathyroid hormone (PTH) and mineral imbalances. Vitamin D sterols and phosphate binders, used as traditional therapies to lower PTH and phosphorus, may provide inadequate long-term control for many dialysis patients. Cinacalcet, by simultaneously lowering PTH, calcium, phosphorus, and calcium-phosphorus levels, may maintain PTH and mineral balance in these individuals. However, as with traditional therapies, long-term data are limited. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENT: Dialysis subjects from at least one of five lead-in studies (double-blind placebo-controlled, including one extension trial) completing up to 52 wk of either cinacalcet or placebo were eligible for this open-label extension study, including an 8-wk dose titration (initiated at 30 mg/d), followed by 24-wk maintenance and up to 132 wk of follow-up. Final efficacy analysis was at week 180.

RESULTS

Three hundred thirty-four of 589 enrolled subjects received cinacalcet from the beginning of the lead-in study. Weekly median PTH values were < or =300 pg/ml (weeks 16 through 180) and median CaxP values were < or =55 mg(2)/dl(2) (weeks 4 through 180). Similar results were exhibited in the 255 subjects who initially received placebo. Among the patients exposed to cinacalcet from the beginning of the lead-in study, 3% of subjects exhibited treatment-related serious adverse events.

CONCLUSIONS

Cinacalcet effectively maintained PTH, Ca and P reductions in dialysis subjects for up to 180 wk.

Cinacalcet HCl and concurrent low-dose vitamin D improves treatment of secondary hyperparathyroidism in dialysis patients compared with vitamin D alone: the ACHIEVE study results

BACKGROUND AND OBJECTIVES

Patients with chronic kidney disease (CKD) receiving dialysis often develop secondary hyperparathyroidism with disturbed calcium and phosphorus metabolism. The National Kidney Foundation-Kidney Disease Outcomes Quality Initiative (KDOQI) was established to guide treatment practices for these disorders. The ACHIEVE study was designed to test two treatment strategies for achieving KDOQI goals.

DESIGN, SETTING, PARTICIPANTS, MEASUREMENTS

Individuals on hemodialysis treated with vitamin D sterols were enrolled in this 33-week study. Subjects were randomly assigned to treatment with either cinacalcet and low-dose vitamin D (Cinacalcet-D) or flexible vitamin D alone (Flex-D) to achieve KDOQI-recommended bone mineral targets. ACHIEVE included a 6-week screening phase, including vitamin D washout, a 16-week dose-titration phase, and an 11-week assessment phase.

RESULTS

Of 173 subjects enrolled, 83% of Cinacalcet-D and 67% of Flex-D subjects completed the study. A greater proportion of Cinacalcet-D versus Flex-D subjects had a >30% reduction in parathyroid hormone (PTH) (68% versus 36%, P < 0.001) as well as PTH <300 pg/ml (44% versus 23%, P = 0.006). The proportion of subjects simultaneously achieving targets for intact PTH (150-300 pg/ml) and calcium-phosphorus product (Ca x P) (<55 mg2/dl2) was also greater (21% versus 14%), but this was not statistically significant. This was attributable to 19% of Cinacalcet-D subjects with a PTH value below the KDOQI target range.

CONCLUSIONS

Achievement of KDOQI targets was difficult, especially with Flex-D. Maintaining calcium and phosphorus target values precluded the use of vitamin D doses necessary to lower PTH to within the narrow target range and highlighted limitations inherent to the KDOQI treatment algorithm.

Treatment of secondary hyperparathyroidism in CKD patients with cinacalcet and/or vitamin D derivatives

The discovery of the calcium-sensing receptor (CaR) 15 yr ago was rapidly followed by the development of drugs modulating its activity, the so-called calcimimetics (increasing the CaR signal) and calcilytics (decreasing the CaR signal). The indication for calcimimetics is treatment of primary and secondary hyperparathyroidism, whereas calcilytics have potential for treatment of osteoporosis. A large number of clinical studies has shown that cinacalcet, the only presently available calcimimetic, effectively reduces serum parathyroid hormone in dialysis patients with secondary hyperparathyroidism. In contrast to the effect of active vitamin D derivatives, it simultaneously decreases serum calcium and phosphorus. Experimental studies showed a concomitant decrease in parathyroid hyperplasia. In the treatment of secondary hyperparathyroidism of dialysis patients, important questions remain unresolved, for example, whether there are reasons to prefer calcimimetics to active vitamin D derivatives and whether combined administration offers advantages compared with calcimimetics or active vitamin D given in isolation. For lowering parathyroid hormone, available evidence from recent studies suggests that combination therapy should be preferred to single drug treatment because of less side-effects and greater efficacy in controlling parathyroid overfunction. Future randomized controlled trial must answer whether calcimimetics impact on cardiovascular events or survival and whether in this respect there are differences between vitamin D sterols and calcimimetics.

1α,24(S)(OH)2D2 normalizes bone morphology and serum parathyroid hormone without hypercalcemia in 25-hydroxyvitamin D-1-hydroxylase (CYP27B1)-deficient mice, an animal model of vitamin D deficiency with secondary hyperparathyroidism

BACKGROUND

Vitamin D compounds are effective in managing elevated PTH levels in secondary hyperparathyroidism (SHPT) of renal failure. However, undesired increases in serum calcium and phosphorus associated with compounds such as calcitriol [1,25(OH)2D3] has prompted a search for compounds with improved safety profiles. 1alpha,24(S)(OH)2D2 (1,24(OH)2D2) is a vitamin D2 metabolite with low calcium-mo bilizing activity in vivo. We studied the efficacy of 1,24(OH)2D2 in mice lacking the CYP27B1 enzyme [25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-OHase)], a novel vitamin D deficiency model with SHPT.

MATERIALS AND METHODS

1alpha-OHase-deficient (-/-) mice and normal (+/-) heterozygous littermates re ceived 1,24(OH)2D2 (100, 300, 1000, and 3000 pg/g/day) or 1,25(OH)2D3 (30, 300, and 500 pg/g/day) for 5 weeks via daily sc injection. Control groups received vehicle.

RESULTS

Vehicle-treated 1alpha-OHase-deficient mice were hypocalcemic and had greatly elevated serum PTH. 1,24(OH)2D2 at doses above 300 pg/g/day normalized serum calcium, serum PTH, bone growth plate morphology, and other bone parameters. No hy percalcemia was observed at any dose of 1,24(OH)2D2 in normal or 1alpha-OHase-deficient animals. In contrast, 1,25(OH)2D3 at only 30 pg/g/day normalized calcemia, serum PTH, and bone parameters, but at higher doses completely suppressed PTH and caused hypercalcemia in both 1alpha-OHase-deficient and normal mice. Treatment with 500 pg/g/day of 1,25(OH)2D3 also induced osteomalacia in normal animals.

CONCLUSION

1,25(OH)2D3 was maximally active at 10-fold lower doses than 1,24(OH)2D2, but induced hypercalcemia and osteomalacia at high doses. 1,24(OH)2D2 normalized serum calcium, serum PTH, and bone histomorphometry without hypercalcemia in 1alpha-OHase-deficient mice with SHPT.

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.

New strategies for the treatment of hyperparathyroidism incorporating calcimimetics

BACKGROUND

Hyperparathyroidism (HPT), characterised by increased parathyroid hormone (PTH) secretion and parathyroid hyperplasia, can be caused by physiologic defects in the parathyroid gland (primary HPT [PHPT]) or as a consequence of declining renal function (secondary HPT [SHPT]).

OBJECTIVE

To review the safety and efficacy of cinacalcet in the treatment of SHPT and PHPT.

METHODS

Studies indexed in NLM/PubMed investigating the safety, efficacy, and pharmacokinetics of cinacalcet for PHPT and SHPT and supporting preclinical evidence.

RESULTS/CONCLUSION

Recent evidence has demonstrated the efficacy of the calcimimetic cinacalcet in the treatment of PHPT and SHPT. Compared with traditional therapies such as vitamin D sterols and phosphate binders, cinacalcet treatment can allow an increased proportion of patients with SHPT to improve Kidney Disease Outcomes Quality Initiative (KDOQI) Bone Metabolism and Disease laboratory parameter target attainment. Recent evidence suggests that improvements in these biochemical parameters with cinacalcet can translate into improved morbidity and mortality. Cinacalcet lowers PTH and calcium in patients following renal transplantation, and also normalises serum calcium in patients with PHPT. Ongoing studies are focusing and future studies are likely to focus on the effect of cinacalcet on clinical outcomes and on novel strategies for the integration of cinacalcet with traditional therapies to improve serum PTH and mineral metabolism control.

Vitamin D receptor activation and survival in chronic kidney disease

Replacement of activated vitamin D has been the cornerstone of therapy for secondary hyperparathyroidism (SHPT). Recent findings from several large observational studies have suggested that the benefits of vitamin D receptor activators (VDRA) may extend beyond the traditional parathyroid hormone (PTH)-lowering effect, and could result in direct cardiovascular and metabolic benefits. The advent of several new analogs of the activated vitamin D molecule has widened our therapeutic armamentarium, but has also made therapeutic decisions more complicated. Treatment of SHPT has become even more complex with the arrival of the first calcium-sensing receptor (CSR) agonist (cinacalcet hydrochloride) and with the uncovering of novel mechanisms responsible for SHPT. We provide a brief overview of the physiology and pathophysiology of SHPT, with a focus on vitamin D metabolism, and discuss various practical aspects of VDRA therapy and its reported association with survival in recent observational studies. A detailed discussion of the available agents is aimed at providing the practicing physician with a clear understanding of the advantages or disadvantages of the individual medications. A number of open questions are also analyzed, including the present and future roles of CSR agonists and 25(OH) vitamin D replacement.

Vitamin D receptor activator selectivity in the treatment of secondary hyperparathyroidism: understanding the differences among therapies

Secondary hyperparathyroidism (SHPT) is a common and serious consequence of chronic kidney disease (CKD). SHPT is a complex condition characterised by a decline in 1,25-dihydroxyvitamin D and consequent vitamin D receptor (VDR) activation, abnormalities in serum calcium and phosphorus levels, parathyroid gland hyperplasia, elevated parathyroid hormone (PTH) secretion, and systemic mineral and bone abnormalities. There are three classes of drugs used for treatment of SHPT: (i) nonselective VDR activators or agonists (VDRAs); (ii) selective VDRAs; and (iii) calcimimetics. The VDRAs act on the VDR, whereas the calcimimetics act on the calcium-sensing receptor. Calcimimetics are commonly used in conjunction with VDRA therapy. By virtue of the differences in their chemical structure, the nonselective and selective VDRAs differ in their effects on gene expression, and ultimately parathyroid gland, bone and intestine function. Medications in all three classes are effective in suppression of PTH; however, clinical studies show that calcimimetics are associated with an unfavourable tolerability profile and hypocalcaemia, whereas nonselective VDRAs, and to a lesser extent selective VDRAs, are associated with dose-limiting hypercalcaemia and hyperphosphataemia. Selective VDRAs also have minimal undesirable effects on calcium absorption in the intestine, and calcium and phosphorus mobilisation in the bone compared with nonselective VDRAs. Calcium load in patients with CKD can lead to vascular calcification, accelerated progression of cardiovascular disease and increased mortality. High serum phosphorus levels are also associated with adverse effects on cardiorenal function and survival. Recent evidence suggests that VDRAs are associated with a survival benefit in CKD patients, with a more favourable effect with selective VDRAs than nonselective VDRAs. Paricalcitol, a selective VDRA, is reported to exert specific effects on gene expression in various cell types that are involved in vascular calcification and the development of coronary artery disease. This article examines the molecular mechanisms that determine selectivity of VDRAs, and reviews the evidence for clinical efficacy, safety and survival associated with the three drug classes used for treatment of SHPT in CKD patients.

Impact of treatment with calcimimetics on hyperparathyroidism and vascular mineralization

Soft tissue calcification that involves primarily the medial portion of the arterial vasculature is a widely recognized and common complication of chronic kidney disease Vascular calcification (VC) causes increased arterial stiffness and contributes to the high cardiovascular mortality and morbidity in dialysis patients. The pathogenesis of VC is complex and includes factors that promote calcification and others that inhibit calcification. Studies in dialysis patients have shown a correlation between VC and a number of uremia-related factors. Overall, abnormalities in calcium and phosphate metabolism, such as hyperphosphatemia and a raised serum calcium-phosphorus product traditionally have been thought of as important determinants in patients with chronic renal failure. Common therapeutic interventions in secondary hyperparathyroidism have come under scrutiny for associations with the development of VC. Calcimimetics provide a means of controlling serum levels of parathyroid hormone in secondary hyperparathyroidism without increasing the calcium-phosphorus product and, more important, may lower the risk for VC in these patients.

Comparison of total parathyroidectomy without autotransplantation and without thymectomy versus total parathyroidectomy with autotransplantation and with thymectomy for secondary hyperparathyroidism: TOPAR PILOT-Trial

BACKGROUND

Secondary hyperparathyroidism (sHPT) is common in patients with chronic renal failure. Despite the initiation of new therapeutic agents, several patients will require parathyroidectomy (PTX). Total PTX with autotransplantation of parathyroid tissue (TPTX+AT) and subtotal parathyroidectomy (SPTX) are currently considered as standard surgical procedures in the treatment of sHPT. Recurrencerates after TPTX+AT or SPTX are between 10% and 12% (median follow up: 36 months). Recent retrospective studies demonstrated a lower rate of recurrent sHPT of 0-4% after PTX without autotransplantation and thymectomy (TPTX) with no higher morbidity when compared to the standard procedures. The observed superiority of TPTX is flawed due to different definitions of outcomes, varying follow up periods and different surgical treatment strategies (with and without thymectomy).

METHODS/DESIGN

Patients with sHPT (intact parathyroid hormone > 10 times above the upper limit of normal) on long term dialysis (>12 months) will be randomized either to TPTX or TPTX+AT and followed for 36 months. Outcome parameters are recurrence rates of sHPT, frequencies of reoperations due to refractory hypoparathyroidism or recurrent/persistent hyperparathyroidism, postoperative morbidity and mortality and quality of life. 50 patients per group will be randomized in order to obtain relevant frequencies of outcome parameters that will form the basis for a large scale confirmatory multicentred randomized controlled trial.

DISCUSSION

sHPT is a disease with a high incidence in patients with chronic renal failure. Even a small difference in outcomes will be of clinical relevance. To assess sufficient data about the rate of recurrent sHPT after both methods, a multicentred, randomized controlled trial (MRCT) under standardized conditions is mandatory. Due to the existing uncertainties the calculated number of patients necessary in each treatment arm (n > 4000) makes it impossible to perform this study as a confirmatory trial. Therefore estimates of different outcomes are performed using a pilot MRCT comparing 50 versus 50 randomized patients in order to establish a hypothesis that can be tested thereafter. If TPTX proves to have a lower rate of recurrent sHPT, no relevant disadvantages and no higher morbidity than TPTX+AT, current surgical practice may be changed.

TRIAL REGISTRATION

International Standard Randomized Controlled Trial Number Registration (ISRCTN86202793).

Vitamin D analogs for secondary hyperparathyroidism: what does the future hold?

Secondary hyperparathyroidism (2 degrees HPT) commonly develops in patients with chronic kidney disease (CKD) in response to high phosphate, low calcium and low 1,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)]. High PTH levels increase the rate of bone turnover, with a net efflux of calcium and phosphate leading to vascular calcification and coronary artery disease. Treatment of 2 degrees HPT with 1alpha,25(OH)(2)D(3) and calcium-based phosphate binders often produces hypercalcemia and over-suppression of PTH, resulting in adynamic bone that cannot buffer excess calcium and phosphate, which increases the risk of vascular calcification. It is essential, then, to reduce PTH levels to a range that supports normal bone turnover and minimizes ectopic calcification. Vitamin D analogs that inhibit PTH gene transcription and parathyroid hyperplasia, and that have less calcemic activity than 1alpha,25(OH)(2)D(3,) have provided a greater safety margin for the treatment of 2 degrees HPT, as well as enhancing the survival of CKD patients. Although several analogs with less calcemic activity are now used in patients (paricalcitol and doxercalciferol in the USA, and OCT and falecalcitriol in Japan), efforts to develop even more selective analogs continue. Parathyroid glands express both 25-hydroxylase and 1alpha-hydroxylase and may be capable of activating prohormones or prodrugs to suppress PTH and parathyroid growth by an autocrine mechanism. Moreover, the introduction of non-calcium-based phosphate binders (sevelamer and lanthanum carbonate) and cinacalcet (an allosteric activator of the calcium receptor that reduces PTH and the serum calciumxphosphate product) may reduce the risk of hypercalcemia with vitamin D therapy. Combining these agents with higher doses of vitamin D compounds may achieve greater suppression of PTH and possibly enhance survival in patients with chronic kidney disease.

Drug insight: vitamin D analogs in the treatment of secondary hyperparathyroidism in patients with chronic kidney disease

Secondary hyperparathyroidism commonly develops in patients with chronic kidney disease (CKD) in response to high phosphate, low calcium and low 1alpha,25-dihydroxyvitamin D(3) (calcitriol) levels. High levels of parathyroid hormone (PTH) accelerate bone turnover, with efflux of calcium and phosphate that can lead to vascular calcification. Treatment of secondary hyperparathyroidism with calcitriol and calcium-based phosphate binders can produce hypercalcemia and oversuppression of PTH, which results in adynamic bone that cannot buffer calcium and phosphate levels, and increased risk of vascular calcification. PTH levels must, therefore, be reduced to within a range that supports normal bone turnover and minimizes ectopic calcification. Vitamin D analogs that inhibit PTH gene transcription and parathyroid hyperplasia (and have reduced calcemic activity) are a safer treatment for secondary hyperparathyroidism than calcitriol; these agents enhance the survival of patients with CKD. Several such analogs are now in use, and analogs with even greater selectivity than those currently used are in development. Parathyroid glands express both 25-hydroxylase and 1alpha-hydroxylase, which suggests that these enzymes might suppress parathyroid function by an autocrine mechanism. The risk of hypercalcemia with vitamin D analog therapy is reduced by the introduction of non-calcium-based phosphate binders and cinacalcet; furthermore, recent trials indicate that early intervention with vitamin D analogs in stage 3 and 4 CKD can correct PTH levels, and could prevent renal bone disease and prolong patient survival.

Minimizing bone abnormalities in children with renal failure

Renal osteodystrophy (ROD), a metabolic bone disease accompanying chronic renal failure (CRF), is a major clinical problem in pediatric nephrology. Growing and rapidly remodeling skeletal systems are particularly susceptible to the metabolic and endocrine disturbances in CRF. The pathogenesis of ROD is complex and multifactorial. Hypocalcemia, phosphate retention, and low levels of 1,25 dihydroxyvitamin D(3) related to CRF result in disturbances of bone metabolism and ROD. Delayed diagnosis and treatment of bone lesions might result in severe disability. Based on microscopic findings, renal bone disease is classified into two main categories: high- and low-turnover bone disease. High-turnover bone disease is associated with moderate and severe hyperparathyroidism. Low-turnover bone disease includes osteomalacia and adynamic bone disease. The treatment of ROD involves controlling serum calcium and phosphate levels, and preventing parathyroid gland hyperplasia and extraskeletal calcifications. Serum calcium and phosphorus levels should be kept within the normal range. The calcium-phosphorus product has to be <5 mmol(2)/L(2) (60 mg(2)/dL(2)). Parathyroid hormone (PTH) levels in children with CRF should be within the normal range, but in children with end-stage renal disease PTH levels should be two to three times the upper limit of the normal range. Drug treatment includes intestinal phosphate binding agents and active vitamin D metabolites. Phosphate binders should be administered with each meal. Calcium carbonate is the most widely used intestinal phosphate binder. In children with hypercalcemic episodes, sevelamer, a synthetic phosphate binder, should be introduced. In children with CRF, ergocalciferol (vitamin D(2)), colecalciferol (vitamin D(3)), and calcifediol (25-hydroxyvitamin D(3)) should be used as vitamin D analogs. In children undergoing dialysis, active vitamin D metabolites alfacalcidol (1alpha-hydroxy-vitamin D(3)) and calcitriol (1,25 dihydroxyvitamin D(3)) are applied. In recent years, a number of new drugs have emerged that hold promise for a more effective treatment of bone lesions in CRF. This review describes the current approach to the diagnosis and treament of ROD.

Doxercalciferol treatment of secondary hyperparathyroidism

OBJECTIVE

To review the pharmacology, pharmacokinetics, effectiveness, safety, and therapeutic considerations related to the use of doxercalciferol in the treatment of secondary hyperparathyroidism.

DATA SOURCES

A MEDLINE search (1966-June 2006) was conducted using the key words vitamin D, ergocalciferols, and secondary hyperparathyroidism. Text word searches were also performed for the terms 1-alpha-hydroxy-vitamin D(2), 1-alpha-hydroxyergocalciferol, Hectorol, and doxercalciferol. Searches were limited to studies published in English and conducted in human subjects.

STUDY SELECTION AND DATA EXTRACTION

All published clinical studies evaluating the safety and effectiveness of doxercalciferol in secondary hyperparathyroidism were reviewed, and anecdotal patient reports were also evaluated. Selected clinical studies involving the use of calcitriol and/or paricalcitol in the treatment of secondary hyperparathyroidism were also included.

DATA SYNTHESIS

Doxercalciferol effectively reduces parathyroid hormone levels in patients with chronic kidney disease (CKD). Both oral and intravenous administration can significantly increase serum calcium and/or phosphorus levels as evidenced by placebo-controlled clinical trials. This agent has not been studied comparatively with calcitriol or paricalcitol to assess relative safety.

CONCLUSIONS

Doxercalciferol is approved for and effective in the treatment of secondary hyperparathyroidism related to CKD, both before and during dialysis, but has not demonstrated a lower incidence of hypercalcemia and/or hyperphosphatemia in relation to other vitamin D therapies. The drug is available in both oral and intravenous dosage forms. Doxercalciferol should be maintained as a formulary alternative for patients unresponsive to or intolerant of other vitamin D therapies, but comparative randomized studies are needed to differentiate its place in therapy.

Mortality risk among hemodialysis patients receiving different vitamin D analogs

Intravenous vitamin D is standard therapy for secondary hyperparathyroidism in hemodialysis (HD) patients. In for-profit dialysis clinics, mortality was higher for patients on calcitriol compared to paricalcitol. Doxercalciferol, a second vitamin D2 analog, is currently available. We assessed mortality associated with each vitamin D analog and with lack of vitamin D therapy in patients who began HD at Dialysis Clinic Inc. (DCI), a not-for-profit dialysis provider. During the 1999-2004 study period we studied 7731 patients (calcitriol: n=3212; paricalcitol: n=2087; doxercalciferol: n=2432). Median follow-up was 37 weeks. Mortality rates (deaths/100 patient-years) were identical in patients on doxercalciferol (15.4, 95% confidence interval (13.6-17.1)) and paricalcitol (15.3 (13.6-16.9)) and higher in patients on calcitriol (19.6 (18.2-21.1)) (P<0.0001). In all models mortality was similar for paricalcitol versus doxercalciferol (hazard ratios=1.0). In unadjusted models, mortality was lower in patients on doxercalciferol (0.80 (0.66, 0.96)) and paricalcitol (0.79 (0.68, 0.92)) versus calcitriol (P<0.05). In adjusted models, this difference was not statistically significant. In all models mortality was higher for patients who did not receive vitamin D versus those who did (1.2 (1.1-1.3)). Mortality in doxercalciferol- and paricalcitol-treated patients was virtually identical. Differences in survival between vitamin D2 and D3 may be smaller than previously reported.

Vitamin D in chronic kidney disease: A systemic role for selective vitamin D receptor activation

Hyperparathyroidism occurs in most patients during the progression of chronic kidney disease (CKD) and one of its initiating events, reduced serum levels of 1,25-dihydroxyvitamin D, results from a decrease in renal 1alpha hydroxylase activity, which converts 25-hydroxyvitamin D to its activated form. The combination of persistently high parathyroid hormone (PTH) and low 1,25-dihydroxyvitamin D is associated with bone loss, cardiovascular disease, immune suppression and increased mortality in patients with end-stage kidney failure. Recent studies in dialysis patients suggest that paricalcitol, a selective activator of the vitamin D receptor (VDR), is associated with a more favorable efficacy to side effect profile than calcitriol, with less morbidity and better survival. One hypothesis derived from such studies suggests that systemic activation of VDRs may have direct effects on the cardiovascular system to decrease mortality in CKD. Although current guidelines for regulating serum calcium, phosphate and PTH recommend specific interventions at the various stages of CKD to prevent or postpone irreversible parathyroid disease and decrease cardiovascular morbidity and mortality, emerging data suggest that vitamin D therapy may prolong survival in this patient population by mechanisms that are independent of calcium, phosphate and PTH. It is suggested that a re-evaluation of current treatment recommendations is needed and that future research should focus on mechanisms that distinguish potential tissue specific benefits of selective VDR activators in patients with CKD.

Vitamin D treatment in chronic kidney disease

Activated vitamin D continues to be the major treatment for suppressing parathyroid hormone (PTH) levels in dialysis patients who have secondary hyperparathyroidism. Active vitamin D compounds are distinguished by their ability to bind with high affinity to vitamin D receptors (VDRs) not only in the parathyroid glands, but in cells throughout the body. Because of recent data showing that pulsatile, intravenous vitamin D treatment (calcitriol or paricalcitol) confers a survival advantage in the dialysis population, there is new interest in understanding the systemic effects of VDR activation, particularly in the predialysis stages of chronic kidney disease (CKD), where high mortality rates from cardiovascular disease have recently been documented. Previous underutilization of calcitriol treatment to control PTH levels in stages 3 and 4 CKD was often due to concerns about its potential for accelerating the progression of CKD as a consequence of hypercalcemia, hypercalciuria, or hyperphosphatemia. Vitamin D analogs with selective VDR activity (such as paricalcitol) have great potential for preventing parathyroid hyperplasia and bone loss in early CKD without adversely affecting kidney function. Whether they also reduce cardiovascular morbidity and mortality in early CKD, as they appear to do in dialysis patients, remains to be determined.

Inhibition of parathyroid hormone: a dose equivalency study of paricalcitol and doxercalciferol

INTRODUCTION

Paricalcitol and doxercalciferol are effective in reducing parathyroid hormone PTH concentrations in patients with secondary hyperparathyroidism. The purpose of this study was to determine the relative dose of doxercalciferol (compared to paricalcitol) required to maintain equivalent PTH concentrations in dialysis patients.

METHODS

Chronic hemodialysis patients treated with a stable dose of paricalcitol for at least 3 months were randomized to receive doxercalciferol at either 35, 50, or 65% of the paricalcitol dose for 6 weeks. Serum iPTH, calcium, phosphorus, and albumin were determined at baseline and monitored every 2 weeks. A linear regression analysis of percent change in iPTH values by dose group was performed to determine the conversion factor.

RESULTS

27 patients were enrolled. Initial iPTH, adjusted serum calcium, serum phosphorus, and CaxP were similar among the treatment groups. Linear regression analysis demonstrated a conversion factor of 0.57 for the dose of doxercalciferol relative to paricalcitol resulting in equivalent suppression of iPTH. Corrected serum calcium, phosphorus, CaxP product, as well as incidence of hypercalcemia, hyperphosphatemia and CaxP >50 were similar for all groups.

CONCLUSION

In patients on a maintenance dose of paricalcitol, dosing doxercalciferol at 55-60% of the paricalcitol dose results in comparable inhibition of PTH.

The vitamin D prodrugs 1α(OH)D2, 1α(OH)D3 and BCI-210 suppress PTH secretion by bovine parathyroid cells

BACKGROUND

Active vitamin D compounds are widely used in the treatment of secondary hyperparathyroidism associated with renal failure. These compounds reduce PTH secretion through vitamin D receptor (VDR)-dependent repression of PTH gene transcription. In previous studies, 1alpha(OH)D3, a vitamin D prodrug, inhibited PTH secretion in cultured bovine parathyroid cells, but it was unclear whether 1alpha(OH)D3 itself or an active metabolite produced this inhibition.

METHODS

We determined the effectiveness of the vitamin D prodrugs 1alpha(OH)D3, 1alpha(OH)D2 and 1alpha(OH)-24(R)-methyl-25-ene-D2 (BCI-210) at inhibiting PTH secretion in bovine parathyroid cell cultures, and examined the metabolism of [3H]1alpha(OH)D2 in these cells.

RESULTS

All three prodrugs suppressed PTH secretion with approximately 10% of the activity of 1,25(OH)2D3; much higher activity than expected based on the VDR affinities of these prodrugs (0.25% of 1,25(OH)2D3). Parathyroid cells activated [3H]1alpha(OH)D2 to both 1,25(OH)2D2 and 1,24(OH)2D2. 1,24(OH)2D2 was detectable at 4 h, increased to a maximum at 8 h, and then decreased. In contrast, 1,25(OH)2D2 levels increased linearly with time, suggesting the presence of constitutively active vitamin D-25-hydroxylase not previously reported in parathyroid cells. The cytochrome P-450 inhibitor ketoconazole (50 microM) reduced 1alpha(OH)D2 metabolism to below detectable levels, but did not significantly affect suppression of PTH by 1alpha(OH)D2.

CONCLUSIONS

The vitamin D prodrugs 1alpha(OH)D3, 1alpha(OH)D2 and BCI-210 suppressed PTH production by cultured parathyroid cells. The ability of 1alpha(OH)D2 to reduce PTH despite inhibition of its metabolism suggests a direct action of this 'prodrug' on the parathyroid gland, but the mechanism underlying this activity is not yet known.

Challenges in the therapy of secondary hyperparathyroidism

Derangements in mineral metabolism are known to occur early in the course of chronic kidney disease (CKD). Recent clinical practice guidelines are designed to focus on the problem early in the course of kidney disease, when it is recommended to evaluate the levels of parathyroid hormone (PTH) and to try to intervene early if the levels are elevated. To begin early intervention for hyperparathyroidism in chronic kidney disease will require involvement of primary care physicians and other subspecialty groups to identify the patients at risk and begin to intervene with measures to control hyperparathyroidism and its consequences on mineral metabolism. It has recently been demonstrated that chronic kidney disease is a significant risk factor for vitamin D deficiency and since abnormalities in vitamin D metabolism are important in the generation of hyperparathyroidism, this is an issue that needs direct attention. Studies are needed to assess the effects of correcting this vitamin D deficiency in early CKD. As kidney disease progresses, efforts to control hyperparathyroidism will likely need to be intensified and several therapeutic options are available, such as phosphate binders, repletion of vitamin D, the use of active vitamin D sterols, or the use of vitamin D analogs. In addition, it is important to define the appropriate PTH values that need to be achieved to minimize complications on bone. Such studies are in progress at the present time to validate the current more specific PTH assays. Strict guidelines have been proposed for the management of bone and mineral metabolism in patients with CKD stage V on dialysis, and although these challenging recommendations were initially opinion-based, there is mounting evidence which provides confirmation of these targets as relevant. Treatment options for patients on dialysis involve the full spectrum of agents which include phosphate binders, active vitamin D sterols (often given parenterally), the use of calcimimetic agents, surgical parathyroidectomy, and evaluation of appropriate levels of dialysate calcium. Similar to early stages of CKD, studies are in progress to refine the PTH targets with the newer PTH assays. With increased focus on the complications of bone and mineral metabolism as part of the continuum of chronic kidney disease, and with a variety of new therapies available, it is anticipated that improved patient outcomes should be achievable in this patient group.

Long-term treatment of secondary hyperparathyroidism with the calcimimetic cinacalcet HCl

BACKGROUND

Patients with secondary hyperparathyroidism often require therapy that provides long-term control of parathyroid hormone concentrations without increasing calcium and phosphorus concentrations. Cinacalcet modulates the calcium-sensing receptor on the parathyroid gland to reduce secretion of parathyroid hormone and lower serum calcium, phosphorus and calcium-phosphorus product in haemodialysis patients.

METHODS

Dialysis patients with secondary hyperparathyroidism [parathyroid hormone (PTH) level > or =300 pg/ml] who were enrolled in one of four phase 2 placebo-controlled studies were eligible to enroll in an open-label extension study in which all patients received cinacalcet. For this extension study, cinacalcet was initiated at 30 mg in all patients and the dose was escalated to a maximum of 180 mg once daily if PTH concentrations were >250 pg/ml. Use of concomitant vitamin D sterols and phosphate binders was not restricted.

RESULTS

The analysis of all patients (n = 59) completing 100 weeks of cinacalcet treatment showed long-term control of PTH and calcium-phosphorus product. Approximately 55% achieved a PTH concentration < or =300 pg/ml at the week-100 study visit, and approximately 60% had at least a 30% reduction in PTH from baseline. Serum calcium, phosphorus and the calcium-phosphorus product did not increase during the study. Concomitant vitamin D sterol and phosphate binder therapy remained stable. Cinacalcet was safe and generally well tolerated at doses up to 180 mg/day.

CONCLUSIONS

In this long-term study, cinacalcet effectively sustained reductions in PTH for up to 3 years without increasing concentrations of serum calcium, phosphorus or calcium-phosphorus product.

Difficulties in Achieving the K/DOQI Practice Guidelines for Bone and Mineral Metabolism

Hyperparathyroidism and alterations in bone and mineral metabolism are known to occur early in the course of chronic kidney disease (CKD). The etiology of these abnormalities is multifactorial. Phosphate retention and alterations in vitamin D metabolism play important roles. The recent practice guidelines from the National Kidney Foundation (NKF) have emphasized the need to approach these problems early in the course of CKD by measuring the levels of parathyroid hormone when glomerular filtration rates (GFRs) fall to less than 60 ml/min. If hyperparathyroidism is detected, then treatment must be undertaken to try to prevent its progression. Strict guidelines have been proposed for the management of these alterations in bone and mineral metabolism when kidney disease progresses to CKD stage V. Although the initial recommendations were often opinion based, evidence is accumulating to support these views. However, with our current therapeutic armamentarium, there is considerable difficulty in achieving these practice guidelines for calcium, phosphorus, calcium-phosphorus product, and parathyroid hormone on a sustained basis. New therapeutic agents are becoming available that will help with phosphorus control and control of hyperparathyroidism, and minimize the calcium load. Additional beneficial effects of vitamin D analogs are being uncovered and are being intensively investigated. It is hoped that with attention to these practice guidelines, control of the abnormalities of mineral metabolism will be improved and will lead to improved patient outcomes.

Vitamin D analogs: new therapeutic agents for secondary hyperparathyroidism

Patients with chronic renal failure frequently develop secondary hyperparathyroidism, primarily as a result of phosphate retention and low serum 1,25(OH)2D3. Replacement therapy with calcitriol or its synthetic precursor alfacalcidol [1alpha(OH)D3] often produces hypercalcemia, especially when combined with calcium-based phosphate binders. In addition, the natural vitamin D compounds can exacerbate the hyperphosphatemia in patients with chronic renal failure. This combined increase in calcium and phosphate has been correlated with vascular calcification leading to coronary artery disease, the most common cause of mortality in renal patients. Several vitamin D analogs have now been developed that retain the direct suppressive action of calcitriol on the parathyroid glands but have less calcemic activity, thereby offering a safer and more effective means of controlling secondary hyperparathyroidism. Maxacalcitol [22-oxa-1,25(OH)2D3] and falecalcitriol [1,25(OH)2-26,27-F6-D3] are currently available in Japan, and paricalcitol [19-nor-1,25(OH)2D2] and doxercalciferol [1alpha(OH)D2] are available in the US. The mechanisms by which these analogs exert their selective actions on the parathyroid glands are under investigation. The low calcemic activity of maxacalcitol has been attributed to its rapid clearance from the circulation. This prevents sustained effects on intestinal calcium absorption and bone resorption, but still allows a prolonged suppression of parathyroid hormone gene expression. The selectivity of the other analogs is achieved by distinct mechanisms. Understanding how these compounds exert their selective actions on the parathyroid glands will aid in the design of safer, more effective analogs.

Cinacalcet HCl, an oral calcimimetic agent for the treatment of secondary hyperparathyroidism in hemodialysis and peritoneal dialysis: a randomized, double-blind, multicenter study

Management of secondary hyperparathyroidism is challenging with traditional therapy. The calcimimetic cinacalcet HCl acts on the calcium-sensing receptor to increase its sensitivity to calcium, thereby reducing parathyroid hormone (PTH) secretion. This phase 3, multicenter, randomized, placebo-controlled, double-blind study evaluated the efficacy and safety of cinacalcet in hemodialysis (HD) and peritoneal dialysis (PD) patients with PTH > or =300 pg/ml despite traditional therapy. A total of 395 patients received once-daily oral cinacalcet (260 HD, 34 PD) or placebo (89 HD, 12 PD) titrated from 30 to 180 mg to achieve a target intact PTH (iPTH) level of < or =250 pg/ml. During a 10-wk efficacy assessment phase, cinacalcet was more effective than control for PTH reduction outcomes, including proportion of patients with mean iPTH levels < or =300 pg/ml (46 versus 9%), proportion of patients with > or =30% reduction in iPTH from baseline (65 versus 13%), and proportion of patients with > or =20, > or =40, or > or =50% reduction from baseline. Cinacalcet had comparable efficacy in HD and PD patients; 50% of PD patients achieved a mean iPTH < or =300 pg/ml. Cinacalcet also significantly reduced serum calcium, phosphorus, and Ca x P levels compared with control treatment. The most common side effects, nausea and vomiting, were usually mild to moderate in severity and transient. Once-daily oral cinacalcet was effective in rapidly and safely reducing PTH, Ca x P, calcium, and phosphorus levels in patients who received HD or PD. Cinacalcet offers a new therapeutic option for controlling secondary hyperparathyroidism in patients with chronic kidney disease on dialysis.

Paricalcitol

Paricalcitol (Zemplar) is a synthetic vitamin D(2) analogue that inhibits the secretion of parathyroid hormone (PTH) through binding to the vitamin D receptor. It is approved in the US and in most European nations for intravenous use in the prevention and treatment of secondary hyperparathyroidism associated with chronic renal failure in adult, and in the US paediatric, patients. Paricalcitol effectively reduced elevated serum PTH levels and was generally well tolerated in children and adults with secondary hyperparathyroidism associated with chronic renal failure. In well designed clinical trials, paricalcitol was as effective as calcitriol and as well tolerated in terms of the incidence of prolonged hypercalcaemia and/or elevated calcium-phosphorus product (Ca x P). Thus, paricalcitol is a useful option for the management of secondary hyperparathyroidism in adults and children with chronic renal failure.

Tissue distribution and activity studies of 1,24-dihydroxyvitamin D2, a metabolite of vitamin D2 with low calcemic activity in vivo

The active vitamin D compound 1alpha,24(S)-dihydroxyvitamin D(2) (1,24(OH)(2)D(2)) is under development as a therapy for disorders including cancer and secondary hyperparathyroidism. 1,24(OH)(2)D(2) is a potent inhibitor of cell proliferation in vitro and, relative to calcitriol (1,25(OH)(2)D(3)), has reduced calcemic activity in vivo. To examine the mechanisms underlying this reduced calcemic activity, we studied the tissue distribution in rats of radiolabeled 1,24(OH)(2)D(2) or 1,25(OH)(2)D(3) over 24h. Serum levels of 1,24(OH)(2)D(2) were lower than those of 1,25(OH)(2)D(3) at all time points; however, tissue levels of radiolabeled compounds followed different patterns. In duodenum and kidney, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) rose to similar levels at early time points; 1,24(OH)(2)D(2) levels then declined more rapidly. In bone marrow, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) were present at similar levels at all time points. In liver, 1,24(OH)(2)D(2) levels were two-fold higher than 1,25(OH)(2)D(3) at 1h post-injection, declining to similar levels by 8h. In vitamin D-deficient rats, doses of 1,24(OH)(2)D(2) 30-fold higher than 1,25(OH)(2)D(3) were required to produce equal stimulation of intestinal calcium absorption. In the same deficient animals, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) were nearly equipotent at stimulating bone calcium mobilization. In cultured bone cells, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) were equipotent at stimulating osteoclast formation and bone resorption. In summary, the reduced calcemic activity of 1,24(OH)(2)D(2) may result from altered pharmacokinetics relative to 1,25(OH)(2)D(3), resulting in relatively rapid decreases in 1,24(OH)(2)D(2) levels and activity in target organs such as intestine. Further studies will be necessary to confirm these findings and to confirm the clinical utility of 1,24(OH)(2)D(2).

Effects of vitamin D compounds on renal and intestinal Ca2+ transport proteins in 25-hydroxyvitamin D3-1α-hydroxylase knockout mice1

BACKGROUND

Vitamin D compounds are used clinically to control secondary hyperparathyroidism (SHPT) due to renal failure. Newer vitamin D compounds retain the suppressive action of 1,25(OH)(2)D(3) on the parathyroid glands and may have less Ca(2+)-mobilizing activity, offering potentially safer therapies.

METHODS

This study investigated the effect of a single dose of compound (1,25(OH)(2)D(3), 1,24(OH)(2)D(2), or 1alpha(OH)D(2)) on renal and intestinal Ca(2+) transport proteins, including TRPV5 and TRPV6, and serum Ca(2+), in a novel SHPT model, the 25-OH-D(3)-1alpha-hydroxylase knockout mouse, which lacks endogenous 1,25(OH)(2)D(3) and is severely hypocalcemic. Animals were injected intraperitoneally with compound (100 ng/mouse).

RESULTS

Serum levels of 1,25(OH)(2)D(3) and 1,24(OH)(2)D(2) peaked at four hours post-injection (pi), then declined rapidly. 1,25(OH)(2)D(2) generated from 1alpha(OH)D(2) peaked at 12 hours pi and then remained stable. Serum Ca(2+) was increased to near-normal within four hours by 1,25(OH)(2)D(3) and 1,24(OH)(2)D(2), and within 12 hours by 1alpha(OH)D(2). 1,25(OH)(2)D(3) and 1,24(OH)(2)D(2) up-regulated duodenal TRPV5 and TRPV6 mRNA to a similar degree within four hours; mRNA levels decreased by 12 hours after 1,24(OH)(2)D(2) treatment, and by 24 hours after 1,25(OH)(2)D(3) treatment. 1,25(OH)(2)D(3) increased kidney levels of TRPV5, calbindin-D(28K), and calbindin-D(9K) mRNA within four hours; 1,24(OH)(2)D(2) did not change kidney TRPV5 levels and modestly increased calbindin D(9K) by 48 hours. 1alpha(OH)D(2) produced later-onset effects, increasing duodenal TRPV6 and calbindin-D(9K) mRNA levels by 12 hours and TRPV5 by 48 hours.

CONCLUSION

In kidney, 1alpha(OH)D(2) increased TRPV5, calbindin-D(28K), and calbindin-D(9K) mRNA levels by 12 hours. This study indicates that Ca(2+) transport proteins, including TRPV5 and TRPV6, are differentially up-regulated by vitamin D compounds.

Doxercalciferol safely suppresses PTH levels in patients with secondary hyperparathyroidism associated with chronic kidney disease stages 3 and 4

BACKGROUND

Calcitriol lowers parathyroid hormone (PTH) levels in patients with chronic kidney disease (CKD) stages 3 and 4, but its use is limited by a low therapeutic index and concerns regarding hypercalcemia and acceleration of kidney disease. We evaluated doxercalciferol (1alpha-hydroxyvitamin D2) as an alternative therapy in a randomized, double-blinded, placebo-controlled, multicenter trial.

METHODS

Fifty-five adults with stage 3 or 4 CKD and an intact PTH (iPTH) level greater than 85 pg/mL (ng/L) completed 8 baseline weeks, followed by 24 weeks of oral therapy with doxercalciferol or placebo. Pretreatment demographics and biochemical features did not differ between groups. Dosages were increased gradually if iPTH level was not decreased by 30% or greater and serum calcium and phosphorus levels were stable. Regular monitoring included plasma iPTH, serum calcium and phosphorus, urinary calcium, bone-specific serum markers, and serum lalpha,25-dihydroxyvitamin D levels. Glomerular filtration rate (GFR) was measured before and after treatment.

RESULTS

Mean plasma iPTH level decreased by 46% from baseline after 24 weeks of doxercalciferol treatment (P <0.001), but was unchanged with placebo. After 6 weeks, iPTH level reductions with doxercalciferol treatment exceeded those with placebo at all subsequent intervals (P <0.001). No clinically significant differences in mean serum calcium or phosphorus or urinary calcium levels or incidence of hypercalcemia, hyperphosphatemia, or hypercalciuria were noted between groups. Serum C- and N-telopeptide and bone-specific alkaline phosphatase levels decreased with doxercalciferol treatment relative to both baseline and placebo (P <0.01). Adverse-event rates and changes in GFR did not differ between groups.

CONCLUSION

Doxercalciferol is safe and effective in controlling secondary hyperparathyroidism of patients with CKD stages 3 and 4.

An update on vitamin D as related to nephrology practice: 2003

In this article, an up-to-date consideration of vitamin D therapeutics in nephrology is reviewed. The condition of vitamin D insufficiency is defined as the level of serum 25(OH)vitamin D at which vitamin D2 or D3 supplementation leads to a reduction of levels of parathyroid hormone (PTH). The risks of such vitamin D insufficiency in the normal population and likely risks in individuals with chronic kidney disease (CKD) stages 3 and 4 are reviewed. The potential for its safe treatment and prevention using moderate supplements of vitamin D2 or vitamin D3 are outlined. The role of altered "vitamin D nutrition" in leading to the observed greater incidence of secondary hyperparathyroidism in African Americans with ESRD compared to other racial groups is considered. The actions of active vitamin D sterols to augment intestinal absorption of both calcium and phosphorus, the effect to reduce levels of PTH, and to be a factor contributing to the rising incidence of low bone turnover (adynamic bone) are discussed. Growing evidence for contributions of elevated levels of serum calcium, serum phosphorus, and the calcium x phosphorus product as factors contributing to vascular and cardiac calcification in ESRD patients are cited. Questions are raised about whether the current practice of vitamin D usage in ESRD patients might be a contributing factor to such vascular abnormalities. The economic factors that likely affect the usage of intravenous vitamin D sterols in the United States are reviewed. It is recommended that potential adverse vascular effects of vitamin D sterols related to the increments of serum Ca and P be carefully evaluated.