What is the optimal regimen for vitamin D?

Dialysis time: does it matter? A reappraisal of existing literature

PURPOSE OF REVIEW

The length of time (Td) required for adequate maintenance hemodialysis therapy is perceived as a substantial patient burden. Technological advancements have allowed shortening Td over the past three decades. However, failure to detect improved outcomes with higher dialysis dose has prompted renewed interest in the potential impact of longer Td.

RECENT FINDINGS

Ongoing trials are focused on increasing the frequency of treatments, although the feasibility of having most patients agreeing to more than five treatments per week remain doubtful. Furthermore, survival was better in short daily hemodialysis with Td of 180 vs. 90 min. Within thrice weekly dialysis, several recent epidemiological studies have shown improved survival associated with Td more than 4 h. Improved outcomes for long in-center nocturnal hemodialysis (6-8 h, 3×/week), similar to what has been performed in Tassin for the last 30 years, have also been reported.

SUMMARY

Compelling rationale and recent outcome data support use of longer Td. Improved management of salt and water may be the cause for the dissociation of dialysis time and small molecule clearance. In most industrialized countries, hemodialysis care systems in place have the capacity to accommodate it. Until such time that results from prospective randomized trials are available, we believe that physicians should prescribe and exert all efforts to convince thrice weekly hemodialysis patients to accept 4 h as minimum Td.

Vitamin D in patients with renal failure: a summary of observational mortality studies and steps moving forward

Although approximately half of patients undergoing hemodialysis receive activated forms of Vitamin D, the primary reason to initiate this therapy has rested solely on the management of secondary hyperparathyroidism. Secondary hyperparathyroidism is likely one of several consequences of Vitamin D deficiency, and only now have other consequences of Vitamin D deficiency emerged. Although previously viewed as a contributor to hypercalcemia and hyperphosphatemia, recent studies suggest Vitamin D may improve cardiovascular structure and function, improve vascular compliance, and reduce pro-inflammatory cytokines, all of which may contribute to the improved survival observed in retrospective studies examining the outcome of patients treated with activated Vitamin D compared to those who were not. The current review examines two recent large-scale studies of hemodialysis patients: one that demonstrated a survival advantage of paricalcitol over calcitriol, and a second that demonstrated a significant survival advantage of any intravenous Vitamin D formulation versus none. In both studies, the findings were independent of mineral and parathyroid hormone levels, suggesting "non-traditional" actions of Vitamin D contributed to the observed survival advantage. Potential steps moving forward in light of these observational studies are subsequently discussed.

VITAMIN D IN HEALTH AND DISEASE: Beyond Minerals and Parathyroid Hormone: Role of Active Vitamin D in End-Stage Renal Disease

Secondary hyperparathyroidism is a common complication of end-stage renal disease (ESRD) that is often treated with activated forms of intravenous vitamin D. The natural course and treatment of secondary hyperparathyroidism in hemodialysis patients is punctuated by episodes of hypercalcemia, hyperphosphatemia, and increased calcium-phosphate product, which in previous studies were linked to increased mortality. Historically these episodes have been attributed to vitamin D, leading some authorities to favor decreased vitamin D use. However, the studies that examined the impact of mineral levels and parathyroid hormone (PTH) on survival did not consistently account for vitamin D therapy itself on hemodialysis patient survival. The current review examines in detail two recent large-scale studies of hemodialysis patients: one that demonstrated a survival advantage of paricalcitol over calcitriol and a second that demonstrated a significant survival advantage of any intravenous vitamin D formulation versus none. In both studies, the effects were independent of mineral and PTH levels, suggesting "nontraditional" actions of vitamin D contributed to the observed survival advantage. Several of these nontraditional actions are reviewed with an emphasis on those that might impact hemodialysis outcomes.

Pharmacokinetics, pharmacodynamics, and safety of cinacalcet hydrochloride in hemodialysis patients at doses up to 200 mg once daily

BACKGROUND

Cinacalcet hydrochloride (HCl) can be used to manage the secondary hyperparathyroidism of patients with chronic kidney disease. This study investigated the pharmacokinetics, pharmacodynamics, safety, and tolerability of cinacalcet HCl over a dose range of 25 to 300 mg/d in patients receiving dialysis.

METHODS

Hemodialysis patients were randomly assigned 4:1 to receive cinacalcet HCl or placebo in this double-blind study. Cinacalcet HCl doses were escalated weekly in 25-mg increments from 25 to 300 mg/d. Noncompartmental methods were used to analyze the pharmacokinetic parameters of cinacalcet (the free-base). The effects of cinacalcet concentration on plasma parathyroid hormone (PTH) and serum calcium levels were evaluated.

RESULTS

Of 23 patients enrolled (17 patients, cinacalcet HCl; 6 patients, placebo), 10 patients (8 patients, cinacalcet HCl; 2 patients, placebo) completed the study. Plasma concentration, median area under the plasma concentration-time curve from time 0 to 24 hours after dosing, and maximal plasma concentration (Cmax ) of cinacalcet increased with doses up to 200 mg once daily. Median oral clearance ranged from 222 to 599 L/h, and median time after dosing when C max occurred ranged from 2 to 3 hours across all doses. The pharmacokinetics were linear over the 25- to 200-mg once-daily dose range, with no substantial increase in exposure at greater than 200 mg. Changes in plasma PTH concentrations correlated inversely with cinacalcet concentration. The concentration-effect relationship was well described by an inhibitory maximal effect model. Cinacalcet HCl was reasonably tolerated, and the incidence of adverse events was similar between groups (76%, cinacalcet; 80%, placebo). Gastrointestinal events were noted at greater doses and may be dose related.

CONCLUSION

Cinacalcet HCl shows a dose-proportional increase in exposure over the range of 25 to 200 mg once daily in patients on hemodialysis therapy, and kinetics were linear up to 200 mg once daily. The incidence of adverse events was similar between groups.

Activated injectable vitamin D and hemodialysis survival: a historical cohort study

Patients with ESRD commonly experience secondary hyperparathyroidism, a condition primarily managed with activated injectable vitamin D. The biologic effects of vitamin D, however, are widespread, and it is possible that activated injectable vitamin D alters survival in ESRD. This hypothesis was tested in a historical cohort study of incident hemodialysis patients who lived throughout the United States between January 1996 and December 1999. The primary outcome was 2-yr survival among those who survived for at least 90 d after initiation of chronic hemodialysis. During this period, 51,037 chronic hemodialysis patients survived for at least 90 d from the initiation of hemodialysis, and in the ensuing 2 yr, 37,173 received activated injectable vitamin D and 13,864 did not. At 2 yr, mortality rates were 13.8/100 person-years in the group that received injectable vitamin D compared with 28.6/100 person-years in the group that did not (P < 0.001). Cox proportional hazards analyses adjusting for several potential confounders and examining injectable vitamin D therapy as a time-dependent exposure suggested that compared with patients who did not receive injectable vitamin D, the 2-yr survival advantage associated with the group that did receive injectable vitamin D was 20% (hazard ratio, 0.80; 95% confidence interval, 0.76 to 0.83). The incidence of cardiovascular-related mortality was 7.6/100 person-years in the injectable vitamin D group, compared with 14.6/100 person-years in the non-vitamin D group (P < 0.001). The benefit of injectable vitamin D was evident in 48 of 49 strata examined, including those with low serum levels of intact parathyroid hormone and elevated levels of serum calcium and phosphorus, situations in which injectable vitamin D is often withheld. Repeating the entire analysis using marginal structural models to adjust for time-dependent confounding by indication yielded a survival advantage of 26% (hazard ratio, 0.74; 95% confidence interval, 0.71 to 0.79) associated with the injectable vitamin D group. In this historical cohort study, chronic hemodialysis patients in the group that received injectable vitamin D had a significant survival advantage over patients who did not. Randomized clinical trials would permit definitive conclusions.

Secondary hyperparathyroidism: Review of the disease and its treatment

BACKGROUND

Most patients with chronic kidney disease (CKD) stage 5 develop secondary hyperparathyroidism (SHPT). SHPT is an adaptive response to CKD and its associated disruptions in the homeostatic control of serum phosphorus, calcium, and vitamin D. The poor control of mineral and parathyroid hormone (PTH) levels characteristic of SHPT is associated with serious clinical consequences.

OBJECTIVE

This review discusses the pathophysiology and consequences of SHPT, as well as the efficacy and limitations of current treatment modalities.

METHODS

Literature searches were conducted using the MEDLINE, EMBASE, and BIOSIS databases. Additional information was obtained from Internet web sites, textbooks, and nephrology congress abstracts.

RESULTS

Patients with uncontrolled SHPT are at higher risk for cardiovascular morbidity and mortality, hospitalization, bone disease, vascular and soft-tissue calcification, and vascular access failure than patients whose mineral and PTH levels are well managed. New National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) targets for calcium, phosphorus, calcium-phosphorus product, and PTH control have recently been published with the aim of improving the management of mineral metabolism in CKD patients. Data from observational studies suggest that the majority of patients currently have PTH and mineral levels outside these target ranges.

CONCLUSIONS

Given the inadequacies of current therapies, novel agents are being developed that may help improve the management of SHPT.

The calcimimetic agent KRN 1493 lowers plasma parathyroid hormone and ionized calcium concentrations in patients with chronic renal failure on haemodialysis both on the day of haemodialysis and on the day without haemodialysis

AIMS

Treatment with vitamin D sterols can lower plasma parathyroid hormone (PTH) in patients with secondary hyperparathyroidism; however, hypercalcaemia, hyperphosphataemia, or both, often develop. Calcimimetic agents, employed in alternative therapeutic approaches, directly inhibit PTH secretion by activating the calcium-sensing receptor in the parathyroid glands.

METHODS

In this study, patients were given orally 25, 50, and 100 mg doses of the calcimimetic agent KRN 1493 each on two occasions, on the day of haemodialysis and on the day without haemodialysis.

RESULTS

In the pharmacokinetic results, because the clearance of KRN 1493 by haemodialysis was much smaller than the systemic clearance, the influence of haemodialysis was not remarkable. In the pharmacodynamic study, on both the days with or without haemodialysis, plasma PTH concentrations decreased in a dose-dependent manner. Serum calcium concentrations decreased in association with the decrease in plasma PTH concentrations. Mild dose-dependent adverse effects (mainly nausea) were seen after the administration of KRN 1493 on both the day of haemodialysis and the day without haemodialysis.

CONCLUSIONS

We conclude that the pharmacokinetics of KRN 1493 after a single administration were similar on the day of haemodialysis and the day without haemodialysis. KRN 1493 is safe and effective in suppressing PTH secretion and serum calcium concentrations on the day of haemodialysis and on the day without haemodialysis in patients with secondary hyperparathyroidism.

New Vitamin D analogues for osteodystrophy in chronic kidney disease

Vitamin D therapy for patients with chronic kidney disease has until recently comprised alfacalcidol or calcitriol, both of which effectively attenuate secondary hyperparathyroidism and the target organ consequences thereof. Unfortunately, both these agents also have significant calcaemic and phosphataemic actions leading to frequent episodes of hypercalcaemia, hyperphosphataemia and an increase in the CaxP product. It is likely that these in turn have adverse effects on cardiovascular and survival outcomes by promoting soft tissue and vascular calcification. These drawbacks have fuelled a search for vitamin D compounds with a wider therapeutic window. Experimentally, some of these have exhibited remarkable dissociation between their ability to suppress parathyroid hormone (PTH) and concomitant calcaemic actions. In the case of 22-oxacalcitriol, the calcaemic potency relative to parathyroid suppression is 100th of that of calcitriol. 22-oxacalcitriol, with paricalcitol and doxercalciferol, are now widely used. Clinical studies of these agents, while confirming efficacy that is at least as good as alfacalcidol/calcitriol, have not consistently shown benefit in head to head comparison. Experience with these agents in the paediatric arena is very limited. One placebo-controlled study has now been completed in children-paricalcitol appeared effective and well tolerated. Calcimimetics, which simultaneously lower PTH, calcium and the CaxP product are about to enter the clinical arena-early studies in adults look promising, although they will need careful evaluation in children. These two therapies are likely to be additive and will probably complement one another effectively.

The calcimimetic AMG 073 as a potential treatment for secondary hyperparathyroidism of end-stage renal disease

Current treatment of secondary hyperparathyroidism in chronic kidney failure with calcium and active vitamin D is potentially limited by hypercalcemia and hyperphosphatemia. AMG 073 represents a new class of compounds for the treatment of hyperparathyroidism known as calcimimetics, which reduce parathyroid hormone (PTH) synthesis and secretion by increasing the sensitivity of the parathyroid calcium-sensing receptor (CaR) to extracellular calcium. The current study evaluates the efficacy and safety of AMG 073 when added to conventional treatment of secondary hyperparathyroidism in end-stage renal disease (ESRD). Seventy-one hemodialysis patients with uncontrolled secondary hyperparathyroidism, despite standard therapy with calcium, phosphate binders, and active vitamin D sterols, were treated in this 18-wk, dose-titration study with single daily oral doses of AMG 073/placebo up to 100 mg. Changes in plasma PTH, serum calcium, serum phosphorus, and calcium x phosphorus levels were compared between AMG 073 and placebo groups. Mean PTH decreased by 33% in the AMG 073 patients compared with an increase of 3% in placebo patients (P = 0.001). A significantly greater proportion of AMG 073 patients (44%) had a mean PTH < or = 250 pg/ml compared with placebo patients (20%; P = 0.029). Also, a significantly greater proportion of AMG 073 patients (53%) had a decrease in PTH > or =30% compared with placebo patients (23%; P = 0.009). Calcium x phosphorus levels decreased by 7.9% in AMG 073 patients compared with an increase of 11.3% in placebo patients (P = 0.013). Adverse event rates were low and mostly mild to moderate in severity; however, the incidence of vomiting was higher in AMG 073 patients. In this study, the calcimimetic AMG 073 at doses up to 100 mg for 18 wk provided a safe and effective means to attain significant reductions in PTH and calcium x phosphorus levels in ESRD patients. AMG 073 represents a novel and promising therapy to improve the management of secondary hyperparathyroidism.

The calcimimetic AMG 073 reduces parathyroid hormone and calcium x phosphorus in secondary hyperparathyroidism

BACKGROUND

A need exists for a therapy that lowers parathyroid hormone (PTH) without increasing calcium x phosphorus in patients with secondary hyperparathyroidism. The calcimimetic AMG 073 increases the sensitivity of the parathyroid calcium-sensing receptor to extracellular calcium, thereby reducing PTH secretion. Consequently, AMG 073 may provide a novel therapy for secondary hyperparathyroidism.

METHODS

Seventy-eight hemodialysis patients with secondary hyperparathyroidism were enrolled into this 18-week, double-blind, randomized, placebo-controlled, dose titration study. Daily oral AMG 073 doses were administered to determine the effect on PTH, serum calcium, phosphorus, and calcium x phosphorus.

RESULTS

The mean baseline PTH was similar in patients administered AMG 073 or placebo (632 +/- 280.1 pg/mL vs. 637 +/- 455.9 pg/mL, respectively). PTH decreased by 26.0% in the AMG 073-treated group, compared with an increase of 22.0% in the placebo group (P < 0.001). A greater proportion in the AMG 073 group (38%) had a decrease in PTH >or=30%, compared with the placebo group (8%) (P = 0.001). Decreases in PTH were independent of baseline vitamin D usage. Patients receiving AMG 073 had an 11.9% decrease in calcium x phosphorus compared with a 10.9% increase in the placebo group (P < 0.001). Use of vitamin D sterols, as well as both calcium and noncalcium-containing phosphate binders. were similar between treatment groups. Administration of AMG 073 was safe and well tolerated in this 18-week study.

CONCLUSIONS

The calcimimetic AMG 073 decreases both PTH and calcium x phosphorus levels in hemodialysis patients with secondary hyperparathyroidism.

Update on vitamin D and its newer analogues: actions and rationale for treatment in chronic renal failure

Vitamin D is an important hormone for mineral homeostasis and the proper formation and maintenance of bone. In addition, vitamin D has broader functions in the body that expand its traditionally known role in mineral balance. In chronic renal failure, calcitriol deficiency contributes to the development and progression of secondary hyperparathyroidism, bone disorders, and altered mineral metabolism. Recent revelations of the broader role of vitamin D also suggest calcitriol deficiency may contribute to decreased cardiac and immune function in chronic renal failure patients. Research on vitamin D has led to a more complete understanding of the actions of vitamin D at the transcriptional level and with respect to the clinical use of vitamin D and its analogs to control parathyroid hormone overactivity and to replace the other D hormone-dependent actions in patients with renal failure. Limitations of vitamin D and its metabolites include hypercalcemia, hyperphosphatemia and suppression of bone turnover with the risk of adynamic bone disease. Vitamin D analogs may offer greater selectivity and potentially greater safety as compared to calcitriol because of their altered relative potency on calcium and phosphorus metabolism. This review focuses on the current understanding of the biological actions of vitamin D and its analogs and the rationale for treating patients with chronic renal failure.