Low-dose intravenous calcitriol treatment of secondary hyperparathyroidism in hemodialysis patients. Italian Group for the Study of Intravenous Calcitriol

Intraperitoneal Pulse Calcitriol in the Treatment of Secondary Hyperparathyroidism in Patients on Continuous Ambulatory Peritoneal Dialysis

Objective

To determine whether it is practicable to use intraperitoneal calcitriol to treat continuous ambulatory peritoneal dialysis (CAPD) patients with secondary hyperparathyroidism and whether this form of therapy is effective and safe.

Design

A prospective, nonrandomized study.

Setting

Division of Nephrology, Tertiary Hospital.

Method

Eight patients from our CAPD population were recruited (5 F,3 M), aged 24 to 63 years (mean 38.9 ± 7.6 yr). They had been on CAPD for 8 to 84 months (mean 47.6 ± 24.6 months). All the patients had bone biopsy -proven secondary hyperparathyroidism with 2 patients showing mixed lesions. The CAPD system was changed to the twinbag system (Ultrabag, Baxter Healthcare, McGaw Park, IL, U.S.A.) in all 8 patients, who were taught to inject the calcitriol directly through the short transfer set and the Tenckhoff catheter into the peritoneal cavity, twice per week before bedtime. Calcium carbonate or calcium acetate was used as the main phosphate binder. Intact parathyroid hormone level (iPTH), serum ionized calcium (iCa), serum phosphate, and serum total alkaline phosphatase (alk. phos.) levels were measured at baseline and then every 4 weeks. The mean duration of follow-up was 10.5 months ± 1.9 months.

Results

There was a significant drop of iPTH level from the pretreatment level of 100.6 ± 35.8 pmoll L to a level of 63.8 ± 48.7 pmoll L at 24 weeks (p = 0.036). The lowest level of iPTH attained was 43.4 ± 27.0 pmol/L at 48 weeks. Serum total alk. phos. also dropped from 232.4 ± 83.3 lUlL pretreatment to 147.9 ± 52.0 lUlL at 24 weeks (p = 0.017). The decrease in alk. phos. level paralleled the decrease in iPTH level. The mean serum iCa level did not show any significant rise throughout the study period. The maximum dose of calcitriol used was 6.6 ± 1.5 μg/week and the average dose of calcitriol was 5.4 ± 1.2 μg/week. One patient did not respond satisfactorily and she subsequently had a parathyroidectomy. Two episodes of peritonitis occurred during the study period, giving a peritonitis rate of one episode per 42 patient-months. There was no significant change in the urea clearance tests or the peritoneal equilibration tests before and after the study.

Conclusion

Intraperitoneal calcitriol is practicable, effective, and safe in the treatment of secondary hyperparathyroidism in CAPD patients.

Hyperparathyroidism of Renal Disease

Renal hyperparathyroidism (rHPT) is a common complication of chronic kidney disease characterized by elevated parathyroid hormone levels secondary to derangements in the homeostasis of calcium, phosphate, and vitamin D. Patients with rHPT experience increased rates of cardiovascular problems and bone disease. The Kidney Disease: Improving Global Outcomes guidelines recommend that screening and management of rHPT be initiated for all patients with chronic kidney disease stage 3 (estimated glomerular filtration rate, < 60 mL/min/1.73 m(2)). Since the 1990s, improving medical management with vitamin D analogs, phosphate binders, and calcimimetic drugs has expanded the treatment options for patients with rHPT, but some patients still require a parathyroidectomy to mitigate the sequelae of this challenging disease.

Mortality rates do not differ among patients prescribed various vitamin D agents

BACKGROUND

Limited well-controlled research exists examining the impact of different formulations of oral vitamin D on clinical outcomes in dialysis patients, specifically those on peritoneal dialysis. For this retrospective mortality analysis, we compared mortality rates of patients on 3 of the most commonly prescribed vitamin D agents.

METHODS

We examined 2 years (7/1/2008 to 6/30/2010) of oral medication records of peritoneal dialysis patients from a large US dialysis organization. Patients were identified whose physicians prescribed a single form of vitamin D (calcitriol, paricalcitol, or doxercalciferol) for ≥ 90% of all patient-months. We excluded incident patients (< 90 days on dialysis) and patients whose physicians treated < 5 peritoneal dialysis patients at a dialysis facility, and we assessed mortality.

RESULTS

The analysis inclusion criteria identified 1,707 patients. The subset in this analysis included 12.6% of all prevalent peritoneal dialysis patients and 11.8% of prevalent patient-months. Patients with physicians who predominately prescribed calcitriol had a lower mortality rate: 9.33 (confidence interval (CI) 7.06, 11.60) deaths per 100 patient-years than the doxercalciferol, 12.20 (CI 9.34, 15.06) or paricalcitol, 12.27 (CI 9.27, 15.28) groups. However, these differences were not statistically significant. A Cox proportional hazards model, adjusting for differences in age, vintage, gender, race, body mass index, and comorbidities also showed no significant differences.

CONCLUSIONS

For this peritoneal dialysis population, instrumental variable analyses showed no significant difference in mortality in patients taking the most common oral vitamin D formulations (calcitriol, doxercalciferol, paricalcitol).

A prospective randomized pilot study on intermittent post-dialysis dosing of cinacalcet

BACKGROUND

Treatment of secondary hyperparathyroidism (SHPT) is important in management of patients with end-stage renal disease on hemodialysis (HD). Calcimimetic agent, cinacalcet provides an option for control of SHPT in patients who fail traditional therapy. It may not have optimal results in non-compliant patients. To enhance compliance, we evaluated effectiveness of post-dialysis dosing of cinacalcet (group AD) as compared to daily home administration (group D) in a prospective randomized trial of HD patients with refractory SHPT.

METHODS

After 2-week run-in phase, patients were randomly assigned to two treatment groups. In group AD (N = 12), patients were administered cinacalcet on the day of dialysis (3 times/week) by dialysis staff, while in control group D (N = 11), cinacalcet was prescribed daily to be taken by patients at home. Intact parathyroid hormone (i-PTH), serum calcium, phosphorus, and alkaline phosphatase were followed for 16 weeks and compared to baseline in both groups. Data were analyzed using between-groups linear regression for repeated measures.

RESULTS

No significant decline in i-PTH occurred in group AD at 16 weeks as compared to a significant drop in group D (p = 0.006). However, subgroup analysis showed effectiveness of post-dialysis dosing in patients with less severe SHPT (p = 0.04).

CONCLUSION

Although daily dosing overall was more effective for treatment of SHPT, dialysis dosing was effective in patients with less severe SHPT. This warrants a larger study considering the limitations of this pilot trial. In the meantime, dialysis dosing can be considered in non-compliant patients with less severe SHPT.

Intravenous alfacalcidol once weekly pulse therapy for secondary hyperparathyroidism in hemodialysis patients

BACKGROUND

This study was carried out to assess the efficacy of intravenous administration of alfacalcidol once weekly versus thrice weekly in patients with poorly controlled secondary hyperparathyroidism.

METHODS

Thirty-six hemodialysis patients with intact parathyroid hormone (i-PTH) > 31.8 pmol/L were divided into two groups. Eighteen patients (Group 1) were given once weekly alfacalcidol for 6 months. The starting dose was 3 µg, which was increased or decreased by 1 µg per week. Eighteen patients (Group 2) were given thrice weekly alfacalcidol for 6 months. The starting dose was 1 µg, which was increased or decreased by 0.5 µg per dose. The dose was increased or decreased according to serum-corrected calcium (CCa), phosphorus (P), and i-PTH. Serum-CCa and P were measured weekly, whereas serum i-PTH and alkaline phosphatase were determined every month.

RESULTS

Intact-PTH reduced significantly (p < 0.001) from 86 ± 33.20 pmol/L to 31.04 ± 7.77 pmol/L and from 83.64 ± 32.12 pmol/L to 33.09 ± 11.37 pmol/L post-treatment in Groups 1 and 2, respectively. Fifty-six percent of the patients had i-PTH ≤ 31.8 pmol/L at the last observation. Serum alkaline phosphatase reduced significantly (p < 0.001) from 227.94 ± 129.86 IU/L to 163.17 ± 95.29 IU/L and from 285.39 ± 232.36 IU/L to 202.56 ± 165.84 IU/L post-treatment in Groups 1 and 2, respectively. There were no significant differences in serum levels of CCa, P, or their product.

CONCLUSION

Intravenous alfacalcidol thrice or once weekly is safe and effectively reduced the levels of i-PTH in hemodialysis patients.

Effects of calcimimetics on extraskeletal calcifications in chronic kidney disease

While the precise mechanisms of vascular calcification (VC) in chronic kidney disease (CKD) remain to be elucidated, there is a close association between VC and secondary hyperparathyroidism (HPT). The elevations in calcium, phosphorus, the Ca x P product, and parathyroid hormone (PTH) observed in patients with CKD and secondary HPT have been associated with VC and increased risk of cardiovascular morbidity and mortality. We have investigated the development of extraskeletal calcification in uremic rats with secondary HPT treated with vitamin D derivatives (calcitriol or paricalcitol), calcimimetics (R-568 or AMG 641), or the combination of both types drugs. Treatment with calcitriol resulted in a significant increase in the extraosseous calcium and phosphorus content and high mortality. By contrast, treatment with calcimimetics, which provided a better control of plasma PTH levels, did not result in extraskeletal mineral accumulation and did not cause mortality. More important, when added to calcitriol, calcimimetics prevented the development of VC and reduced mortality. Paricalcitol administration to uremic rats resulted in calcification levels and mortality rates that were lower than in rats treated with calcitriol but higher than in rats treated with calcimimetics. The mechanism(s) of action responsible for the anticalcification effect of calcimimetics are likely related to the fact that these drugs can control PTH levels without increasing the plasma Ca x P product. In addition calcimimetic activation of vascular calcium-sensing receptor may also modulate the expression of proteins that prevent the development of VC, like matrix Gla protein.

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.

Pharmacological control of secondary hyperparathyroidism in chronic hemodialysis patients: cinacalcet is coming to Japan

Secondary hyperparathyroidism has a significant impact on morbidity and mortality due to skeletal and extraskeletal manifestations. Cinacalcet, a newly developed calcimimetic, is reported to decrease parathyroidism, as well as serum levels of phosphorus (P) and calcium (Ca) and therefore Ca x P product. Available evidence has shown that cinacalcet decreases the rate of parathyroidectomy and bone fracture in hemodialysis patients, but the death rate remains the same. Although, it is not yet available in Japan, cinacalcet is expected to be available as a possible drug for patients undergoing hemodialysis due to secondary hyperparathyroidism associated with refractory hyperphosphatemia and hypercalcemia. Except for the high cost, cinacalcet will be a welcome therapeutic option for end-stage renal disease and probably also for pre-end-stage renal disease patients. Dietary phosphate restriction and adequate hemodialysis, however, are still the main strategy for the control of hyperphosphatemia and secondary hyperparathyroidism.

Calcimimetics for the Treatment of Secondary Hyperparathyroidism in Peritoneal Dialysis Patients

Secondary hyperparathyroidism is a common complication in patients with end-stage renal disease. It has been associated with increased cardiovascular events and mortality. Traditional therapy has been based on vitamin D analogs and phosphate binders; but these therapies often do not control secondary hyperparathyroidism, particularly in peritoneal dialysis patients for whom phosphate clearances are limited and intravenous vitamin D is impractical. Cinacalcet, a calcimimetic, suppresses parathormone secretion by interacting with the calcium-sensing receptor on the surface of parathyroid gland cells. The resulting suppression of parathyroid hormone secretion produces a reduction in serum phosphate level and CaxPO4 product. The present paper reviews the efficacy of cinacalcet in the management of secondary hyperparathyroidism in peritoneal dialysis patients.

Combined therapy with cinacalcet and low doses of vitamin D sterols in patients with moderate to severe secondary hyperparathyroidism

BACKGROUND

Adequate control of all four KDOQI biochemical targets for chronic kidney disease, bone and mineral disorder (CKD-MBD), which include parathyroid hormone (PTH), calcium (Ca), phosphorus (P) and Ca x P, remains difficult and is accomplished in <6% of patients receiving haemodialysis. The objective of the current study was to determine whether treatment with cinacalcet combined with low doses of vitamin D sterols improves control of both PTH and Ca x P among haemodialysis patients with secondary hyperparathyroidism (sHPT).

METHODS

This multicentre, open-label study enrolled haemodialysis subjects (N = 444) with moderate to severe sHPT (mean serum biPTH > 160-430 pg/mL) (approximately iPTH 300-800 pg/mL or ng/L). Cinacalcet was titrated sequentially (30-180 mg/day) during an 8-week dose-titration phase to achieve biPTH <or=160 pg/mL (approximately iPTH 300 pg/mL or ng/L) and efficacy was assessed over 8 weeks. At week 2 of the study, subjects receiving vitamin D sterols had doses reduced to the equivalent of 2 mcg of paricalcitol three times a week or 6 mcg/week. Among the efficacy endpoints were the proportion of subjects with mean biPTH <or=160 pg/mL (approximately iPTH 300 pg/mL or ng/L), with mean Ca x P <or=55 mg(2)/dL(2) (4.4 mmol(2)/L(2)) and with both simultaneously during the assessment phase.

RESULTS

The majority of subjects (n = 375) reached the assessment phase of the study and were included in efficacy analyses; 39 subjects withdrew due to adverse events. Sixty-two percent of subjects achieved the biPTH target, 83% achieved the Ca x P target and 54% reached both targets. Treatment reduced biPTH by 35% (P < 0.0001), calcium by 11% (P < 0.0001), phosphorus by 7% (P < 0.0001) and Ca x P by 17% (P < 0.0001). The proportion of subjects with values for biPTH, for Ca x P and for both biPTH and Ca x P within the target range during the assessment phase did not differ between subjects who received cinacalcet together with vitamin D sterols, and those who received cinacalcet alone.

CONCLUSION

Among subjects with moderate to severe sHPT undergoing haemodialysis, combined therapy with cinacalcet and low doses of vitamin D sterols improved achievement of the biochemical targets for CKD-MBD recommended by the KDOQI guidelines.

Effect of 2-methylene-19-nor-(20S)-1 alpha-hydroxy-bishomopregnacalciferol (2MbisP), an analog of vitamin D, on secondary hyperparathyroidism

Vitamin D analogs are being developed that retain therapeutic effects but are less calcemic and phosphatemic, a concern in CKD patients who are prone to vascular calcification. We tested a new analog of vitamin D, 2MbisP, and found that it suppresses PTH at doses that do not affect serum Ca or P.

INTRODUCTION

Calcitriol is used for the treatment of secondary hyperparathyroidism. However, its use is often limited by the development of hypercalcemia and hyperphosphatemia, an important consideration in patients with chronic kidney disease (CKD) because they are prone to vascular calcification. To minimize this toxicity, structural modifications in the vitamin D molecule have led to the development of calcitriol analogs with selective actions.

MATERIALS AND METHODS

In this study, we compared the effects of 1,25(OH)(2)D(3) and a new analog, 2-methylene-19-nor-(20S)-1 alpha-hydroxy-bishomopregnacalciferol (2MbisP), on the development of secondary hyperparathyroidism and established secondary hyperparathyroidism in uremic rats and on mobilization of calcium and phosphorus from bone in parathyroidectomized rats. The clearance from circulation, half-life, and binding affinities to the vitamin D-binding protein and vitamin D receptor of this compound were also evaluated.

RESULTS

Uremia produced a marked rise in plasma PTH, but treatment every other day for 2 wk with either 1,25(OH)(2)D(3) (4 ng) or 2MbisP (250, 750, 1500, or 3000 ng) suppressed this increase by >50%. The suppression by 1,25(OH)(2)D(3), however, was accompanied by increases in ionized calcium, phosphorus, and the calcium x phosphorus product, whereas these three parameters were unchanged by 2MbisP. The binding affinity of 2MbisP was 10-20 times less for the vitamin D receptor and 1000 times less for the serum vitamin D-binding protein compared with 1,25(OH)(2)D(3). Also, 2MbisP was cleared more rapidly from the circulation (t1/2 = 10 min) than 1,25-(OH)(2)D(3) (t1/2=7-9 h). In parathyroidectomized rats fed calcium-or phosphorus-deficient diets, daily injections of 2MbisP (1500 or 3000 ng), unlike 1,25(OH)(2)D(3) (50 ng), had no effect on calcium or phosphorus mobilization from bone.

CONCLUSIONS

In uremic rats, 2MbisP can suppress PTH at doses that do not affect plasma calcium, phosphorus, and calcium x phosphorus product. This new vitamin D analog may represent an important tool in the treatment of secondary hyperparathyroidism in patients with CKD.

Vitamin D Deficiency and Secondary Hyperparathyroidism Among Patients with Chronic Kidney Disease

BACKGROUND

Chronic kidney disease (CKD) is associated with morbid complications that lead to high mortality and costs. Vitamin D deficiency and secondary hyperparathyroidism (SHPT) are frequent complications of CKD.

METHODS

We reviewed the current literature regarding the prevalence, diagnosis, complications, and management of vitamin D deficiency and SHPT among patients with CKD.

RESULTS

There is a high prevalence of vitamin D deficiency among adolescents and adults in the United States (age and gender dependent). Patients with CKD or those who are dialysis-dependent are much more likely to have low levels of vitamin D in comparison to those without kidney disease. In order to avoid significant complications including SHPT and musculoskelatal diseases, vitamin D needs to be measured routinely by primary care physicians and nephrologists. In the majority of CKD patients, SHPT is not diagnosed until late, leading to advanced cardiovascular and bone diseases.

CONCLUSIONS

In conclusion, current management of vitamin D deficiency and SHPT is suboptimal. Early diagnosis of vitamin D deficiency and SHPT are integral to optimal management of CKD, and additional research is needed in this area.

Influence of parathyroid mass on the regulation of PTH secretion

In advanced uremia, parathyroid hormone (PTH) levels should be controlled at a moderately elevated level in order to promote normal bone turnover. As such, a certain degree of parathyroid gland (PG) hyperplasia has to be accepted. No convincing evidence of apoptosis or of involution of PG hyperplasia exists. However, even considerable parathyroid hyperplasia can be controlled when the functional demand for increased PTH levels is abolished. When 20 isogenic PG were implanted into one parathyroidectomized (PTX) rat normalization of Ca(2+) and PTH levels and normal suppressibility of PTH secretion by high Ca(2+) was obtained. Similarly, normal levels of Ca(2+) and PTH and suppressibility of PTH secretion were obtained when Eight isogenic PG from uremic rats were implanted into normal rats or when long-term uremia and severe secondary hyperparathyroidism (sec. HPT) was reversed by an isogenic kidney transplantation. Normalization of PTH levels after experimental kidney transplantation took place despite a persistent decrease of vitamin D receptor (VDR) mRNA and calcium sensing receptor (CaR) mRNA in PG. Thus, in experimental models PTH levels are determined by the functional demand and not by parathyroid mass, per se. When non-suppressible sec. HPT is present in patients referred to PTX, nodular hyperplasia with differences in gene expression between different nodules has been observed in most cases. An altered expression of some autocrine/paracrine factors has been demonstrated in the nodules. Enhanced expression of PTH-related peptide (PTHrP) has been demonstrated in PG from patients with severe secondary HPT. PTHrP has been shown to stimulate PTH secretion in vivo and in vitro. PTH/PTHrP receptor was demonstrated in the parathyroids. The low Ca(2+) stimulated PTH secretion was enhanced by 300% by PTHrP 1-40. The altered quality of the parathyroid mass and not only the increased parathyroid mass, per se, might be responsible for non-controllable hyperparathyroidism in uremia and after kidney transplantation.

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.

Paricalcitol capsules for the control of secondary hyperparathyroidism in chronic kidney disease

Secondary hyperparathyroidism is a common complication of patients with chronic kidney disease. Treatment with calcitriol, the active form of vitamin D, reduces parathyroid hormone levels, but may result in elevations in serum calcium and phosphorus. New vitamin D analogues have been developed to reduce parathyroid hormone secretion without concomitant hypercalcaemia and hyperphosphataemia. Recent data from studies with paricalcitol capsules, the oral formulation of 19-nor-1,25(OH)2D2, show a significant reduction in parathyroid hormone levels with no change in calcium and phosphorus levels when compared with placebo. Paricalcitol also compares favourably to other oral vitamin D analogues, effectively decreasing parathyroid secretion with less hypercalcaemia and hypercalciuria than other agents.

Basic Science and Dialysis: Parathyroid Growth and Suppression in Renal Failure

In advanced uremia, parathyroid hormone (PTH) levels should be controlled at a moderately elevated level in order to promote normal bone turnover. As such, a certain degree of parathyroid hyperplasia has to be accepted. Uremia is associated with parathyroid growth. In experimental studies, proliferation of the parathyroid cells is induced by uremia and further promoted by hypocalcemia, phosphorus retention, and vitamin D deficiency. On the other hand, parathyroid cell proliferation might be arrested by treatment with a low-phosphate diet, vitamin D analogs, or calcimimetics. When established, parathyroid hyperplasia is poorly reversible. There exists no convincing evidence of programmed parathyroid cell death or apoptosis in hyperplastic parathyroid tissue or of involution of parathyroid hyperplasia. However, even considerable parathyroid hyperplasia can be controlled when the functional demand for increased PTH levels is removed by normalization of kidney function. Today, secondary hyperparathyroidism can be controlled in patients with long-term uremia in whom considerable parathyroid hyperplasia is to be expected. PTH levels can be suppressed in most uremic patients and this suppression can be maintained by continuous treatment with phosphate binders, vitamin D analogs, or calcimimetics. Thus modern therapy permits controlled development of parathyroid growth. When nonsuppressible secondary hyperparathyroidism is present, nodular hyperplasia with suppressed expression of the calcium-sensing receptor (CaR) and vitamin D receptor (VDR) has been found in most cases. An altered expression of some autocrine/paracrine factors has been demonstrated in the nodules. The altered quality of the parathyroid mass, and not only the increased parathyroid mass per se, might be responsible for uncontrollable hyperparathyroidism in uremia and after kidney transplantation.

Calcimimetic R-568 Decreases Extraosseous Calcifications in Uremic Rats Treated with Calcitriol

Calcimimetics decrease parathyroid hormone (PTH) levels in uremic patients with secondary hyperparathyroidism without increasing serum calcium (Ca). The aim of this study was to evaluate the effect of calcimimetic R-568 alone or in combination with calcitriol on vascular and other soft tissue calcifications in uremic rats with secondary hyperparathyroidism. Sham-operated and 5/6 nephrectomized Wistar rats were studied. 5/6 Nephrectomized rats were treated with vehicle, calcitriol (80 ng/kg every other day), R-568 (1.5 and 3 mg/kg per d), and both calcitriol and R-568 1.5 mg/kg, as above. Rats were killed after 14 or 56 d of treatment. Blood was drawn for biochemical measurements. Aortic, heart, kidney, lung, and stomach tissue samples were processed for histopathology and measurement of tissue Ca and phosphorus content. PTH concentrations were significantly reduced by all treatments. Treatment with calcitriol induced significant vascular calcification (aortic Ca increased to 4.2+/-1.2 mg/g at day 14 and to 11.4+/-0.7 mg/g at day 56; P<0.05 versus vehicle). Treatment with R-568 did not induce vascular calcification. Concurrent administration of R-568 with calcitriol reduced the aortic Ca (1.9+/-0.2 mg/g at day 14 and 7.5+/-1.4 mg/g at day 56) in relation to calcitriol alone. Soft tissue calcifications mirrored aortic mineralizations. Survival was significantly (P<0.001) reduced in calcitriol-treated rats, and mortality was attenuated (P=0.01) by concurrent treatment with R-568. In uremic rats, R-568 reduces elevated PTH levels without inducing vascular calcification, prevents calcitriol-induced vascular calcification, and decreases mortality.

Cinacalcet Hydrochloride (Sensipar) in Hemodialysis Patients on Active Vitamin D Derivatives with Controlled PTH and Elevated Calcium × Phosphate

Active vitamin D derivatives attenuate the severity of secondary hyperparathyroidism but often increase serum calcium (Ca) and phosphorus (P) as a result of enhanced intestinal absorption. The calcimimetic cinacalcet HCl lowers parathyroid hormone (PTH) and tends to decrease Ca x P. A 16-wk, open-label clinical trial was conducted in adult hemodialysis patients who had controlled PTH (biointact PTH [biPTH] 80 to 160 pg/ml) and elevated Ca x P (> 55 mg2/dl2) and were receiving paricalcitol > 6 microg/wk (or an equipotent dose of an alternative active vitamin D derivative). At the start of the study, active vitamin D derivatives were decreased to a mean equivalent dose of paricalcitol 6 microg/wk, and cinacalcet was titrated from 30 mg/d to a maximum possible dose of 180 mg/d. Of the 72 study patients, 53 (74%) completed 8 wk of dose titration with cinacalcet. In response to cinacalcet, the following mean percentage changes were observed: biPTH, -1.8%; Ca, -9.7% (P < 0.0001), phosphorus, -11.1% (P < 0.0001), and Ca x P, -20.1% (P < 0.0001). At the end of the study, approximate Kidney Disease Outcomes Quality Initiative targets for biPTH (< or = 160 pg/ml) were achieved in 85% (45 of 53) of patients and for Ca x P (< or = 55 mg2/dl2) in 72% (38 of 53) of patients. Concurrent achievement of both targets occurred in 47% (25 of 53) of patients. In this open-label clinical trial, hemodialysis patients who had controlled PTH but elevated Ca x P and were taking moderate- to high-dose active vitamin D derivatives achieved improved control of mineral metabolism with a combination of low-dose active vitamin D derivatives and cinacalcet. The long-term effects of this treatment regimen on clinical outcomes should be tested prospectively.

Effects of the calcimimetic cinacalcet HCl on cardiovascular disease, fracture, and health-related quality of life in secondary hyperparathyroidism

BACKGROUND

Secondary hyperparathyroidism (HPT) and abnormal mineral metabolism are thought to play an important role in bone and cardiovascular disease in patients with chronic kidney disease. Cinacalcet, a calcimimetic that modulates the calcium-sensing receptor, reduces parathyroid hormone (PTH) secretion and lowers serum calcium and phosphorus concentrations in patients with end-stage renal disease (ESRD) and secondary HPT.

METHODS

We undertook a combined analysis of safety data (parathyroidectomy, fracture, hospitalizations, and mortality) from 4 similarly designed randomized, double-blind, placebo-controlled clinical trials enrolling 1184 subjects (697 cinacalcet, 487 control) with ESRD and uncontrolled secondary HPT (intact PTH > or =300 pg/mL). Cinacalcet or placebo was administered to subjects receiving standard care for hyperphosphatemia and secondary HPT (phosphate binders and vitamin D). Relative risks (RR) and 95% CI were calculated using proportional hazards regression with follow-up times from 6 to 12 months. Health-related quality-of-life (HRQOL) data were obtained from the Medical Outcomes Study Short Form-36 (SF-36), and the Cognitive Functioning scale from the Kidney Disease Quality of Life instrument (KDQOL-CF).

RESULTS

Randomization to cinacalcet resulted in significant reductions in the risk of parathyroidectomy (RR 0.07, 95% CI 0.01-0.55), fracture (RR 0.46, 95% CI 0.22-0.95), and cardiovascular hospitalization (RR 0.61, 95% CI 0.43-0.86) compared with placebo. Changes in HRQOL favored cinacalcet, with significant changes observed for the SF-36 Physical Component Summary score and the specific domains of Bodily Pain and General Health Perception.

CONCLUSION

Combining results from 4 clinical trials, randomization to cinacalcet led to significant reductions in the risk of parathyroidectomy, fracture, and cardiovascular hospitalization, along with improvements in self-reported physical function and diminished pain. These data suggest that, in addition to its effects on PTH and mineral metabolism, cinacalcet had favorable effects on important clinical outcomes.

Achieving NKF-K/DOQI™ bone metabolism and disease treatment goals with cinacalcet HCl

BACKGROUND

The National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (NKF-K/DOQItrade mark) has established guidelines for treatment of secondary hyperparathyroidism (HPT). The ability of cinacalcet HCl (Sensipartrade mark) treatment to improve achievement of target levels of parathyroid hormone (PTH), calcium, phosphorus, and calcium-phosphorus product (Ca x P) was investigated in subjects on dialysis with secondary HPT.

METHODS

Data were combined from three placebo-controlled, double-blind, 26-week studies with similar design that randomized 1136 subjects on dialysis to receive traditional therapy plus cinacalcet or placebo. Oral cinacalcet was titrated from 30 to 180 mg/day. Achievement of K/DOQI goals was determined for each treatment group overall and for subgroups defined by baseline intact PTH (iPTH) and Ca x P levels.

RESULTS

Cinacalcet-treated subjects were more likely to achieve a mean iPTH </=300 pg/mL (31.8 pmol/L) than were control subjects on traditional therapy (56% vs. 10%, P < 0.001). Cinacalcet-treated subjects were more likely to achieve concentrations of serum calcium within 8.4 to 9.5 mg/dL (2.10-2.37 mmol/L) and serum phosphorus within 3.5 to 5.5 mg/dL (1.13-1.78 mmol/L) than were control subjects (49% vs. 24% and 46% vs. 33%, P < 0.001 for each). Cinacalcet also improved achievement of Ca x P < 55 mg(2)/dL(2) (4.44 mmol(2)/L(2)) and concurrent achievement of Ca x P < 55 mg(2)/dL(2) (4.44 mmol(2)/L(2)) and iPTH </=300 pg/mL (31.8 pmol/L) (65% vs. 36% and 41% vs. 6%, P < 0.001 for each).

CONCLUSION

In subjects on dialysis with secondary HPT, cinacalcet facilitates achievement of the K/DOQI-recommended targets for PTH, calcium, phosphorus, and Ca x P.

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.

Bio-Intact Parathyroid Hormone and Intact Parathyroid Hormone in Hemodialysis Patients With Secondary Hyperparathyroidism Receiving Intravenous Calcitriol Therapy

Intact parathyroid hormone (iPTH) assay has been the most widely used for the diagnosis of secondary hyperparathyroidism and evaluation of vitamin D therapy. However, 1-84 PTH assay might be a better diagnostic tool since iPTH detects not only 1-84 PTH but also large C-terminal fragments, which would antagonize PTH action. Therefore, we conducted a multicenter study to evaluate the clinical usefulness of a newly developed immunochemiluminometric assay for 1-84 PTH, Bio-Intact PTH (BiPTH). Thirty-five uremic patients with secondary hyperparathyroidism participated in the study. Intravenous calcitriol therapy was continued for 12 months. iPTH and bone-specific alkaline phosphatase (BAP) were monitored at each dialysis center to control the dose of calcitriol. Serum and plasma samples were collected from each center and both iPTH and BiPTH were measured using Allegro-Lite assay reagents from Nichols Institute Diagnostics (San Clemente, CA, USA). Intravenous calcitriol suppressed iPTH after 1 month as well as BiPTH. Bone-specific alkaline phosphatase decreased after 3 months. A high degree of correlation between Nichols iPTH and BiPTH (y = 0.3913 x + 19.517, r = 0.9561) was demonstrated with a BiPTH/iPTH ratio of approximately 0.44. Significant correlation between BAP and iPTH, or between BAP and BiPTH was not observed. Our limited data failed to demonstrate the superiority of BiPTH to iPTH. Therefore, further investigations would be necessary to examine the relationship between BiPTH and bone histomorphometry.

Rights of chronic renal failure patients undergoing chronic dialysis therapy

The Patient Advocacy Committee of the International Federation of Kidney Foundations (IFKF) has developed a document proposing a set of rights for individuals with end stage renal failure (ESRF). These rights have been approved by the Board of Directors of the IFKF. Twenty rights have been developed and are organized into the following categories: (i) need of treatment and choice of patients; (ii) treatment of ESRF by haemodialysis; (iii) treatment of ESRF by peritoneal dialysis; and (iv) renal transplantation. It is the hope of this Committee and the IFKF that this document will provide a stimulus to more scientific inquiry and discussion as to what rights do patients possess with regard to treatment of chronic kidney disease, regardless of where they live or what may be their economic, social, ethnic or political status.

New vitamin D analogs

BACKGROUND

1,25-(OH)2D3 (calcitriol) controls parathyroid gland growth and suppresses the synthesis and secretion of parathyroid hormone. Because of this, 1,25-(OH)2D3 has been used successfully for the treatment of secondary hyperparathyroidism, which almost always accompanies renal failure. However, the potent effect of 1,25-(OH)2D3 on intestinal calcium and phosphorus absorption and bone mineral mobilization often leads to the development of hypercalcemia and hyperphosphatemia precluding 1,25-(OH)2D3 therapy.

METHODS

This has led to the development of vitamin D analogs that retain the suppressive action on PTH and parathyroid gland growth, but that have less calcemic and phosphatemic activity. Currently, two analogs, 19-nor-1,25-(OH)2D2 and 1,alpha(OH)D2, are being used for the treatment of secondary hyperparathyroidism in the United States, and two are being used in Japan, 22-oxa-calcitriol and 1,25-(OH)2-26,27F6 D3.

RESULTS

All four analogs suppressed PTH, but had less calcemic and phosphatemic activity than 1,25-(OH)2D3. In rats, 19-nor-1,25-(OH)2D2 has been shown to be less calcemic and phosphatemic compared to 1,alpha(OH)D2.

CONCLUSION

Therapeutic doses of 19-nor-1,25-(OH)2D2 could produce a lower Ca x P product compared to 1,alpha(OH)D2, which could be an important consideration in patient treatment. Further studies are necessary to define these differences and to understand the mechanisms behind the differential actions of vitamin D analogs.

Differential effects of acute administration of 19-Nor-1,25-dihydroxy-vitamin D2 and 1,25-dihydroxy-vitamin D3 on serum calcium and phosphorus in hemodialysis patients

BACKGROUND

Treatment of hyperparathyroidism includes the use of 1,25-dihydroxy-vitamin D3 (1,25D3) to suppress parathyroid hormone (PTH), but dosing of 1,25D3 is limited by the development of hypercalcemia and a high calcium x phosphorus (Ca x P) product because of gut absorption of calcium and phosphorus and enhanced bone resorption. The vitamin D analogue 19-nor-1,25(OH)2-vitamin D2 (19-Nor) causes less hypercalcemia and elevated Ca x P, whereas it still suppresses PTH in rats.

METHODS

To determine whether 19-Nor had similar effects in humans, we performed a prospective crossover study to assess bone mobilization. Ten hemodialysis patients on a low-calcium low-phosphorus diet were administered 20 microg of 1,25D3 and 120 and 160 microg of 19-Nor, and changes in calcium, phosphorus, and intact and whole PTH levels were measured over 36 hours.

RESULTS

Ca x P product increased more after 1,25D3 administration than after a six- or eightfold greater dose of 19-Nor and was significantly greater at 6, 12, and 24 hours. Ca x P product at 36 hours was 60.9 +/- 3.4 (4.91 +/- 0.27 mmol2/2) after 1,25D3 administration, 53.2 +/- 2.7 (4.29 +/- 0.22 mmol2/L2) after administration of 120 microg of 19-Nor, and 54.2 +/- 2.7 (4.37 +/- 0.22 mmol2/L2) after administration of 160 microg of 19-Nor. Suppression of intact PTH at 36 hours was similar after administration of 1,25D3 (54.1% +/- 6.0%) and 120 microg of 19-Nor (54.4% +/- 3.4%) and significantly greater after administration of 160 microg of 19-Nor (63.6% +/- 2.3%). The whole PTH assay yielded values approximately 25% to 30% lower than the intact PTH assay, and the percentage of suppression was virtually identical.

CONCLUSION

Consistent with animal studies, 19-Nor provides profound PTH suppression while stimulating bone resorption and/or intestinal absorption less than 1,25D3, resulting in less elevation of serum calcium and phosphorus levels.

Differential effects of 19-nor-1,25-(OH)(2)D(2) and 1alpha-hydroxyvitamin D(2) on calcium and phosphorus in normal and uremic rats

BACKGROUND

Calcitriol, 1,25-(OH)(2)D(3) (1,25D), the most active metabolite of vitamin D, has been used in the treatment of secondary hyperparathyroidism (SH) because it controls parathyroid gland growth and suppresses parathyroid hormone (PTH) synthesis and secretion. Due to the calcemic and phosphatemic actions of 1,25D, two analogs with potentially less side effects, 19-nor-1,25-(OH)(2)D(2) (19-nor) and 1alpha(OH)D(2) (1alphaD(2)) are currently being used in the treatment of SH.

METHODS

This study compares the effects of these two analogs on calcium (Ca) and phosphorus (P) metabolism in normal, uremic, and parathyroidectomized (PTX) rats. Using doses of 50 to 250 ng of 19-nor or 1alphaD(2), experiments were conducted in normal and uremic rats.

RESULTS

In uremic rats, 19-nor did not increase plasma Ca or P while 1alphaD2 caused a dose-dependent increase in both. In addition, while the Ca x P product remained unchanged in 19-nor-treated rats, it increased progressively with 1alphaD(2)administration. In metabolic studies in normal rats treated with vehicle, 10 ng of 1,25D, 100 ng of 19-nor or 100 ng 1alphaD(2), intestinal calcium absorption and urinary calcium excretion were significantly higher in 1alphaD(2)-treated rats compared to those receiving 19-nor. Similar results were seen for intestinal phosphorus absorption and urinary phosphorus excretion. Finally, the skeletal response to these two analogs was tested in PTX rats fed a calcium-deficient diet and treated daily with 100 ng of 19-nor or 1alphaD(2). The increase in plasma calcium in 1alphaD2-treated rats was markedly higher than in those receiving 19-nor. Similar results were seen in plasma phosphorus when these studies were repeated using a phosphorus-deficient diet.

CONCLUSIONS

These studies demonstrate that when given in large doses to rats 19-nor is less calcemic and phosphatemic than 1alphaD(2). The lower Ca x P product in 19-nor treated rats may be an important consideration in patient therapy. Further studies in patients are necessary to define the clinical applicability of these differences.

Use of vitamin D analogs in chronic renal failure

Renal osteodystrophy is the term used to describe the spectrum of bone diseases associated with chronic renal failure. Deficiency of 1,25-dihydroxycholecalciferol (calcitriol) plays a major role in the development of renal osteodystrophy, in particular the evolution of secondary hyperparathyroidism. In recent decades, our understanding of the complex interactions between calcium, phosphorus, vitamin D, and parathyroid hormone (PTH) has increased, resulting in a rational approach to therapy in which vitamin D analogs have become an essential component. The initial vitamin D analogs that have been in widespread clinical use include calcitriol (1,25-[OH](2)D(3)) and alfacalcidol (1alpha-[OH]D(3)). These agents have been extensively studied to optimize their effects on secondary hyperparathyroidism. The occurrence of significant hypercalcemia and hyperphosphatemia limiting their use has led to the development of alternative vitamin D analogs that effectively reduce PTH secretion without causing these complications. Recently, 3 such analogs, 22-oxa-1,25-(OH)(2)D(3) (OCT), 1alpha-(OH)D(2) (doxercalciferol), and 19-nor-1,25-(OH)(2)D(2) (paricalcitol), have been released for clinical use. Only paricalcitol has been studied in comparative human clinical trials with calcitriol in dialysis patients. Preliminary findings suggest a clinical advantage over calcitriol, however, analysis of the larger comparative studies are forthcoming.

Pathogenesis of refractory secondary hyperparathyroidism

Calcitriol is currently used to reduce parathyroid hormone (PTH) levels in uremic patients. However, a significant number of patients fail to respond to calcitriol therapy. The data suggest that a poor response to calcitriol can be anticipated in patients with severe hyperparathyroidism (with a high basal PTH levels) and uncontrolled serum phosphate. The abnormal parathyroid response to calcitriol in uremic patients with severe parathyroid hyperplasia may be attributed, to a large extent, to the development of nodular hyperplasia as a result of clonal transformation from a diffuse polyclonal hyperplasia. The factors involved in the development of polyclonal parathyroid hyperplasia, at earlier stages of secondary hyperparathyroidism, appear to be the same factors that stimulate PTH secretion and synthesis: hypocalcemia, hyperphosphatemia and low serum calcitriol levels. Studies performed in vitro using parathyroid tissue from uremic patients who required parathyroidectomy demonstrate that in nodular hyperplasia there is an abnormal response to calcium and calcitriol, which suggests that there are factors intrinsic to the hyperplastic cell (such as decrease in calcium sensor receptors and vitamin D receptors) responsible for an abnormal regulation of parathyroid function. Accumulation of phosphate is a key factor in the pathogenesis of secondary hyperparathyroidism and a poor response to calcitriol treatment is associated with the failure to control the serum phosphorus. High phosphate stimulates PTH secretion as demonstrated by in vivo and in vitro studies. In addition, animal studies strongly suggest that phosphate increases parathyroid cell proliferation. There are growth-related genes potentially involved in uremic hyperparathyroidism; however, changes in the expression of these genes may be the consequence rather than the cause of parathyroid hyperplasia.

Management of disturbed calcium metabolism in uraemic patients: 1. Use of vitamin D metabolites

Chronic renal failure is characterized by diminished synthesis of, and resistance to, the active vitamin D metabolite 1,25-dihydroxy-vitamin D3 (1,25(OH)2D3, calcitriol). Calcitriol results from the biotransformation of the precursor 25-hydroxy-vitamin D3 (25(OH)D3) to 1,25(OH)2D3. 25(OH)D3 is synthesized in the liver, and 1alpha-hydroxylase, the rate-limiting enzyme for its biotransformation into the most active metabolite, 1,25(OH)2D3, is located in the kidney. The regulation of 1alpha-hydroxylase in renal failure is not well known. Recent work indicates that, in contrast to previous opinion, 1alpha-hydroxylase is predominantly expressed not in the proximal tubule but in the distal tubule [1]. In vivo, the main stimulatory signal is presumably parathyroid hormone (PTH) and the main inhibitory signal hyperphosphataemia. Both signals are altered in renal failure. There is also evidence that the renal 1alpha-hydroxylase becomes substrate-dependent in patients with renal failure. This means that a higher concentration of the precursor 25(OH)2D3 will result in a higher rate of transformation into the active metabolite 1,25(OH)2D3 in renal patients. Calcitriol is not exclusively synthesized in the kidney, but may also be synthesized in extra-renal tissues, e.g. activated monocytes/macrophages [2], particularly in granuloma [3] as shown by anephric uraemic patients who develop hypercalcaemia and elevated calcitriol concentrations when sarcoidosis [4] or tuberculosis [5] supervenes. On the other hand, calcitriol is less effective in uraemia. This may be to some extent due to diminished expression of vitamin D receptors [6], particularly in parathyroid glands when they undergo nodular transformation [7], but there may also be resistance to calcitriol at the post-receptor level [8]. In a series of elegant experiments [9,10], calcitriol resistance has been related to disturbed genomic effects of active vitamin D because the interaction of the vitamin D receptor ligand complex with vitamin D-responsive elements (VDREs) upstream of vitamin D-regulated genes was disturbed by the action of low molecular weight substances in uraemia, which have not been completely characterized. The role of genetically determined polymorphisms of the vitamin D receptor in the genesis of disturbed calcium metabolism of renal failure is currently unclear.

Calcium acetate versus calcium carbonate in the control of hyperphosphatemia in hemodialysis patients

CONTEXT

Hyperphosphatemia has an important role in the development of bone and mineral abnormalities in end-stage renal disease (ESRD).

OBJECTIVE

To compare the phosphorus binding power and the hypercalcemic effect of calcium acetate and calcium carbonate in hemodialysis patients.

TYPE OF STUDY

Crossover, randomized, double-blind study.

PLACE

A private hospital dialysis center.

PARTICIPANTS

Fifty-two patients who were undergoing regular hemodialysis three times a week ([Ca++] dialysate = 3.5 mEq/L).

PROCEDURES

Half of the patients were started on 5.6 g/day of calcium acetate and, after a 2 week washout period, received 6.2 g/day of calcium carbonate. The other half followed an inverse protocol.

MAIN MEASUREMENTS

Clinical interviews were conducted 3 times a week to monitor for side effects. Determinations of serum urea, calcium, phosphorus, hematocrit, Kt/V and blood gas analysis were obtained before and after each treatment.

RESULTS

Twenty-three patients completed the study. A significant increase in calcium plasma levels was only observed after treatment with calcium carbonate [9.34 mg/dl (SD 0.91) vs. 9.91 mg/dl (SD 0.79), P < 0.01]. The drop in phosphorus levels was substantial and significant for both salts [5.64 mg/dl (SD 1.54) vs. 4.60 mg/dl (SD 1.32), P < 0.01 and 5.89 mg/dl (SD 1.71) vs. 4.56 mg/dl (SD 1.57), P < 0.01, for calcium acetate and calcium carbonate respectively]. The percentage reduction in serum phosphorus (at the end of the study) per milliequivalent of salt administered per day tended to be higher with calcium acetate but statistical significance was not found.

CONCLUSION

Calcium acetate can be a good alternative to calcium carbonate in the handling of hyperphosphatemia in ESRD patients. When calcium acetate is used, control of hyperphosphatemia can be achieved with a lower administration of calcium, perhaps with a lower risk of hypercalcemia.

Vitamin D therapy in patients with chronic renal disease: the role of the renal dietitian

Chronic renal failure causes decreased vitamin D production, which profoundly alters parathyroid hormone (PTH) metabolism, and calcium and phosphorus balance. Correcting this deficiency is an important strategy in managing secondary hyperparathyroidism (SHPT) and helping to restore mineral balance. However, hypercalcemia and hyperphosphatemia are common side effects that hamper vitamin D hormone therapy by increasing dietary calcium and phosphorus absorption. This limitation has led to the development of D-hormone analogs that retain the ability to suppress PTH levels without causing drastic changes in calcium and phosphorus metabolism. These analogs have the potential to advance the management of SHPT. Renal dietitians can play a leading role in ensuring successful management of SHPT by participating in early patient intervention for abnormal mineral and vitamin D metabolism, by encouraging long-term phosphorus control, and by updating and implementing clinical protocols that promote optimal hormone levels (D and PTH), mineral levels (phosphorus and calcium), and nutritional factors.

Current medical management of secondary hyperparathyroidism

The treatment of secondary hyperparathyroidism (HPT) in patients with chronic renal disease has improved markedly in recent years. The skeletal pain, disabling fractures, tendon ruptures, and myriad other symptoms associated with HPT can now be avoided, and the quality of life of patients with end-stage renal disease is improved. Control of hyperphosphatemia, maintenance of normocalcemia, and appropriate dosing of vitamin D analogues can prevent HPT in many cases. Palatable, nutritious diets should be followed; serum calcium, phosphorus, alkaline phosphatase, and parathyroid hormone should be monitored; and treatment regimens should be adjusted accordingly. If prevention fails, and even if severe HPT develops, many of these patients can still be controlled medically with correction of hyperphosphatemia and high doses of intravenous calcitriol. In our experience, only a few patients require surgical parathyroidectomy (usually noncompliant patients or patients whose HPT has been poorly managed from early uremia). The essence to medical management is to correct the two most important pathogenetic factors of HPT, hyperphosphatemia, and calcitriol deficiency. We present the current approach to the management of HPT, with highlights of recent advances.

New analogs of vitamin D3

Calcitriol, the most active metabolite of vitamin D, controls parathyroid gland growth and suppresses the synthesis and secretion of parathyroid hormone (PTH). However, because of its potent effects on intestinal calcium absorption and bone mobilization, calcitriol treatment can induce hypercalcemia, often precluding its use at therapeutic doses. Hyperphosphatemia is also a persistent problem among patients undergoing chronic hemodialysis and can be aggravated by therapeutic doses of calcitriol. Several pharmaceutical companies were able to modify the side-chain of the 1,25(OH)2D3, allowing some of these new analogs to retain the action on the parathyroid glands while decreasing their hypercalcemic and hyperphosphatemic effects. The structure-activity relationship for ligand-mediated transcriptional regulation has been studied in detail. In some analogs the serum binding protein (DBP) plays a key role in determining the pharmacokinetics of the vitamin D compound. The affinity to DBP for 22-oxacalcitriol (OCT), an analog of calcitriol for the treatment of secondary hyperparathryoidism, is approximately 300-400 times lower than that of calcitriol and the analog is rapidly cleared from the circulation. The mechanisms for the selectivity of 19-nor-1,25(OH)2D2 (paricalcitol) (Zemplar) another analog of calcitriol, is clearly different from OCT. Although the mechanisms of action is not completely known, it does appear that paricalcitol down-regulates the VDR in the intestine. It is likely that the unique biological profiles of vitamin D analogs in vivo are due to multiple mechanisms. Understanding the molecular basis of the analog selectivity will not only provide an explanation for their unique actions but allow intelligent design of more effective analogs in the future.

Parathyroid function as a determinant of the response to calcitriol treatment in the hemodialysis patient

BACKGROUND

Bolus calcitriol (CTR) is used for the treatment of secondary hyperparathyroidism in dialysis patients. Although CTR treatment reduces parathyroid hormone (PTH) levels in many dialysis patients, a significant number fail to respond.

METHODS

To learn whether or not an analysis of parathyroid function could further illuminate the response to CTR, a PTH-calcium curve was performed before and after at least two months of CTR treatment in 50 hemodialysis patients with a predialysis intact PTH of greater than 300 pg/ml.

RESULTS

For the entire group (N = 50), CTR treatment resulted in a 24% reduction in predialysis (basal) PTH from 773 +/- 54 to 583 +/- 71 pg/ml (P < 0.001), whereas ionized calcium increased from 1.10 +/- 0.02 to 1.22 +/- 0.02 mM (P < 0.001); however, maximal and minimal PTH did not change from pre-CTR values. Based on whether or not the basal PTH decreased by 40% or more during CTR treatment, patients were divided into responders (Rs, N = 25) and nonresponders (NRs, N = 25). Before CTR, the NR group was characterized by a greater basal (959 +/- 80 vs. 586 +/- 51 pg/ml, P < 0.001) and maximal (1899 +/- 170 vs. 1172 +/- 108 pg/ml, P < 0. 001) PTH and serum phosphorus (6.14 +/- 0.25 vs. 5.14 +/- 0.34 mg/dl, P < 0.01). Logistical regression analysis showed that the pre-CTR basal PTH was the most important predictor of the post-CTR basal PTH, and a pre-CTR basal PTH of 750 pg/ml represented a 50% probability of a response. Basal PTH correlated with the ionized calcium in the NR group (r = 0.59, P = 0.002) but not in the R group (r = 0.06, P = NS). In the R group, an inverse correlation was present between ionized calcium and the basal/maximal PTH ratio, an indicator of whether calcium is suppressing basal PTH secretion relative to the maximal secretory capacity (maximal PTH) r = -0.55, P = 0.004; in the NR group, this correlation approached significance but was positive (r = 0.34, P = 0.09). After CTR treatment, serum calcium increased in both groups, and despite marked differences in basal PTH (Rs, 197 +/- 25 vs. NRs, 969 +/- 85 pg/ml), an inverse correlation between ionized calcium and basal/maximal PTH was present in both groups (Rs, r = -0.61, P = 0.001, and NRs, r = -0.60, P = 0.001).

CONCLUSIONS

(a) Dynamic testing of parathyroid function provided insights into the pathophysiology of PTH secretion in hemodialysis patients. (b) The magnitude of hyperparathyroidism was the most important predictor of the response to CTR. (c) Before CTR treatment, PTH was sensitive to calcium in Rs, and serum calcium was PTH driven in NRs, and (d) after the CTR-induced increase in serum calcium, calcium suppressed basal PTH relative to maximal PTH in both groups.

Differential effects of 1,25-dihydroxy-vitamin D3 and 19-nor-1,25-dihydroxy-vitamin D2 on calcium and phosphorus resorption in bone

1,25-Dihydroxy-vitamin D3 [1,25-(OH)2D3] suppresses the secretion and synthesis of parathyroid hormone (PTH) and has been used in the treatment of secondary hyperparathyroidism. However, 1,25-(OH)2D3 can induce hypercalcemia, which often precludes its use. Therefore, an analog of 1,25-(OH)2D3 that would retain its therapeutic effects but produce minor effects on calcium and phosphorus metabolism could be an ideal tool for the treatment of secondary hyperparathyroidism. It has been shown that 19-nor-1,25-dihydroxy-vitamin D2 [19-nor-1,25-(OH)2D2], an analog of 1,25-(OH)2D3, can suppress PTH levels in uremic rats at doses that do not affect plasma ionized calcium levels. The experiments presented here, using parathyroidectomized rats fed diets deficient in either calcium (0.02%) or phosphorus (0.02%), were performed to compare the effects of 1,25-(OH)2D3 and 19-nor-1,25-(OH)2D2 on calcium and phosphorus resorption in bone. Parathyroidectomized rats received daily intraperitoneal injections of vehicle, 1,25-(OH)2D3 (100 ng), or 19-nor-1,25-(OH)2D2 (100 or 1000 ng) for 9 d. Plasma calcium and phosphorus levels were monitored during the study, and ionized calcium levels were determined at the end of the study. By 9 d, 1,25-(OH)2D3 (100 ng/d) increased total calcium levels to 12.4+/-0.26 mg/dl, compared with 6.32+/-0.25 mg/dl (P<0.001) in control animals. The same dose of 19-nor-1,25-(OH)2D2 (100 ng/d) was much less potent (9.45+/-0.28 mg/dl, P<0.001). Similar results were seen with ionized calcium levels [19-nor-1,25-(OH)2D2, 3.61+/-0.12 mg/dl; 1,25-(OH)2D3, 5.03+/-0.16 mg/dl; P<0.001]. Ionized calcium levels were also lower in rats receiving the higher dose (1000 ng) of 19-nor-1,25-(OH)2D2 (4.59+/-0.09 mg/dl, P<0.05). Similar results were seen in rats fed the phosphorus-deficient diet. 1,25-(OH)2D3 (100 ng) increased plasma phosphorus levels from 4.30+/-0.39 mg/dl in vehicle-treated rats to 7.43+/-0.26 mg/dl (P<0.001). The same dose of 19-nor-1,25-(OH)2D2 had no effect (5.19+/-0.32 mg/dl), whereas the high dose (1000 ng) increased plasma phosphorus levels (7.31+/-0.24 mg/dl) in a manner similar to that of 1,25-(OH)2D3 (100 ng). Therefore, 19-nor-1,25-(OH)2D2 is approximately 10 times less effective in mobilizing calcium and phosphorus from the skeleton, compared with 1,25-(OH)2D3. With its ability to suppress PTH at noncalcemic doses, 19-nor-1,25-(OH)2D2 is a potential therapeutic tool for the treatment of secondary hyperparathyroidism in chronic renal failure.

A new analog of 1,25-(OH)2D3, 19-NOR-1,25-(OH)2D2, suppresses serum PTH and parathyroid gland growth in uremic rats without elevation of intestinal vitamin D receptor content

We have previously reported that 19-nor-1,25-(OH)2D2, a new analog of 1,25-(OH)2D3, suppresses parathyroid hormone (PTH) secretion in uremic rats in the absence of hypercalcemia or hyperphosphatemia. In the current study, we examined the effect of 19-nor-1,25-(OH)2D2 on parathyroid gland growth and intestinal vitamin D receptor (VDR) content. After induction of uremia by 5/6 nephrectomy, rats were divided into five experimental groups and received intraperitoneal injections of vehicle, 1,25-(OH)2D3 (2 or 6 ng/rat), or 19-nor-1,25-(OH)2D2 (25 or 100 ng/rat) three times a week for 8 weeks. Twelve normal rats received vehicle and served as the normal control group. During the course of the study, rats were maintained on a 1.0% calcium and 0.8% phosphorus diet. The higher dose of 1,25-(OH)2D3, 6 ng, significantly decreased PTH from 52.7 +/- 10.2 pg/mL in the uremic control group to 25.7 +/- 6.7 pg/mL (P < 0.01). This dose of 1,25-(OH)2D3, however, increased serum levels of both ionized calcium (4.71 +/- 0.05 to 4.85 +/- 0.06 mg/dL; P < 0.05) and phosphorus (4.34 +/- 0.30 to 6.67 +/- 0.63 mg/dL; P < 0.01). Both doses of 19-nor-1,25-(OH)2D2 decreased serum PTH as effectively as 1,25-(OH)2D3 without changes in serum calcium or phosphorus. The 100-ng dose of 19-nor-1,25-(OH)2D2 decreased PTH to 20.7 +/- 3.1 pg/mL (P < 0.01) and suppressed parathyroid gland growth by more than 50%. Both doses of 19-nor-1,25-(OH)2D2 also decreased endogenous 1,25-(OH)2D3 levels compared with uremic control rats (25 ng:30.4 +/- 2.0, P < 0.05, and 100 ng:27.9 +/- 3.2, P < 0.01, v 48.4 +/- 6.6 pg/mL). The 6-ng dose of 1,25-(OH)2D3 elevated intestinal VDR content (138.5 +/- 20.0 fmol/mg protein) compared with animals receiving both doses of 19-nor-1,25-(OH)2D2 (25 ng:84.0 +/- 11.9, P < 0.05, and 100 ng:78.4 +/- 10.9, P < 0.01). This was probably attributable to the marked decrease in endogenous 1,25-(OH)2D3 levels caused by both doses of 19-nor-1,25-(OH)2D2 because intestinal VDR correlated directly with serum 1,25-(OH)2D3 (r = 0.963; P = 0.008). Thus, 19-nor-1,25-(OH)2D2 appears to exert a selective action on the parathyroid glands compared with the intestine. Its low calcemic and phosphatemic properties may result from the decreased endogenous 1,25-(OH)2D3 levels that lead to a reduction in intestinal VDR. This selectivity makes this analog ideal for the treatment of secondary hyperparathyroidism.

Renal osteodystrophy

Renal osteodystrophy is a general complication of chronic renal failure and end-stage renal disease. The nature of renal osteodystrophy has changed since osteomalacia due to aluminum intoxication has become less prevalent. Osteomalacia has been replaced by the adynamic bone disorder. Suppression of osteitis fibrosa, calcitrol and control of secondary hyperparathyroidism has been shown to produce the adynamic bone disorder. Thus, many other factors besides secondary hyperparathyroidism and calcitrol deficiency contribute to the pathogenesis of renal osteodystrophy. Some of these factors, according to our current state of knowledge, are discussed in this chapter along with the presentation and treatment of renal osteodystrophy.