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

Conversion from Intravenous Vitamin D Analogs to Oral Calcitriol in Patients Receiving Maintenance Hemodialysis

BACKGROUND AND OBJECTIVES

In the United States, intravenous vitamin D analogs are the first-line therapy for management of secondary hyperparathyroidism in hemodialysis patients. Outside the United States, oral calcitriol (1,25-dihydroxyvitamin D₃) is routinely used. We examined standard laboratory parameters of patients on in-center hemodialysis receiving intravenous vitamin D who switched to oral calcitriol.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a retrospective cohort study of adult patients treated within Fresenius Kidney Care clinics. During a 6-month period (December 2013 to May 2014), we identified patients on an intravenous vitamin D analog (doxercalciferol or paricalcitol) who switched to oral calcitriol and matched them to patients receiving an intravenous vitamin D analog. Mean serum calcium, phosphate, and intact parathyroid hormone (iPTH) concentrations were examined for up to 12 months of follow-up. We used Poisson and Cox proportional hazards regression models to examine hospitalization and survival rates. The primary analysis was conducted as intention-to-treat; secondary analyses included an as-treated evaluation.

RESULTS

A total of 2280 patients who switched to oral calcitriol were matched to 2280 patients receiving intravenous vitamin D. Compared with patients on intravenous vitamin D, mean calcium and phosphate levels in the oral calcitriol group were lower after the change to oral calcitriol. In contrast, iPTH levels were higher in the oral calcitriol group. At 12 months, the percentage of patients with composite laboratories in target range (calcium <10 mg/dl, phosphate 3.0-5.5 mg/dl, and iPTH 150-600 pg/ml) were comparable between groups (45% versus 45%; P=0.96). Hospital admissions, length of hospital stay, and survival were comparable between groups. An as-treated analysis and excluding those receiving cinacalcet did not reveal significant between-group differences.

CONCLUSIONS

Among patients receiving in-center hemodialysis who were switched to oral calcitriol versus those on an intravenous vitamin D analog, the aggregate of all mineral and bone laboratory parameters in range was largely similar between groups.

Racial-ethnic differences in chronic kidney disease-mineral bone disorder in youth on dialysis

BACKGROUND

Studies in healthy pediatric populations and adults treated with dialysis demonstrate higher parathyroid hormone (PTH) and lower 25-hydroxyvitamin D levels in African-Americans. Despite these findings, African-Americans on dialysis demonstrate greater bone strength and a decreased risk of fracture compared to the Caucasian dialysis population. The presence of such differences in children and young adult dialysis patients is unknown.

METHODS

Differences in the markers of mineral and bone metabolism (MBM) were assessed in 661 incident dialysis patients (aged 1 month to < 21 years). Racial-ethnic differences in PTH, calcium, phosphate, and total alkaline phosphatase (AP) activity were analyzed over the first year of dialysis using multivariate linear mixed models.

RESULTS

African-American race predicted 23% higher serum PTH (95% CI, 4.7-41.3%) when compared to Caucasian patients, while Hispanic ethnicity predicted 17.5% higher PTH (95% CI, 2.3-38%). Upon gender stratification, the differences in PTH were magnified in African-American and Hispanic females: 38% (95% CI, 14.8-69.8%) and 28.8% (95% CI, 4.7-54.9%) higher PTH compared to Caucasian females. Despite higher PTH values, African-American females persistently demonstrated up to 10.9% lower serum AP activity (95% CI, - 20.6-- 0.7%).

CONCLUSIONS

There are racial-ethnic differences in the markers of MBM. Higher PTH is seen in African-American and Hispanic children and young adults on dialysis with a magnification of this difference amongst the female population. There is a need to consider how factors like race, ethnicity, and gender impact the goal-targeted treatment of MBM disorders.

[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.

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.

Converting to doxercalciferol capsules from intravenous paricalcitol or doxercalciferol

OBJECTIVE

The purpose of the 2 studies presented in this article was to determine the clinically appropriate dose of doxercalciferol capsules that is required to maintain similar intact parathyroid hormone control when converting from intravenous (IV) paricalcitol or doxercalciferol.

DESIGN

Both studies were multicenter, open-label, randomized designs comprising the following 3 periods: a screening period, a 5-week run-in period, and a 5-week treatment period.

SETTING

Dialysis centers in the United States.

PATIENTS

Patients with stage 5 chronic kidney disease receiving dialysis 3 times weekly for a minimum of 6 months and with recent intact parathyroid hormone measurements between 15.9 and 63.7 pmol/L (150 to 600 pg/mL) were included.

INTERVENTION

After a 5-week fixed-dose IV paricalcitol or doxercalciferol run-in period, subjects were randomized to doxercalciferol capsules for the 5-week treatment period. Conversion factors for the paricalcitol study were 0.5, 1.0, and 1.5 times the current paricalcitol dose. Conversion factors for the doxercalciferol study were 1.0, 1.5, and 2.0 times the current doxercalciferol injection dose.

RESULTS

The predicted conversion factor for paricalcitol injection to doxercalciferol capsules was 0.92, whereas the factor for doxercalciferol injection to doxercalciferol capsules was 1.49. No statistically significant changes in serum calcium and phosphorus levels were found in either study. The nature of adverse events was consistent with the administration of an active vitamin D therapy to patients with chronic kidney disease receiving dialysis.

CONCLUSION

The studies demonstrate patients on dialysis can be safely and effectively converted from IV paricalcitol or doxercalciferol to oral doxercalciferol.

Extra-skeletal effects of vitamin D deficiency in chronic kidney disease

Cardiovascular diseases (CVD) and infectious diseases represent the two most important causes of death in patients with chronic kidney disease (CKD). The traditional risk factors of CVD do not appear to account sufficiently for the increased risk of CVD in patients with CKD, and vitamin D deficiency appears to be an important non-traditional, and potentially modifiable, CVD risk factor in this patient population. 25-Hydroxyvitamin D (25(OH)D) is converted to its biologically active form, 1,25-dihydroxyvitamin D (1,25(OH)(2)D), by the enzyme 1α-hydroxylase in the kidneys. The recent discovery that many extrarenal tissues also possess both the 1α-hydroxylase enzyme and the vitamin D receptors has provided new insights into the important physiologic autocrine and paracrine roles of vitamin D in various tissues and organs that are mainly dependent on the availability of 25(OH)D from the circulating plasma. Accordingly, the present review focuses on the rapidly expanding body of clinical and experimental evidence that supports a strong association between 25(OH)D deficiency/insufficiency and the risk of adverse CVD outcomes and infectious diseases as well as on the non-calcemic autocrine and paracrine actions of vitamin D both in the general population and in patients with CKD.

Vitamin d receptor activators and clinical outcomes in chronic kidney disease

Vitamin D deficiency appears to be an underestimated risk factor for cardiovascular disease in patients with chronic kidney disease. Evidence from both basic science and clinical studies supports the possible protective role of vitamin D beyond its effect on mineral metabolism. Toxicity of pharmacologic doses of active vitamin D metabolites, in particular calcitriol, is mainly due to the possibility of positive calcium and phosphorus balance. Therefore, vitamin D analogs have been developed, which suppress PTH secretion and synthesis with reduced calcemic and phosphatemic effects. Observational studies suggest that in hemodialysis patients the use of a vitamin D receptor (VDR) activator, such as calcitriol, doxercalciferol, paricalcitol, or alfacalcidol, is associated with a reduced mortality when compared with nonusers of any VDR activator. In this article the existing literature on the topic is reviewed, although a more robust answer to the question of whether or not VDR activators have beneficial effects in hemodialysis patients will hopefully come from a randomized controlled trial.

Vitamin D deficiency and toxicity in chronic kidney disease: in search of the therapeutic window

Both vitamin D deficiency and vitamin D toxicity are associated with cardiovascular complications in chronic kidney disease (CKD). Clinical and experiment data indicate that the association of vitamin D levels with cardiovascular disease is best illustrated as a biphasic, or U-shaped, curve. Children and adolescents with CKD need vitamin D due to the demands of a growing skeleton, to prevent renal rickets. However, this therapy carries the risk of severe side effects and chronic toxicity. Observational studies show that vitamin D deficiency and toxicity are frequently present in patients with CKD. In view of the importance of cardiovascular complications for the long-term survival of young patients, these findings demand a judicious use of vitamin D preparations. In clinical practice, the therapeutic window is rather small, presenting a therapeutic challenge to avoid both vitamin D deficiency and toxicity.

Vitamin D compounds for people with chronic kidney disease requiring dialysis

BACKGROUND

Clinical guidelines recommend vitamin D compounds to suppress serum parathyroid hormone (PTH) in chronic kidney disease (CKD), however treatment may be associated with increased serum phosphorus and calcium, which are associated with increased mortality in observational studies. Observational data also indicate vitamin D therapy may be independently associated with reduced mortality in CKD.

OBJECTIVES

We assessed the effects of vitamin D compounds on clinical, biochemical, and bone outcomes in people with CKD and receiving dialysis.

SEARCH STRATEGY

We searched The Cochrane Renal Group's specialised register, Cochrane's Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, and reference lists of retrieved articles.

SELECTION CRITERIA

Randomised controlled trials (RCTs) in subjects with CKD and requiring dialysis that assessed treatment with vitamin D compounds.

DATA COLLECTION AND ANALYSIS

Data was extracted by two authors. Results are summarised as risk ratios (RR) for dichotomous outcomes or mean differences (MD) for continuous outcomes, with 95% confidence intervals (CI).

MAIN RESULTS

Sixty studies (2773 patients) were included. No formulation, route, or schedule of administration was associated with altered risks of death, bone pain, or parathyroidectomy. Marked heterogeneity in reporting of outcomes resulted in few data available for formal meta-analysis. Compared with placebo, vitamin D compounds lowered serum PTH at the expense of increasing serum phosphorus. Trends toward increased hypercalcaemia and serum calcium did not reach statistical significance but may be clinically relevant. Newer vitamin D compounds (paricalcitol, maxacalcitol, doxercalciferol) lowered PTH compared with placebo, with increased risks of hypercalcaemia, although inadequate data were available for serum phosphorus. Intravenous vitamin D may lower PTH compared with oral treatment, and be associated with lower serum phosphorus and calcium levels, although limitations in the available studies precludes a conclusive statement of treatment efficacy. Few studies were available for intermittent versus daily and intraperitoneal versus oral administration or directly comparative studies of newer versus established vitamin D compounds.

AUTHORS' CONCLUSIONS

We confirm that vitamin D compounds suppress PTH in people with CKD and requiring dialysis although treatment is associated with clinical elevations in serum phosphorus and calcium. All studies were inadequately powered to assess the effect of vitamin D on clinical outcomes and until such studies are conducted the relative importance of changes in serum PTH, phosphorus and calcium resulting from vitamin D therapy remain unknown. Observational data showing vitamin D compounds may be associated with improved survival in CKD need to be confirmed or refuted in specifically designed RCTs.

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.

The role of bone biopsy in patients with chronic renal failure

Renal bone disease is a heterogeneous group of metabolic bone diseases that requires quantitative bone histomorphometry to make the correct differential diagnosis. Included in this group is osteoporosis. However, osteoporosis in stage 4 to 5 chronic kidney disease cannot be diagnosed on the basis of bone mineral density criteria established by the World Health Organization or the presence of fragility fractures because patients with all forms of renal bone disease can demonstrate low bone mineral density and fragility fractures. Clinical cases in patients with either low bone mineral density and/or low-trauma fractures will be used to demonstrate the value of bone biopsy and quantitative histomorphometry in making a diagnosis of the specific renal bone disease and assisting with subsequent management decisions.

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.

Vitamin D analogs: therapeutic applications and mechanisms for selectivity

The vitamin D endocrine system plays a central role in mineral ion homeostasis through the actions of the vitamin D hormone, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], on the intestine, bone, parathyroid gland, and kidney. The main function of 1,25(OH)(2)D(3) is to promote the dietary absorption of calcium and phosphate, but effects on bone, kidney and the parathyroids fine-tune the mineral levels. In addition to these classical actions, 1,25(OH)(2)D(3) exerts pleiotropic effects in a wide variety of target tissues and cell types, often in an autocrine/paracrine fashion. These biological activities of 1,25(OH)(2)D(3) have suggested a multitude of potential therapeutic applications of the vitamin D hormone for the treatment of hyperproliferative disorders (e.g. cancer and psoriasis), immune dysfunction (autoimmune diseases), and endocrine disorders (e.g. hyperparathyroidism). Unfortunately, the effective therapeutic doses required to treat these disorders can produce substantial hypercalcemia. This limitation of 1,25(OH)(2)D(3) therapy has spurred the development of vitamin D analogs that retain the therapeutically important properties of 1,25(OH)(2)D(3), but with reduced calcemic activity. Analogs with improved therapeutic indices are now available for treatment of psoriasis and secondary hyperparathyroidism in chronic kidney disease, and research on newer analogs for these indications continues. Other analogs are under development and in clinical trials for treatment of various types of cancer, autoimmune disorders, and many other diseases. Although many new analogs show tremendous promise in cell-based models, this article will limit it focus on the development of analogs currently in use and those that have demonstrated efficacy in animal models or in clinical trials.

Impact of activated vitamin D and race on survival among hemodialysis patients

Contrary to most examples of disparities in health outcomes, black patients have improved survival compared with white patients after initiating hemodialysis. Understanding potential explanations for this observation may have important clinical implications for minorities in general. This study tested the hypothesis that greater use of activated vitamin D therapy accounts for the survival advantage observed in black and Hispanic patients on hemodialysis. In a prospective cohort of non-Hispanic white (n = 5110), Hispanic white (n = 979), and black (n = 3214) incident hemodialysis patients, higher parathyroid hormone levels at baseline were the primary determinant of prescribing activated vitamin D therapy. Median parathyroid hormone was highest among black patients, who were most likely to receive activated vitamin D and at the highest dosage. One-year mortality was lower in black and Hispanic patients compared with white patients (16 and 16 versus 23%; P < 0.01), but there was significant interaction between race and ethnicity, activated vitamin D therapy, and survival. In multivariable analyses of patients treated with activated vitamin D, black patients had 16% lower mortality compared with white patients, but the difference was lost when adjusted for vitamin D dosage. In contrast, untreated black patients had 35% higher mortality compared with untreated white patients, an association that persisted in several sensitivity analyses. In conclusion, therapy with activated vitamin D may be one potential explanation for the racial differences in survival among hemodialysis patients. Further studies should determine whether treatment differences based on biologic differences contribute to disparities in other conditions.

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 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.

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.