Acute effect of pamidronate on PTH secretion in postmenopausal hemodialysis patients with secondary hyperparathyroidism

Hypophosphatemia in cancer patients

Dysregulation of phosphorus homeostasis resulting in hypophosphatemia is common in cancer patients and can result in serious complications and impact outcomes. Several factors, including critical illness, nutritional status, cancer type and therapy, influence the development of hypophosphatemia. Hypophosphatemia can develop as a result of phosphaturic mesenchymal tumors or as a paraneoplastic phenomenon. The clinical presentation for hypophosphatemia varies depending on the duration and severity of the hypophosphatemia and affects several organ systems. Among other serious effects, hypophosphatemia can impair tissue oxygenation and can cause hemolysis, leukocyte and platelet dysfunction, encephalopathy, seizures, arrhythmias, cardiomyopathy, rhabdomyolysis and coma. Multiple studies have demonstrated that hypophosphatemia is an adverse prognostic marker in inpatients with increased in-hospital stay, mortality and postoperative complications. The phosphate level is homeostatically regulated and maintained in a narrow range by three main hormones: parathyroid hormone, fibroblast growth factor 23 and 1,25-dihydroxyvitaminD₃. Together, these hormones regulate how the intestine, kidneys and bones traffic phosphorus. Several hematological malignancies and cancer therapies are associated with proximal tubular dysfunction (Fanconi syndrome), resulting in phosphaturia. Caution should be taken with parenteral administration of phosphate salts, because secondary complications can develop, principally due to hypocalcemia. The general approach to hypophosphatemia should target the underlying cause. Early recognition and prevention are essential and the approach to hypophosphatemia in the cancer patient, because of the nuances and complexity, should be multidisciplinary.

Bisphosphonate therapy in CKD: the current state of affairs

PURPOSE OF REVIEW

Chronic kidney disease (CKD) is associated with the development of mineral and bone disorders (MBD), including renal osteodystrophy (ROD). ROD is a global disorder of bone strength that is associated with an increased fracture risk. The use of bisphosphonates for fracture risk reduction in CKD remains controversial. This review provides a synopsis of the state-of-the literature regarding the safety and potential antifracture benefits of bisphosphonates in CKD patients.

RECENT FINDINGS

In preclinical studies of animals with CKD 3-4 and evidence of CKD-MBD, bisphosphonates resulted in changes in bone quality that improve bone strength. Bone turnover was generally reduced to a similar extent in animals with and without CKD. Post hoc analyses of randomized trials in patients with CKD 3-4 reported increases in bone mineral density (BMD) and fracture reduction that were similar in patients with and without CKD. There are no primary clinical trial data in patients with CKD-MBD.

SUMMARY

In patients with CKD without evidence of CKD-MBD, the use of bisphosphonates should follow general population guidelines. The lack of data for patients with CKD 4-5D and evidence of CKD-MBD makes treatment decisions challenging. Clinical studies are urgently needed to provide data on the safety and antifracture benefits of bisphosphonates in these cohorts.

Role of Vitamin D in Uremic Vascular Calcification

The risk of cardiovascular death is 10 times higher in patients with CKD (chronic kidney disease) than in those without CKD. Vascular calcification, common in patients with CKD, is a predictor of cardiovascular mortality. Vitamin D deficiency, another complication of CKD, is associated with vascular calcification in patients with CKD. GFR decline, proteinuria, tubulointerstitial injury, and the therapeutic dose of active form vitamin D aggravate vitamin D deficiency and reduce its pleiotropic effect on the cardiovascular system. Vitamin D supplement for CKD patients provides a protective role in vascular calcification on the endothelium by (1) renin-angiotensin-aldosterone system inactivation, (2) alleviating insulin resistance, (3) reduction of cholesterol and inhibition of foam cell and cholesterol efflux in macrophages, and (4) modulating vascular regeneration. For the arterial calcification, vitamin D supplement provides adjunctive role in regressing proteinuria, reverse renal osteodystrophy, and restoring calcification inhibitors. Recently, adventitial progenitor cell has been linked to be involved in the vascular calcification. Vitamin D may provide a role in modulating adventitial progenitor cells. In summary, vitamin D supplement may provide an ancillary role for ameliorating uremic vascular calcification.

The Use of Parenteral Nutrition in a Severely Malnourished Hemodialysis Patient With Hypercalcemia

There is a high prevalence of protein-energy malnutrition (PEM) in chronic dialysis patients. Causes of PEM include the catabolic effects of hemodialysis treatments, acidemia associated with end-stage renal disease, common comorbid conditions, and uremia-induced anorexia. Morbidity and mortality increase with PEM. Before considering parenteral nutrition (PN) as a nutrition intervention in a maintenance dialysis patient, all other efforts to promote optimal nutrition need to be exhausted. The first step is careful evaluation of protein-energy status, followed by intensive nutrition counseling. If necessary, this is followed by oral nutrition supplementation, appetite stimulation, enteral tube feedings, and finally PN. Short-term parenteral nutrition (PN) became a crucial component of the management of a 38-year-old hemodialysis (HD) patient who endured serious complications after kidney transplant rejection. A profound and prolonged malnourished state followed her treatment for necrotizing pancreatitis. She had developed persistent hypercalcemia believed secondary to tertiary hyperparathyroidism (HPT) and immobilization. Later, she developed hungry bone syndrome (HBS) after parathyroidectomy (PTX). She also developed refeeding syndrome after initiation of PN. The patient's persistent, poorly understood hypercalcemia did not resolve even after PTX and removal of all other sources of vitamin D and calcium from her feedings, medications, and dialysis bath. The close communication of the inpatient and outpatient dialysis multidisciplinary teams became a key component to the successful outcome in this complex patient.

Pharmacology of Bisphosphonates in Patients with Chronic Kidney Disease

Bisphosphonates are medications which bind strongly to mineral. They are ingested by osteoclasts and inhibit an enzyme necessary for bone resorption. The gastrointestinal absorption is poor and the only method of excretion is renal. Therefore, in patients with CKD the body accumulates a higher percentage of a dose of bisphosphonate. These medications remain attached to bone mineral for many years. Although the primary action is to inhibit bone resorption, secondarily bone formation is also inhibited, and in patients with CKD bisphosphonate use often leads to adynamic bone. In some experimental models in animals, the bisphosphonates can inhibit vascular calcification but this effect has not been seen in humans. Intravenous bisphosphonates may cause renal damage but oral doses do not reduce creatinine clearance. In stage 3 CKD, in patients who still have normal PTH, calcium, and alkaline phosphatase, randomized trials show similar benefits as in patients without CKD. Data from stage 4 and 5 CKD are very limited and no clear benefit has been shown.

Bisphophonates in CKD patients with low bone mineral density

Patients with chronic kidney disease-mineral and bone disorder (CKD-MBD) have a high risk of bone fracture because of low bone mineral density and poor bone quality. Osteoporosis also features low bone mass, disarranged microarchitecture, and skeletal fragility, and differentiating between osteoporosis and CKD-MBD in low bone mineral density is a challenge and usually achieved by bone biopsy. Bisphosphonates can be safe and beneficial for patients with a glomerular filtration rate of 30 mL/min or higher, but prescribing bisphosphonates in advanced CKD requires caution because of the increased possibility of low bone turnover disorders such as osteomalacia, mixed uremic osteodystrophy, and adynamic bone, even aggravating hyperparathyroidism. Therefore, bone biopsy in advanced CKD is an important consideration before prescribing bisphosphonates. Treatment also may induce hypocalcemia in CKD patients with secondary hyperparathyroidism, but vitamin D supplementation may ameliorate this effect. Bisphosphonate treatment can improve both bone mineral density and vascular calcification, but the latter becomes more unlikely in patients with stage 3-4 CKD with vascular calcification but no decreased bone mineral density. Using bisphosphonates requires considerable caution in advanced CKD, and the lack of adequate clinical investigation necessitates more studies regarding its effects on these patients.

Effects of pamidronate and calcitriol on the set point of the parathyroid gland in postmenopausal hemodialysis patients with secondary hyperparathyroidism

BACKGROUND/AIMS

Secondary hyperparathyroidism may worsen after the administration of pamidronate in postmenopausal hemodialysis (HD) patients. The aim of this study was to evaluate the short-term effect of coadministration of calcitriol and pamidronate on dynamic parathyroid hormone (PTH) secretion.

METHODS

Fifteen postmenopausal women undergoing regular HD with serum intact PTH levels of >200 pg/ml were enrolled. The PTH-ionized calcium (iCa) curve was evaluated by the response to hypo- and hypercalcemia induced with 1 and 4 mEq/l of dialysate calcium, respectively. Parameters were compared after pamidronate was administered and after coadministration of pamidronate and calcitriol. Changes in serum levels of maximal serum PTH (PTHmax), basal PTH (PTHbase) and minimal PTH (PTHmin) were evaluated.

RESULTS

Pamidronate therapy resulted in a decrease in predialysis basal plasma iCa (p < 0.05) and an increase in PTHmax (p < 0.01), PTHbase (p < 0.01) and PTHmin (p < 0.01). The change in serum iCa and PTH was reversed after the coadministration of calcitriol and pamidronate.

CONCLUSION

Our study demonstrated that pamidronate therapy is associated with a reduced plasma iCa and increased PTH secretion. These adverse effects may be reversed by calcitriol. These findings suggest that in considering pamidronate treatment in postmenopausal patients with osteoporosis receiving HD, it might be safer to add calcitriol to prevent the increased PTH secretion.

Bone turnover markers predict changes in bone mineral density after parathyroidectomy in patients with renal hyperparathyroidism

OBJECTIVE

Patients on long-term dialysis may develop secondary hyperparathyroidism (SHPT), which causes varying degrees of bone mass loss. This condition is treated with parathyroidectomy (PTX). We investigated whether serial serum bone turnover markers could predict changes in bone mineral density (BMD) after PTX.

DESIGN AND PATIENTS

Renal patients on maintenance haemodialysis who received PTX for refractory SHPT (n = 26, male/female: 13/13; mean age: 48·6 ± 10·7 year) and control subjects without SHPT (n = 25) were prospectively followed for 1 year at two tertiary hospitals in Taiwan.

MEASUREMENTS

Serum intact parathyroid hormone (iPTH), bone-specific alkaline phosphatase (BAP) and type 5b tartrate-resistant acid phosphatase (TRAP) were measured serially. Additionally, femoral neck (FN) and lumbar spine (LS) BMD were measured before and 1 year after PTX.

RESULTS

After PTX, iPTH levels decreased markedly and persistently. BMDs increased in both the FN and LS, but particularly in the LS. Serum BAP progressively increased to a peak at 2 weeks after PTX. Serum TRAP levels progressively decreased over 6 months after PTX. In univariate correlation analyses, baseline iPTH correlated positively with T-score changes in FN (r = 0·45, P = 0·021) and LS (r = 0·48, P = 0·013). In multivariate regression models, changes in FN T-scores were negatively predicted by baseline BAP levels (r = -0·615, P = 0·005) and baseline FN T-scores (r = -0·563, P = 0·012), and they were positively predicted by baseline TRAP(r = 0·6, P =  0·007). Changes in LS T-scores were positively predicted by baseline TRAP values (r = 0·528, P = 0·01) and negatively predicted by the percentage change in BAP after 2 weeks (r = -0·501, P = 0·015).

CONCLUSIONS

Parathyroidectomy provided marked, sustained improvements in BMD for up to 1 year. Furthermore, markers of bone turnover predicted 1-year changes in FN and LS BMDs after PTX.

Optimizing bone health in chronic kidney disease

Phosphocalcic metabolism disorders often complicate chronic kidney disease (CKD) and worsen as kidney function declines, with a consequence on bone structural integrity. The risk of fracture exceeds that of the normal population in both patients with pre-dialysis CKD and end-stage renal disease (ESRD). The increasing incidence of CKD, the high mortality rate induced by hip fracture, the decreased quality of life and economic burden of fragility fracture make the renal bone disorders a major problem of public health around the world. Optimizing bone health in CKD patients should be a priority. Bone biopsy is invasive. Dual-energy X-ray absorptiometry, commonly used to screen individuals at risk of fragility fracture in the general population, is not adequate to assess advanced CKD because it does not discriminate fracture status in this population. New non-invasive three-dimensional high-resolution imaging techniques, distinguishing trabecular and cortical bone, appear to be promising in the assessment of bone strength and might improve bone fracture prediction in this population. Therapeutic intervention in the chronic kidney disease-mineral and bone disorders (CKD-MBD) should begin early in the course of CKD to maintain serum concentration of biological parameters involved in mineral metabolism in the normal recommended ranges, prevent the development of parathyroid hyperplasia, prevent extra-skeletal calcifications and preserve skeletal health. In this paper, we review studies of mineral and bone disorders in patients with CKD and ESRD, the utility of current techniques to assess bone health and the preventive and therapeutic strategies for managing CKD-MBD.

Persistent hypocalcemia induced by zoledronic acid in a patient with androgen-independent prostate cancer and extensive bone metastases

Zoledronic acid is a highly potent bisphosphonate that has been shown to reduce skeletal-related events in patients with androgen-independent prostate cancer metastatic to bone. We report a patient with androgen-independent prostate cancer and extensive bone metastases. After receiving a single dose of zoledronic acid, the patient developed hypocalcemia that persisted for approximately 60 days despite intravenous and oral calcium supplementation, likely because of excess unopposed osteoblastic activity. This case underscores the need for calcium and vitamin D monitoring and supplementation to avoid bisphosphonate-induced secondary hyperparathyroidism and highlights the possibility that extensive osteoblastic metastasis alone might lead to hypocalcemia.

Dynamics of parathyroid hormone secretion in health and secondary hyperparathyroidism

This review examines the dynamics of parathyroid hormone secretion in health and in various causes of secondary hyperparathyroidism. Although most studies of parathyroid hormone and calcium have focused on the modification of parathyroid hormone secretion by serum calcium, the relationship between parathyroid hormone and serum calcium is bifunctional because parathyroid hormone also modifies serum calcium. In normal animals and humans, factors such as phosphorus and vitamin D modify the basal parathyroid hormone level and the maximal parathyroid hormone response to hypocalcemia. Certain medications, such as lithium and estrogen, in normal individuals and sustained changes in the serum calcium concentration in hemodialysis patients change the set point of calcium, which reflects the serum calcium concentration at which parathyroid hormone secretion responds. Hypocalcemia increases the basal/maximal parathyroid hormone ratio, a measure of the relative degree of parathyroid hormone stimulation. The phenomenon of hysteresis, defined as a different parathyroid hormone value for the same serum calcium concentration during the induction of and recovery from hypo- and hypercalcemia, is discussed because it provides important insights into factors that affect parathyroid hormone secretion. In three causes of secondary hyperparathyroidism--chronic kidney disease, vitamin D deficiency, and aging--factors that affect the dynamics of parathyroid hormone secretion are evaluated in detail. During recovery from vitamin D deficiency, the maximal parathyroid hormone remains elevated while the basal parathyroid hormone value rapidly becomes normal because of a shift in the set point of calcium. Much remains to be learned about the dynamics of parathyroid hormone secretion in health and secondary hyperparathyroidism.

The use of bisphosphonates in cancer patients

Skeletal-related events resulting from bone metastases or osteoporosis can significantly contribute to morbidity and mortality in cancer patients. Expert opinion on the effectiveness of bisphosphonates in this setting is evolving. Here we review current evidence on the risks and benefits of bisphosphonate therapy for a wide variety of cancers, as well as clinical management of its adverse effects. A MEDLINE search of English-language literature (1966 through May 2006) was conducted using the terms bisphosphonate, cancer, multiple myeloma, malignancy, and randomized controlled clinical studies. Studies were selected based on clinical pertinence, with an emphasis on phase III clinical trials. We reviewed bibliographies for other relevant articles. Accumulating evidence reveals that bisphosphonate therapy has a significant effect in preventing skeletal complications in multiple myeloma, breast cancers, and prostate cancer, and in reducing skeletal complications in other metastatic bone malignancies. Emerging data indicate that bisphosphonates are useful for preventing bone loss resulting from cancer or its therapy. The efficacy of bisphosphonates for early-stage breast cancers remains controversial. Significant risks of bisphosphonate therapy include nephrotoxicity, electrolyte abnormalities, and osteonecrosis of the jaw. Bisphosphonate therapy has a clear role in the management of skeletal metastases associated with a variety of cancers. However, significant side effects require ongoing monitoring and treatment.

Disodium pamidronate for treating severe hypercalcemia in a hemodialysis patient

BACKGROUND

A 48-year-old man with a recent diagnosis of multiple myeloma and rapidly progressive oliguric end-stage renal disease requiring hemodialysis, presented with a serum calcium concentration of 3.4 mmol/l (13.6 mg/dl).

INVESTIGATIONS

Serum laboratory analysis, electroencephalogram, MRI of the brain and bone marrow, and kidney biopsies.

DIAGNOSIS

Hypercalcemia secondary to multiple myeloma.

MANAGEMENT

Short-term intravenous disodium pamidronate therapy (30 mg daily) and daily monitoring of serum calcium concentration.