Hyperphosphatemia Treatment & Management
- Author: Eleanor Lederer, MD, FASN; Chief Editor: Vecihi Batuman, MD, FACP, FASN more...
The major strategies for treating hyperphosphatemia are as follows:
Diagnosis of the cause in order to initiate specific therapy: Eg, patients with hyperphosphatemia due to administration of liposomal amphotericin B who continue to require antifungal therapy may be switched to the amphotericin B lipid complex formulation, which contains less inorganic phosphate 
Limitation of phosphate intake: Patients with chronic kidney disease are advised to avoid foods that are especially high in phosphate; high-phosphate foods include dairy products; meats, nuts, and other high-protein foods; processed foods; and dark colas
Enhancement of renal excretion of phosphate: Hyperphosphatemia due to tumor lysis responds to enhancement of urinary losses through forced saline diuresis
The clinical condition most often requiring curtailment of ingestion is renal failure. Because intestinal absorption of phosphate and phosphate content in a typical diet is high, maintenance of phosphate homeostasis is dependent on renal excretion of the ingested excess. Therefore, when renal failure develops and hyperphosphatemia ensues, the sole means of controlling it is limitation of intake.
Optimal phosphate control in dialysis patients is extremely challenging. Despite the remarkable improvements made in dialysis techniques over the years, phosphate control has not been substantially improved. An alternative approach for dialysis-dependent patients that is presently being investigated is daily nocturnal dialysis. Dialysis performed in this manner, as opposed to intermittent thrice-weekly dialysis, seems to markedly decrease or even abolish the necessity for phosphate binders.
Dey et al reported achieving phosphate control with thrice-weekly sessions by using hemodiafiltration, which combines diffusion and convection, rather than hemodialysis. Their program consisted of nocturnal sessions lasting a median of 8 hours. In the 14 patients in their study, pre-dialysis phosphate levels fell from a mean of 1.52 ± 0.4 to 1.06 ± 0.1 mmol/L (P <0.05), and use of phosphate binders became unnecessary.
Surgery may sometimes be required for removal of large calcium phosphate deposits occurring in patients with tumoral calcinosis or long-standing renal failure. Perform parathyroidectomy in patients with renal failure who have tertiary (autonomous) hyperparathyroidism complicated by hypercalcemia, hyperphosphatemia, and severe bone disease.
The following consultations may be required:
Endocrinologist: To determine if the patient has hypoparathyroidism or one of the various forms of pseudohypoparathyroidism
Nephrologist: To evaluate and treat hyperphosphatemia associated with renal failure
Calcium levels, phosphate levels, and renal function should be monitored at intervals consonant with the severity of the underlying disorder.
Dietary restriction alone may suffice for control of hyperphosphatemia in persons with mild renal insufficiency, but it is inadequate for patients with advanced renal insufficiency or complete renal failure. Such individuals require the addition of phosphate binders to inhibit gastrointestinal absorption of phosphate. These medications, which are taken concomitantly with meals, directly interact with the phosphate in the food, preventing intestinal absorption. The following classes of phosphate binders are widely used :
Aluminum-containing phosphate binders
Calcium-containing phosphate binders
Phosphate binders that contain no aluminum or calcium
Administration of phosphate binders is the only truly long-term therapy for chronic hyperphosphatemia due to renal failure. Monitor calcium and phosphate levels, especially when treating patients with calcium-containing phosphate binders, because of the possibility of severe, life-threatening hypercalcemia.
Calcium citrate and aluminum-containing binders should probably not be used together, because the citrate may enhance aluminum absorption.
Aluminum-containing phosphate binders
The aluminum-containing binders were the first to be used to treat hyperphosphatemia, but they have largely been abandoned because of the toxic effects of absorbed aluminum. Initially, the amount of aluminum absorbed was thought to be trivial; with long-term use, however, many patients developed a constellation of clinical symptoms attributable to aluminum, including dementia, severe osteomalacia, and anemia.
Bone biopsies performed on patients with aluminum intoxication revealed deposition of aluminum along the mineralizing front of bone, preventing normal mineralization. Aluminum levels in the fasting state and after a challenge with desferrioxamine confirmed the increased total body aluminum load. Aluminum-containing phosphate binders should be used only when other agents have failed to adequately control phosphate levels.
Calcium-containing phosphate binders
The next phosphate binders to be introduced were the calcium-containing binders, such as calcium carbonate and calcium citrate. These drugs, which are still used extensively, have the advantage of inhibiting phosphate absorption while providing the patient with a required mineral, calcium. The disadvantage of these drugs has been the relatively high incidence of hypercalcemia occurring in patients. There have also been concerns about the contribution of large exogenous calcium loads to the occurrence of soft tissue calcification in end-stage renal disease.
Several studies, including the Calcium Acetate Renagel Evaluation (CARE) study, have shown that calcium acetate is more cost-effective than sevelamer (discussed below) as a phosphate binder. Although concern has been raised about its purported link to cardiovascular calcification, calcium acetate can be used effectively with doses of elemental calcium that meet the Kidney Disease Outcome Quality Initiative (KDOQI) guidelines.
Phosphate binders with no aluminum or calcium
The above concerns about calcium-containing binders led to the development of a class of phosphate binders that contain neither aluminum nor calcium. At present, several drugs in this class, including the following, are in clinical use:
Sucroferric oxyhydroxide (Velphoro)
Lanthanum carbonate (Fosrenol)
Ferric citrate (Auryxia)
For patients taking calcium-containing phosphate binders who have had demonstrable extraskeletal calcification or recurrent hypercalcemia, sevelamer and sucroferric oxyhydroxide are excellent alternatives and are well-tolerated in the control of serum phosphorus in dialysis patients.
Sucroferric oxyhydroxide (Velphoro) is an iron-based phosphate binder that when taken with meals adsorbs dietary phosphate in the GI tract.
Approval for sucroferric oxyhydroxide (1-3 g/day) was based on the results of a phase 3 study that compared the drug’s dose titration and maintenance phases with those of sevelamer (2.4-14.4 g/day). Sucroferric oxyhydroxide and sevelamer efficacy were maintained during long-term use, with no notable difference in safety observed between the treatment groups. Moreover, sucroferric oxyhydroxide had a lower pill burden than did sevelamer.[45, 46]
In an open-label phase 3 extension study that compared sucroferric oxyhydroxide with sevelamer in 644 dialysis patients with hyperphosphatemia, sucroferric oxyhydroxide maintained its serum phosphorus-lowering effect over 1 year. Sucroferric oxyhydroxide was generally well tolerated over the long term, and patients showed no evidence of iron accumulation.
Sevelamer and calcium-containing phosphate binders can be used in combination to minimize adverse effects; however, the major barrier to their use is patient noncompliance. The patient is required to ingest 3-6 large capsules with every meal, which is more than most human beings can comply with for extended periods. A study, however, demonstrated that once-daily sevelamer was as effective as thrice-daily sevelamer in the control of serum phosphorus, which may improve patient compliance.
In addition to its effects as a phosphate binder, sevelamer has also been shown to improve the lipid profile in patients with hyperphosphatemia.
Lanthanum has been shown to be a safe and equally efficacious agent in short-term studies, but concerns of long-term administration and toxicity exist. Furthermore, these agents are significantly more expensive than calcium salts, which may contribute to patient noncompliance. A 16-week, phase 4 study conducted by Vemuri et al found that patients who converted from other phosphate-binder medications to lanthanum carbonate maintained productive serum phosphorus levels with much satisfaction and lessened tablet burden.
Oral ferric citrate was approved in September 2014 for the control of serum phosphorus levels in patients with chronic kidney disease on dialysis. Approval was based on a randomized trial in 441 adults with end-stage renal disease who were receiving hemodialysis or peritoneal dialysis 3 times per week for at least 3 months. Participants were treated either with ferric citrate or with active control (calcium acetate or sevelamer carbonate) for 52 weeks. Phosphorus levels were similar in the ferric citrate and active control groups, as were adverse events, which occurred in 39.1% of patients receiving ferric citrate and 49.0% of patients receiving active control. Patients receiving ferric citrate had significantly higher mean ferritin levels (899 ng/mL vs 628 ngmL; P < 0.001), transferrin saturation (39% vs 30%; P < 0.001), and less need for IV iron (12.95 mg/week vs 26.88 mg/week; P < 0.001) compared with active control.
Although long-term ingestion of aluminum-containing binders has known toxic effects, no definitive studies suggest that the chronic use of any of the other binders confers either a benefit or a disadvantage in terms of mortality.
Theoretically, the high calcium load of a calcium-containing phosphate binder could perpetuate or worsen vascular calcification, which does correlate with cardiovascular mortality in chronic kidney disease patients, when compared with non–calcium-containing phosphate binders. In fact, the use of non–calcium-containing binders does result in less vascular calcification; however, a beneficial effect on mortality has not been consistently demonstrated.[51, 52, 53, 54, 55, 56]
Increased Renal Excretion
The strategy for treatment of hyperphosphatemia in patients with normal renal function is to enhance renal excretion. This can be accomplished most effectively by volume repletion with saline coupled with forced diuresis with a loop diuretic such as furosemide or bumetanide.
The marked increase in intravascular volume with saline globally inhibits proximal renal tubule absorption of solutes, in this specific case, phosphate, thus promoting phosphaturia.
The increased distal tubule delivery of phosphate overwhelms the ability of that portion of the nephron to absorb phosphate, leading to a negative phosphate balance.
Management of Secondary Hyperparathyroidism
Just as better control of hyperphosphatemia in patients with renal failure helps to prevent the nearly universal development of secondary hyperparathyroidism, better control of hyperphosphatemia is achieved through control of secondary hyperparathyroidism. The agents commonly used to control secondary hyperparathyroidism are vitamin D metabolites and the calcium-sensing receptor agonists.
A study by Hansen et al found that alfacalcidol and paricalcitol were equally effective in the suppression of secondary hyperparathyroidism in patients on hemodialysis.
Management of Hypoparathyroidism
For the rare cases of hypoparathyroidism, calcium and vitamin D are prescribed, predominantly for treatment of the hypocalcemia. Given with meals, the oral calcium can ameliorate the hyperphosphatemia of hypoparathyroidism, although this effect has to be carefully balanced against the phosphate absorption–promoting effects of the vitamin D. Over the long term, this therapy may result in nephrocalcinosis. Recombinant PTH injections can be considered but are not commonly used in clinical practice, because of the efficacy of calcium and vitamin D, as well as the cost and inconvenience of injected PTH.
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