Phosphate binders
Phosphate binders are oral agents that bind dietary phosphate in the gut so it passes unabsorbed into the stool, used to treat the hyperphosphatemia of chronic kidney disease and dialysis once dietary phosphate restriction alone fails. Diagnosis rests on a serum phosphate above 4.5 mg/dL with calcium, intact parathyroid hormone, and staged kidney function. First-line treatment favors a non-calcium binder such as sevelamer carbonate over calcium-based or aluminum-based agents.
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What this article covers
- Overview
What the class is: oral drugs taken with meals that bind dietary phosphate in the gastrointestinal (GI) tract, excreted unabsorbed in stool.
- Epidemiology
Who needs binder therapy: patients with CKD stage G3a through G5, especially those on maintenance hemodialysis or peritoneal dialysis, since calcium and phosphorus typically stay normal until the…
- Risk factors
Advanced CKD or ESKD: an eGFR under 30 mL/min/1.73 m2 is the dominant driver, since the kidney can no longer excrete enough filtered phosphate.
- Pathophysiology
The FGF-23-PTH-vitamin D axis: as nephron mass falls, FGF-23 and PTH raise phosphate excretion per nephron while suppressing conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (calcitriol)…
- Clinical features
Calcium-based binders: constipation, and with cumulative exposure, hypercalcemia and accelerated vascular calcification.
- Differential diagnosis
Non-calcium binder versus calcium-based binder: guideline consensus favors a non-calcium agent first, but a calcium-based agent may still be used when cost limits access, unless the patient already…
- Diagnosis
Hyperphosphatemia that warrants binder therapy is defined by a serum phosphate above 4.5 mg/dL (1.45 mmol/L) that persists despite dietary phosphate restriction in a patient with CKD stage G3a to G5 or on dialysis.
- Management
First, restrict dietary phosphate, limiting processed foods with phosphate additives; this alone may normalize mild hyperphosphatemia and precedes any drug.
- Complications
Vascular and coronary calcification: accelerated by cumulative calcium exposure from calcium-based binders and by uncontrolled hyperphosphatemia over years of CKD progression.
- Prognosis
Mortality association: elevated phosphorus, PTH, and FGF-23 are each associated with increased cardiovascular events and mortality in CKD and ESKD, though prospective trial data confirming a…
- Prevention
Serial monitoring: assess phosphorus, calcium, and PTH serially in CKD stage G3a to G5, with routine monthly monitoring standard once a patient reaches maintenance dialysis.
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Related articles
- Chronic kidney disease
Chronic kidney disease is abnormal kidney structure or function present for more than 3 months, staged by the Kidney Disease: Improving Global Outcomes (KDIGO) system using estimated glomerular filtration rate and albuminuria, and managed with blood pressure control, renin-angiotensin blockade, an SGLT2 inhibitor, and correction of its metabolic complications.
- Chronic kidney disease mineral and bone disorders
Chronic kidney disease-mineral and bone disorder (CKD-MBD) is the syndrome of disturbed calcium, phosphorus, PTH, vitamin D, and FGF-23 homeostasis, abnormal bone mineralization (renal osteodystrophy), and vascular calcification that develops as kidney function declines. Management centers on serial phosphorus/calcium/PTH monitoring, dietary phosphorus restriction plus phosphate binders (noncalcium-based preferred) to normalize phosphorus, avoiding hypercalcemia and unnecessary calcitriol before dialysis, and calcimimetics or activated vitamin D for uncontrolled secondary hyperparathyroidism on dialysis, reserving parathyroidectomy for tertiary disease.
- Secondary hyperparathyroidism
Secondary hyperparathyroidism is an appropriate, physiologic rise in parathyroid hormone driven by hypocalcemia or impaired vitamin D activation, most commonly from chronic kidney disease and less often from vitamin D deficiency or malabsorption. Management targets the underlying stimulus with dietary phosphorus restriction, phosphate binders, vitamin D repletion or active vitamin D analogs, and calcimimetics, reserving parathyroidectomy for disease refractory to medical therapy.
- Hypocalcemia
Hypocalcemia is a low serum calcium concentration, most often from insufficient parathyroid hormone action (postsurgical or autoimmune hypoparathyroidism, hypomagnesemia, or PTH resistance) or from vitamin D deficiency and chronic kidney disease. Severe or symptomatic disease requires urgent intravenous calcium, while chronic disease is managed with oral calcium, vitamin D repletion, and calcitriol when PTH is absent or the kidney cannot activate vitamin D.
- Calciphylaxis
Calciphylaxis, also called calcemic uremic arteriopathy, is a form of vascular calcification that produces extensive calcification of the skin, muscles, and subcutaneous tissue, leading to ischemic ulceration and necrosis, most often in patients with end-stage renal disease. There is no single diagnostic test; management centers on normalizing serum calcium and phosphate, increasing the intensity of dialysis, non-calcium phosphate binders and calcimimetic therapy, and aggressive pain control and wound care.