Phosphate binders

Phosphate binders are a group of medications used to reduce the absorption of phosphate and taken with meals and snacks. They are typically used in patients with chronic renal failure (CRF) as they cannot get rid of the phosphate that gets into their blood (i.e. the serum phosphate in chronic renal failure is typically elevated).

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Clinical use

For patients with chronic renal failure, controlling serum phosphate is important because it is associated with bone pathology and regulated together with serum calcium by the parathyroid hormone (PTH). High (serum) phosphate levels (known as hyperphosphatemia) normally results in an elevation of the PTH level, which then leads to more phosphate excretion into the urine.^[1] If the kidneys do not function properly the phosphate level increases. Also, the serum calcium levels tend to be low. This is because the kidneys in chronic renal failure do not produce the active form of vitamin D (1,25-dihydroxycholecalciferol), which is important for calcium absorption from food. Low serum calcium levels, like high phosphate, also lead to a high PTH.

A high PTH leads to a large mobilization of calcium from the bone and, if it is not replaced, bone is lost. Bone loss and damage due to CRF is called renal osteodystrophy. To avoid a high PTH and bone loss in patients with CRF, CRF patients typically avoid high phosphate intake and take calcium supplements, vitamin D and phosphate binders.

Mechanism of action

These agents work by binding to phosphate in the GI tract, thereby making it unavailable to the body for absorption. Hence, these drugs are usually taken with meals to bind any phosphate that may be present in the ingested food. Phosphate binders may be simple molecular entities (such as aluminum, calcium, or lanthanum salts) that react with phosphate and form an insoluble compound. Phosphate binders, such as sevelamer, may also be polymeric structures which bind to phosphate and are then excreted.

Adverse effects

With regard to phosphate binders, aluminum-containing compounds (such as aluminum hydroxide) are the least preferred because prolonged aluminum intake can cause encephalopathy and osteomalacia. If calcium is already being used as a supplement, additional calcium used as a phosphate binder may cause hypercalcemia and tissue-damaging calcinosis. One may avoid these adverse effects by using phosphate binders that do not contain calcium or aluminum as active ingredients, such as lanthanum carbonate or sevelamer.

Common phosphate binders

• Aluminum hydroxide (Alucaps®)
• Calcium carbonate (Calcichew®, Titralac®)
• Calcium acetate (Phosex®, PhosLo®)
• Lanthanum carbonate (Fosrenol®)
• Sevelamer (Renagel®, Renvela®))

References

1. ^  Lederer E, Ouseph R, Erbeck K. Hyperphosphatemia, eMedicine.com, URL: http://www.emedicine.com/med/topic1097.htm, Accessed on July 14, 2005.

Common Phosphate Binders (Generic)

• Lanthanum - medlineplus.org
• Sevelamer - medlineplus.org