Phosphorus Binders (Phosphate Binders) and the Dialysis Diet

The main part of treatment that people on dialysis control is their diet. A major part of managing your dialysis diet is controlling the amount of phosphorus-containing foods you eat. But what exactly is phosphorus? And, why is phosphorus also called phosphate?

Phosphorus is the second most common mineral in the body, after calcium. Phosphorus helps your body use energy, build strong bones and teeth, maintain a normal pH balance and carry oxygen to tissues. Basically, phosphorus (P) is an element you may remember from chemistry class. When oxygen is added to phosphorus it becomes phosphate (PO4). The two are chemically different, but the names are used interchangeably. 

High phosphorus in the body

Extra phosphorus is removed from the body through urine made by healthy kidneys. So, when kidney failure occurs, phosphorus can build up in the blood. This build up of excess phosphate is called hyperphosphatemia. Excess phosphorus causes problems with the bones and heart. With too much phosphorus in your bloodstream, you could experience problems such as: anxiety, fatigue, breathing difficulties, sores due to calcium-phosphorus deposits in the skin and severe itching. Over the long term additional symptoms of hyperphosphatemia include: bone pain and weakness, decreased mobility, bones that break easily, uncontrolled parathyroid hormone levels and problems with the blood vessels and heart.

When there is too much phosphorus in the blood, calcium is pulled out of the bones. As a result, renal bone disease, or osteodystrophy can develop. In addition, sharp calcium-phosphorus crystals can form and are deposited in body tissues including eyes, joints, heart and lungs.

How does the body get phosphorus?

Phosphorus is common in most foods. The small intestines absorb it from the foods you eat and then store the phosphorus in your bones. Since the mineral is so prevalent, people with end stage renal disease (ESRD) are instructed to read ingredient labels — the Nutrition Facts printed on all foods. Because the government does not require “phosphorus” be included on food labels, you should also be on the lookout for hidden sources of phosphorus.

Phosphorus is abundant in protein foods such as meats, dairy products, nuts and dried beans. Other common high-phosphorus foods include cola drinks, canned and processed foods containing phosphate ingredients and chocolate.  According to the Food and Nutrition Board, over the last 20 years, phosphorus intake by Americans has increased from 10% to 15%. Part of this increase is attributed to phosphorus-containing food additives in processed food. It is very rare that people have a phosphorus deficiency; in most cases people get too much.

The important role of phosphorus binders (phosphate binders)

For people on dialysis, controlling your renal diet alone usually won’t keep your phosphorus levels in a healthy range. This is where phosphorus binders come in. Phosphorus binders prevent the body from absorbing the phosphorus from the food you eat.

Phosphorus binders help to pass excess phosphorus out of the body in the stool, reducing the amount of phosphorus that gets into the blood. Usually phosphate binders are taken within 5 to 10 minutes before or immediately after meals and snacks. Your doctor and renal dietitian will tell you when you should take your phosphate binders and discuss how many phosphate binders you need to take when you eat. Smaller meals and snacks usually require a lower number of phosphorus binders; with larger meals you may take more phosphorus binders.

People on dialysis get monthly lab results that show if their phosphorus level is in a healthy range (3.0 to 5.5 mg/dL or as close to the laboratory reference range as possible). If your phosphorus levels are not in a healthy range, you can talk with your doctor or renal dietitian and take action to change what you are eating. Your doctor or renal dietitian may also adjust your phosphorus binder prescription, if you need another brand or should be taking a different amount.

How do phosphorus binders (phosphate binders) work?

Phosphorus binders work in one of two ways. Some phosphate binders, such as Renvela® , work like a sponge and soak up the phosphates in the food so that it doesn’t get into the blood. Instead it is carried through the digestive tract and eliminated in the stool. Other phosphorus binders, such as Fosrenol®, Phoslo® and Tums® , work like a magnet. The phosphorus in the food connects to the phosphorus binder and it is carried through the digestive tract to be eliminated.

Some people may be prescribed a combination of phosphorus binders to help keep their phosphorus level in a healthy range. 

Common types of phosphorus binders (phosphate binders)

There are three common types of phosphorus binders: calcium-based phosphorus binders; aluminum-free, calcium-free phosphorus binders, aluminum-based phosphorus binders and magnesium-based phosphorus binders.

  • Calcium-based phosphorus binders have largely replaced aluminum-based binders. Calcium-based phosphate binders may also serve as calcium supplements. Calcium acetate, also called PhosLo®, is one commonly used phosphorus binder. There are many others, usually containing calcium carbonate. Tums® is a form of calcium carbonate, which can also be effective. Because most people will need to take several phosphate binders with every meal, there may be concern about dialysis patients absorbing too much calcium from these medicines, so calcium levels must be monitored. Additionally, some of the calcium from these binders is absorbed into the bloodstream and may deposit in small blood vessels, causing organ damage. 
  • Aluminum-free, calcium-free phosphorus binders, such as Renagel® (sevelamer) and Renvela (sevelamer carbonate), are another type of phosphate binders. These phosphorus binders mix with phosphorus in the intestinal tract, but do not contain aluminum or calcium, so they don’t cause problems with excess aluminum or calcium load. Chewable Fosrenol®, lanthanum carbonate, is another aluminum and calcium free binder.
  • Aluminum-based phosphorus binders have been shown to have toxic side effects that cause bone disease and damage the nervous system, therefore they are rarely prescribed as a long term phosphorus binder today. Aluminum based binders may be prescribed for short term use when phosphorus is poorly controlled and other binders are not effective.
  • Magnesium-based phosphorus binders may be used as an alternative to calcium-based phosphate binders when it is necessary for a patient to have a lower calcium intake. Magnesium levels should be monitored. This phosphate binder may be appropriate for peritoneal dialysis (PD) patients, who tend to run lower magnesium levels.

Phosphorus binders combined with a low-phosphate diet can help keep you active and healthy. Talk to your doctor or renal dietitian to find out more about phosphorus binders and which combination may work best for you.

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