People who suffer from chronic kidney disease take a variety of medications on a daily basis, among them is a type of medication called phosphate binder. What is phosphate and phosphate binder? How does it work? Why do patients with chronic kidney disease need it in the first place?
Relationship between chronic kidney disease and phosphate
Phosphate is a mineral found in our bones. Along with calcium, phosphate is needed to build strong healthy bones, as well as, keeping other parts of your body healthy. Phosphate can be found in many foods, both organic and processed.
However, too much phosphate in our blood can counterintuitively damage our bones by pulling out calcium from them, making the bones brittle and weak. High phosphate and calcium levels in the blood can also lead to dangerous calcium deposits in blood vessels, lungs, eyes, and heart. Over time this can lead to increased risk of heart attack, stroke or death.
Image credit: Vervloet, M. G., Sezer, S., Massy, Z. A., Johansson, L., Cozzolino, M., & Fouque, D. (2016). The role of phosphate in kidney disease. Nature Reviews Nephrology, 13(1), 27–38. doi:10.1038/nrneph.2016.164
Nobody would argue with the fact that the kidney is one of the important organs in our body: it regulates fluid and electrolyte, absorbs nutrients, getting rid of wastes and secrete hormones crucial to our well-being. One of the crucial roles of the kidney is regulating the level of phosphate in our blood—not too low and not too high. A normal phosphate level is 2.5 to 4.5 mg/dL. You can ask your doctor your phosphate level from your blood test if you are keen to know.
People with chronic kidney disease have a problem with abnormally high levels of phosphate, because their kidneys aren’t functioning well to properly regulate minerals in the blood such as phosphate.
Solution: phosphate binder
Phosphate binder is a general term that refers to a group of medications that when taken, can reduce the amount of phosphate ingested through food. Not every patient with chronic kidney disease would receive phosphate binder, and it is up to the doctor whether the patient will benefit from such phosphate-lowering therapy.
Here are some examples of phosphate binders:
Calcium carbonate 500mg
Calcium carbonate is the cheapest and most accessible phosphate binder. Besides functioning as a calcium supplement, calcium carbonate can also reduce phosphate content in food. For this to happen, it’s important that calcium carbonate is taken by chewing it with food or crushed it and sprinkled over the food. Calcium would then combine with the dietary phosphate in food to form insoluble calcium phosphate, which is not absorbed by the body and get excreted through faeces.
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Usual dose: 2g three times daily, chew with meal
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Available in: chewable tablets, tablet, capsules, suspension and powder
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Side effect/precautions:
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Constipation
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May interact with some medications such as alendronate and tetracycline antibiotics.
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Risk of hypercalcaemia (too much calcium in blood)
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Absorption is best under acidic gastric pH (pH 1.5). However, many patients who are of older age or receive proton pump inhibitors (E.g. omeprazole, pantoprazole, esomeprazole) have reduced gastric acid. As a result, the effect of calcium carbonate may be subpar.
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Calcium acetate
Calcium acetate is a better phosphate binder than calcium carbonate for two reasons:
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Calcium acetate has lower elemental calcium (or in plain language, it releases less calcium than calcium carbonate), hence the risk of hypercalcaemia is lower.
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Calcium acetate is effective over a wide range of gastric pH, hence its absorption is not affected even if used in patients with reduced gastric acid.
However, calcium acetate is not available in Malaysia.
Sevelamer 800mg
Image credit: MIMS Thailand
Image credit: MIMS Malaysia
Sevelamer is the first non-calcium based phosphate binder. Sevelamer reduces phosphate in the blood by exchanging chloride ions for phosphate ions in a high pH medium (pH 7), like in the small intestine. The complex resulting from sevelamer–phosphate binding is insoluble and easily excreted via the faeces.
Not only is sevelamer excellent in pulling phosphate out from the blood, it has an extra benefit: sevelamer has a beneficial effect on the lipid profile and can reduce the circulating concentration of total cholesterol and LDL (‘bad cholesterol’). The downside is that sevelamer is expensive.
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Usual dose: 1.6g three times daily with meals, can slowly reduce to 800mg three times daily
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Available in: tablets
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Side effects: nausea, vomiting, diarrhoea, indigestion, flatulence and constipation
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Interactions: Sevelamer has demonstrated interaction with ciprofloxacin (an antibiotic) and mycophenolate mofetil (an immunosuppressant for organ transplant or autoimmune disease), and therefore these drugs should be dosed separately from sevelamer. Levothyroxine should also not be taken within 2 hours of taking sevelamer.
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Available brands in Malaysia: Renvela®, Cavsamir®
Lanthanum 500mg/750mg/1000mg
Lanthanum is another excellent non-calcium based phosphate binder. It works similarly to sevelamer: by binding to dietary phosphate to form an insoluble complex that is not absorbed by the body and gets excreted from faeces.
An advantage of lanthanum is that it works regardless of the pH of the gastrointestinal system.
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Usual dose: 750mg to 3g per day. Max: 3.75g/day
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Available in: chewable tablet and powder (not available in Malaysia)
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Side effects: nausea, vomiting, swelling in hands and feets (peripheral oedema)
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Interactions: Lanthanum may increase pH in the stomach. As a result, medications which absorption can be affected by high pH, such as chloroquine, hydroxychloroquine and ketoconazole should not be taken within 2 hours of taking lanthanum. Ciprofloxacin and levothyroxine should also not be taken within 2 hours of taking lanthanum.
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Available brands in Malaysia: Fosrenol®
Low phosphate diet
Besides taking phosphate binder according to your doctor’s instructions, it’s also important that you keep an eye on the phosphate content in your diet. Phosphate can be found in foods (organic phosphate) and is naturally found in protein-rich foods such as meats, poultry, fish, nuts, beans and dairy products. Phosphate found in animal foods is absorbed more easily than phosphate found in plant foods.
Phosphate that has been added to food in the form of an additive or preservative (inorganic phosphorus) is found in foods such as fast foods, ready to eat foods, canned and bottled drinks, enhanced meats, and most processed foods. Phosphate from food additives is completely absorbed. Avoiding phosphate additives can lower your intake of phosphorus.
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References
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Schucker, J. J., & Ward, K. E. (2005). Hyperphosphatemia and phosphate binders. American Journal of Health-System Pharmacy, 62(22), 2355–2361. doi:10.2146/ajhp050198
Cover image credit: "12th March: Kidneys" by scribbletaylor is licensed under CC BY-NC 2.0
