Phosphates, Phosphorus

by MedlinePlus

Phosphorus is a mineral found in many foods, such as milk, cheese, dried beans, peas, colas, nuts, and peanut butter. Phosphate is the most common form of phosphorus. In the body, phosphate is the most abundant intracellular anion. It is critical for energy storage and metabolism, for the utilization of many B-complex vitamins, to buffer body fluids, for kidney excretion of hydrogen ions, for proper muscle and nerve function, and for maintaining calcium balance. Phosphorus is vital to the formation of bones and teeth, and healthy bones and soft tissues require calcium and phosphorus to grow and develop throughout life. Inadequate intake of dietary phosphate can lead to hypophosphatemia (low levels of phosphate in the blood), which can lead to long-term potentially serious complications. Conversely, excess phosphate intake can lead to hyperphosphatemia (high blood phosphorus levels), which can occur particularly in people with impaired kidney function, and can lead to potentially serious electrolyte imbalances, adverse effects, or death.

Normal levels: In adults, phosphorus makes up approximately 1% of total body weight. It is present in every cell of the body, although 85% of the body's phosphorus is found in the bones and teeth. Normal plasma concentrations range from 0.8 to 1.6 mmol/L, or 2.5 to 5 mg/dL (0.032 mmol phosphate = 1 mg). Phosphorus is absorbed more efficiently than calcium. Nearly 70 percent of phosphorus is absorbed via the intestines, although the rate depends on levels of calcium and vitamin D and the activity of parathyroid hormone (which regulates the metabolism of phosphorus and calcium).

Uses: Phosphates are used clinically to treat hypophosphatemia, hypercalcemia (high blood calcium levels), as saline laxatives, and in the management of calcium-based kidney stones. They may also be of some benefit to patients with vitamin D resistant rickets, multiple sclerosis, and diabetic ketoacidosis.

Kidney failure/dialysis: People with kidney failure and on chronic dialysis experience elevated phosphate levels, and are often prescribed phosphate binders such as Renagel, PhosLo, Tums, or calcium carbonate in order to lower blood phosphate levels.

Potassium phosphate: May be used to treat patients with low potassium levels (hypokalemia).

Synonyms

Brand Names:Fleet Enema, Fleet Phospho-soda, K-Phos MF, K-Phos Neutral, K-Phos No. 2, K-Phos Original, Neutra-Phos, Neutra-Phos-K, Uro-KP-Neutral.

Note on terminology: The term "phosphates" in this monograph refers to anhydrous sodium acid phosphate, dibasic sodium phosphate, dipotassium phosphate anhydrous, monobasic potassium acid phosphate, monobasic sodium phosphate, phosphorus, potassium phosphate, sodium biphosphate, and sodium phosphate.

Caution: Do not confuse phosphate salts with toxic substances such as organophosphates, or with tribasic sodium phosphates and tribasic potassium phosphates, which are strongly alkaline.

Evidence

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Uses based on scientific evidence

Constipation

Occasional constipation is an FDA-approved use of phosphates in adults and children, both in oral form or as an enema (for example, Fleet Enema). Phosphates are also used to restore bowel activity after surgery. Should not be used for greater than 1 week.

Hypercalcemia (high blood calcium levels)

Phosphate salts (except for calcium phosphate) are effective in the treatment of hypercalcemia. However, intravenous phosphate for treating hypercalcemia may not be recommended, due to concerns about lowering blood pressure, excessively lowering calcium levels, heart attack, tetany, or kidney failure. Sudden hypotension (low blood pressure), kidney failure, or death have been reported after phosphate infusion.

Hypophosphatemia (low blood phosphorus level)

Hypophosphatemia is an FDA-labeled use of phosphates in adults.Causes: Because phosphorus is so widespread in food, dietary phosphorus deficiency is usually seen only in cases of near total starvation. Other individuals at risk of hypophosphatemia include those with malnutrition, malabsorption, reduced kidney reabsorption of phosphates, respiratory alkalosis, excessive insulin use, some types of cancer, alcoholism, diabetics recovering from diabetic ketoacidosis, critically ill hospitalized patients, and anorexic patients on refeeding regimens that are high in calories but too low in phosphorus.Effects: Hypophosphatemia may cause muscle weakness, bone pain, rickets (in children), osteomalacia (in adults), anemia, increased susceptibility to infection, loss of appetite, numbness and tingling of the extremities, and difficulty walking. Severe hypophosphatemia may result in breathing difficulties (respiratory failure), rhabdomyolysis, congestive heart failure, or death. Hypophosphatemia causes an increase in intestinal calcium absorption and increased calcium in the blood, which can inhibit formation of new bone and can potentially lead to a greater risk of kidney stones. Vitamin D3 and its metabolites influence phosphate absorption from the gut and also affect kidney tubular reabsorption of phosphate.Management: Taking sodium phosphate or potassium phosphate is effective for preventing and treating most causes of hypophosphatemia, and should be directed under medical supervision. The underlying cause of the hypophosphatemia should be identified and corrected whenever possible. Oral phosphate therapy is generally used in milder cases, and rectal or dialysis-based administration is available. Intravenous therapy with potassium phosphate may be used in severe cases or in patients who cannot receive other forms of phosphates, and should be administered in dilute form and slowly in order to avoid serious potential complications such as abnormal heart rhythms. Patients with hypophosphatemia often also have hypomagnesemia (low magnesium levels), and therefore magnesium levels should be measured. Phosphates should be considered to prevent hypophosphatemia in patients receiving tube feeds or total parenteral nutrition (TPN), and in those with chronic kidney phosphate-wasting.

Kidney stones (calcium oxalate stones)

Kidney stones (nephrolithiasis) are an FDA-labeled use of phosphates in adults. Taking potassium and sodium phosphate salts orally may help prevent kidney stones in patients with hypercalciuria (high urine calcium levels), and in patients with kidney stones made of calcium oxalate. However, phosphate administration when stones are composed of magnesium-ammonium-phosphate or calcium phosphate may increase the rate of stone formation.

Laxative/bowel preparation for procedures

This is an FDA-labeled use of phosphates in adults and children. Sodium phosphate taken orally or as an enema may be used for bowel cleansing in preparation for surgery, imaging studies, or endoscopy (for example, Fleet Phospho-soda, Fleet Enema). Phosphates appear to increase peristalsis and cause an influx of fluids into the intestine via osmotic action. Aluminum phosphate is used orally to neutralize gastric acid.

Refeeding syndrome prevention

After periods of severe malnutrition or starvation (for example, anorexia nervosa), intravenous phosphate may be necessary in order to prevent a refeeding syndrome. Phosphate levels should be closely monitored in such patients.

Burns

Patients with serious burns may lose phosphate, and replacement may be necessary.

Diabetic ketoacidosis

The use of prophylactic phosphate therapy in diabetic ketoacidosis is controversial and may be considered, particularly in cases of low phosphate levels.

Hypercalciuria (high urine calcium levels)

Long term, slow release neutral potassium phosphate has been shown to reduce calcium excretion in subjects with absorptive hypercalciuria, and appears to be well tolerated. This use of phosphates may be considered to prevent kidney stone formation.

Hyperparathyroidism

This use of phosphates has not been clearly demonstrated as being beneficial in scientific studies.

Total parenteral nutrition (TPN)

Critically ill patients receiving intravenous feedings often have low phosphate levels. Phosphate levels should be closely monitored in such patients, particularly if kidney function is impaired. Inorganic phosphates avoid incompatibility with calcium in TPN solutions. Addition of phosphate to TPN solutions should be under the supervision of a licensed nutritionist.

Vitamin D resistant rickets

This use of phosphates has not been clearly demonstrated as being beneficial in scientific studies.

Exercise performance

Several studies report that taking phosphates orally does not improve exercise performance.

Uses based on tradition or theory

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Cancer, clear cell carcinoma, depression, hypophosphatemic encephalopathy, multiple sclerosis, radioactive (thallium) parathyroid scanning enhancement, uterine papillary serous carcinoma.

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