potassium acid phosphate

Medically Reviewed on 5/15/2023

Generic Name: potassium acid phosphate

Brand Names: KPhos Original, NeutraPhos

Drug Class: Urinary Acidifying Agents

What is potassium acid phosphate, and what is it used for?

Potassium acid phosphate is a medication used to acidify the urine. Reducing the pH levels in the urine and making it more acidic helps keep the urinary calcium soluble, restores the acid-base balance and reduces rash and odor caused by ammoniacal urine. Potassium acid phosphate also increases the antibacterial activity of methenamine, an antibiotic. Potassium phosphate is a combination salt of potassium and phosphorus.

Potassium is an important electrolyte in the body that is essential for conduction of nerve impulses in heart, brain, and skeletal muscle, contraction of cardiac, skeletal and smooth muscles, carbohydrate metabolism, gastric secretion, and maintenance of normal kidney function and acid-base balance.

Phosphate is another essential electrolyte that has many vital biochemical functions in metabolic processes and enzyme reactions in almost all organs and tissues. Phosphate plays important roles in maintaining a steady state of calcium level, as a buffer in acid-base equilibrium, and in the excretion of hydrogen ion in the kidneys. Phosphate is also essential for nucleic acid structure, cell membrane structure, energy storage and transfer, cell signaling, stable mineral levels and bone mineralization.

The bacteria in the urinary tract produce urease, an enzyme that splits the urea in the urine into ammonia and carbon dioxide, increasing the alkalinity of the urine. Bacteria flourish, and struvite stones, also known as infection stones, form in an alkaline environment. Acidifying the urine with potassium acid phosphate inhibits ammonia production, growth of bacteria and formation of struvite stones. Potassium phosphate also reduces urinary calcium levels and keeps it soluble.


  • Do not use potassium acid phosphate in the following conditions:
    • High phosphate levels (hyperphosphatemia)
    • High potassium levels (hyperkalemia)
    • Infected urinary phosphate stones
    • Severe kidney impairment
  • Potassium acid phosphate increases serum potassium levels. Use with caution in patients who require regulation of serum potassium levels.
  • Potassium acid phosphate may cause a mild laxative effect, particularly in the initial period of therapy. Lower dosage appropriately if laxative effects persist or discontinue the drug, if necessary.
  • Potassium acid phosphate may precipitate the passage of pre-existing kidney stones. Caution patients of this possibility.
  • Use potassium acid phosphate with caution in the following conditions:
  • To protect against gastrointestinal injury from oral ingestion of concentrated potassium salts, advise patients to completely dissolve the tablet in the recommended amount of water before swallowing.
  • Phosphate therapy may be beneficial for rickets. However, it should be used with caution because it can increase the risk of extra-skeletal calcification.
  • Antacids containing aluminum, calcium or magnesium can prevent the absorption of phosphate. Advise patients to avoid such antacids.
  • Concurrent use with potassium-containing medications or potassium-sparing diuretics can cause hyperkalemia. Monitor potassium levels in such patients.
  • Concurrent use of salicylates can increase serum salicylate levels because salicylate excretion is reduced in acidified urine. Monitor patient’s salicylate levels to avoid salicylate toxicity.


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What are the side effects of potassium acid phosphate?

Common side effects of potassium acid phosphate include:

Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:

  • Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
  • Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
  • Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
  • Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

What are the dosages of potassium acid phosphate?


  • 500 mg


Elevated Urinary pH

  • 1-2 tabs (500-1000 mg) dissolved in 6-8 oz of water; take orally four times daily with meals and at bedtime


  • Safety and efficacy not established


  • Potassium acid phosphate can increase serum levels of potassium and phosphates, and cause severe diarrhea and muscle spasms. Severe overdose can be life-threatening and cause irregular heartbeat and seizures.
  • Overdose may be treated with discontinuation of potassium acid phosphate, correction of electrolyte levels, and other supportive measures as needed.

What drugs interact with potassium acid phosphate?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

  • Potassium acid phosphate has no listed severe interactions with other drugs.
  • Serious interactions of potassium acid phosphate include:
  • Potassium acid phosphate has moderate interactions with at least 109 different drugs.
  • Potassium acid phosphate has mild interactions with at least 29 different drugs.

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

Pregnancy and breastfeeding

  • There are no animal reproductive studies on the safety of potassium acid phosphate use during pregnancy. Use in pregnant women only if clearly necessary and benefits outweigh potential fetal risks. Use with extra caution in patients with conditions such as preeclampsia, where they are more likely to develop hyperkalemia.
  • Potassium and phosphorous are normal constituents of breastmilk. It is not known if supplementation has effect on milk production or increases the levels in milk. Use with caution in nursing mothers based on the mother’s clinical need, the developmental and health benefits of breastfeeding and the potential risks to the breastfed infant from exposure to potassium phosphate or the mother’s underlying condition.

What else should I know about potassium acid phosphate?

  • Take potassium acid phosphate exactly as prescribed.
  • Dissolve potassium acid phosphate tablet completely in recommended amount of water before swallowing. Concentrated potassium acid phosphate can cause injury to the stomach lining.
  • Inform your physician if potassium acid phosphate causes a persistent laxative effect.
  • Potassium acid phosphate may precipitate the passage of pre-existing kidney stones.
  • Avoid concurrent use of antacids or other medications containing aluminum, magnesium, or calcium because they may interfere with the absorption of phosphorus.
  • Store potassium acid phosphate safely out of reach of children.
  • In case of overdose seek medical help or contact Poison Control.

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Potassium acid phosphate is a medication used to acidify the urine. Reducing the pH levels in the urine and making it more acidic helps keep the urinary calcium soluble, restores the acid-base balance and reduces rash and odor caused by ammoniacal urine. Common side effects of potassium acid phosphate include nausea, vomiting, stomach pain, diarrhea, gas (flatulence), high blood potassium levels (hyperkalemia), high levels of phosphorus in blood (hyperphosphatemia), low blood calcium (hypocalcemia), reduced magnesium in blood, chest pain, and others. Consult your doctor if pregnant or breastfeeding.

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Medically Reviewed on 5/15/2023