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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Other
Sodium Phosphate, Dibasic, Anhydrous is an inorganic salt used primarily as a saline laxative and electrolyte replenisher. It works by increasing osmotic pressure in the intestinal lumen to promote bowel evacuation.
Name
Sodium Phosphate, Dibasic, Anhydrous
Raw Name
SODIUM PHOSPHATE, DIBASIC, ANHYDROUS
Category
Other
Drug Count
13
Variant Count
20
Last Verified
February 17, 2026
RxCUI
1872384, 1872443, 1872447, 200251, 1251241
UNII
22ADO53M6F, 593YOG76RN, 4J9FJ0HL51, O3B55K4YKI, 4846Q921YM, CI71S98N1Z, D07L04MRWI, A1Y870209Z, 660YQ98I10, 1K573LC5TV, ETJ7Z6XBU4, 451W47IQ8X, 36KCS0R750, 91D9GV0Z28
About Sodium Phosphate, Dibasic, Anhydrous
Sodium Phosphate, Dibasic, Anhydrous is an inorganic salt used primarily as a saline laxative and electrolyte replenisher. It works by increasing osmotic pressure in the intestinal lumen to promote bowel evacuation.
Detailed information about Sodium Phosphate, Dibasic, Anhydrous
References used for this content
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Sodium Phosphate, Dibasic, Anhydrous.
Sodium Phosphate, Dibasic, Anhydrous (chemical formula Na2HPO4) is a highly purified inorganic salt that serves multiple critical roles in modern clinical medicine. It belongs to a class of medications known as saline laxatives or osmotic cathartics when used for bowel cleansing, and it is also classified as an electrolyte replenisher when used to treat phosphorus deficiencies. In the pharmaceutical industry, it is frequently utilized as a buffering agent to maintain the pH stability of various injectable and oral medications.
This compound is anhydrous, meaning it contains no water of crystallization, which distinguishes it from its hydrated forms (like the heptahydrate or dodecahydrate) in terms of potency by weight and solubility characteristics. Historically, sodium phosphate salts have been used for over a century; however, their application in high-dose bowel preparations was refined in the late 20th century. The FDA has approved various formulations containing this ingredient, though it has issued several safety communications, most notably in 2008 and 2014, regarding the risk of acute phosphate nephropathy associated with high-dose oral versions used for colonoscopy preparation.
The primary therapeutic mechanism of Sodium Phosphate, Dibasic, Anhydrous is rooted in the principle of osmosis. When administered orally or rectally in pharmacological doses, the phosphate ions are only partially absorbed by the intestinal mucosa. The presence of these poorly absorbable ions creates an osmotic gradient within the small intestine and colon. This gradient draws significant volumes of water from the surrounding tissues into the intestinal lumen.
At the molecular level, the increased water content softens the stool and increases the total volume of intestinal contents. This distension of the intestinal wall triggers stretch receptors, which in turn stimulates rhythmic contractions known as peristalsis. This process results in a rapid and thorough evacuation of the bowels, typically occurring within thirty minutes to six hours depending on the route of administration. Beyond its laxative effects, the dibasic phosphate ion acts as a critical component of the body's extracellular fluid buffering system, helping to maintain the acid-base balance by reacting with strong acids or bases to prevent significant shifts in pH.
Understanding the movement of Sodium Phosphate, Dibasic, Anhydrous through the body is essential for preventing toxicity, particularly in patients with compromised organ function.
Healthcare providers typically prescribe Sodium Phosphate, Dibasic, Anhydrous for several distinct clinical indications:
Sodium Phosphate, Dibasic, Anhydrous is rarely used as a standalone ingredient and is typically found in combination with Sodium Phosphate Monobasic. Available forms include:
> Important: Only your healthcare provider can determine if Sodium Phosphate, Dibasic, Anhydrous is right for your specific condition.
The dosage of Sodium Phosphate, Dibasic, Anhydrous varies significantly based on the intended clinical outcome. For the treatment of occasional constipation using an oral solution, the typical adult dose ranges from 10 to 20 grams of phosphate salts per day, taken as a single dose or divided. For bowel cleansing prior to a medical procedure, the dosage is much higher and is usually administered in a 'split-dose' regimen. For example, a common protocol involves taking approximately 30 to 45 grams of the combined phosphate salts in the evening before the procedure, followed by a second identical dose on the morning of the procedure. When administered via a rectal enema, a single 118 mL or 133 mL bottle is standard for adults.
Pediatric use of Sodium Phosphate, Dibasic, Anhydrous must be approached with extreme caution due to the high risk of electrolyte imbalances and dehydration in smaller bodies. For children aged 5 to 11 years, the dose for constipation is typically half of the adult dose (approximately 5 to 10 grams). It is generally NOT recommended for children under the age of 2 years in any form, and oral bowel prep formulations are often restricted to patients 18 years of age and older. Always consult a pediatrician before administering any phosphate-containing product to a child.
Sodium Phosphate, Dibasic, Anhydrous is strictly contraindicated in patients with severe renal impairment (Creatinine Clearance < 30 mL/min). In patients with mild to moderate renal impairment, the dose must be significantly reduced, or an alternative laxative should be used. Failure to adjust the dose can lead to fatal hyperphosphatemia and calcium-phosphate crystal deposition in the kidneys.
While the liver does not metabolize phosphate, patients with hepatic impairment often have associated fluid balance issues or renal secondary complications. Dosage should be determined cautiously by a specialist.
Patients over the age of 65 are at a higher risk for dehydration and kidney injury. Healthcare providers often recommend lower doses and more intensive hydration protocols for this population.
When taking this medication for bowel preparation, it is vital to follow a strict hydration protocol. You should consume at least 8 ounces of clear liquid with every dose and continue drinking clear liquids (water, ginger ale, clear broth, apple juice) throughout the process to prevent dehydration. If taking the tablet form, do not crush or chew the tablets; swallow them whole. For oral solutions, mixing the medication with a cold beverage can help mask the naturally salty and bitter taste. Storage should be at room temperature (20°C to 25°C), away from moisture and direct sunlight.
If you are using this medication for a scheduled bowel prep and miss a dose, contact your healthcare provider or the endoscopy center immediately. Missing a dose may result in an incomplete cleansing of the bowel, which could lead to the cancellation of your procedure. For occasional constipation, if you miss a dose, take it as soon as you remember, unless it is nearly time for your next dose.
An overdose of Sodium Phosphate, Dibasic, Anhydrous is a medical emergency. Symptoms of an overdose include severe vomiting, abdominal pain, seizures, irregular heartbeat, and extreme thirst. In severe cases, it can lead to 'phosphate nephropathy,' a form of sudden kidney failure. If an overdose is suspected, contact a poison control center or seek emergency medical attention immediately.
> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose without medical guidance.
Because Sodium Phosphate, Dibasic, Anhydrous is designed to induce rapid bowel movements, many of its common effects are extensions of its therapeutic action. Most patients will experience:
These symptoms typically begin within 30 to 60 minutes of ingestion and should resolve once the bowel is fully evacuated.
Some patients may experience more distressing but non-emergency side effects, including:
Rare but serious reactions can occur, often in patients with underlying risk factors:
> Warning: Stop taking Sodium Phosphate, Dibasic, Anhydrous and call your doctor immediately if you experience any of these.
Sodium Phosphate, Dibasic, Anhydrous is not intended for long-term or chronic use. Chronic use of saline laxatives can lead to 'cathartic colon,' where the bowels become dependent on the medication to function. It can also cause chronic electrolyte imbalances and permanent kidney damage if used frequently over many months or years.
The FDA has issued a Black Box Warning for certain oral sodium phosphate products (such as OsmoPrep) used for bowel cleansing. The warning states that these products can cause acute phosphate nephropathy, a type of acute kidney failure. Risk factors for this condition include age over 55, dehydration, hypovolemia (low blood volume), baseline kidney disease, bowel obstruction, or active colitis. It is also more likely in patients taking certain medications like ACE inhibitors, ARBs, or NSAIDs.
Report any unusual symptoms to your healthcare provider.
Sodium Phosphate, Dibasic, Anhydrous is a potent medication that significantly alters the body's fluid and electrolyte balance. It must never be used as a routine laxative without medical supervision. The most critical safety concern is the maintenance of adequate hydration before, during, and after use. Patients must be aware that the 'diarrhea' produced by this drug is not natural and can lead to rapid, life-threatening dehydration if fluids are not aggressively replaced.
FDA Black Box Warning Summary: Rare but serious cases of acute phosphate nephropathy have been reported in patients using oral sodium phosphate products for colon cleansing. Some cases resulted in permanent impairment of renal function and required long-term hemodialysis. The risk is highest in patients with pre-existing renal disease, those of advanced age, and those taking medications that affect renal perfusion or function. Healthcare providers should ensure patients are well-hydrated and consider baseline and post-procedure lab monitoring for at-risk individuals.
For high-risk patients, healthcare providers may require the following tests before and after administration:
While the drug itself does not have sedative properties, the frequency of bowel movements and the potential for dizziness or lightheadedness due to fluid shifts make it unsafe to drive or operate heavy machinery during the active phase of the bowel prep.
Alcohol should be strictly avoided while taking Sodium Phosphate, Dibasic, Anhydrous. Alcohol is a diuretic and will significantly increase the risk of dehydration and electrolyte imbalances, potentially leading to kidney injury.
If you experience severe vomiting, signs of an allergic reaction, or a complete lack of bowel movement after taking the medication, you should stop the protocol and contact your doctor immediately. Do not attempt to 'force' the prep if your body is reacting poorly.
> Important: Discuss all your medical conditions with your healthcare provider before starting Sodium Phosphate, Dibasic, Anhydrous.
Sodium Phosphate, Dibasic, Anhydrous can significantly alter blood test results for up to 24-48 hours after use. It may cause falsely elevated phosphate levels, decreased calcium levels, and temporary elevations in BUN and creatinine. It may also interfere with certain urine tests for protein.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking.
Sodium Phosphate, Dibasic, Anhydrous must NEVER be used in the following circumstances:
In these cases, a doctor must carefully weigh the benefits against the risks:
Patients who have had a previous hypersensitivity reaction to any phosphate-containing products, including certain intravenous buffers or food additives, should use this medication with extreme caution or avoid it entirely. While true 'allergy' is rare, the physical intolerance to the high salt concentration is common.
> Important: Your healthcare provider will evaluate your complete medical history before prescribing Sodium Phosphate, Dibasic, Anhydrous.
Sodium Phosphate, Dibasic, Anhydrous is classified as FDA Pregnancy Category C. There are no adequate and well-controlled studies in pregnant women. It is unknown whether the significant fluid and electrolyte shifts caused by the medication could affect fetal development or trigger preterm labor. Most healthcare providers prefer alternative, non-osmotic laxatives or gentler PEG-based preps for pregnant patients. Use during pregnancy should only occur if the potential benefit justifies the potential risk to the fetus.
It is known that phosphate is excreted in human milk. While the amount absorbed by the infant is likely small, there is a theoretical risk that the mother's dehydration could reduce milk supply or that the infant could experience diarrhea. Nursing mothers should consult their doctor; some may choose to 'pump and dump' for 24 hours following the use of a high-dose bowel prep.
Use in children is highly restricted. The risk of 'water intoxication' or severe dehydration is much higher in pediatric patients. Oral sodium phosphate for bowel prep is generally not FDA-approved for patients under 18. For constipation, it should only be used in children over age 2 under strict medical supervision.
Patients over age 65 are at the highest risk for adverse events. Age-related declines in kidney function (even if creatinine levels look 'normal') make this population more susceptible to acute phosphate nephropathy. Furthermore, the risk of orthostatic hypotension (dizziness upon standing) increases the risk of falls during the frequent trips to the bathroom.
This is the most critical special population. In patients with any degree of kidney disease, the 'safety valve' for removing excess phosphate is broken. Even 'mild' impairment requires a different choice of laxative to avoid permanent kidney damage.
Patients with cirrhosis or ascites (fluid in the abdomen) are very sensitive to sodium intake. The high sodium content of this medication can worsen fluid retention and should be used with extreme caution.
> Important: Special populations require individualized medical assessment.
Sodium Phosphate, Dibasic, Anhydrous acts as a hypertonic saline laxative. Upon ingestion, the dibasic phosphate (HPO4^2-) and sodium (Na+) ions create a high osmotic pressure within the intestinal lumen. Because these ions are poorly absorbed, they draw water across the semi-permeable intestinal membrane via osmosis. This increases the intraluminal volume, which mechanically stimulates the stretch receptors in the enteric nervous system, triggering the defecation reflex and increasing propulsive peristalsis.
The onset of action for the oral form is typically 30 minutes to 3 hours. For the rectal enema, the onset is much faster, usually 2 to 5 minutes. The duration of the effect lasts until the osmotic gradient is neutralized or the salt is fully evacuated, usually within 6 to 12 hours. There is no evidence of the development of pharmacological tolerance with single-use applications, though chronic use can lead to a loss of normal bowel tone.
| Parameter | Value |
|---|---|
| Bioavailability | 1% - 20% (systemic absorption of phosphate) |
| Protein Binding | Negligible |
| Half-life | Variable (dependent on renal function) |
| Tmax | 1 - 3 hours (peak serum phosphate) |
| Metabolism | None (inorganic ion) |
| Excretion | Renal (>90% of absorbed dose); Fecal (unabsorbed) |
Sodium Phosphate, Dibasic, Anhydrous is categorized as a Saline Laxative and an Electrolyte Replenisher. It is related to other saline cathartics such as Magnesium Citrate and Sodium Sulfate, though it carries a unique risk profile regarding renal crystal deposition.
Medications containing this ingredient
Common questions about Sodium Phosphate, Dibasic, Anhydrous
Sodium Phosphate, Dibasic, Anhydrous is primarily used as a potent saline laxative to clear the bowels before medical procedures like colonoscopies or X-rays. It works by drawing water into the intestines, which softens the stool and stimulates bowel movements. Additionally, it is used in smaller doses to treat occasional constipation when other methods have failed. In a hospital setting, it may also be used as an electrolyte supplement to treat low phosphorus levels in the blood. It is also frequently used as a buffering agent in other medications to maintain pH stability.
The most common side effects include abdominal bloating, nausea, stomach cramping, and frequent, watery diarrhea. These effects are actually part of how the drug works to clear the bowels for a medical procedure. Some people also experience a mild headache or dizziness, which is often a sign of mild dehydration. Most of these symptoms are temporary and should resolve once the bowel cleansing process is complete. However, if you experience severe vomiting or cannot keep fluids down, you should contact your doctor immediately.
No, you should strictly avoid alcohol while taking Sodium Phosphate, Dibasic, Anhydrous. Alcohol is a diuretic, meaning it encourages your body to lose more water through urination. Since the phosphate salt already causes significant fluid loss through the bowels, adding alcohol greatly increases your risk of severe dehydration. Dehydration is a major risk factor for the serious kidney damage associated with this medication. It is best to stick to water and clear, electrolyte-rich liquids recommended by your healthcare provider.
Sodium Phosphate, Dibasic, Anhydrous is generally not the first choice for pregnant women and is classified as FDA Category C. This means that there isn't enough high-quality research in humans to guarantee its safety for the developing fetus. The significant fluid and electrolyte shifts it causes could potentially be harmful during pregnancy. Most doctors will recommend a gentler alternative, such as a PEG-based laxative, for constipation or bowel prep. Always consult your obstetrician before taking this or any other laxative while pregnant.
The timing depends on how the medication is administered. When taken as an oral solution or tablet, it typically begins to work within 30 minutes to 3 hours, though some people may take slightly longer. If used as a rectal enema, the effect is almost immediate, usually occurring within 2 to 5 minutes. Because the effects can be rapid and powerful, you should stay near a bathroom once you have taken the dose. The 'cleansing' process usually continues for several hours until the bowels are empty.
Since this medication is usually taken as a one-time dose or a short-term 'prep' for a procedure, there is no need to 'taper' off of it. However, you should not stop a bowel prep halfway through without consulting your doctor, as this will likely result in an unsuccessful colonoscopy. If you are using it for constipation and find you need it every day, you should stop and see a doctor. Long-term use can lead to 'laxative dependency,' where your bowels stop functioning normally on their own. Sudden discontinuation after chronic use might cause temporary constipation.
If you miss a dose during a bowel preparation for a medical procedure, call your doctor or the endoscopy clinic immediately for instructions. Missing a dose may mean your colon will not be clean enough for the doctor to see clearly, which could lead to a missed diagnosis or the need to repeat the entire process. If you are taking it for simple constipation, just take the dose when you remember. Do not 'double up' on doses to make up for a missed one, as this increases the risk of electrolyte toxicity. Always prioritize staying hydrated if you have to adjust your dosing schedule.
No, Sodium Phosphate, Dibasic, Anhydrous does not cause weight gain; in fact, it often causes a temporary decrease in weight due to the loss of stool and significant amounts of water. Any weight lost during a bowel prep is 'water weight' and will return once you resume normal eating and drinking. It is not a safe or effective tool for weight loss and should never be used for that purpose. Using laxatives for weight control is dangerous and can lead to serious heart and kidney problems. If you are concerned about your weight, discuss a healthy plan with your healthcare provider.
You must be very careful when taking other medications with Sodium Phosphate, Dibasic, Anhydrous. Because it causes rapid bowel movements, it can 'flush out' other oral medications before they have a chance to be absorbed by your body. Furthermore, certain drugs like ACE inhibitors, NSAIDs (like ibuprofen), and diuretics can interact with phosphate to cause serious kidney damage. You should generally take other medications at least 2 hours before or after the phosphate dose. Always provide your doctor with a full list of your current medications before starting a phosphate-based bowel prep.
Yes, Sodium Phosphate, Dibasic, Anhydrous is widely available in generic forms and is a common ingredient in many over-the-counter and prescription products. It is often sold as 'Saline Laxative' or 'Bowel Cleansing System.' Generic versions are chemically identical to brand-name products and are held to the same FDA standards for quality and potency. Using a generic version is typically more cost-effective. However, ensure that you are buying the specific formulation (oral vs. rectal) that your healthcare provider has recommended for your procedure.