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Sodium phosphate: Drug information

Sodium phosphate: Drug information
(For additional information see "Sodium phosphate: Patient drug information" and see "Sodium phosphate: Pediatric drug information")

For abbreviations, symbols, and age group definitions used in Lexicomp (show table)
ALERT: US Boxed Warning
Nephropathy (tablet):

There have been rare but serious reports of acute phosphate nephropathy in patients who received oral sodium phosphate products for colon cleansing prior to colonoscopy. Some cases have resulted in permanent impairment of renal function and some patients required long-term dialysis. While some cases have occurred in patients without identifiable risk factors, patients at increased risk of acute phosphate nephropathy may include those with increased age, hypovolemia, increased bowel transit time (such as bowel obstruction), active colitis, or baseline kidney disease, and those using medicines that affect renal perfusion or function (such as diuretics, angiotensin-converting enzyme [ACE] inhibitors, angiotensin receptor blockers, and possibly nonsteroidal anti-inflammatory drugs [NSAIDs]).

Advise patients of the importance of following the recommended split dosage regimen and the importance of adequate hydration before, during, and after use of oral sodium phosphate products. Avoid additional sodium phosphate–based purgative or enema products.

Brand Names: US
  • Fleet Enema Extra [OTC];
  • Fleet Enema [OTC];
  • Fleet Pedia-Lax Enema [OTC];
  • GoodSense Enema [OTC];
  • LaCrosse Complete [OTC];
  • OsmoPrep
Brand Names: Canada
  • Fleet Enema
Pharmacologic Category
  • Cathartic;
  • Electrolyte Supplement, Parenteral;
  • Laxative, Bowel Evacuant
Dosing: Adult

Note: If phosphate repletion is required and a phosphate product is not available at your institution, consider the use of sodium glycerophosphate pentahydrate (Glycophos) as a suitable substitute. Concentration and dosing are different from FDA-approved products; use caution when switching between products. Refer to Sodium Glycerophosphate Pentahydrate monograph.

Caution: With orders for IV phosphate, there is considerable confusion associated with the use of millimoles (mmol) versus milliequivalents (mEq) to express the phosphate requirement. The most reliable method of ordering IV phosphate is by millimoles, then specifying the potassium or sodium salt. Intravenous doses listed as mmol of phosphate.

Acute treatment of hypophosphatemia

Acute treatment of hypophosphatemia: IV: It is difficult to provide concrete guidelines for the treatment of severe hypophosphatemia because the extent of total body deficits and response to therapy are difficult to predict. Aggressive doses of phosphate may result in a transient serum elevation followed by redistribution into intracellular compartments or bone tissue. It is recommended that repletion of severe hypophosphatemia be done IV because large doses of oral phosphate may cause diarrhea and intestinal absorption may be unreliable. Intermittent IV infusion should be reserved for severe depletion situations; requires continuous cardiac monitoring. Guidelines differ based on degree of illness, need/use of TPN, and severity of hypophosphatemia. If hypokalemia exists (some clinicians recommend threshold of <4 mmol/L), consider phosphate replacement strategy with potassium (eg, potassium phosphates). Obese patients and/or severe renal impairment were excluded from phosphate supplement trials. Note: 1 mmol phosphate = 31 mg phosphorus; 1 mg phosphorus = 0.032 mmol phosphate.

Critically ill adult patients receiving concurrent enteral/parenteral nutrition (Brown 2006; Clark 1995): Note: Round doses to the nearest 7.5 mmol for ease of preparation. If administering with phosphate-containing parenteral nutrition, do not exceed 15 mmol/L within parenteral nutrition. May use adjusted body weight for patients weighing >130% of ideal body weight (and BMI <40 kg/m2) by using [IBW + 0.25 (ABW-IBW)]:

Low dose, serum phosphorus level 2.3 to 3 mg/dL (0.74 to 0.96 mmol/L): 0.16 to 0.32 mmol/kg over 4 to 6 hours.

Intermediate dose, serum phosphorus level 1.6 to 2.2 mg/dL (0.51 to 0.71 mmol/L): 0.32 to 0.64 mmol/kg over 4 to 6 hours.

High dose, serum phosphorus <1.5 mg/dL (<0.5 mmol/L): 0.64 to 1 mmol/kg over 8 to 12 hours.

Bowel cleansing prior to colonoscopy

Bowel cleansing prior to colonoscopy: Oral tablets:

Note: Do not use additional laxatives, especially other sodium phosphate products. A minimum of 7 days should elapse prior to repeat use.

OsmoPrep: A total of 32 tablets and 2 quarts of clear liquids (8 ounces of clear liquids with each dose) divided as follows:

Evening before colonoscopy: 4 tablets every 15 minutes for 5 doses (total of 20 tablets).

3 to 5 hours prior to colonoscopy: 4 tablets every 15 minutes for 3 doses (total of 12 tablets).

Laxative

Laxative (Fleet): Rectal: Contents of one 4.5 oz enema as a single dose.

Parenteral nutrition

Parenteral nutrition: IV: 10 to 15 mmol/1,000 kcal (Hicks 2001) or 20 to 40 mmol/24 hours (Mirtallo 2004 [ASPEN guidelines]).

Dosing: Kidney Impairment: Adult

IV: There are no specific dosage adjustments provided in the manufacturer's labeling. However, because ionized inorganic phosphate is excreted by the kidneys, use with caution in patients with impaired renal function.

Oral: There are no specific dosage adjustments provided in the manufacturer's labeling for the oral tablets. However, because ionized inorganic phosphate is excreted by the kidneys, use with caution when used for bowel cleansing prior to colonoscopy, particularly in patients with severe impairment (CrCl <30 mL/minute).

Rectal: There are no dosage adjustments provided in the manufacturer's labeling. However, because ionized inorganic phosphate is excreted by the kidneys, use with caution in patients with impaired renal function.

Dosing: Hepatic Impairment: Adult

There are no dosage adjustments provided in the manufacturer's labeling.

Dosing: Pediatric

(For additional information see "Sodium phosphate: Pediatric drug information")

Note: If phosphate repletion is required and a phosphate product is not available at your institution, consider the use of sodium glycerophosphate pentahydrate (Glycophos) as a suitable substitute. Concentration and dosing are different from FDA approved products; use caution when switching between products. Refer to sodium glycerophosphate pentahydrate monograph.

Caution: With orders for IV phosphate, there is considerable confusion associated with the use of millimoles (mmol) versus milliequivalents (mEq) to express the phosphate requirement. The most reliable method of ordering IV phosphate is by millimoles, then specifying the potassium or sodium salt. Note: Consider the contribution of sodium when determining the appropriate phosphate replacement. 1 mmol phosphate = 31 mg phosphorus; 1 mg phosphorus = 0.032 mmol phosphate.

Hypophosphatemia, acute: Repletion of severe hypophosphatemia should be treated with IV phosphate since large doses of oral phosphate may cause diarrhea and intestinal absorption may be unreliable. Guidelines differ based on degree of illness, need/use of TPN, and severity of hypophosphatemia. If hypokalemia exists, consider phosphate replacement strategy with potassium (eg, potassium phosphates).

IV doses may be incorporated into the patient's maintenance IV fluids; intermittent IV infusion should be reserved for severe depletion situations. Note: Doses listed as mmol of phosphate.

Children and Adolescents: Note: The regimens below have only been studied in adult patients; however, many institutions have used them in children safely and successfully (ASPEN [Corkins 2015]). Patients with severe renal impairment were excluded from adult phosphate supplement trials.

General replacement guidelines (including ICU patients) (Kraft 2005): Note: The initial dose may be increased by 25% to 50% if the patient is symptomatic secondary to hypophosphatemia and lowered by 25% to 50% if the patient is hypercalcemic (Lentz 1978).

Low dose: IV: 0.08 to 0.16 mmol/kg over 4 to 6 hours; use if serum phosphorus level 2.3 to 2.7 mg/dL.

Intermediate dose: IV: 0.16 to 0.32 mmol/kg over 4 to 6 hours; use if serum phosphorus level 1.5 to 2.2 mg/dL.

High dose: IV: 0.32 to 0.64 mmol/kg over 4 to 6 hours; use if serum phosphorus <1.5 mg/dL.

Patients receiving TPN (Clark 1995):

Low dose: IV: 0.16 mmol/kg over 4 to 6 hours; use if serum phosphorus level 2.3 to 3 mg/dL (0.73 to 0.96 mmol/L).

Intermediate dose: IV: 0.32 mmol/kg over 4 to 6 hours; use if serum phosphorus level 1.6 to 2.2 mg/dL (0.51 to 0.72 mmol/L).

High dose: IV: 0.64 mmol/kg over 8 to 12 hours; use if serum phosphorus <1.5 mg/dL (<0.5 mmol/L).

Critically ill adult trauma patients receiving TPN (Brown 2006):

Low dose: IV: 0.32 mmol/kg over 4 to 6 hours; use if serum phosphorus level 2.3 to 3 mg/dL (0.73 to 0.96 mmol/L).

Intermediate dose: IV: 0.64 mmol/kg over 4 to 6 hours; use if serum phosphorus level 1.6 to 2.2 mg/dL (0.51 to 0.72 mmol/L).

High dose: IV: 1 mmol/kg over 8 to 12 hours; use if serum phosphorus <1.5 mg/dL (<0.5 mmol/L).

Parenteral nutrition, maintenance phosphorus requirement (ASPEN [Mirtallo 2004]):

Infants and Children ≤50 kg: IV: 0.5 to 2 mmol/kg/day of phosphorus as an additive to parenteral nutrition solution.

Children >50 kg and Adolescents: IV: 10 to 40 mmol/day of phosphorus as an additive to parenteral nutrition solution.

Constipation or fecal impaction:

Note: Do not use in children <2 years of age; FDA warns against use due to risk of severe dehydration and serum electrolyte abnormalities leading to serious complications such as acute kidney injury, arrhythmias, and death (FDA Drug Safety Communication 2014). Due to tolerability and route of administration, enemas are generally reserved for severe constipation (Paul 2021).

Pediatric enema: 59 mL sodium phosphates delivered dose in 66 mL bottle (eg, Pedia-Lax enema):

Children 2 to <5 years: Rectal: 29 mL (½ of the contents of one 59 mL pediatric enema) as a single dose; may repeat once; manufacturer recommends no more than one enema in 24 hours (Loening-Baucke 1993; manufacturer's labeling).

Children 5 to <12 years: Rectal: 59 mL (the contents of one pediatric enema) as a single dose; may repeat once; manufacturer recommends no more than one enema in 24 hours (Loening-Baucke 1993; manufacturer's labeling).

Adult enema: 118 mL sodium phosphates delivered dose in 133 mL bottle (eg, Fleet enema):

Children ≥12 years and Adolescents: Rectal: Administer 118 mL (the contents of one adult enema) as a single dose; may repeat once; manufacturer recommends no more than one enema in 24 hours (Loening-Baucke 1993; manufacturer's labeling).

Dosing: Kidney Impairment: Pediatric

IV: There are no specific dosage adjustments provided in the manufacturer's labeling. However, because ionized inorganic phosphate is excreted by the kidneys, use with caution in patients with impaired kidney function.

Rectal: There are no dosage adjustments provided in the manufacturer's labeling. However, because ionized inorganic phosphate is excreted by the kidneys, use with caution in patients with impaired kidney function.

Dosing: Hepatic Impairment: Pediatric

There are no dosage adjustments provided in manufacturer's labeling. Use with caution, especially in clinical states associated with edema and sodium retention including liver disease.

Dosing: Older Adult

Use with caution due to increased risk of renal impairment in the elderly. Refer to adult dosing.

Dosage Forms: US

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Solution, Intravenous:

Generic: Phosphate 15 Mmol and sodium 20 mEq per 5 mL (5 mL); Phosphate 45 Mmol and sodium 60 mEq per 15 mL (15 mL); Phosphate 150 Mmol and sodium 200 mEq per 50 mL (50 mL)

Solution, rectal [enema]:

Fleet Enema: Monobasic sodium phosphate monohydrate 19 g and dibasic sodium phosphate heptahydrate 7 g per 118 mL delivered dose (133 mL) [contains sodium 4.4 g/118 mL]

Fleet Enema Extra: Monobasic sodium phosphate monohydrate 19 g and dibasic sodium phosphate heptahydrate 7 g per 197 mL delivered dose (230 mL) [contains sodium 4.4 g/197 mL]

Fleet Pedia-Lax™ Enema: Monobasic sodium phosphate monohydrate 9.5 g and dibasic sodium phosphate heptahydrate 3.5 g per 59 mL delivered dose (66 mL) [contains sodium 2.2 g/59 mL]

GoodSense Enema: Monobasic sodium phosphate monohydrate 19 g and dibasic sodium phosphate 7 g per 118 mL delivered dose (133 mL) [contains benzalkonium chloride]

LaCrosse Complete: Monobasic sodium phosphate monohydrate 19 g and dibasic sodium phosphate heptahydrate 7 g per 118 mL delivered dose (133 mL) [contains sodium 4.4 g/118 mL]

Generic: Monobasic sodium phosphate monohydrate 19 g and dibasic sodium phosphate heptahydrate 7 g per 118 mL delivered dose (133 mL)

Tablet, oral [scored]:

OsmoPrep: Monobasic sodium phosphate monohydrate 1.102 g and dibasic sodium phosphate anhydrous 0.398 g [sodium phosphate 1.5 g per tablet; gluten free]

Generic Equivalent Available: US

Yes: Enema, injection, oral solution

Dosage Forms Considerations

Sodium 4 mEq is equivalent to sodium 92 mg

Phosphorous 3 mmol is equivalent to phosphorus 93 mg

Medication Guide and/or Vaccine Information Statement (VIS)

An FDA-approved patient medication guide, which is available with the product information and as follows, must be dispensed with this medication:

OsmoPrep:https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/021892s014lbl.pdf#page=13

Administration: Adult

IV: Administer by intermittent IV infusion; do not administer IV push. Must be diluted prior to parenteral administration. In general, the dose, concentration of infusion, and rate of administration may be dependent on patient condition/indication and specific institution policy. For patients with severe symptomatic hypophosphatemia (ie, <1.5 mg/dL), may administer at rates up to 15 mmol/hour (Charron 2003). In patients with renal dysfunction and/or less severe hypophosphatemia, slower administration rates (eg, over 4 to 6 hours) or oral repletion is recommended.

Bowel cleansing (oral tablets): A clear liquid diet should be used prior to and during tablet administration. Have patient drink 8 ounces of clear liquids with each dose of sodium phosphate; have patient rehydrate before and after colonoscopy. Clear liquids may include water, flavored water, pulp-free lemonade, ginger ale, or apple juice; avoid alcohol, milk, purple or red colored liquids, and pulp-containing foods/liquids. Avoid use of other laxatives during the bowel cleansing and administration of other oral medications within 1 hour before or after each bowel-cleansing tablet. Refer to the manufacturer's labeling and/or the medication guide for additional administration instructions.

Administration: Pediatric

Parenteral: Note: In general, the dose, concentration of infusion, and rate of administration may be dependent on patient condition and specific institution policy.

Intermittent IV infusion: Must be diluted in appropriate IV solution and volume prior to administration and infused slowly to avoid toxicity; in pediatric patients, suggested maximum concentrations used by some centers: Peripheral line: 0.05 mmol/mL; Central line: 0.12 mmol/mL (maximum concentrations were determined with consideration for maximum sodium concentration). Infusion of doses over 4 to 6 hours for mild/moderate hypophosphatemia or 8 to 12 hours for severe hypophosphatemia has been recommended (Brown 2006; Clark 1995; Lentz 1978). Faster administration rates (eg, 30 mmol over 2 hours, 45 mmol over 3 hours) have been reported in adults with moderate to severe hypophosphatemia without adverse effects (Charron 2003); major adverse effects have been reported in adults administered doses ≥50 mmol infused over ≤3 hours (Lentz 1978). Do not infuse with calcium-containing IV fluids.

Parenteral nutrition solution: Calcium-phosphate stability in parenteral nutrition solutions is dependent upon the pH of the solution, temperature, and relative concentration of each ion. The pH of the solution is primarily dependent upon the amino acid concentration. The higher the percentage of amino acids the lower the pH, the more soluble the calcium and phosphate. Individual commercially available amino acid solutions vary significantly with respect to pH lowering potential and subsequent calcium phosphate compatibility; consult product specific labeling for additional information.

Rectal: For administration of 29 mL (one-half of a 59 mL pediatric enema), unscrew cap and remove 30 mL of liquid; replace cap. For administration of full pediatric or adult enema, no manipulation is required. Administer with patient lying on left side and knees bent or with patient kneeling and head and chest leaning forward until left side of face is resting comfortably. Gently insert enema tip into rectum with a slight side-to-side movement and tip pointing toward the navel; have patient bear down. Squeeze the bottle until dose is administered; gently remove enema tip from rectum.

Use: Labeled Indications

IV: Source of phosphate in large volume IV fluids and parenteral nutrition; treatment and prevention of hypophosphatemia.

Oral tablets: Bowel cleansing prior to colonoscopy.

Rectal: Short-term treatment of constipation.

Medication Safety Issues
Sound-alike/look-alike issues:

Fleet enemas may be confused with a saline enema (mixture of sodium chloride and water)

Visicol [DSC] may be confused with Vicodin

Pediatric patients: High-risk medication:

KIDs List: Sodium phosphate rectal enema, when used in infants and children <2 years of age, is identified on the Key Potentially Inappropriate Drugs in Pediatrics (KIDs) list and should be avoided due to risk of electrolyte abnormalities, acute kidney injury, arrhythmia, and death (strong recommendation; high quality of evidence) (PPA [Meyers 2020]).

Administration issues:

Enemas are available in pediatric and adult sizes; prescribe by "volume" not by "bottle."

Because inorganic phosphate exists as monobasic and dibasic anions, with the mixture of valences dependent on pH, ordering by mEq amounts is unreliable and may lead to large dosing errors. In addition, IV phosphate is available in the sodium and potassium salt; therefore, the content of these cations must be considered when ordering phosphate. The most reliable method of ordering IV phosphate is by millimoles, then specifying the potassium or sodium salt.

Adverse Reactions

The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.

>10%:

Gastrointestinal: Bloating (31%), nausea (26%), abdominal pain (23%)

Endocrine & metabolic: Hyperphosphatemia (≤96%), hypokalemia (on colonoscopy day; 18% to 22%)

1% to 10%: Gastrointestinal: Vomiting (4%), aphthous stomatitis (3%)

Postmarketing and/or case reports: Anaphylaxis, angioedema, bronchospasm, calcium nephrolithiasis, cardiac arrhythmia, dysphagia, dyspnea, facial edema, hypernatremia, hypersensitivity reaction, hypocalcemia, increased blood urea nitrogen, increased serum creatinine, lip edema, paresthesia, pharyngeal edema, pruritus, renal disease (acute phosphate), renal failure syndrome, renal insufficiency, renal tubular necrosis, seizure, skin rash, tongue edema, urticaria

Contraindications

Hypersensitivity to sodium phosphate salts or any component of the formulation; additional contraindications vary by product:

IV preparation: Diseases with hyperphosphatemia, hypocalcemia, or hypernatremia.

Tablets: Acute phosphate nephropathy, bowel obstruction, bowel perforation, gastric bypass or stapling surgery, toxic colitis, toxic megacolon.

Warnings/Precautions

Concerns related to adverse effects:

• Hypersensitivity: Serious reactions, including anaphylaxis, have been reported.

• Nephropathy: [US Boxed Warning]: Acute phosphate nephropathy (APN) has been reported (rarely) with use of oral products as a colon cleanser prior to colonoscopy. Some cases have resulted in permanent renal impairment (some requiring dialysis). Risk factors for acute phosphate nephropathy may include increased age (>55 years of age), preexisting renal dysfunction, bowel obstruction, active colitis, or dehydration, and the use of medicines that affect renal perfusion or function (eg, ACE inhibitors, angiotensin receptor blockers, diuretics, and possibly NSAIDs), although some cases have been reported in patients without apparent risk factors. Advise patients of the importance of following the recommended split dosage regimen and the importance of adequate hydration before, during and after use of oral sodium phosphate products. Avoid additional sodium phosphate-based purgative or enema products. Obtain baseline and postprocedure labs in patients at risk of nephropathy; consider hospitalization and intravenous hydration during bowel cleansing for patients unable to hydrate themselves (eg, frail patients). Use is contraindicated in patients with acute phosphate nephropathy. APN has also been reported (rarely) following the use of sodium phosphate enemas. This has been primarily observed in elderly patients with and without preexisting renal impairment and with those receiving standard or doses exceeding usual doses (Ori 2012).

• QT prolongation: Prolongation of the QT interval has been reported (associated with hypokalemia, hypocalcemia).

Disease-related concerns:

• Cardiovascular: Use caution in patients with heart failure (contraindicated with enema products), unstable angina, history of myocardial infarction, arrhythmia, cardiomyopathy; use caution in patients with or at risk for arrhythmias (eg, cardiomyopathy, prolonged QT interval, history of uncontrolled arrhythmias, recent MI) or with concurrent use of other QT-prolonging medications; pre-/postdose ECGs and lab tests should be considered in high-risk patients.

• Electrolyte disturbances: Fluid and electrolyte disturbances may occur. Use with caution in patients with preexisting electrolyte imbalances, dehydration, or risk of electrolyte disturbance (hypocalcemia, hyperphosphatemia, hypernatremia); obtain baseline and postprocedure labs in high-risk patients. Correct dehydration prior to using for bowel preparations.

• GI disorders: Use caution in patients with any of the following: Gastric retention or hypomotility, ileus, severe, chronic constipation, or severe active ulcerative colitis. Use is contraindicated in patients with bowel obstruction (including pseudo) or perforation, congenital megacolon, gastric bypass or bariatric surgery, toxic colitis, or toxic megacolon.

• Inflammatory bowel disease: Use with caution in patients with an acute exacerbation of chronic inflammatory bowel disease; phosphate absorption may be increased. Oral sodium phosphate products may induce colonic aphthous ulceration, which should be considered when interpreting colonoscopic findings in patients with inflammatory bowel disease.

• Renal impairment: Use with caution in patients with renal impairment; patients may be at risk for sodium retention and edema. Close monitoring required to avoid hyperphosphatemia. Obtain baseline and postprocedure labs in patients with renal impairment.

• Seizure disorder: Use with caution in patients with a history of seizures, those at higher risk of seizures or on medication that lowers seizure threshold; obtain baseline and postprocedure labs in high-risk patients.

Special populations:

• Bulimia nervosa patients: Laxatives and purgatives have the potential for abuse by bulimia nervosa patients.

• Debilitated patients: Use with caution in debilitated patients; consider each patient's ability to hydrate properly.

• Older adult: Use with caution in elderly patients; ensure they are able to hydrate themselves if using for bowel preparation.

• Impaired gag reflex: Use with caution in patients with impaired gag reflex and those prone to regurgitation or aspiration.

Dosage form specific issues:

• Aluminum: The parenteral product may contain aluminum; toxic aluminum concentrations may be seen with high doses, prolonged use, or renal dysfunction. Premature neonates are at higher risk due to immature renal function and aluminum intake from other parenteral sources. Parenteral aluminum exposure of >4 to 5 mcg/kg/day is associated with CNS and bone toxicity; tissue loading may occur at lower doses (Federal Register 2002). See manufacturer's labeling.

• Benzyl alcohol and derivatives: Some dosage forms may contain sodium benzoate/benzoic acid; benzoic acid (benzoate) is a metabolite of benzyl alcohol; large amounts of benzyl alcohol (≥99 mg/kg/day) have been associated with a potentially fatal toxicity ("gasping syndrome") in neonates; the "gasping syndrome" consists of metabolic acidosis, respiratory distress, gasping respirations, CNS dysfunction (including convulsions, intracranial hemorrhage), hypotension, and cardiovascular collapse (AAP ["Inactive" 1997]; CDC 1982); some data suggests that benzoate displaces bilirubin from protein binding sites (Ahlfors 2001); avoid or use dosage forms containing benzyl alcohol derivative with caution in neonates. See manufacturer's labeling.

• Enemas: Available in pediatric and adult sizes; prescribe by "volume" not by "bottle."

Other warnings/precautions:

• Bowel evacuation: Appropriate use: If using as a bowel evacuant, correct electrolyte abnormalities before administration. Ensure adequate clear liquid intake prior to and during bowel evacuation regimens; inadequate fluid intake may lead to excessive fluid loss and hypovolemia. Other oral medications may not be well absorbed when given during bowel evacuation because of rapid intestinal peristalsis.

• Constipation: Appropriate use: Rare but potentially serious adverse effects (including death) may occur when exceeding recommended doses of over-the-counter (OTC) sodium phosphate preparations to treat constipation. Severe dehydration and alterations in serum electrolytes (eg, calcium, sodium, phosphate) leading to renal/cardiac adverse effects have been reported, mostly when single maximum doses were exceeded or when more than 1 dose was taken per day. Patients should be advised to adhere to the product labeling and not exceed maximum recommended doses. Rectal preparations should never be administered to children younger than 2 years of age (FDA Drug Safety Communication 2014).

Metabolism/Transport Effects

None known.

Drug Interactions

Note: Interacting drugs may not be individually listed below if they are part of a group interaction (eg, individual drugs within “CYP3A4 Inducers [Strong]” are NOT listed). For a complete list of drug interactions by individual drug name and detailed management recommendations, use the Lexicomp drug interactions program by clicking on the “Launch drug interactions program” link above.

Angiotensin II Receptor Blockers: May enhance the nephrotoxic effect of Sodium Phosphates. Specifically, the risk of acute phosphate nephropathy may be enhanced. Management: Consider avoiding this combination by temporarily suspending treatment with ARBs, or seeking alternatives to oral sodium phosphate bowel preparation. If the combination cannot be avoided, maintain adequate hydration and monitor renal function closely. Risk D: Consider therapy modification

Angiotensin-Converting Enzyme Inhibitors: May enhance the nephrotoxic effect of Sodium Phosphates. Specifically, the risk of acute phosphate nephropathy may be enhanced. Management: Consider avoiding this combination by temporarily suspending treatment with ACEIs, or seeking alternatives to oral sodium phosphate bowel preparation. If the combination cannot be avoided, maintain adequate hydration and monitor renal function closely. Risk D: Consider therapy modification

Antacids: May decrease the absorption of Phosphate Supplements. Management: This applies only to oral phosphate administration. Separating administration of oral phosphate supplements from antacid administration by as long as possible may minimize the interaction. Risk D: Consider therapy modification

Burosumab: Phosphate Supplements may enhance the adverse/toxic effect of Burosumab. Risk X: Avoid combination

Calcium Salts: May decrease the absorption of Phosphate Supplements. Management: This applies only to oral phosphate and calcium administration. Administering oral phosphate supplements as far apart from the administration of an oral calcium salt as possible may be able to minimize the significance of the interaction. Risk D: Consider therapy modification

Diuretics: May enhance the nephrotoxic effect of Sodium Phosphates. Specifically, the risk of acute phosphate nephropathy may be enhanced. Management: Consider avoiding this combination by temporarily suspending treatment with diuretics, or seeking alternatives to oral sodium phosphate bowel preparation. If the combination cannot be avoided, hydrate adequately and monitor fluid and renal status. Risk D: Consider therapy modification

Erdafitinib: Serum Phosphate Level-Altering Agents may diminish the therapeutic effect of Erdafitinib. Management: Avoid coadministration of serum phosphate level-altering agents with erdafitinib before initial dose increase period based on serum phosphate levels (Days 14 to 21). Risk D: Consider therapy modification

Iron Preparations: May decrease the absorption of Phosphate Supplements. Management: Administer oral phosphate supplements as far apart from the administration of an oral iron preparation as possible to minimize the significance of this interaction. Risk D: Consider therapy modification

Magnesium Salts: May decrease the serum concentration of Phosphate Supplements. Management: Administer oral phosphate supplements as far apart from the administration of an oral magnesium salt as possible to minimize the significance of this interaction. Risk D: Consider therapy modification

Multivitamins/Minerals (with ADEK, Folate, Iron): May decrease the serum concentration of Phosphate Supplements. Management: Administer oral phosphate supplements as far apart from the administration of an iron-containing oral multivitamin as possible to minimize the significance of this interaction. Risk D: Consider therapy modification

Nonsteroidal Anti-Inflammatory Agents: Sodium Phosphates may enhance the nephrotoxic effect of Nonsteroidal Anti-Inflammatory Agents. Specifically, the risk of acute phosphate nephropathy may be enhanced. Management: Consider avoiding this combination by temporarily suspending treatment with NSAIDs, or seeking alternatives to oral sodium phosphate bowel preparation. If the combination cannot be avoided, maintain adequate hydration and monitor renal function closely. Risk D: Consider therapy modification

Sucralfate: May decrease the absorption of Phosphate Supplements. Management: This applies only to oral phosphate administration. Administering oral phosphate supplements at least 2 hours before sucralfate may reduce the significance of the interaction. Risk D: Consider therapy modification

Tricyclic Antidepressants: May enhance the adverse/toxic effect of Sodium Phosphates. Specifically, the risk of seizure and/or loss of consciousness may be increased in patients with significant sodium phosphate induced fluid/electrolyte abnormalities. Risk C: Monitor therapy

Pregnancy Considerations

Animal reproduction studies have not been conducted.

Breastfeeding Considerations

Phosphorus, sodium, and potassium are normal constituents of human milk. According to the manufacturer, the decision to continue or discontinue breastfeeding during therapy should take into account the risk of infant exposure, the benefits of breastfeeding to the infant, and benefits of treatment to the mother.

Dietary Considerations

Some products may contain phenylalanine and/or sodium.

Phosphorous:

Dietary adequate intake (AI) (IOM 1997):

1 to 6 months: 3.2 mmol/day (100 mg/day).

7 to 12 months: 8.9 mmol/day (275 mg/day).

Dietary recommended daily allowance (RDA) (IOM 1997):

1 to 3 years: 14.8 mmol/day (460 mg/day).

4 to 8 years: 16.1 mmol/day (500 mg/day).

9 to 18 years: 40.3 mmol/day (1,250 mg/day).

Monitoring Parameters

IV: Serum calcium, sodium and phosphorus levels; renal function; after IV phosphate repletion, repeat serum phosphorus level should be checked 2 to 4 hours later.

Oral: Bowel cleansing: Baseline and postprocedure labs (electrolytes, calcium, phosphorus, BUN, creatinine) in patients with renal impairment or who are taking medications or with conditions that increase the risk of fluid and electrolyte abnormalities, seizures, arrhythmias, or renal impairment; ECG in patients with risks for prolonged QT or arrhythmias. Ensure euvolemia before initiating bowel preparation.

Reference Range

Note: Reference ranges may vary depending on the laboratory.

Serum calcium: 8.4 to 10.2 mg/dL.

Serum phosphorus: Both low and high ends of the normal range are higher in children than in adults.

Infants: 4.5 to 7.5 mg/dL (1.45 to 2.42 mmol/L).

Children: ~4.0 to 6.0 mg/dL (1.29 to 1.94 mmol/L).

Adults: 2.5 to 4.5 mg/dL (0.81 to 1.45 mmol/L).

Mechanism of Action

As a laxative, exerts osmotic effect in the small intestine by drawing water into the lumen of the gut, producing distention and promoting peristalsis and evacuation of the bowel; phosphorous participates in bone deposition, calcium metabolism, utilization of B complex vitamins, and as a buffer in acid-base equilibrium

Pharmacokinetics

Onset of action: Cathartic: 3 to 6 hours; Rectal: 2 to 5 minutes

Absorption: Oral: ~1% to 20%

Excretion: Oral forms excreted in feces; IV forms are excreted in the urine with over 80% to 90% of dose reabsorbed by the kidney

Pharmacokinetics: Additional Considerations

Altered kidney function: Oral: Elimination of the large oral phosphate load may be impaired. Use with caution.

Older adult: Oral: Plasma half-life is 2-fold higher in subjects >70 years of age.

Pricing: US

Enema (Fleet Enema Rectal)

7-19 g/118 mL (per mL): $0.01

Enema (Fleet Pediatric Rectal)

3.5-9.5 g/59 mL (per mL): $0.03

Solution (Sodium Phosphates Intravenous)

15 mmole/5ml (per mL): $3.87

45 mmole/15ml (per mL): $1.22 - $2.89

150 mmole/50ml (per mL): $2.89

Tablets (OsmoPrep Oral)

1.102-0.398 g (per each): $9.99

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