Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Powder for solution, oral:
Phos-NaK: Dibasic potassium phosphate, monobasic potassium phosphate, dibasic sodium phosphate, and monobasic sodium phosphate per packet (100s) [sugar free; equivalent to elemental phosphorus 250 mg (8 mmol), sodium 160 mg (6.9 mEq), and potassium 280 mg (7.1 mEq) per packet; fruit flavor]
Generic: Dibasic potassium phosphate, monobasic potassium phosphate, dibasic sodium phosphate, and monobasic sodium phosphate per packet
Tablet, oral:
Av-Phos 250 Neutral: Monobasic potassium phosphate 155 mg, dibasic sodium phosphate 852 mg, and monobasic sodium phosphate 130 mg [equivalent to elemental phosphorus 250 mg (8 mmol), sodium 298 mg (13 mEq), and potassium 45 mg (1.1 mEq)]
K-Phos Neutral: Monobasic potassium phosphate 155 mg, dibasic sodium phosphate 852 mg, and monobasic sodium phosphate 130 mg [equivalent to elemental phosphorus 250 mg (8 mmol), sodium 298 mg (13 mEq), and potassium 45 mg (1.1 mEq)]
K-Phos No. 2: Potassium acid phosphate 305 mg and sodium acid phosphate 700 mg [equivalent to elemental phosphorus 250 mg (8 mmol), sodium 134 mg (5.8 mEq), and potassium 88 mg (2.3 mEq)]
Phospha 250 Neutral: Monobasic potassium phosphate 155 mg, dibasic sodium phosphate 852 mg, and monobasic sodium phosphate 130 mg [equivalent to elemental phosphorus 250 mg (8 mmol), sodium 298 mg (13 mEq), and potassium 45 mg (1.1 mEq)]
Phospho-Trin 250 Neutral: Monobasic potassium phosphate 155 mg, dibasic sodium phosphate 852 mg, and monobasic sodium phosphate 130 mg [equivalent to elemental phosphorus 250 mg (8 mmol), sodium 298 mg (13 mEq), and potassium 45 mg (1.1 mEq)]
Virt-Phos 250 Neutral: Monobasic potassium phosphate 155 mg, dibasic sodium phosphate 852 mg, and monobasic sodium phosphate 130 mg [equivalent to elemental phosphorus 250 mg (8 mmol), sodium 298 mg (13 mEq), and potassium 45 mg (1.1 mEq)]
Generic: Monobasic potassium phosphate 155 mg, dibasic sodium phosphate 852 mg, and monobasic sodium phosphate 130 mg [equivalent to elemental phosphorus 250 mg (8 mmol), sodium 298 mg (13 mEq), and potassium 45 mg (1.1 mEq)]
Pharmacology
Mechanism of Action
See individual agents.
Pharmacokinetics/Pharmacodynamics
Absorption
1% to 20%
Excretion
Oral forms excreted in feces
Onset of Action
Catharsis: Oral: 3 to 6 hours
Use: Labeled Indications
Phosphate supplement: As a phosphorus supplement
Urinary acidification: To increase urinary phosphate and pyrophosphate
K-Phos No. 2: Urinary acidifier for patients with elevated urinary pH to help keep calcium soluble and reduce odor and rash caused by ammoniacal urine; increases the antibacterial activity of methenamine.
Contraindications
Hyperphosphatemia; infected urinary phosphate stones; severe renal impairment (<30% of normal)
Dosage and Administration
Dosing: Adult
Note: Dosage expressed in terms of elemental phosphorus.
Phosphate supplement: Oral: 250 to 500 mg 4 times daily
Urinary acidification (K-Phos No. 2): Oral: 250 mg 4 times daily; may be increased to 250 mg every 2 hours when the urine is difficult to acidify (maximum: 2,000 mg/day)
Dosing: Geriatric
Refer to adult dosing.
Dosing: Pediatric
Note: Consider the contribution of sodium and potassium cations when determining appropriate phosphate replacement. Each mmol of phosphate contains 31 mg elemental phosphorus. Dosage expressed in terms of phosphate/phosphorus.
Phosphorus: Adequate intake (AI) (IOM 1997): Oral:
1 to 6 months: 3.2 mmol/day
7 to 12 months: 8.9 mmol/day
Phosphorus: Recommended Daily Allowance (RDA) and Estimated Average Requirement (EAR) (IOM 1997): Oral:
1 to 3 years: RDA: 14.8 mmol/day, EAR: 12.3 mmol/day
4 to 8 years: RDA: 16.1 mmol/day, EAR: 13.1 mmol/day
9 to 18 years: RDA: 40.3 mmol/day, EAR: 34 mmol/day
Hypophosphatemia, maintenance therapy: Note: Dose should be individualized and may vary based on underlying etiology: Infants, Children, and Adolescents: 2 to 3 mmol/kg/day in divided doses, usually at least 4 divided doses (Kliegman 2016)
Dietary supplementation: Oral: Av-Phos 250 Neutral, K-Phos Neutral, Phospha 250 Neutral, Virt-Phos 250 Neutral: Children >4 years and Adolescents: 250 mg (1 tablet) 4 times daily (with meals and at bedtime)
Reconstitution
Oral powder: Mix 1 packet in 75 mL water or juice; stir well and administer promptly. Proper dilution may help prevent GI injury associated with concentrated oral potassium preparations.
Administration
Administer with a full glass of water at mealtime and at bedtime.
Oral powder: Must be diluted in water or juice prior to administration.
Dietary Considerations
Take with meals. In addition to phosphate, products contain potassium and sodium.
Storage
Oral powder: Store at room temperature; protect from moisture.
Tablets: Store at 20°C to 25°C (68°F to 77°F). Protect from light and moisture. Contact of Virt-Phos with moisture may produce surface discoloration or erosion.
Drug Interactions
Aliskiren: Potassium Salts may enhance the hyperkalemic effect of Aliskiren. Monitor therapy
Alpha-/Beta-Agonists (Indirect-Acting): Urinary Acidifying Agents may decrease the serum concentration of Alpha-/Beta-Agonists (Indirect-Acting). Monitor therapy
Amantadine: Urinary Acidifying Agents may decrease the serum concentration of Amantadine. Monitor therapy
Amphetamines: Urinary Acidifying Agents may decrease the serum concentration of Amphetamines. Monitor therapy
Angiotensin II Receptor Blockers: Potassium Salts may enhance the hyperkalemic effect of Angiotensin II Receptor Blockers. Monitor therapy
Angiotensin-Converting Enzyme Inhibitors: Potassium Salts may enhance the hyperkalemic effect of Angiotensin-Converting Enzyme Inhibitors. Monitor therapy
Antacids: May decrease the serum concentration of Potassium Phosphate. Management: Consider separating administration of antacids and oral potassium phosphate by at least 2 hours to decrease risk of a significant interaction. Consider therapy modification
Burosumab: Phosphate Supplements may enhance the adverse/toxic effect of Burosumab. 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. Consider therapy modification
ChlorproPAMIDE: Urinary Acidifying Agents may increase the serum concentration of ChlorproPAMIDE. Monitor therapy
Drospirenone: Potassium Salts may enhance the hyperkalemic effect of Drospirenone. Monitor therapy
Eplerenone: May enhance the hyperkalemic effect of Potassium Salts. Management: This combination is contraindicated in patients receiving eplerenone for treatment of hypertension. 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). Consider therapy modification
Heparin: May enhance the hyperkalemic effect of Potassium Salts. Monitor therapy
Heparins (Low Molecular Weight): May enhance the hyperkalemic effect of Potassium Salts. Monitor therapy
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. Exceptions: Ferric Carboxymaltose; Ferric Derisomaltose; Ferric Gluconate; Ferric Hydroxide Polymaltose Complex; Ferric Pyrophosphate Citrate; Ferumoxytol; Iron Dextran Complex; Iron Sucrose. 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. Consider therapy modification
Mecamylamine: Urinary Acidifying Agents may decrease the serum concentration of Mecamylamine. Monitor therapy
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. Consider therapy modification
Nicorandil: May enhance the hyperkalemic effect of Potassium Salts. Monitor therapy
Potassium-Sparing Diuretics: Potassium Salts may enhance the hyperkalemic effect of Potassium-Sparing Diuretics. Consider therapy modification
Salicylates: Potassium Phosphate may increase the serum concentration of Salicylates. Monitor therapy
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. Consider therapy modification
Adverse Reactions
Also see individual agents.
Frequency not defined:
Cardiovascular: Bradycardia, cardiac arrhythmia, chest pain, edema, lower extremity edema, tachycardia
Central nervous system: Confusion, dizziness, fatigue, headache, heaviness of the legs, numbness, paresthesia, seizure, tingling sensation, tetany (with large doses of phosphate)
Endocrine & metabolic: Alkalosis, hyperkalemia, weight gain
Gastrointestinal: Diarrhea, flatulence, nausea, oral paresthesia, sore throat, stomach pain, vomiting
Genitourinary: Decreased urine output
Local: Local pain (hands and feet)
Neuromuscular & skeletal: Arthralgia, asthenia, limb pain, muscle cramps, muscle weakness of the extremities, ostealgia, paralysis
Renal: Acute renal failure
Respiratory: Dyspnea
Miscellaneous: Increased thirst
Warnings/Precautions
Concerns related to adverse effects:
- Laxative effect: A mild laxative effect may occur within the first few days of therapy; if the laxative effect persists, reduce the dose or discontinue use until diarrhea improves.
Disease-related concerns:
- Adrenal insufficiency: Use with caution in patients with severe adrenal insufficiency (eg, Addison disease)
- Cardiac disease: Use with caution in patients with cardiac disease, including heart failure (especially patients receiving digoxin) and hypertension.
- Dehydration: Use with caution in patients with acute dehydration.
- Edema: Use with caution in patients with peripheral or pulmonary edema.
- Hepatic impairment: Use with caution in patients with cirrhosis or severe hepatic impairment.
- Hypernatremia: Use with caution in patients with hypernatremia.
- Myotonia congenita: Use with caution in patients with myotonia congenita.
- Pancreatitis: Use with caution in patients with acute pancreatitis.
- Parathyroid disease: Use with caution in patients with hypoparathyroidism.
- Preeclampsia: Use with caution in pregnant patients with preeclampsia of pregnancy.
- Renal calculi: Patients with renal calculi may pass preformed stones when phosphate therapy is initiated.
- Renal impairment: Use with caution in patients with renal impairment or chronic renal disease; use is contraindicated in patient with severe renal impairment (<30% of normal).
- Rickets: Use with caution in patients with rickets; may increase the risk of extraskeletal calcification.
- Tissue breakdown: Use with caution in patients with extensive tissue breakdown (eg, severe burns).
Concurrent drug therapy issues:
- Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.
Monitoring Parameters
Serum potassium, sodium, calcium, phosphorus, magnesium (to facilitate potassium repletion), and renal function at periodic intervals
Pregnancy
Pregnancy Risk Factor
C
Pregnancy Considerations
Animal reproduction studies have not been conducted with this combination. See individual agents.
Patient Education
What is this drug used for?
- It is used to treat or prevent low phosphate levels.
Frequently reported side effects of this drug
- Abdominal pain
- Vomiting
- Nausea
Other side effects of this drug: Talk with your doctor right away if you have any of these signs of:
- High potassium like abnormal heartbeat, confusion, dizziness, passing out, weakness, shortness of breath, or numbness or tingling feeling.
- Fast heartbeat
- Severe diarrhea
- Severe headache
- Muscle cramps
- Seizures
- Shortness of breath
- Excessive weight gain
- Swelling of arms or legs
- Severe loss of strength and energy
- Bone pain
- Joint pain
- Feeling of heaviness in arms or legs
- Unable to pass urine
- Increased thirst
- Signs of a significant reaction like wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat.
Note: This is not a comprehensive list of all side effects. Talk to your doctor if you have questions.
Consumer Information Use and Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this medicine. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not specific medical advice and does not replace information you receive from the healthcare provider. You must talk with the healthcare provider for complete information about the risks and benefits of using this medicine.
