Usage
Sodium acid phosphate is prescribed for the treatment of:
- Hypercalcemia: Elevated blood calcium levels due to conditions such as hyperparathyroidism, multiple myeloma, and other cancers.
- Hypophosphatemia: Low blood phosphate levels caused by vitamin D-resistant rickets and osteomalacia.
It is classified as a phosphate supplement/binder and a laxative. It can also be used as a urinary acidifier.
Mechanism of Action (Hypercalcemia): Phosphate ions bind to calcium in the gut, reducing calcium absorption and increasing its excretion.
Mechanism of Action (Hypophosphatemia): Provides a source of phosphate to replenish depleted levels.
Mechanism of Action (Laxative): Sodium phosphate acts as an osmotic laxative, drawing water into the intestinal lumen, softening the stool, and stimulating bowel movements.
Mechanism of Action (Urinary acidifier): Metabolized to phosphoric acid in the kidneys which increases urine acidity.
Alternate Names
- Monosodium phosphate
- Sodium dihydrogen phosphate
- Phosphate Sandoz (Brand name)
- Fleet Enema (Brand name, for rectal sodium phosphate)
- K-Phos (Brand name, in combination with Potassium phosphate)
How It Works
Pharmacodynamics:
- Hypercalcemia: Lowers serum calcium levels by forming insoluble calcium phosphate salts in the gut and reducing its intestinal absorption.
- Hypophosphatemia: Elevates serum phosphate levels directly.
- Laxative: Increases intraluminal osmotic pressure, drawing water into the intestine and stimulating peristalsis.
- Urinary acidifier: Increases urinary acidity by releasing hydrogen ions.
Pharmacokinetics:
- Absorption: Oral absorption is variable and incomplete, but generally adequate for managing the abovementioned conditions. Rectal administration facilitates more rapid absorption.
- Metabolism: Limited metabolism, some conversion to phosphoric acid occurs in the kidneys.
- Elimination: Primarily renal excretion, also excreted via feces as calcium and magnesium phosphate salts.
Dosage
Standard Dosage
Adults:
- Hypercalcemia: Up to 6 tablets daily, dissolved in 50-70ml of water. Dosage adjustment based on individual patient response and serum calcium levels.
- Hypophosphatemia: 4-6 tablets daily, dissolved in 50-70ml of water.
Children:
- Hypercalcemia: Up to 3 tablets daily (for children 5 years and older). Dosage adjustment as needed.
- Hypophosphatemia: 2-3 tablets daily (for children 5 years and older).
Special Cases:
- Elderly Patients: Careful dosage titration is recommended, starting at the lower end of the dosing range, due to potential age-related decline in renal function. Monitor serum calcium, phosphate, and electrolytes.
- Patients with Renal Impairment: Use with caution. Dosage adjustment may be necessary. Close monitoring of renal function, electrolyte levels, and serum phosphate is essential.
- Patients with Hepatic Dysfunction: Safety and efficacy not fully established. Use with caution, close monitoring advised.
- Patients with Comorbid Conditions: Caution in patients with heart failure, arrhythmia, angina, cardiomyopathy, electrolyte disturbances, or a history of seizures.
Dosage Adjustments
Dose modifications are based on serum calcium, phosphate, and creatinine levels, as well as individual patient response and tolerance. Renal and hepatic impairment necessitate cautious dose adjustments and monitoring.
Side Effects
Common Side Effects
- Nausea
- Vomiting
- Diarrhea
- Abdominal pain/cramping
- Bloating
- Headache
- Dizziness
Rare but Serious Side Effects
- Electrolyte disturbances (hyperphosphatemia, hypocalcemia, hypernatremia, hypokalemia)
- Cardiac arrhythmias (including QT prolongation)
- Acute phosphate nephropathy (kidney injury)
- Seizures
Long-Term Effects
- Soft tissue calcification and nephrocalcinosis (with IV phosphate)
- Potential for chronic kidney disease with prolonged high doses.
Adverse Drug Reactions (ADR)
- Severe hypocalcemia
- Cardiac arrhythmias (requiring immediate intervention)
- Acute phosphate nephropathy (requiring discontinuation and supportive care)
Contraindications
- Hypersensitivity to sodium acid phosphate.
- Renal failure (for enema and oral use in high doses for bowel prep).
- Bowel obstruction.
- Perforated bowel.
- Congestive heart failure (for enema).
Drug Interactions
- Antacids: Reduce phosphate absorption.
- Calcium supplements and Vitamin D: Can increase risk of hyperphosphatemia and soft tissue calcification.
- Drugs affecting renal function (NSAIDs, ACE inhibitors, ARBs, diuretics): Increase the risk of nephrotoxicity.
- Burosumab
Pregnancy and Breastfeeding
- Pregnancy: Use with caution if benefits outweigh risks. Limited data available on human pregnancy.
- Breastfeeding: Limited information regarding excretion in breast milk. Use with caution and consult with your physician.
Drug Profile Summary
- Mechanism of Action: Phosphate binder/supplement; osmotic laxative; urinary acidifier.
- Side Effects: Nausea, vomiting, diarrhea, abdominal pain, electrolyte imbalances, arrhythmias, nephrotoxicity.
- Contraindications: Hypersensitivity, renal failure (in some cases), bowel obstruction.
- Drug Interactions: Antacids, calcium supplements, drugs affecting renal function.
- Pregnancy & Breastfeeding: Use with caution; limited data.
- Dosage: Varies based on indication and patient factors. See detailed dosage guidelines above.
- Monitoring Parameters: Serum calcium, phosphate, creatinine, electrolytes (sodium, potassium, magnesium), renal function tests.
Popular Combinations
Specific information on “popular combinations” is limited. However, potassium phosphate is often combined with sodium acid phosphate in some preparations (e.g., K-Phos) for hypophosphatemia treatment.
Precautions
- General Precautions: Assess renal function, electrolyte levels, and serum calcium before and during therapy. Ensure adequate hydration. Monitor for electrolyte disturbances and cardiac arrhythmias.
- Specific Populations: Caution is advisable in elderly patients and those with renal impairment or cardiovascular disease. Avoid use in children younger than 5 years for hyper/hypo phosphatemia.
- Lifestyle Considerations: No specific lifestyle considerations are mentioned in the provided sources besides adequate hydration.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Sodium acid phosphate?
A: The dosage varies according to the indication and patient-specific factors (age, renal function, etc.). For hypercalcemia in adults, it can be up to 6 tablets/day; for hypophosphatemia, it’s 4-6 tablets/day. Pediatric and special population dosing requires careful adjustment.
Q2: How should Sodium acid phosphate tablets be administered?
A: Dissolve the tablets in 50-70ml of water before oral administration.
Q3: What are the common side effects of Sodium acid phosphate?
A: Common side effects include nausea, vomiting, diarrhea, abdominal pain, and bloating.
Q4: What are the serious side effects to watch out for?
A: Serious side effects include electrolyte disturbances (hyperphosphatemia, hypocalcemia, hypernatremia), cardiac arrhythmias (including QT prolongation), and acute phosphate nephropathy.
Q5: Is Sodium acid phosphate safe in pregnancy?
A: Use with caution during pregnancy if benefits outweigh the potential risks. Consult with a physician for careful risk-benefit assessment.
Q6: Can Sodium acid phosphate be used in patients with kidney disease?
A: Use with extreme caution in patients with renal impairment, as it can exacerbate kidney problems. Close monitoring and dose adjustments are necessary. For rectal administration and high oral doses for bowel preparation, it’s contraindicated in patients with renal failure.
Q7: What should be monitored during Sodium acid phosphate therapy?
A: Serum calcium, phosphate, creatinine, electrolytes, and renal function tests should be monitored regularly during treatment.
Q8: How does sodium acid phosphate interact with antacids?
A: Antacids can reduce the absorption of phosphate, decreasing the effectiveness of sodium acid phosphate. Administer with caution if concomitant use is unavoidable.
Q9: What patient education should be provided when prescribing Sodium acid phosphate?
A: Counsel patients on the importance of proper administration (dissolving tablets in water), potential side effects (especially GI related), the need for adequate hydration, and the importance of regular monitoring of blood parameters. Advise patients to report any significant side effects immediately. Emphasize strict adherence to the prescribed dosage and to avoid using other phosphate-containing laxatives or enemas concurrently without consulting a physician.
