Usage
Monobasic sodium phosphate, often used in combination with dibasic sodium phosphate, is primarily prescribed as a bowel cleanser to prepare the colon for procedures like colonoscopies or surgeries. It can also be used in the treatment of hypophosphatemia (low phosphate levels in the blood). It is classified as a saline laxative and an electrolyte replenisher. The combination of monobasic and dibasic sodium phosphate works by increasing fluid in the small intestine, stimulating bowel movements.
Alternate Names
Monobasic sodium phosphate may be referred to as sodium dihydrogen phosphate, sodium phosphate monobasic, or monosodium phosphate. Brand names include Fleet Enema (in combination with dibasic sodium phosphate), Phospho-Soda (in combination with dibasic sodium phosphate), and Visicol (in combination with dibasic sodium phosphate).
How It Works
Pharmacodynamics: Monobasic sodium phosphate, especially when combined with dibasic sodium phosphate, acts as an osmotic laxative. It increases the amount of water in the small intestines, causing distension and stimulating peristalsis, leading to bowel evacuation.
Pharmacokinetics: When taken orally, sodium phosphate salts are poorly absorbed. The unabsorbed phosphate salts increase the osmotic pressure in the intestinal lumen, drawing water into the intestines. This increased water content softens the stool and promotes bowel movement. A small amount of phosphate may be absorbed systemically. Sodium phosphate that is absorbed is primarily excreted by the kidneys. It can also be excreted in breast milk.
Mode of Action: The primary mode of action is through osmotic effects, not through receptor binding, enzyme inhibition, or neurotransmitter modulation. Elimination primarily occurs through renal excretion.
Dosage
Standard Dosage
Adults (Oral, for Colonoscopy Preparation):
The typical dosage is a combination of monobasic and dibasic sodium phosphate, usually with 20 tablets taken the evening before the colonoscopy and 12 tablets taken the morning of the procedure, each with 8 ounces of clear liquids every 15 minutes. Visicol tablets have a slightly different regimen (consult the package insert). The oral solution is administered as 45mL diluted in 120mL of water, repeated in 10-12 hours.
Children:
Oral sodium phosphate solutions are generally not recommended for children under 18 years of age for bowel cleansing. Rectal enemas containing sodium phosphates are available for children (Fleet for Children, Pedia-Lax), with dosage adjusted according to age. However, use is not recommended in children younger than 2 years.
Special Cases:
- Elderly Patients: Use with extreme caution. Closely monitor electrolyte levels and hydration status due to the increased risk of dehydration and electrolyte imbalances.
- Patients with Renal Impairment: Use with caution, especially in severe renal impairment (creatinine clearance < 30 mL/minute). Monitor electrolyte levels and renal function.
- Patients with Hepatic Dysfunction: Dose adjustments might not be required as the drug is mainly renally cleared.
- Patients with Comorbid Conditions (e.g., heart failure, ascites): Use with extreme caution due to the risk of fluid and electrolyte disturbances. Contraindicated in patients with conditions such as symptomatic heart failure, ascitic conditions, or pre-existing fluid/electrolyte disturbances.
Clinical Use Cases
The primary clinical use case for oral monobasic sodium phosphate (in combination with dibasic sodium phosphate) is for bowel cleansing before colonoscopy. Other clinical uses are less common for this route of administration.
- Intubation, Surgical Procedures, Mechanical Ventilation, ICU Use, Emergency Situations: Intravenous sodium phosphate is utilized in these situations as an electrolyte replenisher. Dosage is patient-specific and guided by serum phosphate levels.
Dosage Adjustments
Dose reductions are usually necessary for elderly patients and those with renal impairment. Monitor electrolytes closely in these populations.
Side Effects
Common Side Effects
- Nausea
- Abdominal pain/cramping
- Bloating
- Diarrhea
Rare but Serious Side Effects
- Kidney problems (including acute phosphate nephropathy, renal failure)
- Electrolyte disturbances (hypokalemia, hypocalcemia, hyperphosphatemia)
- Cardiac arrhythmias
- Seizures
- Allergic reactions (rash, itching, hives)
Long-Term Effects
Chronic kidney disease can occur with repeated or excessive use of sodium phosphates.
Adverse Drug Reactions (ADR)
Acute phosphate nephropathy, cardiac arrhythmias, and seizures require immediate medical attention.
Contraindications
- Hypersensitivity to sodium phosphates
- History of acute phosphate nephropathy
- Congestive heart failure, ascites
- Severe renal impairment
- Perforated bowel
Drug Interactions
- Medications that prolong the QT interval
- Medications that lower the seizure threshold (e.g., tricyclic antidepressants)
- Drugs affecting renal function (e.g., diuretics, NSAIDs, ACE inhibitors)
- Calcium and aluminum-containing antacids (reduce phosphate absorption)
Pregnancy and Breastfeeding
Use with caution during pregnancy only if the benefits outweigh the potential risks. It’s advisable to express and discard breast milk for 24 hours after the last dose of sodium phosphate for bowel cleansing.
Drug Profile Summary
- Mechanism of Action: Osmotic laxative
- Side Effects: Nausea, abdominal pain, bloating, diarrhea (common); kidney problems, arrhythmias, seizures (rare but serious)
- Contraindications: Hypersensitivity, acute phosphate nephropathy, heart failure, renal impairment
- Drug Interactions: QT prolonging drugs, seizure-lowering medications, drugs affecting renal function
- Pregnancy & Breastfeeding: Use with caution; express and discard breast milk for 24 hours after the last dose (for bowel cleansing).
- Dosage: Varies based on indication (bowel cleansing vs. hypophosphatemia) and formulation (oral, rectal, IV)
- Monitoring Parameters: Electrolytes (sodium, potassium, calcium, phosphate), renal function, hydration status
Popular Combinations
Monobasic sodium phosphate is typically combined with dibasic sodium phosphate for bowel cleansing.
Precautions
- General Precautions: Assess fluid and electrolyte status, renal function.
- Specific Populations: Use with caution in the elderly, pregnant women, and breastfeeding mothers. Not recommended for children (oral solution for bowel prep).
- Lifestyle Considerations: Ensure adequate hydration.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Monobasic sodium phosphate for bowel cleansing?
A: For adults, a combination of monobasic and dibasic sodium phosphate is usually given: 20 tablets the evening before and 12 tablets the morning of the procedure, each with 8 ounces of clear liquids every 15 minutes. The oral solution is administered as 45mL diluted in 120mL of water, repeated in 10-12 hours.
Q2: What are the serious side effects of sodium phosphate?
A: Serious side effects include kidney problems (acute phosphate nephropathy), electrolyte imbalances, cardiac arrhythmias, and seizures.
Q3: Can sodium phosphate be used in patients with kidney disease?
A: Use with extreme caution in patients with kidney disease, especially severe renal impairment. Close monitoring is crucial.
Q4: Are there any drug interactions with sodium phosphate?
A: Yes, sodium phosphate interacts with drugs that prolong the QT interval, lower the seizure threshold, and affect renal function.
Q5: Can pregnant or breastfeeding women use sodium phosphate?
A: Use cautiously during pregnancy if clearly needed. For breastfeeding mothers, it is recommended to express and discard breast milk for 24 hours after the last dose if using sodium phosphate for bowel cleansing.
Q6: How does sodium phosphate work as a bowel cleanser?
A: It works by increasing the amount of water in the intestines, softening the stool and causing bowel movements.
Q7: What are the signs of dehydration associated with sodium phosphate use?
A: Thirst, dizziness, decreased urination, and vomiting can be signs of dehydration.
Q8: What should patients avoid while taking sodium phosphate for bowel cleansing?
A: Patients should avoid solid foods, liquids containing pulp, and any liquids colored purple or red. They should drink plenty of clear liquids.
Q9: What should I do if a patient experiences serious side effects after taking sodium phosphate?
A: Discontinue the medication immediately and provide appropriate supportive care. Contact nephrology for suspected acute phosphate nephropathy. For cardiac arrhythmias and seizures provide immediate medical attention.
Q10: Is monobasic sodium phosphate ever given intravenously?
A: Yes, intravenous sodium phosphate (usually combined with potassium phosphate) is used to treat hypophosphatemia in clinical settings like the ICU.
