Potassium dihydrogen phosphate

Usage

• Potassium dihydrogen phosphate is primarily used to treat hypophosphatemia (low phosphate levels in the blood). It can also be used to treat conditions where both phosphate and potassium levels are low, and oral supplementation is not feasible. Additionally, it is used to provide phosphate and potassium during intravenous feeding (parenteral nutrition).
• Pharmacological Classification: Electrolyte supplement, Urinary acidifier.
• Mechanism of Action: Potassium dihydrogen phosphate works by directly supplying phosphate ions to the body. These ions are essential for many bodily functions including energy production, nerve and muscle function, and bone health. It also acts to acidify the urine which can help prevent the formation of certain types of kidney stones.

Alternate Names

• Monobasic potassium phosphate
• Potassium phosphate monobasic
• KH₂PO₄

How It Works

• Pharmacodynamics: Potassium dihydrogen phosphate increases serum phosphate concentrations. It also lowers urinary pH, thereby inhibiting the crystallization of calcium-containing kidney stones.
• Pharmacokinetics:
  • Absorption: When administered intravenously, it is directly absorbed into the bloodstream. When administered orally, phosphate salts are absorbed from the small intestine by passive diffusion and active transport. Absorption can be affected by factors like the presence of calcium, aluminum, or magnesium.
  • Metabolism: Phosphate is not metabolized in the body but is incorporated into various organic compounds.
  • Elimination: Primarily excreted by the kidneys, with the rate of excretion dependent on serum phosphate concentration, parathyroid hormone levels, and dietary intake. Some phosphate is also eliminated in the feces.

Dosage

Standard Dosage

Adults:

• Intravenous: For severe hypophosphatemia (serum phosphate < 0.3 mmol/L), up to 10 mmol of phosphate can be administered over 12 hours, repeated every 12 hours until serum phosphate levels are above 0.3 mmol/L. The rate of infusion should not exceed 0.2 mmol/kg/hour. For less severe hypophosphatemia, lower doses are used, guided by serum phosphate levels.

Children:

• Intravenous: 0.15-0.33 mmol/kg administered over 6 hours. The dose may be repeated at 6-hour intervals until serum phosphate exceeds 0.6 mmol/L. The dose should not exceed the maximum recommended adult dose. The rate of infusion should not exceed 0.2 mmol/kg/hour.

Special Cases:

• Elderly Patients: Dose adjustment may be required.
• Patients with Renal Impairment: Reduce the dosage based on the severity of impairment. In severe renal impairment, the use of potassium dihydrogen phosphate is contraindicated.
• Patients with Hepatic Dysfunction: Monitor for electrolyte imbalances.
• Patients with Comorbid Conditions: Close monitoring of electrolytes is necessary.

Clinical Use Cases

Dosage is always determined by the patient’s specific needs and should be titrated according to serum phosphate levels and clinical response.

Dosage Adjustments

• Dosage adjustments are necessary for patients with renal impairment and should be guided by electrolyte monitoring.

Side Effects

Common Side Effects

• Swelling of feet or lower legs
• Weight gain

Rare but Serious Side Effects

• Muscle weakness or cramps
• Convulsions
• Confusion
• Tiredness
• Irregular or slow heart rate
• Unexplained anxiety
• Tingling or numbness of the hands or feet
• Breathing difficulties
• Increased thirst and decreased urination
• Hyperkalemia
• Hyperphosphatemia
• Hypocalcemia

Adverse Drug Reactions (ADR)

• Acute renal failure
• Cardiac arrhythmias
• Tetany (with large doses)

Contraindications

• Hyperkalemia
• Hyperphosphatemia
• Hypocalcemia
• Severe renal impairment
• Hypersensitivity to potassium phosphate

Drug Interactions

• Calcium-containing medications: May increase the risk of soft tissue calcification.
• Potassium-sparing diuretics (e.g., spironolactone, triamterene): Increased risk of hyperkalemia.
• ACE inhibitors (e.g., lisinopril): Increased risk of hyperkalemia.
• Angiotensin receptor blockers (ARBs) (e.g., valsartan): Increased risk of hyperkalemia.
• Digitalis glycosides (e.g., digoxin): Increased risk of hyperkalemia, which can increase digitalis toxicity.
• Salicylates: Potassium dihydrogen phosphate can decrease salicylate excretion, potentially leading to salicylate toxicity.

Pregnancy and Breastfeeding

• The safety of potassium dihydrogen phosphate during pregnancy and breastfeeding has not been established. Use only if the potential benefits outweigh the potential risks to the fetus or infant.

Drug Profile Summary

• Mechanism of Action: Replaces phosphate and potassium deficits.
• Side Effects: Common: Swelling, weight gain. Serious: Electrolyte imbalances, arrhythmias, renal failure.
• Contraindications: Hyperkalemia, hyperphosphatemia, hypocalcemia, severe renal impairment.
• Drug Interactions: Calcium, potassium-sparing diuretics, ACE inhibitors, ARBs, digitalis, salicylates.
• Pregnancy & Breastfeeding: Safety not established.
• Dosage: Individualized based on patient need and electrolyte levels.
• Monitoring Parameters: Serum phosphate, potassium, calcium, magnesium, creatinine. ECG for rapid intravenous infusions.

Popular Combinations

Potassium dihydrogen phosphate is often used in combination with other electrolytes in parenteral nutrition solutions tailored to individual patient needs.

Precautions

• General Precautions: Monitor serum electrolyte levels, especially calcium, potassium, and phosphate. Closely observe cardiac and renal function, particularly during intravenous administration. Monitor ECG during rapid intravenous infusions.
• Specific Populations: Adjust dosage in patients with renal impairment. Use with caution in elderly patients.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Potassium dihydrogen phosphate?

A: Dosage is individualized based on patient needs, electrolyte levels, and clinical condition. See detailed dosage guidelines above.

Q2: What are the primary uses of Potassium dihydrogen phosphate?

A: Treatment of hypophosphatemia, treatment of combined potassium and phosphate depletion when oral therapy is not possible, and providing phosphate and potassium during parenteral nutrition.

Q3: What are the serious side effects of Potassium dihydrogen phosphate?

A: Serious side effects include electrolyte imbalances (hyperkalemia, hyperphosphatemia, hypocalcemia), acute renal failure, and cardiac arrhythmias.

Q4: What are the contraindications to using Potassium dihydrogen phosphate?

A: Contraindications include hyperkalemia, hyperphosphatemia, hypocalcemia, and severe renal impairment.

Q5: What drugs interact with Potassium dihydrogen phosphate?

A: Interacting drugs include calcium supplements, potassium-sparing diuretics, ACE inhibitors, ARBs, digoxin, and salicylates.

Q6: Can Potassium dihydrogen phosphate be used during pregnancy and breastfeeding?

A: Safety during pregnancy and breastfeeding has not been established. Use only if clearly needed and under careful medical supervision.

Q7: How should Potassium dihydrogen phosphate be administered?

A: Potassium dihydrogen phosphate can be administered intravenously or orally. Intravenous formulations must be diluted before infusion. Oral formulations are available as tablets, capsules, solutions, and powders.

Q8: How should I monitor patients receiving Potassium dihydrogen phosphate?

A: Monitor serum phosphate, potassium, calcium, and magnesium levels regularly. Monitor renal function and cardiac function. Continuous ECG monitoring is recommended for rapid intravenous infusions.

Q9: What precautions should I take when prescribing Potassium dihydrogen phosphate?

A: Use with caution in patients with renal impairment or cardiac disease. Monitor serum electrolytes closely. Adjust dosage based on patient response and tolerance.