What is the recommended dose and administration of potassium phosphate for correcting hypophosphatemia and what volume of saline solution should it be diluted in over how many hours?

Potassium Phosphate Correction Protocol

For intravenous potassium phosphate correction of hypophosphatemia, dilute the dose in 100-250 mL of normal saline or D5W and infuse at a maximum rate of 6.8 mmol phosphorus/hour (10 mEq potassium/hour) through a peripheral line, or up to 15 mmol phosphorus/hour (22 mEq potassium/hour) through a central line, with continuous ECG monitoring required for rates exceeding 10 mEq potassium/hour. 1

Dosing Based on Severity

Severe Hypophosphatemia (Serum Phosphorus <1 mg/dL)

• Administer 0.44-0.64 mmol/kg of phosphorus (corresponding to 0.64-0.94 mEq/kg of potassium), up to a maximum single dose of 45 mmol phosphorus (66 mEq potassium) 1
• Alternative simplified approach: 0.16 mmol/kg of phosphorus infused at 1-3 mmol/hour until serum phosphorus reaches 2 mg/dL 2

Moderate Hypophosphatemia (Serum Phosphorus 1-1.7 mg/dL)

• Administer 0.32-0.43 mmol/kg of phosphorus (corresponding to 0.47-0.63 mEq/kg of potassium) 1

Mild Hypophosphatemia (Serum Phosphorus 1.8 mg/dL to Lower Normal)

• Administer 0.16-0.31 mmol/kg of phosphorus (corresponding to 0.23-0.46 mEq/kg of potassium) 1

Dilution and Concentration Guidelines

For Adults and Pediatric Patients ≥12 Years

• Peripheral line: Maximum concentration of 6.8 mmol phosphorus/100 mL (10 mEq potassium/100 mL) 1
• Central line: Maximum concentration of 18 mmol phosphorus/100 mL (26.4 mEq potassium/100 mL) 1
• Recommended total volume: 100-250 mL of normal saline or D5W 1

For Pediatric Patients <12 Years

• Peripheral line: Maximum concentration of 0.27 mmol phosphorus/10 mL (0.4 mEq potassium/10 mL) 1
• Central line: Maximum concentration of 0.55 mmol phosphorus/10 mL (0.8 mEq potassium/10 mL) 1
• Use the smallest volume considering daily fluid requirements 1

Infusion Rate Guidelines

Standard Peripheral Access

• Maximum rate: 6.8 mmol phosphorus/hour (10 mEq potassium/hour) 1
• This translates to approximately 1 mL/hour of undiluted potassium phosphate solution (which contains 3 mmol phosphorus and 4.4 mEq potassium per mL), making this a safe default rate 3

Central Venous Access

• Maximum rate: 15 mmol phosphorus/hour (22 mEq potassium/hour) 1
• Continuous ECG monitoring is mandatory for any infusion rate exceeding 10 mEq potassium/hour 1

Pre-Administration Requirements

Mandatory Laboratory Checks

• Check serum potassium before administration: Do NOT give potassium phosphate if serum potassium ≥4 mEq/dL; use an alternative phosphorus source instead 1
• Normalize serum calcium before administration: Potassium phosphate is contraindicated in hypocalcemia 1
• Verify absence of hyperphosphatemia (contraindication) 1

Critical Safety Precautions

• Never infuse with calcium-containing IV fluids due to precipitation risk 1
• Never administer undiluted - this causes life-threatening hyperkalemia and cardiac events 1
• Inspect solution for precipitates before and after dilution 1

Monitoring During Treatment

Immediate Monitoring

• Continuous ECG monitoring if infusion rate exceeds 10 mEq potassium/hour 1
• Check serum phosphorus, potassium, calcium, and magnesium every 1-2 days until stable 4

Target Levels

• Target serum phosphorus: 2.5-3.0 mg/dL (lower end of normal range) 4
• Avoid complete normalization as fasting phosphate levels are not fully restored by IV supplementation 4

Special Populations

Moderate Renal Impairment (eGFR 30-60 mL/min/1.73m²)

• Start at the low end of the dose range 1
• Monitor electrolytes more frequently 1

Severe Renal Impairment or ESRD

• Contraindicated - high risk of life-threatening hyperkalemia 1

Practical Example for a 70 kg Adult with Severe Hypophosphatemia

• Calculate dose: 0.5 mmol/kg × 70 kg = 35 mmol phosphorus (51.3 mEq potassium)
• Dilute in 250 mL normal saline (concentration: 14 mmol/100 mL, within peripheral limits)
• Infuse at 6.8 mmol/hour through peripheral line = approximately 4 hours total infusion time
• Alternative: Use central line at 15 mmol/hour = approximately 2.3 hours with continuous ECG monitoring 1

Common Pitfalls to Avoid

• Do not exceed 45 mmol phosphorus (66 mEq potassium) as a single dose - risk of fatal hyperkalemia 1
• Do not infuse faster than 10 mEq potassium/hour peripherally without ECG monitoring 1
• Do not give if serum potassium is already normal or elevated - use sodium phosphate instead 1
• Do not mix with calcium-containing solutions - causes immediate precipitation 1
• Hyperphosphatemia can cause hypocalcemia with tetany and cardiac arrhythmias 1

Transition to Oral Therapy

Once serum phosphorus reaches >2 mg/dL and patient can tolerate oral intake, transition to oral phosphate 750-1,600 mg elemental phosphorus daily divided into 2-4 doses, combined with active vitamin D (calcitriol 0.5-0.75 mcg daily) for chronic hypophosphatemia 5, 4