IV Phosphate Dosing for Hypophosphatemia
For severe hypophosphatemia requiring IV replacement, the maximum initial or single dose is 45 mmol of phosphorus (66 mEq potassium), infused at approximately 6.8 mmol/hour (10 mEq potassium/hour) through a peripheral line, with continuous ECG monitoring recommended for higher infusion rates. 1
Critical Safety Warnings
Never administer IV phosphate undiluted or as a rapid IV push - this has resulted in cardiac arrest, arrhythmias, hypotension, and death. 1
- Single doses ≥50 mmol phosphorus and/or rapid infusion rates (over 1-3 hours) have caused death, cardiac arrest, QT prolongation, hyperkalemia, hyperphosphatemia, and seizures 1
- Always dilute and infuse slowly - the recommended rate is approximately 6.8 mmol phosphorus/hour (10 mEq potassium/hour) 1
Dosing by Severity
Severe Hypophosphatemia (<1.0 mg/dL)
Weight-based approach:
- High-dose regimen: 1.0 mmol/kg infused over 12 hours for patients with severe hypophosphatemia and multiple contributing factors 2
- Alternative validated regimen: 0.32 mmol/kg infused over 12 hours, repeated every 12 hours until serum phosphorus ≥2 mg/dL 3
- Fixed-dose approach: 9 mmol every 12 hours has proven safe and effective 4
Moderate Hypophosphatemia (1.0-2.0 mg/dL)
- Moderate-dose regimen: 0.64 mmol/kg infused over 12 hours 2
- This dose effectively increases serum phosphorus to normal range within 24-36 hours 2
Mild Hypophosphatemia (2.0-2.5 mg/dL)
- Low-dose regimen: 0.32 mmol/kg infused over 12 hours 2
- Consider oral supplementation instead if patient can tolerate enteral route 5
Alternative Individualized Dosing Formula
For ICU patients, a calculated approach may be used:
- Phosphate dose (mmol) = 0.5 × body weight (kg) × (1.25 - [serum phosphate in mmol/L]) 6
- Infuse at maximum rate of 10 mmol/hour 6
- This formula is effective but more accurate for moderate than severe hypophosphatemia 6
Potassium vs Sodium Phosphate Selection
- Use potassium phosphate when serum potassium <4 mEq/L 2
- Use sodium phosphate when serum potassium ≥4 mEq/L 2
- Do NOT administer potassium phosphate if serum potassium ≥4 mEq/dL - use an alternative phosphorus source instead 1
Contraindications to IV Phosphate
Absolute contraindications include: 1
- Hyperkalemia
- Severe renal impairment (eGFR <30 mL/min/1.73m²) or end-stage renal disease
- Hyperphosphatemia
- Hypercalcemia or significant hypocalcemia
Monitoring Requirements
Check before administration:
- Serum potassium - if ≥4 mEq/dL, do not use potassium phosphate 1
- Renal function - contraindicated if eGFR <30 1
- Serum calcium - contraindicated if hypercalcemia present 1
Monitor during and after treatment:
- Serum phosphorus, potassium, calcium, and magnesium every 12 hours initially 3, 4
- Continuous ECG monitoring for infusion rates exceeding 6.8 mmol/hour 1
- Check for calcium-phosphate precipitates in IV lines and solution 1
Special Populations
Moderate renal impairment (eGFR 30-60 mL/min/1.73m²):
Cardiac disease patients:
Common Pitfalls to Avoid
- Do not exceed 45 mmol phosphorus as initial single dose - higher doses significantly increase risk of fatal complications 1
- Do not infuse faster than 6.8 mmol/hour through peripheral line without continuous ECG monitoring 1
- Do not mix with calcium-containing solutions - risk of fatal pulmonary emboli from calcium-phosphate precipitates 1
- Do not use phosphate repletion for ferric carboxymaltose-induced hypophosphatemia - it worsens the condition by raising PTH and increasing phosphaturia; use vitamin D supplementation instead 7