Treatment for Severe Hypophosphatemia
For severe hypophosphatemia, intravenous phosphate replacement is recommended at a dose of 0.32 mmol/kg body weight over 12 hours, which can be repeated every 12 hours until serum phosphate reaches ≥2 mg/dL. 1
Intravenous Phosphate Administration
Dosing and Administration
- For adults and pediatric patients ≥12 years with severe hypophosphatemia, administer potassium phosphate IV at an initial dose of 0.32 mmol/kg over 12 hours when oral or enteral replacement is not possible 2, 1
- Maximum initial dose should not exceed phosphorus 45 mmol (potassium 66 mEq) 2
- Infusion rate through a peripheral venous catheter should not exceed phosphorus 6.8 mmol/100 mL (potassium 10 mEq/100 mL) 2
- For central venous administration, maximum concentration can be higher: phosphorus 18 mmol/100 mL (potassium 26.4 mEq/100 mL) 2
- Continuous ECG monitoring is recommended for higher infusion rates 2
Preparation
- Potassium phosphate must be diluted before administration in 0.9% Sodium Chloride or 5% Dextrose 2
- Never administer undiluted phosphate solution as it can cause severe adverse effects 2
- Do not infuse with calcium-containing IV fluids to prevent precipitation 2
Patient Monitoring
Pre-administration Assessment
- Check serum potassium, calcium, and phosphorus levels prior to administration 2
- Normalize calcium before administering phosphate to prevent complications 2
- Only administer potassium phosphate to patients with serum potassium <4 mEq/dL 2
- For patients with potassium ≥4 mEq/dL, use an alternative phosphorus source 2
Ongoing Monitoring
- Monitor serum phosphate, calcium, potassium, and magnesium levels at 6 hours, 12 hours, and every 12 hours thereafter 1
- Watch for signs of hypocalcemia, hyperkalemia, and hyperphosphatemia 2
- Monitor for symptoms of phosphate repletion including improved muscle strength and neurological function 3
Special Considerations
Renal Impairment
- In patients with moderate renal impairment (eGFR ≥30 to <60 mL/min/1.73m²), start at the low end of the dose range 2
- For severe renal impairment, a slower infusion rate is recommended: 2.5-3.0 mg phosphate/kg body weight every 6-8 hours 4
- Patients with impaired kidney function have lower risk of developing hypophosphatemia due to reduced GFR 5
Iron-Induced Hypophosphatemia
- For hypophosphatemia caused by ferric carboxymaltose (FCM), the most important management is cessation of FCM 5
- Phosphate repletion should be avoided in FCM-induced hypophosphatemia as it raises PTH and worsens phosphaturia 5
- Treatment should be directed at mitigating secondary hyperparathyroidism with vitamin D supplementation 5
X-Linked Hypophosphatemia
- For X-linked hypophosphatemia, oral phosphate supplements (20-60 mg/kg/day of elemental phosphorus) combined with active vitamin D is recommended 5
- Phosphate should be given as frequently as possible (4-6 times daily) to maintain stable blood levels 5
- Avoid doses >80 mg/kg daily to prevent gastrointestinal discomfort and hyperparathyroidism 5
Potential Complications
Risks of IV Phosphate Administration
- Hyperphosphatemia can cause formation of insoluble calcium phosphorus products leading to hypocalcemia 2
- Pulmonary vascular emboli and pulmonary distress related to precipitates can occur 2
- Hyperkalemia, including life-threatening cardiac events, especially with excessive doses or rapid infusion 2
- Vein irritation, damage, or thrombosis with peripheral administration 2
Prevention of Complications
- Dilute phosphate appropriately based on central vs. peripheral administration 2
- Visually inspect solution for particulate matter before and after dilution 2
- Check infusion set and catheter periodically for precipitates 2
- In patients at risk for aluminum toxicity (especially those with renal impairment), maintain total aluminum exposure at no more than 5 mcg/kg/day 2