What is the recommended dose of Potphos (phosphate supplement) for treating hypophosphatemia?

Potassium Phosphate (Potphos) Dosing

For oral phosphate supplementation in hypophosphatemia, start with 750-1,600 mg of elemental phosphorus daily divided into 2-4 doses for adults, or 20-60 mg/kg/day divided into 4-6 doses for pediatric patients, always combined with active vitamin D (calcitriol 0.5-0.75 μg daily for adults) to prevent secondary hyperparathyroidism. 1

Adult Oral Dosing

Initial dose: 750-1,600 mg elemental phosphorus daily, divided into 2-4 doses to minimize gastrointestinal side effects 1

• Potassium-based phosphate salts are preferred over sodium-based preparations because they reduce the risk of hypercalciuria 1
• Dosing frequency depends on severity: severe hypophosphatemia (<1.5 mg/dL) requires 6-8 times daily dosing initially 1
• Once alkaline phosphatase normalizes, reduce frequency to 3-4 times daily 2

Pediatric Oral Dosing

Initial dose: 20-60 mg/kg/day of elemental phosphorus, divided into 4-6 doses daily 2, 3

• Maximum dose: Do not exceed 80 mg/kg/day to prevent gastrointestinal discomfort and secondary hyperparathyroidism 1, 2
• Young patients with elevated alkaline phosphatase require 4-6 times daily dosing 2
• Reduce to 3-4 times daily once alkaline phosphatase normalizes 2

Mandatory Adjunctive Vitamin D Therapy

Phosphate supplements must always be combined with active vitamin D to prevent secondary hyperparathyroidism and enhance intestinal phosphate absorption 1, 2

Vitamin D Dosing:

• Adults: Calcitriol 0.5-0.75 μg daily OR alfacalcidol 0.75-1.5 μg daily 1
• Pediatric: Calcitriol 20-30 ng/kg/day OR alfacalcidol 30-50 ng/kg/day 2, 3
• Timing: Give active vitamin D in the evening to reduce calcium absorption after meals and minimize hypercalciuria 1

Intravenous Dosing (When Oral Route Inadequate)

For severe hypophosphatemia (<1 mg/dL): 0.32-0.64 mmol/kg (up to maximum 45 mmol phosphorus/66 mEq potassium as single dose) 4

IV Administration Guidelines:

• Check serum potassium before administration - if ≥4 mEq/dL, use alternative phosphorus source 4
• Maximum infusion rate through peripheral line: 6.8 mmol/hour phosphorus (10 mEq/hour potassium) 4
• Maximum infusion rate through central line: 15 mmol/hour phosphorus (22 mEq/hour potassium) 4
• Continuous ECG monitoring required for infusion rates >10 mEq/hour potassium 4

Monitoring Protocol

Initial phase: Check serum phosphorus, calcium, potassium, and magnesium every 1-2 days until stable 3

• Monitor serum phosphorus and calcium at least weekly during initial supplementation 1
• Check alkaline phosphatase and PTH every 3-6 months to assess treatment adequacy 3
• Monitor urinary calcium excretion to prevent nephrocalcinosis (occurs in 30-70% of patients on chronic therapy) 1, 3
• Target phosphorus levels at lower end of normal range (2.5-3.0 mg/dL) rather than complete normalization 3

Critical Dosing Considerations and Pitfalls

Never administer phosphate supplements with calcium-containing foods or supplements - this causes intestinal precipitation and reduces absorption 1, 2

• Dose adjustments: Do not adjust more frequently than every 4 weeks; 2-month intervals preferred for stability 3
• Renal impairment: In patients with eGFR 30-60 mL/min/1.73m², start at low end of dose range and monitor closely 4
• Avoid potassium citrate in patients with X-linked hypophosphatemia - alkalinization increases phosphate precipitation risk 1
• If PTH elevated: Reduce phosphate dose or increase active vitamin D 3
• If PTH suppressed: Increase phosphate or decrease active vitamin D 3

Special Population Considerations

Patients with immobilization >1 week: Discontinue or reduce active vitamin D; restart when ambulating to prevent hypercalciuria 1

• Severe renal impairment (eGFR <30 mL/min/1.73m²): Avoid IV phosphate due to hyperphosphatemia risk 3, 4
• X-linked hypophosphatemia: Requires lifelong combination therapy with phosphate and active vitamin D 1, 3