How to correct hypophosphatemia using Glycophos (Sodium Glycerophosphate)?

Correcting Hypophosphatemia with Sodium Glycerophosphate (Glycophos)

For moderate to severe hypophosphatemia, administer sodium glycerophosphate at 20-60 mg/kg/day of elemental phosphorus divided into 4-6 doses, with each cc containing 1 mmol phosphate (31 mg elemental phosphorus), and always combine with active vitamin D therapy to prevent secondary hyperparathyroidism. 1, 2

Dosing Calculation and Administration

Converting Glycophos to Elemental Phosphorus

• Each cc of sodium glycerophosphate contains 1 mmol of phosphate, which equals 31 mg of elemental phosphorus 1
• For a 70 kg adult with moderate hypophosphatemia:
  • Target dose: 20-60 mg/kg/day = 1,400-4,200 mg elemental phosphorus/day
  • This translates to approximately 45-135 cc of Glycophos per day
  • Divide into 4-6 doses = 7.5-33 cc per dose 1, 2

Maximum Dosing Limits

• Never exceed 80 mg/kg/day (approximately 2,480 mg for a 70 kg adult or 80 cc of Glycophos) to prevent gastrointestinal discomfort and secondary hyperparathyroidism 1, 2

Dosing Frequency Strategy

• Give 4-6 times daily initially in patients with elevated alkaline phosphatase levels 2, 3
• Reduce to 3-4 times daily once alkaline phosphatase normalizes 2, 3
• More frequent dosing reduces osmotic load per dose and minimizes gastrointestinal side effects 2

Severity-Based Approach

Severe Hypophosphatemia (Serum Phosphorus <1.0 mg/dL)

• In DKA patients with cardiac dysfunction, anemia, respiratory depression, or serum phosphate <1.0 mg/dL, add 20-30 mEq/L potassium phosphate to replacement fluids 4
• For life-threatening hypophosphatemia (<2.0 mg/dL), consider intravenous phosphate at 0.16 mmol/kg administered at 1-3 mmol/hour until level reaches 2 mg/dL 5
• In renal failure patients, slower infusion rates (2.5-3.0 mg phosphate/kg body weight every 6-8 hours) are safer, continuing until serum phosphate reaches 5.0-5.5 mg/dL 6

Moderate Hypophosphatemia (1.0-2.5 mg/dL)

• Oral supplementation with sodium glycerophosphate at 20-60 mg/kg/day divided into 4-6 doses is appropriate 1, 2
• Start at lower end of dosing range (20 mg/kg/day) and titrate upward based on response 3

Mandatory Concurrent Active Vitamin D Therapy

Active vitamin D must be given with every phosphate supplementation regimen to prevent secondary hyperparathyroidism, counter calcitriol deficiency, and increase intestinal phosphate absorption. 1, 2

Vitamin D Dosing

• Calcitriol: 20-30 ng/kg/day in children or 0.50-0.75 μg daily in adults 1
• Alfacalcidol: 30-50 ng/kg/day in children or 0.75-1.5 μg daily in adults 1
• Alfacalcidol requires 1.5-2.0 times the dose of calcitriol due to differences in oral bioavailability 2
• Give active vitamin D in the evening to reduce calcium absorption after meals and minimize hypercalciuria 1

Critical Administration Guidelines

Timing and Drug Interactions

• Never administer phosphate supplements with calcium-containing foods or supplements, as precipitation in the intestinal tract reduces absorption 1, 2, 3
• Serum phosphate levels increase rapidly after oral intake but return to baseline within 1.5 hours, which is why frequent dosing is essential 2

Sodium Load Considerations

• Each cc of Glycophos contains 2 mmol of sodium (46 mg) [@Question Context]
• For a 70 kg adult receiving 60 mg/kg/day (approximately 135 cc), this adds 270 mmol (6,210 mg) of sodium daily
• Monitor for volume overload, especially in patients with heart failure or renal impairment [@6@]

Monitoring Protocol

Initial Monitoring (Until Stable)

• Check serum phosphorus, calcium, potassium, and magnesium every 1-2 days until stable [1, @3@]
• Monitor for hyperkalemia, particularly in severe hypophosphatemia cases receiving potassium phosphate [@8@]
• Check renal function (eGFR) to detect complications [@2@, 2]

Target Levels

• Target phosphorus levels at the lower end of normal range (2.5-3.0 mg/dL or 0.81-0.97 mmol/L) rather than complete normalization [1, @3@]
• Fasting phosphate levels are not fully restored by oral supplements alone [@3@]

Long-Term Monitoring (Every 3-6 Months)

• Monitor alkaline phosphatase and PTH levels to assess treatment adequacy [@2@, 2]
• Check urinary calcium excretion to detect early hypercalciuria, which occurs in 30-70% of treated patients and can lead to nephrocalcinosis [@3@]

Dose Adjustment Algorithm

Based on PTH Levels

• If PTH levels are elevated: reduce phosphate dose or increase active vitamin D [@3@]
• If PTH levels are suppressed: increase oral phosphate or decrease active vitamin D 2

Timing of Adjustments

• Do not adjust doses more frequently than every 4 weeks, with 2-month intervals preferred for stability 2

Special Populations and Precautions

Renal Impairment

• Use lower doses and monitor more frequently in patients with reduced kidney function [@2@, 2]
• Avoid IV phosphate in severe renal impairment (eGFR <30-60 mL/min/1.73m²) due to risk of hyperphosphatemia [@3@]
• Carefully monitor serum phosphate levels in patients with eGFR <60 mL/min/1.73m² 2

Immobilization

• Decrease or stop active vitamin D if patients are immobilized for prolonged periods (>1 week) to prevent hypercalciuria and nephrocalcinosis risk [@2@, @4@]
• Restart therapy when patient begins ambulating [@2@, @4@]

ICU Patients on CRRT

• Electrolyte abnormalities including hypophosphatemia occur in 60-80% of ICU patients on intensive continuous renal replacement therapy due to excessive removal [@3@]
• Hypophosphatemia during CRRT is associated with worsening respiratory failure, prolonged mechanical ventilation, cardiac arrhythmias, and prolonged hospitalization 2

Critical Pitfalls to Avoid

• Never give IV phosphate when serum phosphorus is already within normal range before treatment initiation [@3@]
• Avoid large doses of active vitamin D without monitoring urinary calcium, as this promotes hypercalciuria and nephrocalcinosis [@3@]
• Do not use insufficient doses of active vitamin D, which leads to low intestinal calcium absorption, persistent rickets, and elevated ALP/PTH [@3@]
• Avoid complete discontinuation of phosphate supplements if medically necessary, as this may worsen the underlying condition 2
• In DKA, overzealous phosphate therapy can cause severe hypocalcemia, though prospective studies have not shown benefit on clinical outcomes [@1