What is the recommended dosage of potassium phosphate (KP) for treating hypophosphatemia in children?

Potassium Phosphate Dosage in Children with Hypophosphatemia

For children with hypophosphatemia, the recommended dosage of potassium phosphate is 20-60 mg/kg/day of elemental phosphorus divided into 4-6 doses daily, with a maximum dose of 80 mg/kg/day to prevent gastrointestinal discomfort and hyperparathyroidism. 1, 2

Dosing Based on Severity of Hypophosphatemia

Severe Hypophosphatemia (<1.0 mg/dL or <0.32 mmol/L)

• Initial dose: 0.44-0.64 mmol/kg of elemental phosphorus (corresponding to 0.64-0.94 mEq/kg of potassium) 3
• Administer in 4-6 divided doses daily for optimal absorption and maintenance of serum levels 1
• Maximum single dose: 45 mmol phosphorus (66 mEq potassium) 3

Moderate Hypophosphatemia (1.0-1.7 mg/dL or 0.32-0.55 mmol/L)

• Initial dose: 0.32-0.43 mmol/kg of elemental phosphorus (corresponding to 0.47-0.63 mEq/kg of potassium) 3
• Administer in 3-4 divided doses daily 1, 2

Mild Hypophosphatemia (1.8 mg/dL to lower end of normal range)

• Initial dose: 0.16-0.31 mmol/kg of elemental phosphorus (corresponding to 0.23-0.46 mEq/kg of potassium) 3
• Administer in 2-3 divided doses daily 2

Administration Guidelines

Oral Administration

• Phosphate supplements should be taken as frequently as possible to maintain stable blood levels 1
• Avoid administering with calcium-containing foods or supplements as this reduces absorption 1, 2
• For young patients with high alkaline phosphatase (ALP) levels, divide into 4-6 doses daily 1
• Frequency can be reduced to 3-4 times daily when ALP normalizes 1

Intravenous Administration

• Maximum concentration for peripheral venous catheter: 0.27 mmol/10 mL (0.4 mEq/10 mL) for children <12 years 3
• Maximum concentration for central venous catheter: 0.55 mmol/10 mL (0.8 mEq/10 mL) for children <12 years 3
• Maximum infusion rate should be carefully monitored, especially in younger children 3
• Continuous ECG monitoring recommended for infusion rates higher than 0.5 mEq/kg/hour for children weighing less than 20 kg 3

Special Considerations

X-linked Hypophosphatemia

• Combination therapy with phosphate supplements and active vitamin D is recommended 1, 2
• Initial calcitriol dose: 20-30 ng/kg/day or alfacalcidol 30-50 ng/kg/day 1
• For children >12 months: empirical starting dose of 0.5 μg daily of calcitriol or 1 μg of alfacalcidol 1, 2
• Progressive increase in phosphate dose for insufficient clinical response, but avoid exceeding 80 mg/kg/day 1

Parenteral Nutrition

• For preterm infants during the first days of life: 1.0-2.0 mmol/kg/day (31-62 mg/kg/day) 1
• For growing premature infants: 1.6-3.5 mmol/kg/day (50-108 mg/kg/day) 1
• For term newborns to 6 months: 0.7-1.3 mmol/kg/day (20-40 mg/kg/day) 1
• For children 7-12 months: 0.5 mmol/kg/day (15 mg/kg/day) 1
• For children 1-18 years: 0.2-0.7 mmol/kg/day (6-22 mg/kg/day) 1

Monitoring

• Check serum phosphorus, calcium, and potassium levels prior to administration 3
• Monitor serum phosphorus, calcium, and PTH levels regularly during treatment 1, 2
• Assess for clinical improvement of rickets, growth, and bone pain 1
• Monitor for potential complications such as hypercalciuria and nephrocalcinosis 1, 2
• For secondary hyperparathyroidism, increase active vitamin D dose and/or decrease phosphate dose 1, 2

Potential Complications and Precautions

• Avoid doses >80 mg/kg/day to prevent gastrointestinal discomfort and hyperparathyroidism 1
• To prevent nephrocalcinosis, keep calciuria levels within normal range 1
• Consider measures to decrease urinary calcium concentration if needed (regular water intake, potassium citrate, limited sodium intake) 1
• Do not administer phosphate supplements with calcium-containing foods or supplements 1, 2
• Normalize calcium before administering potassium phosphates 3
• Avoid administration with calcium-containing intravenous fluids 3