Treatment of neonatal hypophosphataemia: answers

Abstract

QUESTION 1

What daily dose, in mmol, of phosphate is required to treat this child?

• 1.2 mmol/kg/day × 1.2 kg = 1.44 mmol/day

QUESTION 2

What volume, in ml, of 21.6% sodium glycerophosphate will be needed to provide the daily dose calculated in Question 1?

• From the chemical formula it can be seen that each molecule of sodium glycerophosphate contains one atom of phosphate. Therefore, 1 mole of sodium glycerophosphate molecules will contain 1 mole of phosphate atoms
• The stock solution is 21.6% w/v so 100 ml of the stock will contain 21.6 g of sodium glycerophosphate
• 21.6 g of glycerophosphate/molecular mass of 216 g/mol = 0.1 moles/100 ml = 100 mmol/100 ml = 1 mmol/ml
• To give 1.44 mmol/day they need to be infused with 1.44 mmol/1 mmol/ml = 1.44 ml/day
• This would require an hourly infusion rate of (1.44 ml/day/24 hours/day) = 0.06 ml/hour of stock solution