Phosphate

Chemical

Phosphate – most abundant intracellular anion

Indications

  1. Severe hypophosphataemia (serum <0.3mmol/L)
  2. Hypercalcaemia

Presentation

Oral formulation

  1. Phosphate Sandoz effervescent tablets: 500mg sodium phosphate monobasic

 

IV formulation

  1. Sodium Dihydrogen Phosphate: 10ml ampoule contains (10mmol Na+, 10mmmol PO4–, 20mmol H+)
  2. Potassium Dihydrogen Phosphate: 10ml ampoule contains 1.361g of KH2PO4 (10mmol K+, 10mmol PO4–, 20mmol H+)

 

Incompatible with calcium/magnesium containing solutions → admixture will lead to precipitation

Dose

10-20mmol over 2-3 hours (max infusion rate 0.2mmol/kg/hr)

Route

IV

  • Dilute in 250-500ml bag of 0.9% NaCl or 5% dextrose → peripheral line
  • Dilute in 50-250ml of 0.9% NaCl or 5% dextrose → CVC

Onset

Immediate

MoA

  • Bone structure
  • Energy storage and transfer
  • Metabolic pathways
  • Utilisation of B complex vitamins
  • Buffering of body fluids
  • Renal excretion of hydrogen ions

Drug Interactions

Avoid co administration of aluminium, calcium, magnesium salts with phosphate → bind phosphate and impair absorption from GIT

PK

A

NA

D

65% of infused PO4 remains extracellular

M

NA

E

Mainly renal elimination

Adverse Effects

  • Hypotension, fluid retention
  • GI upset, nausea, diarrhoea
  • Hyperphosphataemia: muscle weakness, paraesthesia, convulsions, cardiomyopathy, respiratory failure, haematological abnormalities
  • Extraskeletal calcification (eg nephrocalcinosis)
  • Hypocalcemia
  • Hyperkalaemia, hypernatremia

Author: Novia Tan