Management of Hypophosphataemia

Introduction

Hypophosphataemia may be asymptomatic, but clinical symptoms usually become apparent when plasma phosphate concentrations fall below 0.3mmol/L. Possible symptoms include: weakness, anorexia, malaise, tremor, paraesthesia, seizures, acute respiratory failure, arrhythmias, altered mental status and hypotension.

Assessment / monitoring

Serum phosphate (reference range 0.8-1.5mmol/L)
Symptoms as above

Drug therapy / treatment options

Suggested starting doses:

Mild Hypophosphataemia (0.6-0.79mmol/L)

No treatment required.

Moderate Hypophosphataemia (0.3-0.59mmol/L):

Phosphate Sandoz^® 1-2 tablets orally three times daily (each tablet contains 16mmol phosphate, 3mmol potassium and 20mmol sodium). Oral replacement is usually sufficient but consider intravenous replacement if patient has phosphate level 0.3-0.5mmol/L and is symptomatic or nil-by-mouth or unlikely to absorb oral phosphate.

Sodium glycerophosphate 21.6% IV 20mmol (20ml) in 500ml glucose 5% over 12 hours. The 20ml solution contains 20mmol phosphate (1mmol/ml) and 40mmol sodium (2mmol/ml).

Notes:

The dose should be reviewed daily according to phosphate levels.
Diarrhoea is a common side effect of oral phosphate therapy and may necessitate a reduction in dose. Give in at least 120 ml of water to reduce risk of diarrhoea.

Severe Hypophosphataemia (<0.3mmol/L):

Phosphate level <0.3mmol/L and patient has impaired renal function:

Sodium glycerophosphate 21.6% IV 20mmol (20ml) in 500ml glucose 5% over 12 hours.
Phosphate level <0.3mmol/L and patient has normal renal function:

Sodium glycerophosphate 21.6% IV 40mmol given as 2 x 12 hour infusions, i.e. 20mmol (20ml) in 500ml glucose 5% over 12 hours x 2.
- Considering that the normal adult intake of phosphate is about 35 mmol per day, a reasonable typical IV replacement is 20-40mmol per day.
- For intravenous replacement sodium glycerophosphate 21.6% has replaced Addiphos^® as treatment of choice for hypophosphataemia as it contains no potassium and therefore removes associated risks.
Notes:
- Serum phosphate, potassium, calcium and magnesium levels should be monitored every 12-24 hours during IV phosphate administration.
- Monitor renal function regularly.
- Repeat the dose within 24 hours if an adequate level (>0.64mmol/L) has not been achieved.
- Hypotension, hyperphosphataemia, hypocalcaemia, hypernatraemia, dehydration and metastatic calcification are possible adverse effects of intravenous phosphate therapy.

Guideline reviewed: May 2023

Page last updated: May 2023