Normal range: 0·7 to 1·0mml/L

This guidance is for magnesium DEFICIENCY only, for treatment of pre-eclampsia, cardiac arrhythmias or asthma refer to relevant specialists.

These guidelines do not apply to critically ill patients or to patients at risk of refeeding syndrome. For refeeding syndrome please see Policy for prevention and management of refeeding syndrome in adults

Aetiology

  • GI losses eg diarrhoea, malabsorption
  • diabetes
  • alcoholism
  • diuretics
  • other drugs eg PPIs, amphotericin, cisplatin, aminoglycosides
  • pancreatitis

Clinical Features

  • paraesthesia
  • cramps
  • twitching
  • carpopedal spasm
  • ECG changes – widening of QRS, prolonged PR interval
  • ventricular arrhythmias
  • increased risk of digoxin toxicity
  • apathy
  • depression

Hypomagnesaemia Treatment Regimen

Magnesium Level Action Monitor
0·5 to 0·7mmol/L

Oral or via enteral feeding tube: The contents of one magnesium aspartate dihydrate oral powder sachet (Magnaspartate®) (10mmol Mg) once or twice daily. See point 1

Adults with eGFR less than 30mL/min should have above recommendations halved

 Check magnesium levels daily. Continue treatment for 48 hours after magnesium levels return to normal.
Less than 0·5mmol/L

All infusions must be administered via an infusion pump.

IV: Peripheral Administration. See point 2 

Not for patients with heart block or existing myocardial damage. See point 3.

20mmol (10mL magnesium sulfate 50% injection (2mmol/mL)) in 250mL glucose 5% over 3 hours. See point 4.
Give a total of three doses at 12 hour intervals
ie dose 1 at t = 0 hours
dose 2 at t = 12 hours and dose 3 at t = 24 hours
This may not be enough to replete magnesium stores and treatment may need to be continued. See point 5.

Adult with impaired eGFR less than 30mL/min should receive 50% of the recommended dose delivered over a longer period
ie 10mmol (5mL) magnesium sulfate 50% (2mmol/mL) in 250mL glucose 5% over 6 hours. See point 4. Give a total of three doses at 12 hour intervals.

Monitor BP, heart rate, respiratory rate, urine output and for signs of hypermagnesaemia during infusion. See point 6.

ECG monitoring is not routinely required in the stable patient.

For eGFR >30mL/min:
Check magnesium 6 hours after last infusion ends
(ie t=30 hours)
Following this, check magnesium daily until stable and underlying cause resolved.

For eGFR <30mL/min:
Check magnesium levels 6 hours after the end of second infusion prior to starting the third infusion.
If levels are >0.7mmol/L retest 6 hours later and take advice from Consultant Nephrologist before administering third IV dose.
  1.  Start with a low dose and titrate up to minimise the risks of diarrhoea; higher doses are more likely to cause diarrhoea. The oral route is not always realistic where patient is symptomatic or where the deficit is severe as large doses will need to be given. These higher doses can cause diarrhoea regardless of careful titration. Parental treatment of such patients may need to be considered.
  2. Other parental routes can be employed if the IV route is not available- seek advice from Medicines Information telephone 01463 704288 or e-mail nhshighland.medicineinformation@nhs.scot
  3. haemodynamically unstable patients should have bolus Mg. 1 to 2 grams of magnesium sulfate (8 to 16 mEq [4 to 8 mmol]) can be given initially over 2 to 15 minutes
  4. If fluid restricted, dose may be diluted in 100ml glucose 5%.
  5. Symptomatic hypomagnesaemia is associated with a deficit of 0·5 to 1mmol/kg; up to 160mmol magnesium over up to 5 days may be required.
  6. Hypermagnesaemia symptoms include respiratory depression, loss of deep tendon reflexes, nausea, vomiting, flushing of the skin, thirst, hypotension due to peripheral vasodilatation, drowsiness, confusion, slurred speech, double vision, muscle weakness, bradycardia, coma, and cardiac arrest.

Toxicity is most likely to occur in patients with chronic kidney disease. Serious toxicity eg respiratory depression or arrhythmias may be reversed temporarily by 5mmol IV calcium.

Abbreviations

Abbreviation Meaning
ECG Electrocardiogram
eGFR Estimated Glomerular Filtration Rate
GI Gastrointestinal
PPI Proton pump inhibitors

Editorial Information

Last reviewed: 28/04/2022

Next review date: 28/04/2025

Author(s): Renal Department .

Approved By: TAM Subgroup of ADTC

Reviewer name(s): Dr S Lambie, Consultant.

Document Id: TAM292