Hypomagnesaemia

The UK Medicines Information group have provided excellent guidance on how to replace magnesium.

Clinical features

  • Usually asymptomatic
  • Irritability & lethargy
  • Nausea/vomiting
  • Psychiatric: confusion, depression, psychosis
  • Neuromuscular: Tremors, cramps, tetany, weakness & seizures
  • ECG: prolonged PR, ST depression, altered T waves, arrhythmias

Causes

  • Dietary such as refeeding syndrome
  • GI losses (D&V, high stoma output)
  • PPIs
  • Alcoholism
  • Hypercalcaemia
  • Endocrinopathies (aldosteronism, SIADH, DKA)
  • Renal losses
  • Post-parathyroidectomy

Investigations

  • Ensure you’ve checked the other electrolytes (U&Es, calcium)
  • Urinary magnesium can help

Management

  • See the information above however typically deficiency is replaced orally as per trust guidelines
  • IV replacement is another option with 8-16 mmol in 100-200ml of 0.9% sodium chloride or 5% dextrose. However again use the information above & local policies.
  • Be careful of causing diarrhoea & rapid accumulation in poor renal function

References & further reading

  • Hamilton, R.J., 2018. Tarascon adult emergency pocketbook. Jones & Bartlett Learning.
  • Katzel, J.A., Vucuscu, R., Garcia, R., 2013. Wards 101 pocket clinician’s survival guide. Börm Bruckmeier Publishing.
  • Lewis III, J. L., 2018. Hypomagnesemia. MSD Manual Professional Version.
  • OUH Local Guidelines – http://nssg.oxford-haematology.org.uk/oxford/clinical-care/H-95-guidelines-for-management-of-hypomagnesaemia-in-adult-clinical-haematology.pdf.

By Dr Shoaib Hussain

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