There is no national guidance on the treatment of hypomagnesaemia, and practice varies widely between hospital Trusts. The guidance in this document reflects practice at Leeds Teaching Hospitals NHS Trust.
Magnesium replacement should be prescribed for patients with a serum magnesium concentration of 0.4mmol/L or less.
Oral magnesium therapy should be considered first-line. Most oral magnesium preparations are unlicensed. The standard dose of oral magnesium for hypomagnesaemia is 24mmol daily in divided doses, however oral magnesium salts frequently cause diarrhoea.
If the oral route is not appropriate, intravenous magnesium therapy may be considered. Magnesium sulfate (sulphate) is the salt of choice. The licensed dose for the treatment of hypomagnesaemia is 5 grams magnesium sulfate in 1 litre sodium chloride 0.9% or glucose 5%, however local practice may vary.
Intramuscular or subcutaneous magnesium replacement may be considered if the oral and intravenous route is not available. Subcutaneous magnesium administration is unlicensed.
Magnesium is renally cleared. Magnesium (especially via the intravenous route) should be used with caution in patients with renal impairment.