Treatment of low and high magnesium levels

A: There is no national guidance on the treatment of hypomagnesaemia or hypermagnesaemia, and practice varies widely between hospitals. This information reflects practice at Leeds Teaching Hospitals NHS Trust.

Hypomagnesaemia

Magnesium replacement should be prescribed for patients with a serum magnesium concentration £0.4mmol/L or for those with symptoms of hypomagnesaemia. Oral magnesium therapy should be considered first line. Most oral magnesium preparations are unlicensed and there is no clear evidence of greater efficacy or safety for one preparation over another.

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 can be considered. Magnesium sulphate is the IV preparation of choice. The licensed dose for treating hypomagnesaemia is 5g of magnesium sulphate in 1L sodium chloride 0.9% or glucose 5%, infused IV over 12 hours. Many patients will be unable to tolerate such a large volume of fluid and so practice is likely to vary locally.

Magnesium is renally cleared so it should be used with caution in patients with renal impairment (especially when given IV).

Hypermagnesaemia

In asymptomatic patients with a serum magnesium level of 2–4mmol/L, remove the source of magnesium, maintain good urine output and measure serum magnesium levels again after 24 hours.

In symptomatic patients or those with serum magnesium level above 4mmol/L consider a slow IV injection of 10ml calcium gluconate 10%. Recheck serum magnesium levels after four hours; if the concentration has not declined sufficiently the IV calcium dose can be repeated, otherwise dialysis may be required.

Monitor serum magnesium levels and other electrolytes as appropriate. Because magnesium is renally cleared, closer monitoring is likely to be required for patients with renal impairment.