Management of Hypomagnesaemia

This guideline is intended for the management of hypomagnesaemia in adults who are not receiving enteral feeds or under the care of the Nutrition Team. Further advice should be sought from the hospital Nutrition Team if required.

Use of magnesium for other indications, e.g. eclampsia or coronary artery disease, is outside the scope of this guideline. Please refer to relevant specialist guidelines.

The reference range for plasma magnesium is 0.7-1mmol/L.

Plasma concentrations should be used in conjunction with presenting signs and symptoms to diagnose hypomagnesaemia (see notes below).

Adults with normal renal function

Magnesium levels should be monitored, and the dose adjusted as necessary. See flowchart below.

Adults with renal impairment

In patients with renal impairment (eGFR <30ml/min) reduced urinary magnesium excretion puts the patient at risk of hypermagnesaemia. See flowchart below for dosing guidance.

Additional information

• Magnesium is mainly an intracellular ion, so plasma concentrations are not an exact measurement of total body stores.
• Magnesium depletion is often associated with other electrolyte abnormalities - reduced K⁺, Ca²⁺, PO₄^3- or Na⁺ levels may co-exist with a low Mg²⁺.
• Symptoms of hypomagnesaemia usually become apparent when magnesium level is ≤0.4mmol/L – including muscle cramps, vertigo, nystagmus, arrhythmias and seizures.
• Consider reviewing medicines that can cause hypomagnesaemia such as proton pump inhibitors (PPIs), loop diuretics, cisplatin chemotherapy, aminoglycosides, theophylline, calcineurin inhibitors (tacrolimus, ciclosporin).
• Establish and correct cause if possible.

• Flowchart Management of hypomagnesaemia

N.B. Doses shown in the flowchart are suggested starting doses. Further advice is available from the Biochemistry Department.