Hypomagnasaemia

1. Is the patient unwell?

• ABCDE approach 

2. Is the result a true value?

• Could the sampling method have affected the result?
• Is there a previous level?

3. Does the patient have any symptoms or signs?

• May indicate the significance and rapidity of electrolyte change
• Neuromuscular- muscle spasm, weakness, vertigo, ataxia, seizure
• Bone – osteoporosis/ osteomalacia (chronic only)
• ECG changes – QRS prolongation, PR prolongation, ventricular arrhythmia

4. Are there culprit drugs? - consider stopping them

• Alcohol, PPIs, aminoglycosides, amphotericin, ciclosporin, cisplatin, diuretics

5. Causes? - treat them

• Diarrhoea, intestinal fistula, malabsorption, acute pancreatitis

Care in Myaesthenia Gravis - magnesium replacement can worsen muscle weakness - contact neurology to advise

Severe (Mg²⁺ < 0.3 mmol/L OR symptoms OR ECG changes)

• 20 mmol magnesium sulphate (10 ml of 50% magnesium sulphate) in 500 ml 0.9% saline OR 5% dextrose at 21-42 ml per hour (as slow as possible but can be sped up if clinically indicated and discussed with senior).
  reduce dose by 50% if eGFR <25
• Check Mg²⁺ at end of infusion
• Infusion can be repeated daily

Moderate (Mg²⁺ 0.3-0.7 mmol/L AND asymptomatic)

• Magnaspartate (10 mmol magnesium per sachet) 1 sachet twice daily for 7 days (NHS Lothian first line)
  OR
  Magnesium glycerophosphate (neomag, 4 mmol magnesium per tablet) 2 tablets three times daily for 7 days (NHS Lothian second line).
  note - contact renal (in working hours) if eGFR <30 - treatment would be off-label but may be appropriate
• Monitor for side effect of diarrhoea
• Recheck levels weekly

Note: oral replacement of magnesium can worsen diarrhoea,so if intestinal disruption is thought to be the cause of hypomagnasaemia, consider IV magnesium instead even in moderate hypomagnasaemia

Seek senior advice if concerns

Cardiac monitoring or HDU review?

• Cardiac monitoring needed in severe hypomagnasaemia only if patient a candidate for escalation of care
• Consider HDU review if significant ECG changes or risk of arrhythmia, particularly if patient is bradycardic or concern regarding heart block