Hypomagnesaemia

Classification

  • Normal: 1.1-0.7
  • Mild: 0.69-0.5
  • Moderate: 4.9-4.0
  • Severe: <0.4

Signs/Symps (normally <0.5)

  • MSK: Muscle Twitch, Tremor, Tetany, Cramps
  • CNS: Apathy, Depression, Hallucination, Agitation, Confusion, Seizure
  • CVS: Tachycardia, Hypertension, Arrhythmia, Digoxin Toxicity
  • BioChem: Hypokalaemia, Hypocalcaemia, Hypophosphataemia, Hyponatraemia

Causes

  • Reduced Intake:  Diarrhoea & Vomiting, Small bowel resection Malabsorption states , Alcoholism 
  • Increased Loss: Chronic renal failure, Drainage from fistula, Refeeding syndrome 
  • Drugs: Aminoglycosides, Amphotericin, Carboplatin, Ciclosporin, Cisplatin, Diuretics (Loop & Thiazides), Foscarnet, Proton pump inhibitors (PPIs), Salbutamol, Tacrolimus.

Treatment

[Mg] <0.4 or Symptomatic:

  • Magnesium Sulfate 5g (20mmol) over 3hrs, in 1000ml 0.9% NaCl or 5% Glucose
    • Serious Arrhythmias – 2g (8mmol) can be given over 10-15min
    • Actively Seizing – 2-4g (8-16mmol) can be given over 10-15min
  • Admit – Patients may require large doses up to 40g (160mmol) over 5 days

[Mg] ≥0.4 and Asymptomatic:

  • Oral magnesium replacement should be considered as first choice where possible.
    • A rapid raise in [Mg] i.e. IV replacement, reduces the stimulus to retain magnesium.
  • Magnesium Aspartate 10-20mmol/day (1-2 sachets/day)
  • Diarrhoea/Increased stoma output may occur
  • GP to monitor [Mg]

 

References

 

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