Classification

• Normal: 1.1-0.7
• Mild: 0.69-0.5 – No symptoms or non-specific symptoms, such as lethargy, muscle cramps, or muscle weakness
• Severe: <0.5 – Severe neurologic symptoms such as nystagmus, tetany, seizures, and cardiac arrhythmias

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] <0.5 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] ≥0.5 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

• BNF: Magnesium Sulfate
• BNF Magnesium Aspartate
• UKMI – Acute Hypomagnesaemia
• CHFT – 2016