Hypomagnesium

Question 1

What are the clinical features?

Answer 1

• Clinical features:
○ Usually it is asymptomatic
○ Irritability/lethargy
○ Nausea/vomiting
○ Psychiatry: confusion, depression, psychosis
○ Carpopedal spasm
○ Hyperinsulinism
○ Neuromuscular: Tremors, ataxia, cramps, tetany, weakness, seizures, vertigo
ECG: prolonged PR, ST depression, altered T waves, arrythmia’s

Question 2

What causes low Mg

Answer 2

• Drugs: Diuretics PPIs, ciclosporin, foscarnet, amphotericin B, pentamidine, cancer chemotherapy especially cisplatin
  
  • GI loss: Severe diarrhea, vomiting, high stoma output
  • Malnutrition and fistula
  • Endocrinopathies: aldosteronism, SIADH, DKA
  • Renal losses
  • Ketoacidosis
  • Gitleman’s and Bartter’s
  • Acute pancreatitis
  • Alcohol abuse
  • TPN or fluid therapy long term
  • Lactation
  • Dietary e.g refeeding
  • Low calcium
  • Low phosphate
  • Low K+
  • Post parathyroidectomy
  • Hypercalcemia secondary to hyperparathyroidism-calcium and magnesium functionally compete for transport in the thick ascending limb of the loop of Henle
  • Renal tubular excess
• Cirrhosis

Question 3

Do you investigate low Mg

Answer 3

Leads to hypocalcaemia (due to reducing PTH secretion) and hypokalaemia (due to NA/K+ ATPAS)
Ensure that you have checked the other electrolytes (UE/Calcium), urinary mg can help

Question 4

How do you manage low Mg

Answer 4

Typically deficiency is replaced orally as per trust guidelines
• Magnesium replacement should be prescribed for patients with a serum magnesium concentration of 0.4 mmol/L or less
○ For patients with a serum magnesium concentration of 0.4 - 0.7 mmol/L, magnesium replacement should be considered if the patient presents with symptoms of hypomagnesaemia or following a clinical risk/benefit decision
• IV replacement is another option with 8-16 mmol in 100-200ml of 0.9% sodium chloride or 5% dextrose. However again use the information above & local policies.
• Be careful of causing diarrhoea & rapid accumulation in poor renal function