⚠️ Hypomagnesaemia: Often occurs in refeeding syndrome or with long-term PPI use. Magnesium is essential for PTH release, potassium balance, and cardiac stability. Deficiency may cause seizures, arrhythmias, refractory hypocalcaemia/hypokalaemia.

💊 Severity & Definition

🙂 Mild: 0.5–0.7 mmol/L → oral replacement if symptomatic.
😟 Moderate: 0.4–0.5 mmol/L → oral if asymptomatic, IV if symptomatic.
🚨 Severe: <0.4 mmol/L → IV replacement; risks include seizures, tetany, arrhythmias.

🧬 Key Associations

⬇️ Hypocalcaemia → Mg needed for PTH secretion.
⬇️ Hypokalaemia → Mg needed for Na⁺/K⁺ ATPase activity.

📊 Common Causes

Cause	Clinical Features	Investigations	Management
🍺 Chronic Alcoholism	Cramps, tremor, seizures, hypocalcaemia signs	Mg, Ca, K, renal/liver function	IV/oral Mg, correct electrolytes, alcohol support
💩 GI Losses (Diarrhoea, Malabsorption)	Weakness, cramps, paraesthesia, hypoK/hypoCa	Mg, Ca, K, phosphate, stool/malabsorption screen	Oral Mg, treat underlying cause, monitor electrolytes
💊 Renal Losses (Diuretics, Gitelman)	Cramps, fatigue, metabolic alkalosis, hypoK	Serum/urine Mg, Ca, K, renal function	Stop causative drug, oral Mg, consider amiloride, genetic counselling
💊 PPIs	Chronic use → cramps, tetany, weakness (esp elderly)	Mg, Ca, K, review meds	Stop/reduce PPI, oral Mg, monitor levels if PPI must continue
🩸 Diabetes Mellitus	Polyuria, cramps, paraesthesia; may present in DKA	Mg, glucose, HbA1c, urine Mg/K	Optimise glycaemic control, Mg supplementation, treat DKA
🔥 Acute Pancreatitis	Abdominal pain, N+V, hypoCa + hypoK + hypoMg	Mg, Ca, K, amylase/lipase, imaging	Supportive care, IV Mg, correct electrolytes, manage pancreatitis
🍽 Refeeding Syndrome	Weakness, arrhythmias, respiratory failure after nutrition restart	Mg, phosphate, Ca, K	Slow refeeding, electrolyte replacement, close monitoring
💉 Drugs (Aminoglycosides, Amphotericin)	Weakness, tremors, seizures, arrhythmias with hypoK/hypoCa	Mg, Ca, K, renal function, med history	Stop/switch drug, Mg replacement, monitor electrolytes

💊 Replacement Guidelines (UK)

🔍 Review underlying cause (stop culprit drugs e.g., PPIs, diuretics)
🔄 Max 50 mmol/day IV (up to 160 mmol/5 days cumulative)
📉 Severe (<0.5 mmol/L or symptomatic):
- 8 mmol (≈2 g) MgSO₄ in 100 ml 5% Dextrose or 0.9% Saline IV over 15–30 min
- Then 20 mmol (≈5 g) IV in 100–500 ml over 6–24 hrs
- Check Mg 2–12 hrs post-infusion; repeat daily until normalized
- Give Mg before K⁺ if coexisting hypokalaemia (never mix in same IV bag)
🙂 Mild (0.5–0.7 mmol/L):
- Oral Mg unless symptomatic
- Options: Magnesium aspartate 1 sachet BD; Magnesium glycerophosphate 2 × 4 mmol chewable tablets TDS

🧠 Symptoms (Usually if Mg <0.5 mmol/L)

Nausea, vomiting, lethargy, drowsiness
Tetany, tremor, twitching, agitation
Vertigo, confusion, seizures, cardiac arrhythmias

⚠️ Cautions

Renal excretion → risk of hypermagnesaemia in renal failure
Use reduced IV doses if eGFR <30 mL/min/1.73 m²
Avoid rapid infusion in hypotension or AV block

🩺 Case Examples

Case 1 – GI Losses
60-year-old man with chronic diarrhoea, cramps, tremor, palpitations. ECG: prolonged QT, frequent ectopics. Labs: Mg²⁺ 0.35 mmol/L, K⁺ 3.0 mmol/L, Ca²⁺ 2.05 mmol/L.
Management: 💉 IV magnesium if symptomatic/ECG changes, correct K⁺/Ca²⁺. Avoid digoxin until Mg corrected.

Case 2 – Drug-Induced
72-year-old woman on loop diuretic + PPI, presents with weakness, dizziness. Labs: Mg²⁺ 0.40 mmol/L, K⁺ normal, Ca²⁺ low-normal. ECG: flat T waves.
Management: 💊 Stop/review drugs, oral or IV Mg depending on severity, monitor electrolytes. Avoid ongoing unnecessary PPI use.

📚 Reference

Royal Cornwall NHS – Hypomagnesaemia Guideline

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Hypomagnesaemia ✅