⚠️ Hypomagnesaemia: May occur in refeeding syndrome and is a recognised complication of prolonged PPI therapy. Magnesium is vital for PTH release, potassium balance, and cardiac stability — deficiency can cause seizures, arrhythmias, and refractory hypocalcaemia or hypokalaemia.

💉 Management Summary: Mg²⁺ <0.5 mmol/L OR <0.7 mmol/L + severe symptoms
⛔ Low Mg²⁺ blocks PTH release → low Ca²⁺ + risk of arrhythmias/seizures. 🚑 Acute replacement: Mg²⁺ 8 mmol (≈2 g MgSO₄) in 100 ml 5% Dextrose or 0.9% Saline over 15–30 mins → then 20 mmol (≈5 g) over 6 hrs. 📉 Monitor: ECG & deep tendon reflexes (lost in severe hypoMg). ⚡ Correct coexisting hypokalaemia/hypocalcaemia. 🚫 Avoid in complete AV block/severe bradycardia; use caution in renal failure.

💉 Management Summary: Mg²⁺ <0.5 mmol/L OR <0.7 mmol/L + severe symptoms

⛔ Low Mg²⁺ blocks PTH release → low Ca²⁺ + risk of arrhythmias/seizures.
🚑 Acute replacement: Mg²⁺ 8 mmol (≈2 g MgSO₄) in 100 ml 5% Dextrose or 0.9% Saline over 15–30 mins → then 20 mmol (≈5 g) over 6 hrs.
📉 Monitor: ECG & deep tendon reflexes (lost in severe hypoMg).
⚡ Correct coexisting hypokalaemia/hypocalcaemia.
🚫 Avoid in complete AV block/severe bradycardia; use caution in renal failure.

🧾 Definition (4 mmol Mg = 1 g MgSO₄)

🙂 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 = seizure, tremor, arrhythmias, tetany.

🧩 Associations

⬇️ Hypocalcaemia → Mg²⁺ needed for PTH secretion.
⬇️ Hypokalaemia → Mg²⁺ needed for Na⁺/K⁺ ATPase activity.

📊 Causes of Hypomagnesaemia

Cause	Clinical Features	Investigations	Management
🍺 Chronic Alcoholism	Cramps, tremor, seizures, irritability, hypocalcaemia signs (Chvostek/Trousseau).	Mg, Ca, K, renal/liver function.	IV/oral Mg, dietary support, alcohol dependence treatment, correct electrolytes.
💩 GI Losses (Diarrhoea, Malabsorption)	Weakness, fatigue, cramps, paraesthesia; often with hypoK/hypoCa.	Mg, Ca, K, phosphate, stool studies, malabsorption screen.	Oral Mg, treat underlying diarrhoea/malabsorption, monitor electrolytes.
💊 Renal Losses (Diuretics, Gitelman)	Cramps, fatigue, metabolic alkalosis, hypoK.	Serum/urine Mg, Ca, K, renal function, genetic test if Gitelman suspected.	Stop causative drug, oral Mg, consider amiloride, genetic counselling.
💊 Proton Pump Inhibitors	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 if present.
🔥 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, Mg/PO₄/K replacement, close monitoring.
💉 Drugs (Aminoglycosides, Amphotericin)	Weakness, tremors, seizures, arrhythmias with hypoK/hypoCa.	Mg, Ca, K, renal function, med history.	Stop/switch drug if possible, Mg replacement, renal/electrolyte monitoring.

🧬 Aetiology & Physiology

Mostly intracellular, stabilises cell membranes, competes with calcium at voltage-gated channels.
Clinical uses: 💊 pre-eclampsia, severe asthma, torsades de pointes.

🧠 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 doses if eGFR <30.

💊 Management

🔍 Review underlying cause (stop culprit drugs e.g. PPIs, diuretics).
🔄 Max 50 mmol/day (up to 160 mmol/5 days).
📉 Severe (<0.5 mmol/L):
- 8 mmol (2 g) MgSO₄ in 100 ml IV fluid over 15 mins.
- + 20 mmol Mg in 100–500 ml fluid IV over 6–24 hrs.
- Check Mg 2 hrs post infusion.
- Give Mg before K⁺ if coexisting hypokalaemia (never mix in same bag).
🙂 Mild (0.5–0.7 mmol/L):
- Oral Mg unless symptomatic.
- If symptomatic → IV regimen as above.
- Oral options:
  - Magnesium aspartate (Magnaspartate®) 1 sachet (10 mmol) BD.
  - Magnesium glycerophosphate (Neomag®) 2 × 4 mmol chewable tablets TDS.

📚 Reference

Royal Cornwall NHS – Hypomagnesaemia Guideline

🩺 Case 1 — GI Losses

A 60-year-old man with chronic diarrhoea due to inflammatory bowel disease presents with muscle cramps, tremor, and palpitations. ECG shows prolonged QT interval with frequent ventricular ectopics. Labs reveal Mg²⁺ 0.35 mmol/L (low), K⁺ 3.0 mmol/L, Ca²⁺ 2.05 mmol/L. Management: 💉 IV magnesium sulphate replacement if symptomatic/ECG changes, otherwise oral magnesium supplements. Correct associated hypokalaemia and hypocalcaemia. Avoid: ❌ Using digoxin until magnesium is corrected (risk of arrhythmia). Avoid rapid IV infusion which can cause hypotension.

🩺 Case 2 — Drug-Induced

A 72-year-old woman with atrial fibrillation and hypertension presents with weakness and dizziness. She has been on a loop diuretic and a PPI for several months. Labs: Mg²⁺ 0.40 mmol/L, K⁺ normal, Ca²⁺ low-normal. ECG shows flat T waves. Management: 💊 Stop/review offending drugs (loop diuretic, long-term PPI). Give oral or IV magnesium replacement depending on severity. Monitor electrolytes closely. Avoid: ❌ Ignoring mild hypomagnesaemia — it predisposes to arrhythmias and potentiates digoxin toxicity. Avoid ongoing PPI use without indication.

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Hypomagnesaemia