Acute Hypomagnesaemia Protocol

The magnesium dose, the route, and the rate it can safely be given at · v1.2

Enter the magnesium, the concurrent potassium and calcium, the ECG findings, the symptoms and whether oral replacement is tolerated.
You get a stepwise replacement protocol, with the effects on the other electrolytes flagged.
On a proton pump inhibitor, replacement alone will not correct it.
A level inside the reference range does not exclude depletion, so read the number against the patient rather than on its own.

Children and adolescents under 18.
The cause of the low magnesium.
Magnesium in pregnancy, where magnesium sulphate is given for a different reason, at different doses, against a different set of monitoring rules.
Hypermagnesaemia.
Correction of the potassium and the calcium. It flags what the magnesium is doing to both and leaves the correcting to the tools that own them.

Chronic alcohol use is the commonest cause of hypomagnesaemia on a medical ward, through renal magnesium wasting, and it carries a consequence that is easy to miss: the thiamine-dependent enzymes need magnesium as a cofactor, so thiamine repletion can fail entirely while the magnesium is low. If this patient drinks, correct both together and see the Alcohol Withdrawal: CIWA-Ar and Thiamine Protocol.

1. Biochemical Status

Serum Magnesium (mg/dL)

ECG Findings

Concurrent Serum K+ (mEq/L) · optional

Concurrent Serum Ca (mg/dL) · optional

2. Symptoms & Access

Clinical Symptoms

Oral Tolerance

3. Clinical Modifiers & Causes

Loop / Thiazide Diuretics Furosemide, Torsemide, HCTZ. Most common drug cause.

Proton Pump Inhibitor (PPI) Chronic PPI use impairs intestinal Mg absorption. Increasingly recognised cause.

Chronic Alcohol Use Poor intake + renal wasting + GI losses. May coexist with thiamine deficiency.

Nephrotoxic Drugs Amphotericin B, Cisplatin, Aminoglycosides, Calcineurin inhibitors (Tacrolimus/Cyclosporine).

GI Losses Chronic diarrhoea, malabsorption, short bowel syndrome, NG suction.

DKA / Refeeding Syndrome Osmotic diuresis (DKA) or intracellular shift (refeeding). Anticipate Mg depletion.

1. Why Magnesium Affects Potassium, Calcium and Rhythm

Magnesium is a cofactor for over 300 enzymatic reactions, including the Na+/K+-ATPase pump that holds the potassium gradient, the adenylate cyclase that carries PTH signalling, and ATP metabolism itself. Fixing magnesium first is often the key to fixing everything else.

Refractory hypokalaemia (ROMK channel activation → renal K wasting).
Refractory hypocalcaemia (impaired PTH secretion and skeletal PTH resistance).
Cardiac arrhythmias (prolonged QT, Torsades de Pointes).

2. IV MgSO4: Rate Limits & Safety

Severity	Dose	Rate	Notes
Mild (1.5-1.7)	1-2g MgSO4	Over 1 to 2 hours	Oral preferred if tolerated
Moderate (1.0-1.4)	2-4g MgSO4	Over 4 to 6 hours	IV preferred. Follow with oral maintenance.
Severe (< 1.0)	4-6g MgSO4 loading	First 2g over 15 to 30 minutes, or 5 to 15 minutes with seizures or torsades, then remainder over 6 to 12 h	Monitor for Mg toxicity: loss of DTRs, resp depression
Cardiac arrest / TdP	2g MgSO4 IV push	Over 2 to 5 minutes	Undiluted push is acceptable in arrest settings

MgSO4 Toxicity Signs (in order of appearance):
(1) Loss of deep tendon reflexes (DTRs). CHECK BEFORE EACH DOSE. (2) Respiratory depression. (3) Hypotension. (4) Cardiac arrest (bradycardia → asystole). Antidote: IV Calcium Gluconate 10%, 10 to 20 mL (1 to 2 g) over 5 to 10 minutes. It antagonises magnesium rather than removing it, so the effect is transient and the dose may need repeating. Haemodialysis is what removes magnesium in anuria or established renal failure.

3. The PPI Problem

Chronic PPI use, which in Indian practice is close to universal, reduces intestinal magnesium absorption by inhibiting the TRPM6/7 channels. Omeprazole, Pantoprazole, Rabeprazole: any of them, at any dose.

The effect is not dose-dependent, and it appears only after months to years of use, which is why it is missed in a patient who has taken the drug uneventfully for a decade.
It is NOT corrected by IV or oral Mg replacement while the PPI continues, because the absorptive defect is still there.
Management: switch to H2-blocker (Ranitidine/Famotidine) if possible. If PPI is essential, add high-dose oral Mg supplementation and monitor levels regularly.

4. Oral Magnesium: Indian Formulations

Preparation	Elemental Mg	Bioavailability	GI Tolerance	Indian Brands
Magnesium Oxide	60% by weight	Low (4%)	Poor (diarrhoea)	Mag-SR, Magox
Magnesium Hydroxide	42%	Low	Laxative effect	Milk of Magnesia
Magnesium Citrate	16%	Moderate	Good	Limited availability
Magnesium Glycinate	14%	High	Best tolerated	MagTech, Now Foods
Magnesium L-Threonate	8%	High (CNS penetration)	Good	Specialty import

Practical note: The most commonly available oral Mg in Indian government hospitals is Magnesium Oxide (Mag-SR 400 mg = ~240 mg elemental Mg). Despite poor bioavailability, it is effective at higher doses. The limitation is the diarrhoea, which wastes magnesium of its own and works against the very thing you are treating.

5. Magnesium and Torsades de Pointes

IV MgSO4 2g is the first-line treatment for Torsades de Pointes (TdP), regardless of the serum magnesium level, because magnesium suppresses the early afterdepolarisations (EADs) that trigger it. This is one of the few situations where Mg is given emergently even if the serum level is normal. Administer 2g IV MgSO4 over 2 to 5 minutes in active TdP. Follow with an infusion of 1 to 2g/hour for 4 to 6 hours.

Abbreviations: ACLS (Advanced Cardiac Life Support) · AF (Atrial Fibrillation) · ATP (Adenosine Triphosphate) · ATPase (Adenosine Triphosphatase) · BD (Twice Daily) · Ca (Calcium) · CIWA-Ar (Clinical Institute Withdrawal Assessment for Alcohol, revised) · CNS (Central Nervous System) · DKA (Diabetic Ketoacidosis) · DTR (Deep Tendon Reflex) · EAD (Early Afterdepolarisation) · ECG (Electrocardiogram) · eGFR (Estimated Glomerular Filtration Rate) · GI (Gastrointestinal) · H2-blocker (Histamine H2 Receptor Antagonist) · HCTZ (Hydrochlorothiazide) · IV (Intravenous) · K+ (Potassium) · KCl (Potassium Chloride) · Mg (Magnesium) · MgSO4 (Magnesium Sulphate) · NG (Nasogastric) · NPO (Nil Per Os) · NS (Normal Saline) · PPI (Proton Pump Inhibitor) · PTH (Parathyroid Hormone) · QTc (Corrected QT Interval) · ROMK (Renal Outer Medullary Potassium channel) · TdP (Torsades de Pointes) · TDS (Three Times Daily) · TRPM (Transient Receptor Potential Melastatin) · VF (Ventricular Fibrillation) · VT (Ventricular Tachycardia)

References

Ayuk J, Gittoes NJL. How should hypomagnesaemia be investigated and treated? Clin Endocrinol. 2011;75(6):743-746.
Cheungpasitporn W, Thongprayoon C, Qian Q. Dysmagnesemia in hospitalized patients: prevalence and prognostic importance. Mayo Clin Proc. 2015;90(8):1001-1010.
Hess MW, Hoenderop JG, Bindels RJ, Drenth JP. Systematic review: hypomagnesaemia induced by proton pump inhibition. Aliment Pharmacol Ther. 2012;36(5):405-413.
Huang CL, Kuo E. Mechanism of hypokalemia in magnesium deficiency. J Am Soc Nephrol. 2007;18(10):2649-2652.
Kolte D, Vijayaraghavan K, Khera S, et al. Role of magnesium in cardiovascular diseases. Cardiol Rev. 2014;22(4):182-192.
Hansen BA, Bruserud Ø. Hypomagnesemia in critically ill patients. J Intensive Care. 2018;6:21.
Van Laecke S. Hypomagnesemia and hypermagnesemia. Acta Clin Belg. 2019;74(1):41-47.
Kumar SR, Kumar KGS, Gayathri R. Hypomagnesemia in patients with type 2 diabetes mellitus. J Assoc Physicians India. 2024;72(7):25-28.
Radhakrishnan A, Chauhan I, Thakur JS, Azad R, Dhadwal M. Hypomagnesemia in post thyroidectomy patient: an underestimated entity. Indian J Otolaryngol Head Neck Surg. 2023;75(3):1986-1991.

How to Cite This Tool

DOIhttps://doi.org/10.5281/zenodo.22401534

AMA Style:Umakanth S. Acute Hypomagnesaemia Protocol. Version 1.2. MEDiscuss Clinical Decision Support System. Published 2026. Accessed . https://mediscuss.org/cdss/acute-hypomagnesaemia. doi:10.5281/zenodo.22401534

Vancouver Style:Umakanth S. Acute Hypomagnesaemia Protocol [Internet]. Version 1.2. MEDiscuss.org; 2026 [cited ]. Available from: https://mediscuss.org/cdss/acute-hypomagnesaemia. doi:10.5281/zenodo.22401534

Category Therapeutic & Management PathwaysProtocol

Specialties Internal Medicine, Nephrology, Critical Care

Written and maintained by

Dr Shashikiran Umakanth

Last revised 24 August 2026

How these tools are written and reviewed

Acute Hypomagnesaemia Protocol

How to use this tool

What this tool does not cover

1. Why Magnesium Affects Potassium, Calcium and Rhythm

2. IV MgSO4: Rate Limits & Safety

3. The PPI Problem

4. Oral Magnesium: Indian Formulations

5. Magnesium and Torsades de Pointes

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