Magnesium is a cofactor for over 300 enzymatic reactions, including the Na+/K+-ATPase pump (critical for K homeostasis), adenylate cyclase (critical for PTH signalling and Ca homeostasis), and ATP metabolism. Hypomagnesaemia causes: (1) Refractory hypokalaemia (ROMK channel activation → renal K wasting), (2) Refractory hypocalcaemia (impaired PTH secretion + skeletal PTH resistance), (3) Cardiac arrhythmias (prolonged QT, Torsades de Pointes). Fixing magnesium first is often the key to fixing everything else.
| 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 5 to 15 min, 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 |
Chronic PPI use (Omeprazole, Pantoprazole, Rabeprazole - ubiquitous in Indian practice) reduces intestinal magnesium absorption via inhibition of TRPM6/7 channels. This effect is not dose-dependent and can occur with any PPI. Onset: typically after months to years of use. It is NOT corrected by IV or oral Mg replacement while the PPI continues - the absorptive defect persists. Management: switch to H2-blocker (Ranitidine/Famotidine) if possible. If PPI is essential, add high-dose oral Mg supplementation and monitor levels regularly.
| 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 main limitation is GI side effects (diarrhoea), which ironically can worsen Mg depletion.
IV MgSO4 2g is the first-line treatment for Torsades de Pointes (TdP), regardless of the serum magnesium level. Magnesium works by suppressing early afterdepolarisations (EADs) that trigger TdP. 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.
AMA Style:
Umakanth S. Acute Hypomagnesaemia Protocol. MEDiscuss. Published 2026. Accessed .
Vancouver Style:
Umakanth S. Acute Hypomagnesaemia Protocol [Internet]. MEDiscuss.org; 2026 [cited ]. Available from:
