Magnesium Replacement Strategies in Hypomagnesemia

Oral Magnesium Replacement

Magnesium oxide is the preferred oral formulation because it provides the highest elemental magnesium content and is converted to magnesium chloride in gastric acid (Gastroenterology Society recommendation) 2
Oral magnesium should be given in divided doses throughout the day, with the largest portion at bedtime to take advantage of slower intestinal transit (Gastroenterology Society recommendation) 2
Most oral magnesium salts are poorly absorbed and may exacerbate diarrhea; therefore dose adjustments based on tolerability are essential (Gastroenterology Society recommendation) 2
Long‑term oral supplementation should be continued in patients with ongoing magnesium losses such as malabsorption or renal wasting (Gastroenterology Society recommendation) 2
If oral magnesium alone fails to normalize serum levels, add 1‑α‑hydroxycholecalciferol starting at 0.25 µg daily and titrate up to 9 µg daily (Gastroenterology Society recommendation) 2
Serum calcium must be monitored regularly during vitamin D (1‑α‑hydroxycholecalciferol) therapy to avoid hypercalcemia (American Society of Clinical Oncology) 3
Rehydration to correct secondary hyperaldosteronism is the most important first step in patients with high stomal output or diarrhea (Gastroenterology Society recommendation) 2

For severe or symptomatic hypomagnesemia, give intravenous magnesium sulfate 1–2 g IV push for life‑threatening arrhythmias or add 4–12 mmol to saline infusions for less urgent correction (American Heart Association) 4
In torsades de pointes or polymorphic ventricular tachycardia related to hypomagnesemia, administer magnesium sulfate 1–2 g IV bolus (American Heart Association) 4
If torsades recurs despite the initial magnesium dose, increase heart rate with pacing or isoproterenol to suppress the arrhythmia (American College of Cardiology) 5
Target serum magnesium ≥2.0 mmol/L (≈4.8 mg/dL) in patients with acquired QT prolongation and torsades (American College of Cardiology) 5
For non‑emergent correction, add 4–12 mmol magnesium sulfate to intravenous or subcutaneous saline infusions (Gastroenterology Society recommendation) 2
Subcutaneous magnesium sulfate (0.5–1 L saline with 4 mmol magnesium) can be administered 1–3 times weekly for patients requiring intermittent parenteral therapy (Gastroenterology Society recommendation) 2
Hypermagnesemia (>2.2 mEq/L) may cause bradycardia, hypotension, respiratory depression, and cardiac arrest (American Heart Association) 4
Oral magnesium oxide may be ineffective in patients with severe malabsorption; parenteral therapy is required (Gastroenterology Society recommendation) 2

For torsades de pointes, ensure concurrent correction of potassium to ≥4.0 mmol/L and magnesium to ≥2.0 mmol/L (American College of Cardiology) 5
Avoid administering a bolus of potassium during cardiac arrest when hypokalemia is suspected, as this practice is potentially harmful (American Heart Association) 4