Magnesium Repletion Guidelines

Initial Assessment and Treatment

The American College of Cardiology recommends checking renal function immediately and avoiding magnesium supplementation if creatinine clearance is <20 mL/min due to life-threatening hypermagnesemia risk 1, 2
Assess volume status and correct water and sodium depletion first with IV saline to eliminate secondary hyperaldosteronism, which increases renal magnesium wasting 1, 3
Check potassium and calcium levels, as hypomagnesemia causes refractory hypokalemia and hypocalcemia that won't respond to replacement until magnesium is corrected 3
Obtain ECG if any cardiac symptoms, looking for QTc prolongation, peaked T waves, or arrhythmias 4, 1

For mild/asymptomatic cases, start oral magnesium oxide 12 mmol at night (approximately 500 mg elemental magnesium) and increase to 24 mmol daily if needed 1, 3
For severe/symptomatic cases or cardiac emergencies, give IV magnesium sulfate 1-2 g over 15 minutes immediately 1, 3
The American Heart Association recommends giving 1-2 g magnesium sulfate IV bolus over 5 minutes regardless of measured magnesium level in cardiac emergencies 4, 1

Recheck magnesium level 2-3 weeks after starting supplementation and assess for side effects 2, 3
Check magnesium every 3 months once on stable dosing, with more frequent monitoring if high GI losses, renal disease, or on medications affecting magnesium 1, 2
Aim for serum magnesium >1.8 mg/dL (normal range 1.8-2.2 mEq/L) as the target level 1

Do not give magnesium if creatinine clearance <20 mL/min, and use extreme caution if CrCl 20-30 mL/min 1, 2
Do not supplement magnesium before correcting volume depletion with IV saline, as ongoing hyperaldosteronism will cause continued renal magnesium wasting despite supplementation 1, 3
Watch for magnesium toxicity during IV replacement, with symptoms including loss of patellar reflexes, respiratory depression, hypotension, and bradycardia 3