Magnesium Replacement for Hypomagnesemia
For hypomagnesemia, administer IV magnesium sulfate 1-2 g as a bolus for severe cases (serum Mg <1.2 mg/dL) or symptomatic patients, and for mild deficiency, give 1 g IM every six hours for four doses. 1, 2
Dosing Based on Severity
Severe Hypomagnesemia (Serum Mg <1.2 mg/dL or Symptomatic)
- IV therapy: 1-2 g of MgSO₄ as bolus IV push 1
- For cardiac manifestations (arrhythmias, torsades de pointes): 1-2 g MgSO₄ IV bolus 1
- For very severe cases: Up to 250 mg/kg body weight IM within 4 hours 2
- Alternative approach: 5 g (approximately 40 mEq) added to 1 liter of 5% Dextrose or 0.9% Sodium Chloride for slow IV infusion over 3 hours 2
Mild to Moderate Hypomagnesemia
- IM therapy: 1 g (8.12 mEq) IM every 6 hours for 4 doses (total 32.5 mEq/24 hours) 2
- Oral therapy: For asymptomatic patients with mild deficiency, oral magnesium supplements are appropriate 3
Administration Guidelines
IV Administration
- Rate should not exceed 150 mg/minute (1.5 mL of a 10% solution) 2
- Solutions for IV infusion must be diluted to ≤20% concentration prior to administration 2
- Common diluents: 5% Dextrose Injection or 0.9% Sodium Chloride Injection 2
IM Administration
- Deep IM injection of undiluted (50%) solution is appropriate for adults 2
- For children: Solution should be diluted to ≤20% concentration prior to injection 2
Monitoring and Follow-up
- Monitor serum magnesium levels 1-2 weeks after starting supplementation 4
- Watch for signs of hypermagnesemia (hypotension, respiratory depression) 4
- For patients on parenteral nutrition: Monitor magnesium levels every 1-2 days initially, then 1-2 times weekly 4
- For chronic intestinal disorders: Check magnesium levels every 2-3 months 4
- Target serum magnesium level should be >0.6 mmol/L 4
Special Considerations
- Verify adequate renal function before administering magnesium supplementation 3
- For patients with renal insufficiency: Maximum dosage is 20 g/48 hours with frequent serum magnesium monitoring 2
- Continuous magnesium infusions may be beneficial for patients with recurrent SACT-related hypomagnesemia 5
- For patients with high-output ileostomies causing chronic hypomagnesemia, subcutaneous magnesium administration may be considered 6
- Hypomagnesemia often coexists with hypokalemia and hypocalcemia, which may be refractory to correction until magnesium is repleted 7
Pitfalls and Caveats
- Serum magnesium is not an accurate measurement of total body magnesium status, as <1% of magnesium stores are in the blood 4
- Avoid magnesium administration in patients with hypermagnesemia 4
- For cardiac arrest with suspected hypermagnesemia, administer IV calcium instead of magnesium 4
- Continuous maternal administration of magnesium sulfate in pregnancy beyond 5-7 days can cause fetal abnormalities 2
- Magnesium deficiency can persist despite normal serum levels due to intracellular depletion 7
- Regular monitoring is essential in patients with ongoing risk factors for magnesium deficiency 4
By following these evidence-based guidelines for magnesium replacement, you can effectively manage hypomagnesemia while minimizing potential complications.