Treatment of Hypermagnesemia
For hypermagnesemia causing cardiac arrest or severe cardiotoxicity, immediately administer intravenous calcium (calcium chloride 10% 5-10 mL OR calcium gluconate 10% 15-30 mL IV over 2-5 minutes) as the primary antidote, while simultaneously discontinuing all magnesium sources and initiating dialysis for severe cases. 1
Immediate Management Algorithm
Step 1: Discontinue All Magnesium Sources
- Stop all magnesium-containing medications immediately (antacids, laxatives, supplements, cathartics) 1, 2
- Remove magnesium from intravenous fluids and parenteral nutrition 2
- In patients with gastrointestinal retention of magnesium-containing products (particularly magnesium oxide tablets), perform gastrointestinal decontamination with magnesium-free laxatives to prevent continued absorption and rebound hypermagnesemia 3
Step 2: Administer Calcium as Antidote (For Severe Cases)
- Calcium acts as a direct antagonist to magnesium's cardiac and neuromuscular effects 1, 3
- Give calcium chloride 10% 5-10 mL IV over 2-5 minutes OR calcium gluconate 10% 15-30 mL IV over 2-5 minutes 1
- This is critical for patients with bradycardia, cardiac arrhythmias, hypotension, or cardiorespiratory compromise 3, 4
Step 3: Enhance Magnesium Excretion
For patients with normal renal function:
- Administer intravenous normal saline to promote renal excretion 2, 4
- Add loop diuretics (furosemide) to increase urinary magnesium elimination 4
For patients with renal impairment or severe hypermagnesemia (>6 mEq/L):
- Initiate hemodialysis or continuous renal replacement therapy (CRRT) immediately 1, 2, 5
- Dialysis is the definitive treatment for removing magnesium from the serum, particularly in patients with acute or chronic kidney disease 5, 3, 6
Clinical Context by Severity
Moderate Hypermagnesemia (>2.2 mEq/L)
- Presents with muscular weakness, paralysis, ataxia, drowsiness, confusion, vasodilation, and hypotension 1
- Treatment focuses on discontinuing magnesium sources and promoting renal excretion with IV fluids and diuretics 2, 4
Severe Hypermagnesemia (>6 mEq/L)
- Causes depressed level of consciousness, bradycardia, cardiac arrhythmias, hypoventilation, and cardiorespiratory arrest 1
- Requires immediate calcium administration and dialysis 1, 5, 3
Critical Pitfalls to Avoid
Incomplete gastrointestinal decontamination leads to rebound hypermagnesemia: Magnesium oxide tablets retained in the colon continue to be absorbed even after initial treatment, causing recurrent elevation of serum magnesium levels 3. Imaging (abdominal CT or X-ray) may reveal hyperdense magnesium-containing products in the GI tract 3.
Inadequate dialysis duration: Brief or incomplete dialysis sessions result in rebound hypermagnesemia from continued GI absorption or tissue redistribution 3. Continue dialysis until magnesium levels normalize and the source is eliminated 5, 3.
Delayed recognition in patients with normal renal function: Hypermagnesemia can occur even with normal kidney function when there is bowel obstruction, prolonged colonic retention, or excessive magnesium intake 3, 4. The combination of constipation and magnesium-containing laxatives creates a dangerous cycle of retention and absorption 5, 3.
Underestimating cardiovascular toxicity: Prolonged hypotension and bradycardia from hypermagnesemia can lead to myocardial infarction, hypoxic encephalopathy, and death despite successful magnesium reduction 3, 6. Aggressive hemodynamic support with calcium, inotropics, and transcutaneous pacing may be necessary 3.
Monitoring During Treatment
- Monitor serum magnesium levels frequently during treatment 2, 5
- Target normal magnesium range: 1.3-2.2 mEq/L 1
- Monitor for signs of magnesium toxicity resolution: improved mental status, normalized heart rate and blood pressure, return of deep tendon reflexes 2, 5
- Check serum electrolytes, carbon dioxide level, and blood pressure frequently 7
Prevention in High-Risk Populations
Avoid magnesium-containing preparations in patients with:
- Acute or chronic kidney disease 5, 6
- Bowel obstruction or severe constipation 3, 4
- Elderly patients with multiple comorbidities 5, 6
When magnesium-containing laxatives are used, ensure adequate renal function and avoid prolonged use 8, 6. Magnesium and sulfate salts should be used cautiously in renal impairment 8.