What is the treatment for hypermagnesemia?

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, supplements, laxatives, and antacids immediately 2, 3
• This is the most critical first step, as continued absorption from retained magnesium products (especially magnesium oxide tablets in the GI tract) can cause rebound hypermagnesemia even after initial treatment 3

Step 2: Administer Calcium as Antagonist

• Calcium acts as a direct antagonist to magnesium's cardiotoxic effects 3, 4
• For cardiac arrest or severe cardiotoxicity: Give calcium chloride 10% 5-10 mL OR calcium gluconate 10% 15-30 mL IV over 2-5 minutes 1
• Calcium provides immediate hemodynamic improvement by counteracting magnesium's effects on cardiac conduction and neuromuscular function 3

Step 3: Gastrointestinal Decontamination

• Use magnesium-free laxatives to remove retained magnesium products from the GI tract 3
• This is particularly critical for patients who ingested magnesium oxide tablets, as CT imaging may show hyperdense tablets retained in the colon that continue absorbing 3
• Incomplete GI decontamination leads to continuous absorption and rebound hypermagnesemia despite dialysis 3

Step 4: Intravenous Fluid Therapy

• Administer IV fluids to promote renal excretion in patients with preserved kidney function 2, 4
• In patients with normal renal function, aggressive hydration combined with calcium administration may be sufficient without requiring dialysis 4

Step 5: Renal Replacement Therapy

• Initiate hemodialysis or continuous renal replacement therapy (CRRT) for severe hypermagnesemia (>6 mg/dL) or in patients with renal impairment 5, 2, 3, 6
• Dialysis is essential for patients with end-stage renal disease or acute renal failure, as they cannot excrete magnesium renally 5, 6
• CRRT effectively removes magnesium from serum and should be continued until levels normalize 5, 3

Clinical Manifestations by Severity

Moderate Hypermagnesemia (>2.2 mEq/L)

• Neurological symptoms: muscular weakness, paralysis, ataxia, drowsiness, confusion 1
• Cardiovascular: vasodilation and hypotension 1

Severe Hypermagnesemia (>6 mEq/L)

• Depressed level of consciousness, bradycardia, cardiac arrhythmias 1
• Hypoventilation and cardiorespiratory arrest 1
• Metabolic encephalopathy 5

Critical Pitfalls to Avoid

Incomplete Dialysis

• Ensure adequate duration of dialysis to prevent rebound hypermagnesemia 5, 3
• One case demonstrated bradycardia and hypotension developing after incomplete dialysis, requiring repeat treatment 3

Failure to Perform GI Decontamination

• Retained magnesium oxide tablets in the colon cause continuous absorption even during dialysis 3
• Always obtain abdominal imaging if oral magnesium ingestion is suspected to identify retained tablets 3

Delayed Recognition in Normal Renal Function

• Hypermagnesemia can occur in patients with normal kidney function if magnesium intake is excessive 5, 4
• Do not assume normal renal function protects against toxicity—two reported cases had serum magnesium levels of 10.4 and 13.2 mEq/L despite normal kidney function 4

Unrecognized Acute Renal Failure

• Always verify renal function before administering magnesium-containing preparations 6
• One fatal case involved pre-operative bowel preparation with magnesium cathartic in unrecognized acute renal failure, resulting in one of the highest serum magnesium concentrations ever reported 6

Supportive Care

Cardiovascular Support

• Use high-dose inotropics and transcutaneous pacing for refractory bradycardia and hypotension 3
• However, calcium administration provides more reliable hemodynamic improvement than inotropics alone 3

Respiratory Support

• Provide mechanical ventilation for hypoventilation or respiratory failure 4, 6
• Hypermagnesemia causes respiratory muscle weakness requiring ventilatory support until magnesium levels normalize 4

Monitoring

• Monitor serum magnesium levels continuously during treatment, especially in high-risk patients with renal impairment or those receiving magnesium-containing medications 2
• Target normal magnesium range (1.3-2.2 mEq/L) 1