Treatment of Hypermagnesemia
For severe symptomatic hypermagnesemia, immediately discontinue all magnesium-containing medications and administer intravenous calcium (calcium chloride 10% 5-10 mL or calcium gluconate 10% 15-30 mL IV over 2-5 minutes), followed by urgent hemodialysis or continuous renal replacement therapy for life-threatening presentations. 1
Immediate Assessment and Stabilization
When hypermagnesemia is suspected, the clinical presentation guides urgency:
Severe hypermagnesemia presents with progressive neurological manifestations including muscular weakness, paralysis, ataxia, drowsiness, confusion, and depressed level of consciousness at serum magnesium levels >2.2 mEq/L, with life-threatening toxicity occurring at 6-10 mmol/L. 1
Cardiovascular effects include vasodilation, hypotension, bradycardia, cardiac arrhythmias, and cardiorespiratory arrest. 1 Respiratory compromise can progress from hypoventilation to complete respiratory paralysis at extremely high levels. 1
Critical First Steps:
- Discontinue all magnesium-containing medications immediately including antacids, laxatives, supplements, and cathartics. 1
- Obtain an ECG to assess for conduction abnormalities. 1
- Initiate continuous cardiac monitoring for bradycardia, hypotension, and arrhythmias. 1
- Prepare for mechanical ventilation if hypoventilation or respiratory depression develops. 1
Pharmacological Management
Calcium Administration (First-Line Antidote)
For cardiac arrest with known or suspected hypermagnesemia, administer IV calcium in addition to standard ACLS care (Class IIb, LOE C-EO). 2 This is the immediate pharmacological intervention that can be lifesaving.
For severe symptomatic hypermagnesemia without cardiac arrest, give calcium chloride 10% 5-10 mL or calcium gluconate 10% 15-30 mL IV over 2-5 minutes. 1 Calcium directly antagonizes the neuromuscular and cardiac effects of magnesium.
Fluid Therapy
Intravenous fluid therapy with normal saline promotes renal magnesium excretion in patients with preserved kidney function. 3 However, this is only effective when renal function is adequate.
Renal Replacement Therapy
Urgent hemodialysis or continuous renal replacement therapy (CRRT) should be initiated for life-threatening presentations of hypermagnesemia, particularly when basic supportive interventions such as calcium gluconate and fluid therapy are ineffective. 1, 4
Indications for Dialysis:
- Magnesium levels >6-10 mmol/L with symptoms 1
- Cardiac arrest or severe arrhythmias 4
- Respiratory paralysis requiring mechanical ventilation 5
- Concurrent acute kidney injury or chronic kidney disease 5
- Failure of calcium and fluid therapy to improve symptoms 4
Hemodialysis is more effective than CRRT for rapid magnesium removal in emergency situations, though CRRT may be used for hemodynamically unstable patients. 5 Dialysis solutions should not contain magnesium during treatment. 1
Special Clinical Scenarios
Hypermagnesemia in Obstetric Patients
Severe hypermagnesemia is most likely to occur in the obstetric setting in patients being treated with IV magnesium for preeclampsia or eclampsia. 2 At very elevated levels, hypermagnesemia can lead to altered consciousness, bradycardia or ventricular arrhythmias, and cardiac arrest. 2
For pregnant women with preeclampsia/eclampsia receiving magnesium sulfate, monitor closely for oliguria and toxicity; empirical calcium administration may be lifesaving in overdose. 1
Hypermagnesemia with Normal Renal Function
Hypermagnesemia can occur even in patients with normal kidney function, particularly in the setting of bowel obstruction or decreased gastrointestinal motility, which increases magnesium absorption from antacids or laxatives. 6 The combination of magnesium-containing medications with gastrointestinal pathology creates a perfect storm for toxicity. 7, 6
Monitoring During Treatment
- Continuous cardiac monitoring for rhythm disturbances 1
- Serial magnesium levels every 2-4 hours during acute treatment 4
- Assess deep tendon reflexes as they return with falling magnesium levels 1
- Monitor respiratory status closely, as respiratory depression may persist even as magnesium levels decline 1
- Check calcium, potassium, and renal function concurrently 1
Common Pitfalls to Avoid
Never assume normal renal function excludes risk of severe hypermagnesemia when patients are taking magnesium-containing preparations, especially with concurrent gastrointestinal pathology. 6 Bowel obstruction, ileus, or severe constipation dramatically increase magnesium absorption. 6
Do not delay hemodialysis in severe cases while attempting conservative management with fluids and calcium alone. 4 If the patient has cardiac instability, respiratory compromise, or magnesium levels >10 mg/dL, dialysis should be initiated immediately. 4, 5
Failing to recognize iatrogenic causes is a critical error. 4 Always obtain a complete medication history including over-the-counter antacids, laxatives, and supplements. 7 Even "routine" doses of magnesium hydroxide (3,000 mg daily) can cause fatal hypermagnesemia in susceptible patients. 7
Patients with end-stage renal disease or GFR <30 mL/min should never receive magnesium-containing medications, as they cannot excrete excess magnesium. 1 This is an absolute contraindication. 1