Side Effects of Hypermagnesemia
Hypermagnesemia can cause life-threatening complications including cardiovascular abnormalities, neuromuscular dysfunction, and respiratory depression, with severity of symptoms directly correlating to serum magnesium levels. 1
Classification and Clinical Manifestations
Hypermagnesemia is classified based on serum magnesium levels:
- Mild (2.2-2.5 mEq/L): Often asymptomatic or with minimal symptoms
- Moderate (2.5-5.0 mEq/L): Hyporeflexia, nausea, vomiting, facial flushing, lethargy
- Severe (>5.0 mEq/L): Complete loss of deep tendon reflexes, severe hypotension, respiratory depression, heart blocks, coma 1
Cardiovascular Effects
- ECG changes: Prolongation of PR, QRS, and QT intervals
- Facial flushing and hypotension
- Advanced stages: AV conduction block, severe bradycardia, refractory hypotension
- Potential for cardiac arrest in severe cases 1, 2
Neurological Effects
- Progressive loss of deep tendon reflexes (early sign)
- Sedation and somnolence
- Muscle weakness
- Respiratory depression in severe cases
- Altered level of consciousness ranging from drowsiness to coma 1, 3
Other Manifestations
- Gastrointestinal: Nausea and vomiting
- Metabolic: Hypophosphatemia
- Fluid balance: Hyperosmolar dehydration 1
Risk Factors
Hypermagnesemia typically occurs in:
- Patients with renal insufficiency (kidneys are primary route of magnesium excretion)
- Elderly patients taking magnesium-containing medications
- Obstetric patients receiving magnesium sulfate for preeclampsia/eclampsia
- Individuals with normal renal function but bowel obstruction taking magnesium-containing medications
- Patients receiving megadoses of magnesium supplements 1, 4, 5
Management
Immediate Interventions
- Discontinue all magnesium-containing medications or supplements
- For moderate to severe cases, administer intravenous calcium as a physiological antagonist:
- Calcium chloride 10% 5-10 mL or calcium gluconate 10% 15-30 mL over 2-5 minutes 1
Supportive Measures
- Respiratory support for patients with respiratory depression
- Hemodynamic support for hypotension
- Continuous cardiac monitoring for moderate to severe cases 1
Definitive Treatment
- Intravenous fluid therapy to enhance renal excretion (if renal function is intact)
- Hemodialysis or continuous renal replacement therapy for severe cases, especially with renal insufficiency 1, 2, 5
Prevention
- Regular monitoring of magnesium levels in high-risk patients
- Avoid magnesium-containing medications in patients with renal insufficiency
- Verify renal function before administering large amounts of oral magnesium
- Ensure correct composition of dialysate for patients on dialysis 1
Special Considerations
- Fatal outcomes have been reported in cases of severe hypermagnesemia, particularly when diagnosis and treatment are delayed 4, 2, 5
- Even patients with normal renal function can develop severe hypermagnesemia with excessive magnesium intake 5
- Pediatric patients may be particularly vulnerable to magnesium toxicity 4
Remember that hypermagnesemia, while relatively uncommon, requires prompt recognition and management to prevent potentially fatal complications.