What is the antidote for magnesium toxicity?

Antidote for Magnesium Toxicity

The primary antidote for magnesium toxicity is intravenous calcium, specifically calcium chloride (10%) 5-10 mL or calcium gluconate (10%) 15-30 mL administered over 2-5 minutes. 1

Clinical Manifestations of Magnesium Toxicity

Hypermagnesemia is defined as a serum magnesium concentration >2.2 mEq/L (normal range: 1.3-2.2 mEq/L). The clinical manifestations progress with increasing severity of hypermagnesemia:

• At levels of 2.5-5 mmol/L: ECG changes including prolonged PR, QRS, and QT intervals 1
• At levels of 4-5 mmol/L: Neurological effects including loss of tendon reflexes, sedation, severe muscular weakness, and respiratory depression 1
• At levels of 6-10 mmol/L: AV nodal conduction block, bradycardia, hypotension, and cardiac arrest 1
• Additional symptoms include muscular weakness, paralysis, ataxia, drowsiness, confusion, vasodilation, hypotension, depressed level of consciousness, and hypoventilation 1

Management Algorithm for Magnesium Toxicity

Step 1: Immediate Interventions

• Administer intravenous calcium as the primary antidote:
  • Calcium chloride (10%) 5-10 mL OR
  • Calcium gluconate (10%) 15-30 mL
  • Administer IV over 2-5 minutes 1

Step 2: Supportive Care

• Ensure adequate airway, breathing, and circulation 1
• Provide respiratory support if hypoventilation is present 2
• Monitor cardiac function with continuous ECG 1
• Discontinue any ongoing magnesium administration 3

Step 3: Enhanced Elimination

• Initiate fluid therapy to promote renal excretion of magnesium 2
• Consider forced diuresis if renal function is intact 3
• In severe cases or when basic interventions fail, initiate hemodialysis to rapidly reduce magnesium levels 2

Special Considerations

Pregnancy-Related Magnesium Toxicity

• Magnesium toxicity is particularly relevant in obstetric settings where magnesium sulfate is used for preeclampsia/eclampsia 1
• Iatrogenic overdose is possible in pregnant women receiving magnesium sulfate, particularly if oliguria develops 1
• Empirical calcium administration may be lifesaving in these cases 1

Common Pitfalls and Caveats

• Magnesium toxicity can be easily overlooked in patients with renal failure who may develop toxicity at relatively lower doses 1
• Errors in drug administration can occur due to variations in units of measurement on drug labels and written orders 4
• Failure to recognize early signs of magnesium toxicity (loss of deep tendon reflexes) can lead to progression to more severe manifestations 1
• Calcium administration should be prompt in cases of severe cardiotoxicity, as delays can lead to cardiac arrest 4

Evidence Quality

The recommendations for calcium administration as an antidote for magnesium toxicity are based on American Heart Association guidelines with Class IIb, Level of Evidence C recommendation 1. While this represents expert consensus rather than high-quality randomized controlled trials, it is the standard of care in emergency situations where magnesium toxicity leads to cardiac complications 1.