Antidote for Magnesium Toxicity

Clinical Manifestations and Management

The American Heart Association recommends intravenous calcium as the primary antidote for magnesium toxicity, specifically calcium chloride (10%) 5-10 mL or calcium gluconate (10%) 15-30 mL administered over 2-5 minutes, for patients with severe hypermagnesemia 1, 2, 3
Hypermagnesemia is defined as a serum magnesium concentration >2.2 mEq/L, and clinical manifestations progress with increasing severity, including ECG changes, neurological effects, and cardiac complications, with symptoms such as muscular weakness, paralysis, and respiratory depression 4, 5
The American Heart Association guidelines recommend prompt calcium administration in cases of severe cardiotoxicity, with a Class IIb, Level of Evidence C recommendation, based on expert consensus rather than high-quality randomized controlled trials 1, 3
Magnesium toxicity can be particularly relevant in obstetric settings where magnesium sulfate is used for preeclampsia/eclampsia, and iatrogenic overdose is possible in pregnant women receiving magnesium sulfate, particularly if oliguria develops 4, 5
Empirical calcium administration may be lifesaving in cases of magnesium toxicity, especially in patients with severe cardiotoxicity or those who are pregnant and receiving magnesium sulfate 4, 5

Patients with renal failure may develop magnesium toxicity at relatively lower doses, and failure to recognize early signs of magnesium toxicity can lead to progression to more severe manifestations 4, 5
Monitoring cardiac function with continuous ECG is crucial in patients with magnesium toxicity, as cardiac complications can occur rapidly 4

Mild hypermagnesemia (serum magnesium 2.5–5 mmol/L) is associated with characteristic ECG abnormalities, notably a prolonged PR interval and a widened QRS complex. – American Heart Association (AHA) recommendation. 6

In patients with severe symptomatic hypermagnesemia, the primary antidote is an immediate intravenous calcium bolus (calcium chloride 10 % 5–10 mL or calcium gluconate 10 % 15–30 mL administered over 2–5 minutes); magnesium‑containing agents should be stopped and urgent hemodialysis initiated for life‑threatening presentations. – AHA guideline. 6

When cardiac arrest occurs in the setting of suspected or confirmed hypermagnesemia, empirical intravenous calcium administration is considered reasonable (Class IIb, Level of Evidence C). – AHA recommendation. 6

Severe hypermagnesemia most frequently arises in obstetric patients receiving intravenous magnesium sulfate for pre‑eclampsia/eclampsia, placing this group at high risk for toxicity and cardiac arrest. – AHA observation. 6

Cardiac arrest can develop as a direct consequence of severe hypermagnesemia, particularly among obstetric patients treated with magnesium sulfate. – AHA report. 6