PaEasy Emergency Medicine Practice Exam 2026 - Free Emergency Medicine Practice Questions and Study Guide

When magnesium levels are dangerously high, the priority is to counteract its effects on the heart and nerves while you remove the excess magnesium. Giving calcium intravenously acts as an antidote to the effects of magnesium on cardiac conduction and neuromuscular excitability. Calcium stabilizes cell membranes and increases the threshold for depolarization, which can quickly reverse bradycardia, hypotension, and decreased reflexes seen in severe hypermagnesemia. This effect is temporary, so while calcium buys time, magnesium must be removed from the body—through stopping the Mg-containing source, ensuring adequate fluids, and, if needed, renal replacement therapy such as hemodialysis in those with renal failure.

Oral magnesium would worsen the situation, and while hemodialysis is effective at removing magnesium, it is a definitive treatment used when rapid removal is necessary or in patients with renal failure, not the immediate antidote. IV potassium is not relevant to correcting hypermagnesemia.