Which sign is most characteristic of hypermagnesemia?

• A. Hypoactive reflexes
• B. Hyperactive reflexes
• C. Flushing
• D. Tachycardia

Answer: (A)

Hypermagnesemia dampens neuromuscular activity, so reflexes become subdued. Magnesium acts as a natural NM blocker, reducing calcium-triggered acetylcholine release at the neuromuscular junction and stabilizing neuronal membranes, which lowers excitability. As magnesium levels rise, deep tendon reflexes decline from normal to diminished (hyporeflexia), and in severe cases can progress to areflexia. Additional signs may include lethargy, hypotension, bradycardia, and potential respiratory depression, but flushing is less specific and tachycardia is not typical. So the hallmark sign is hypoactive reflexes.