Which sign indicates magnesium sulfate toxicity?

• A. Absence of deep tendon reflexes
• B. Nausea
• C. Hypotension
• D. Respiratory depression

Answer: (A)

Magnesium sulfate toxicity is best detected by the loss of deep tendon reflexes. This reflex suppression happens as magnesium levels rise and neuromuscular transmission is slowed, making absence of reflexes the earliest and most reliable warning sign that toxicity is occurring.

Nausea can occur with magnesium therapy but isn’t specific for toxicity, and hypotension or respiratory depression can happen later or for other reasons. If reflexes disappear, stop the infusion and alert the clinician promptly; monitor respirations and readiness to support the airway, and be aware that calcium gluconate is the antidote if toxicity is confirmed or suspected.