A patient receiving magnesium sulfate shows signs of toxicity. Which finding indicates this toxicity?

• A. Respirations 8 breaths per minute
• B. Deep tendon reflexes 2+
• C. Urine output 40 mL/hour
• D. Blood pressure 140/90

Answer: (A)

Magnesium sulfate is used to prevent seizures in preeclampsia, but it can depress the central nervous system and neuromuscular function when levels get too high. A respiratory rate of eight breaths per minute shows significant respiratory depression from magnesium toxicity, which is a life-threatening sign requiring immediate action. In contrast, a normal deep tendon reflex of 2+, urine output of 40 mL/hour, or a blood pressure of 140/90 do not indicate toxicity and can be compatible with treatment or the underlying condition. If toxicity is suspected, stop the magnesium infusion right away, support the airway and breathing, and have calcium gluconate available as the antidote while monitoring the patient and notifying the provider.