Which finding would indicate magnesium sulfate toxicity rather than a therapeutic effect?

Which finding would indicate magnesium sulfate toxicity rather than a therapeutic effect?

• A. 4+ reflexes
• B. Respiratory rate 10/min
• C. Urinary output 50 ml/h
• D. Decreased body temperature

Answer: (B)

Magnesium sulfate acts as a CNS depressant and smooth muscle relaxant, and it’s used to prevent seizures in preeclampsia and tocolysis. The line between therapeutic effects and toxicity is shown by symptoms that reflect how deeply the drug is depressing the nervous system. A respiratory rate of 10 breaths per minute indicates significant respiratory depression from elevated magnesium levels, which is a hallmark of toxicity. This slower breathing shows the medication is suppressing the brainstem centers that drive respiration and requires immediate action (stop the infusion, assess airway, and follow protocol, often with calcium gluconate as antidote). By contrast, a finding like 4+ reflexes would be unusual for toxicity, since magnesium toxicity more commonly causes diminished or absent reflexes. Urinary output and temperature don’t directly indicate magnesium toxicity in the same clear way as depressed respiration.

Magnesium sulfate acts as a CNS depressant and smooth muscle relaxant, and it’s used to prevent seizures in preeclampsia and tocolysis. The line between therapeutic effects and toxicity is shown by symptoms that reflect how deeply the drug is depressing the nervous system. A respiratory rate of 10 breaths per minute indicates significant respiratory depression from elevated magnesium levels, which is a hallmark of toxicity. This slower breathing shows the medication is suppressing the brainstem centers that drive respiration and requires immediate action (stop the infusion, assess airway, and follow protocol, often with calcium gluconate as antidote).

By contrast, a finding like 4+ reflexes would be unusual for toxicity, since magnesium toxicity more commonly causes diminished or absent reflexes. Urinary output and temperature don’t directly indicate magnesium toxicity in the same clear way as depressed respiration.