A client at 32 weeks gestation with severe PIH is treated with magnesium sulfate. Which assessment finding indicates a therapeutic drug level has been achieved?

A client at 32 weeks gestation with severe PIH is treated with magnesium sulfate. Which assessment finding indicates a therapeutic drug level has been achieved?

• A. 4+ reflexes
• B. Urinary output of 50 ml per hour
• C. A decrease in respiratory rate from 24 to 16
• D. A decreased body temperature

Answer: (C)

Magnesium sulfate for seizure prevention in severe PIH works by gently depressing neuromuscular transmission and the CNS. The therapeutic effect appears as a controlled, mild CNS/neuromuscular slowdown rather than outright toxicity. A sign that the drug is at therapeutic level is a noticeable but safe decrease in respiratory rate, such as dropping from about 24 to around 16 breaths per minute, reflecting CNS depressant action without yet compromising ventilation. You’d want to keep the rate above roughly 12–14 breaths per minute and watch closely for any further decline or other toxicity signs (like absent reflexes, confusion, or respiratory arrest). Other options either reflect normal physiology not related to drug level (urinary output) or indicate potential toxicity or non-effect (deep tendon reflexes that are still hyperactive, or temperature change).

Magnesium sulfate for seizure prevention in severe PIH works by gently depressing neuromuscular transmission and the CNS. The therapeutic effect appears as a controlled, mild CNS/neuromuscular slowdown rather than outright toxicity. A sign that the drug is at therapeutic level is a noticeable but safe decrease in respiratory rate, such as dropping from about 24 to around 16 breaths per minute, reflecting CNS depressant action without yet compromising ventilation. You’d want to keep the rate above roughly 12–14 breaths per minute and watch closely for any further decline or other toxicity signs (like absent reflexes, confusion, or respiratory arrest). Other options either reflect normal physiology not related to drug level (urinary output) or indicate potential toxicity or non-effect (deep tendon reflexes that are still hyperactive, or temperature change).