Magnesium sulphate is the drug of choice for prevention of eclamptic seizures. In a woman receiving MgSO4, which clinical sign indicates early magnesium toxicity that should prompt dose reduction?
- A Respiratory rate < 16/min
- B Urinary output < 30 mL/hr
- C Loss of deep tendon reflexes (DTR) ✓
- D Serum magnesium > 7.5 mEq/L
Correct answer: C. Loss of deep tendon reflexes (DTR)
Explanation
Magnesium toxicity monitoring: therapeutic range is 4–8 mg/dL (3.5–7 mEq/L); loss of patellar reflex (DTR) occurs at 7–10 mg/dL (6–8 mEq/L) and is the first clinical sign of toxicity that should prompt stopping MgSO4; respiratory paralysis occurs at 10–13 mg/dL; cardiac arrest at > 15 mg/dL. Clinical monitoring (DTR every 30 min, respiratory rate > 12/min, UO > 25–30 mL/hr) is mandatory; patellar reflex loss is the primary safety endpoint.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.