A woman who ingested a household cleaning solution develops severe tetany and carpopedal spasm within hours. Urine examination shows abundant envelope-shaped crystals. The ingested poison most likely acts by:

• A Binding sulfhydryl groups of cellular enzymes
• B Blocking the neuromuscular junction by competitive inhibition of acetylcholine
• C Inhibiting cytochrome oxidase and causing histotoxic anoxia
• D Chelating serum ionized calcium to form insoluble calcium salts ✓

Explanation

Oxalic acid (found in bleaching powders and some metal cleaners) combines with ionized calcium to form insoluble calcium oxalate, producing hypocalcemic tetany and envelope-shaped calcium oxalate crystals in urine. It also causes local corrosion and renal tubular damage. Binding of sulfhydryl groups describes arsenic and mercury, while cytochrome oxidase inhibition describes cyanide, so those distractors describe entirely different mechanisms.

Reference: Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.