A woman who drank a clear liquid from an unlabeled bottle develops severe abdominal pain, vomiting, and later tetanic spasms with carpopedal spasm. Serum calcium is 6 mg/dL. Urine microscopy shows envelope-shaped crystals. Which poison was ingested?
- A Sulphuric acid
- B Oxalic acid ✓
- C Nitric acid
- D Carbolic acid
Correct answer: B. Oxalic acid
Explanation
Oxalic acid combines with ionized calcium to form insoluble calcium oxalate, producing profound hypocalcemia with tetany, and the crystals appear as envelope-shaped oxalate dihydrate forms in urine. Sulphuric and nitric acids are corrosive but do not bind calcium or produce oxalate crystalluria, killing options A and C. Carbolic acid causes nephrotoxicity and dark green urine from oxidized phenol conjugates but no hypocalcemia, eliminating D.
Reference: Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology, 7th ed.
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