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FM13.{1-10,21} | Toxicology: General Principles — Graded Quiz
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A 30-year-old man is brought unconscious after consuming an unknown substance. Examination shows miosis, bradycardia, excessive salivation, bronchospasm, and urinary incontinence. Blood for cholinesterase is sent. The MOST appropriate immediate antidote is:
Correct. This is classic organophosphate (SLUDGE/DUMBELS) toxidrome. Atropine is the primary antidote, given IV in high doses titrated to drying of secretions (not just heart rate). PAM is given alongside but atropine is the life-saving immediate drug.
OP antidote order: 1. Atropine (large doses, titrate to secretion drying — NOT heart rate). 2. PAM/pralidoxime (within 24-48h before ageing). Atropine treats muscarinic features; PAM regenerates AChE.
SLUDGE features confirm OP poisoning. Atropine (muscarinic antagonist) is the first and primary antidote. PAM is added but ineffective after AChE 'ageing' (24-48h). Activated charcoal is ineffective for OP absorbed >1 hour ago.
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At autopsy of a suspected arsenic poisoning case, a sample of blood is collected. The correct preservative for this blood sample intended for chemical toxicological analysis is:
Correct. Blood for toxicological analysis must be preserved with sodium fluoride (NaF), which prevents fermentation/decomposition without interfering with chemical analysis. Solid viscera go in saturated NaCl. Formalin is absolutely prohibited.
Autopsy sample preservation rules: Blood → NaF. Viscera → Saturated NaCl. Urine → no preservative. Vitreous humor → no preservative. Hair/nails → dry, no preservative.
Blood → sodium fluoride (NaF). Solid viscera (liver, kidney, stomach contents) → saturated NaCl. NEVER formalin for any toxicology sample.
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A toxin with a small volume of distribution (Vd ≈ 0.6 L/kg), low protein binding, and renal excretion is found in overdose. The most effective method to enhance its elimination is:
Correct. Small Vd + low protein binding + renal excretion = ideal candidate for dialysis. This profile fits lithium perfectly. Dialysis is most effective for such compounds.
Dialysable poisons: SLIME — Salicylates, Lithium, Isopropanol/Isoniazid, Methanol/Metformin, Ethylene glycol. All share small Vd and low protein binding.
Dialysis works best for: small Vd (<1 L/kg), low protein binding, water solubility, and renal clearance. Large Vd compounds (like TCAs, digoxin) are not effectively dialysed.
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A doctor in the emergency department is treating a patient with suspected homicidal poisoning. Regarding the medicolegal duties, which statement is MOST accurate?
Correct. In all medicolegal cases including homicidal poisoning, the doctor must both treat and report. Neither duty supersedes the other — they occur simultaneously.
Medicolegal case duties: (1) Treat the patient — this is the primary duty, cannot be withheld. (2) Report to police — simultaneous, not sequential. Failure to report is an offence under IPC.
Both duties — treatment AND reporting — are equally obligatory. Delaying treatment or delaying reporting are both professional and legal violations.
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Haemodialysis is indicated in poisoning with all of the following EXCEPT:
Correct. Tricyclic antidepressants have a very large Vd (10-20 L/kg) and are highly protein-bound — haemodialysis removes negligible amounts. Management is supportive with sodium bicarbonate for cardiac arrhythmias.
TCAs in overdose: QRS widening on ECG → IV sodium bicarbonate (not dialysis). Large Vd means drug is 'hidden' in tissues, inaccessible to dialysis.
Haemodialysis is effective for methanol, ethylene glycol, salicylates, and lithium (all with small Vd and dialysable properties). TCAs — large Vd + high protein binding → dialysis ineffective.
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A worker in a lead battery factory presents with abdominal colic, constipation, and peripheral motor neuropathy. Which biological monitoring test best reflects recent lead absorption?
Correct. Blood lead level (BLL) is the gold standard for assessing CURRENT lead exposure/absorption. ZPP reflects exposure over the preceding 3-4 months (red cell lifespan). Radiological lead lines are signs of chronic deposition.
Occupational lead monitoring: BLL is the screening tool. Normal BLL: <5 μg/dL (ACGIH). Chelation considered >45 μg/dL with symptoms. EDTA provocation test assesses body burden.
BLL = current exposure marker. ZPP = exposure over last 3-4 months. Urinary ALA = reflects haeme synthesis disruption, less specific. Lead lines on X-ray are a chronic finding.
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A 22-year-old woman is found unresponsive. Examination reveals cherry-red discolouration of the skin and mucous membranes, hypoxia despite normal SpO₂ on pulse oximetry, and no response to oxygen alone. The most appropriate specific antidote is:
Correct. Cherry-red appearance + tissue hypoxia with normal SpO₂ (pulse oximetry cannot distinguish HbCO or HbCN from HbO₂) is a classic presentation of CO or cyanide poisoning. Hydroxocobalamin is the specific antidote for cyanide poisoning — it binds cyanide to form cyanocobalamin.
Cyanide antidote ladder: hydroxocobalamin (safest, no methaemoglobinaemia) > dicobalt edetate (fast but toxic if diagnosis wrong) > sodium thiosulphate + sodium nitrite (older regimen). Pulse oximetry is unreliable in CO/CN poisoning.
Cherry-red + normal SpO₂ but profound hypoxia points to CO or cyanide poisoning. For cyanide: hydroxocobalamin (preferred) or dicobalt edetate. For CO: 100% oxygen or hyperbaric oxygen.
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In the management of acute poisoning, the correct sequence of priority is:
Correct. The universal approach: Resuscitate (ABC) first → Decontaminate (gastric lavage/AC/skin wash as appropriate) → Identify & use specific antidote → Supportive care.
Acute poisoning management sequence: Resuscitate → Decontaminate → Antidote (if available) → Supportive care. Only ~5% of poisonings have a specific antidote — supportive care remains the mainstay.
ABC resuscitation ALWAYS comes first. Even if an antidote is available, a dead airway kills faster than any poison.
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The Reinsch test becomes positive (metallic deposit on copper strip) when the biological fluid is acidified with:
Correct. The Reinsch test requires acidification with dilute hydrochloric acid. In this medium, arsenic and other heavy metals deposit onto the copper strip as metallic coats.
Reinsch test technical detail: copper strip + dilute HCl + boiling biological fluid. Nitric acid is used for wet ashing in sample preparation for AAS — different step.
The Reinsch test uses hydrochloric acid (NOT nitric acid, which would dissolve the copper strip). The test detects arsenic, antimony, bismuth, and mercury.
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An environmental forensic examination of a river contaminated with industrial effluent from a chlor-alkali plant would most likely find elevated levels of:
Correct. Chlor-alkali plants (producing chlorine and sodium hydroxide by electrolysis of brine) classically use mercury cell technology, releasing inorganic mercury into waterways. Bacteria convert it to methylmercury — bioaccumulated in fish (Minamata disease model).
Minamata disease = methylmercury poisoning from industrial contamination. Classical occupational/environmental toxicology exam topic. Methylmercury selectively damages the cerebellum and visual cortex.
Chlor-alkali plants → mercury contamination. Chromium VI: tanning industries. Lead: battery plants, smelters. Arsenic: pesticide manufacture, gold mining.
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