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FM13.11-20,FM14.{2-3,15-16} | Toxicology: Specific Poisons — Graded Quiz
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Police bring a suspected drunk driver for examination. You plan to collect blood for alcohol analysis. The skin at the venepuncture site should be cleaned with:
Correct. Alcohol-based antiseptics (spirit, isopropyl alcohol) must NEVER be used to clean the venepuncture site when collecting blood for BAC analysis — they can artifactually elevate the result. Use aqueous iodine or povidone-iodine.
Blood for BAC: (1) Non-alcoholic skin antiseptic. (2) NaF/oxalate tube. (3) Seal and label immediately. (4) Chain of custody documentation from collection to lab. Critical forensic evidence — any procedural error can invalidate results in court.
Using alcoholic antiseptics at the venepuncture site artificially raises the BAC result — this could convict an innocent person. Always use iodine-based (non-alcoholic) skin preparation.
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A farmer ingests paraquat weed killer. Which statement about management is MOST accurate?
Correct. Paraquat undergoes redox cycling in the lung, generating superoxide radicals. High oxygen concentrations dramatically accelerate this process → more radical generation → accelerated pulmonary fibrosis. Oxygen is given ONLY if SpO₂ drops below 70-80% (as a last resort).
Paraquat: (1) O₂ contraindicated. (2) AC effective only within 1-2h. (3) Urine dithionite test (blue colour = positive) confirms. (4) Prognosis determined by ingested dose and plasma level. Paraquat causes progressive lung fibrosis (Paraquat lung).
CRITICAL: Oxygen is CONTRAINDICATED in paraquat poisoning — it worsens the oxidative lung injury. Also: activated charcoal must be given within 1-2 hours (not 6). Paraquat has a large Vd, making dialysis poorly effective.
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A 10-year-old child is brought with acute onset of vomiting, diarrhoea, 'rice-water' stools, peripheral neuropathy, and Mees' lines on nails. Hair analysis is ordered. This presentation is most consistent with:
Correct. Acute arsenic poisoning: rice-water stools (mimics cholera), garlic smell on breath/vomit, peripheral neuropathy. Mees' lines (4-6 weeks after exposure). Hair arsenic analysis (segmental — each cm = ~1 month) can date exposure.
Arsenic hair analysis: arsenic deposits in hair at rate of 1 cm/month. Segmental hair analysis can create a timeline of exposure. Arsenic in hair >1 μg/g is significant.
Rice-water stools + garlic smell + Mees' lines + peripheral neuropathy = arsenic. Thallium also causes Mees' lines but adds alopecia. Lead causes constipation not diarrhoea.
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A patient bitten by a neurotoxic snake (common krait) develops progressive bilateral ptosis and descending paralysis 4 hours later. The 20 Minute Whole Blood Clotting Test (20WBCT) is performed and blood clots normally. Anti-snake venom (ASV) administration should be:
Correct. The 20WBCT is a screening test specifically for HAEMOTOXIC envenomation (vipers — coagulopathy). Neurotoxic envenomation (krait, cobra) does NOT cause coagulopathy. Clinical signs of systemic envenomation (ptosis, descending paralysis) are the indication for ASV regardless of 20WBCT.
ASV indications: (1) Haemotoxic: 20WBCT positive, bleeding. (2) Neurotoxic: ptosis, respiratory paralysis, descending paralysis — give ASV even if 20WBCT normal. Neostigmine + atropine is adjunct for post-synaptic neurotoxins (cobra), NOT for krait (pre-synaptic).
20WBCT tests for coagulopathy (haemotoxic envenomation only). A normal 20WBCT does NOT exclude neurotoxic envenomation. Ptosis + descending paralysis = systemic envenomation → give ASV.
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A 55-year-old woman is on long-term warfarin for atrial fibrillation. She accidentally takes 10× her usual dose. Her INR is 11. She has no active bleeding. The MOST appropriate immediate management is:
Correct. For major supratherapeutic anticoagulation without active bleeding: PCC provides immediate factor replacement (faster than FFP, lower volume), and Vitamin K₁ provides sustained reversal over 12-24 hours. This is current best practice.
Warfarin reversal: (1) Life-threatening bleeding: PCC + Vit K IV. (2) Major non-bleeding supratherapeutic: PCC + Vit K. (3) Minor/asymptomatic: Vit K alone or dose reduction. Vitamin K₁ onset: IV = 4-6h, oral = 12-24h.
Vitamin K alone takes 12-24 hours. FFP alone requires large volumes, has virus risks. PCC + Vitamin K₁ is the combination for urgent reversal of warfarin without active bleeding.
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Carbon monoxide (CO) poisoning causes cellular hypoxia primarily because haemoglobin bound to CO (HbCO) has which property?
Correct. CO causes hypoxia by two mechanisms: (1) 240× higher affinity for Hb than O₂ → less O₂ carried. (2) HbCO shifts ODC left (Haldane effect) → remaining HbO₂ does not release O₂ to tissues. Additionally, CO inhibits cytochrome oxidase directly.
CO poisoning: cherry-red skin (HbCO), SpO₂ falsely normal on standard pulse oximetry (cannot distinguish HbCO from HbO₂ — CO-oximetry needed). Treatment: 100% O₂ (competes with CO at Hb — half-life of HbCO: room air 5h, 100% O₂ 80min, HBO 20min).
CO toxicity involves BOTH mechanisms: reduced O₂ carriage (240× affinity) AND impaired O₂ delivery (left-shifted ODC). CO also directly inhibits mitochondrial cytochrome oxidase — all three mechanisms contribute.
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The NDPS Act 1985 regulates narcotics and psychotropic substances in India. Under this Act, which offence carries a mandatory minimum sentence of 10 years rigorous imprisonment?
Correct. Under NDPS Act 1985, trafficking in 'commercial quantity' (defined for each substance) carries a minimum 10 years RI. Small quantity possession may attract up to 6 months. Medical prescription of opioids for legitimate purposes is exempted.
NDPS Act 1985 key provisions: (1) Defines 'small' vs 'commercial' quantity per substance. (2) Bail restrictions for commercial quantity offences. (3) Doctors must maintain narcotic register. (4) Licit morphine use for palliative care is protected.
NDPS Act 1985: small quantity (personal use) → up to 6 months; intermediate quantity → up to 10 years; commercial quantity (trafficking) → mandatory minimum 10-20 years.
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Yellow phosphorus poisoning (rat poison) produces a characteristic finding on post-mortem examination. Which of the following best describes this finding?
Correct. Yellow phosphorus is luminescent — the vomitus and organs may emit a faint glow in the dark (phosphorescence) and smell of garlic. The liver shows periportal and midzonal necrosis. Yellow phosphorus is the toxic form (white phosphorus = same); red phosphorus is non-toxic.
Yellow phosphorus poisoning: classic 3-phase course: (1) Vomiting, garlic smell, phosphorescent vomitus. (2) Apparent recovery (24-48h). (3) Hepatorenal failure. No specific antidote — supportive. Induced emesis is AVOIDED (phosphorus ignites in air).
Yellow phosphorus hallmark: phosphorescent vomitus + garlic smell + fatty/necrotic liver. Cherry-red = CO. Blue nails = methaemoglobinaemia (nitrites, dapsone). Yellow P is found in rodenticides and firecrackers.
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During a forensic toxicology practical, a student tests gastric contents from an alleged arsenic poisoning case. The Reinsch test is performed but yields a silver-grey metallic deposit on the copper strip. The NEXT confirmatory step is:
Correct. The Reinsch test cannot differentiate arsenic from antimony and bismuth — all deposit silver-grey. Treating with hypochlorite: arsenic deposit dissolves (forms arsenate), while antimony deposit is insoluble. The Marsh test is then used as the definitive confirmatory test.
Arsenic identification workflow: Reinsch (screening, detects As, Sb, Bi, Hg) → Hypochlorite to differentiate As from Sb → Marsh test (arsenic-specific: arsine gas → arsenic mirror) → AAS for quantification.
Reinsch test = screening for multiple heavy metals. To differentiate arsenic from antimony: hypochlorite test (arsenic dissolves). Confirmatory = Marsh test.
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Amanita phalloides (Death Cap mushroom) poisoning causes its most severe injury to:
Correct. Amanita phalloides contains amatoxins (alpha-amanitin), which inhibit RNA polymerase II, causing hepatic and renal necrosis. The GI phase (0-24h) is followed by apparent recovery, then hepatorenal failure at 3-5 days.
Mushroom poisoning types: (1) Amatoxin (A. phalloides) = hepatorenal. (2) Ibotenic acid/muscimol (A. muscaria) = anticholinergic-like CNS. (3) Muscarine (Clitocybe) = cholinergic. (4) Psilocybin = hallucinogens.
A. phalloides = alpha-amanitin = inhibits RNA pol II = liver + kidney necrosis. The classic triphasic presentation: GI → latent → hepatorenal failure. No antidote; liver transplant may be needed.
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