Forensic Toxicology (General, Organophosphorus, Corrosives, Metals, Narcotics, Alcohol) MCQs

Forensic Medicine · 73 free questions with answers & explanations.

  1. A 28-year-old pesticide worker is brought unconscious with miosis, bradycardia, excessive salivation, and urinary incontinence. Blood cholinesterase is markedly reduced. Which of the following BEST explains why pralidoxime (2-PAM) becomes ineffective if delayed beyond 24–48 hours in organophosphorus poisoning?
  2. A post-mortem examination reveals gastric mucosa with a soap-like, whitish, firm consistency and a characteristic sweetish smell. The stomach contents leave a gritty sensation on touch. Which corrosive acid is most likely responsible?
  3. In chronic arsenic poisoning, the pathognomonic skin sign is Mees' lines on nails. However, which of the following MOST reliably confirms chronic arsenic exposure over the prior 3–6 months?
  4. A 35-year-old man is found dead after consuming an unknown substance. Autopsy reveals cherry-red discolouration of blood and tissues, petechiae in the brain, and no specific odour. The COHb (carboxyhemoglobin) saturation is 72%. Which finding on post-mortem chemistry MOST distinguishes carbon monoxide poisoning from cyanide poisoning, both of which cause cellular asphyxia?
  5. In alcohol toxicology, the Widmark equation is used to back-calculate blood alcohol concentration (BAC) at an earlier time. The Widmark 'r' factor (distribution factor) differs between males (0.68) and females (0.55). This difference is PRIMARILY due to which physiological characteristic?
  6. A 28-year-old farmer is brought to the emergency department with profuse salivation, miosis, bradycardia, and muscle fasciculations. His serum butyrylcholinesterase activity is markedly depressed. Which enzyme assay is considered the MOST sensitive and specific indicator of organophosphate toxicity at the tissue level?
  7. In acute organophosphate poisoning, pralidoxime (PAM) is ineffective if administered after a certain critical window because the OP-AChE bond undergoes a process rendering it irreversible. What is this process called?
  8. A 35-year-old woman ingests an unknown substance. On examination she has hemorrhagic brownish-black discoloration of lips and oral mucosa, but NO evidence of charring. Gastric lavage returns a dark fluid with a strong pungent odour. Autopsy of a similar victim reveals necrosis of the gastric mucosa with a characteristic leathery brownish-black appearance. Which poison is MOST consistent with these findings?
  9. A man suspected of chronic arsenic poisoning undergoes forensic investigation. Mees' lines are found in his nails. Which is the MOST specific method for detecting chronic arsenic exposure in a living person?
  10. A forensic toxicologist analyzing a blood sample uses the principle of hapten-antibody competition. No chromatographic separation is performed. The assay produces a color change inversely proportional to the concentration of the analyte. Which analytical technique is being described?
  11. In lead poisoning, the characteristic basophilic stippling of red blood cells results from aggregation of which organelle?
  12. A 28-year-old farmer is brought unconscious with miosis, bradycardia, excessive secretions and fasciculations after spraying insecticide. Which specific biochemical test on blood BEST confirms organophosphorus poisoning and helps distinguish it from carbamate poisoning?
  13. A patient is brought in with bright cherry-red lividity, nausea, headache and a blood carboxyhaemoglobin (COHb) level of 40%. Which intracellular mechanism MOST directly explains the cellular hypoxia in CO poisoning beyond simple displacement of O2 from haemoglobin?
  14. In chronic arsenic poisoning, the MOST diagnostically significant change observed on a transverse section of the hair shaft using neutron activation analysis is:
  15. A man is found dead with a smell of almonds from his mouth. Autopsy reveals bright red blood and viscera. Cyanide poisoning is suspected. Which postmortem biochemical mechanism BEST explains the bright red appearance of venous blood in cyanide poisoning?
  16. A 35-year-old with chronic alcoholism presents with formic acidosis, methanol level of 80 mg/dL and visual symptoms. Fomepizole is unavailable. The pharmacological rationale for using ethanol as an antidote for methanol poisoning is BEST explained by:
  17. A 28-year-old agricultural worker is brought unconscious with profuse secretions, miosis, and bradycardia. Atropine 4 mg IV is given but DUMBELS features persist. The next most critical pharmacological step is:
  18. In organophosphate poisoning, pralidoxime (PAM) reactivates acetylcholinesterase by:
  19. A patient with suspected arsenic poisoning undergoes Reinsch test. A bright silvery metallic deposit appears on the copper strip. To distinguish arsenic from antimony in this deposit, the next confirmatory step is:
  20. A 35-year-old man develops painful ascending peripheral neuropathy with 'rain-drop pigmentation,' Mees' lines on nails, and Aldrich-Mees lines after a 6-week illness. Urine arsenic is 250 µg/L (normal <50). The mechanism of chronic arsenic toxicity causing peripheral neuropathy is:
  21. A 24-year-old male is brought unconscious after ingesting paint thinner. His blood methanol level is 40 mg/dL and he has metabolic acidosis with high anion gap. Which biochemical step is blocked by fomepizole to prevent methanol toxicity?
  22. Post-mortem vitreous humour is considered the best specimen for alcohol estimation because:
  23. Cyanide toxicity causes cellular asphyxia by binding to which component of the mitochondrial electron transport chain?
  24. A 45-year-old with suspected lead poisoning has basophilic stippling on peripheral smear and urinary ALA elevated to 60 µg/dL. The mechanism by which lead inhibits haem synthesis is:
  25. Organophosphate (OP) poisoning becomes refractory to oxime therapy (pralidoxime) once 'ageing' of the OP-AChE complex occurs. The mechanism of ageing involves:
  26. A farmer ingests an unknown substance and presents with miosis, excessive salivation, muscle fasciculations, and bradycardia. His serum acetylcholinesterase (AChE) is 15% of normal. Pralidoxime is administered after 48 hours. The MOST likely reason for its failure is:
  27. Paraquat (methyl viologen) produces its primary pulmonary toxicity through which mechanism?
  28. Carbon monoxide (CO) produces its cellular toxicity through all the following mechanisms EXCEPT:
  29. A patient after ingesting methanol develops severe metabolic acidosis with high anion gap, visual disturbances, and 'snowstorm vision'. The toxic metabolite responsible for optic nerve toxicity is:
  30. In acute ethanol intoxication, the medicolegal blood alcohol concentration (BAC) threshold above which a person is presumed impaired for driving in India under the Motor Vehicles (Amendment) Act is:
  31. Cyanide poisoning differs from carbon monoxide poisoning in which of the following features?
  32. Lead poisoning in adults characteristically produces a 'Burton's line' — a bluish-grey gingival line. The chemical basis of this line is formation of which compound in the gingival tissue?
  33. In organophosphate poisoning, intermediate syndrome (IMS) differs from acute cholinergic crisis in that IMS occurs 24–96 hours after poisoning and involves weakness of which specific muscle groups?
  34. A man presents with severe epistaxis, gingival bleeding, alopecia, Mees' lines on his fingernails, and painful peripheral neuropathy over 3 months. Hair analysis by atomic absorption spectrophotometry shows elevated levels of a heavy metal. Which metal is most likely, and through which mechanism does it produce Mees' lines?
  35. In a case of suspected chronic ethanol dependence, forensic determination of whether alcohol was consumed shortly before death (vs. postmortem alcohol formation) is BEST established by which finding?
  36. A suspected opioid overdose victim is brought dead. Which postmortem sample would be MOST suitable for toxicological confirmation of heroin (diacetylmorphine) use, given that heroin is rapidly hydrolysed to 6-monoacetylmorphine (6-MAM) and then to morphine?
  37. A patient dies 72 hours after suspected arsenic poisoning. At autopsy the stomach contents have been sent for analysis. Mees' lines (transverse white bands on nails) are found. The BEST specimen for confirming arsenic poisoning in this delayed death scenario is:
  38. The 'mushroom worker's lung' from Amanita phalloides poisoning is primarily caused by which toxin class, and what is the mechanism of death?
  39. In alcohol-related medico-legal cases, the Henry's Law constant is used to calculate blood alcohol concentration (BAC) from expired breath alcohol. The standard blood:breath ratio used in breath analysers is:
  40. Methanol (methyl alcohol) poisoning causes blindness and metabolic acidosis through which specific toxic metabolite?
  41. In a forensic toxicology case, a urine sample is found to contain morphine and codeine. This finding can indicate which of the following scenarios?
  42. A worker in a smelting factory develops colicky abdominal pain, constipation, wrist drop, bluish line at the gingival margin, and punctate basophilic stippling of red blood cells. Urine ALA excretion is markedly elevated. The MOST specific diagnostic marker for this condition is:
  43. Stomach wash fluid in a case of corrosive acid ingestion (sulphuric acid) is positive for haemoglobin on testing. The mechanism of haemoglobin appearance in stomach washings after acid ingestion is:
  44. In alcohol-related forensic toxicology, postmortem blood alcohol concentration (BAC) may be higher than antemortem levels due to putrefaction. Which biological specimen is MOST reliable for estimating antemortem alcohol exposure in a decomposed body?
  45. In mass casualty organophosphorus compound (OPC) poisoning, intermediate syndrome (IMS) is a clinical entity distinct from acute cholinergic crisis. The CORRECT statement about IMS is:
  46. In chronic arsenic (inorganic) poisoning, Mees' lines are observed on the fingernails. The correct statement about Mees' lines in the forensic context is:
  47. In forensic alcohol analysis, the Widmark formula is used to estimate blood alcohol concentration (BAC) from the amount consumed. The formula is C = A / (r × W), where C is BAC (g/dL), A is alcohol consumed (grams), W is body weight (kg), and r is the Widmark distribution factor. The correct r values for males and females respectively are:
  48. In a death suspected to be due to cyanide poisoning, the cherry-red colour of the skin and mucosae is caused by:
  49. A forensic toxicologist uses hair analysis for retrospective drug detection. The approximate window of detection for cocaine in a single strand of hair 10 cm long, given a hair growth rate of 1 cm/month, is:
  50. A 35-year-old farmer is brought unconscious with miosis, excessive salivation, bradycardia, bronchoconstriction, and muscle fasciculations. Plasma cholinesterase is 15% of normal. The treatment includes atropine titrated to dry secretions PLUS oxime (pralidoxime). Pralidoxime is effective ONLY if given within what time frame after organophosphorus (OP) exposure, and why?
  51. Chronic arsenic poisoning over months to years produces a characteristic dermatological triad. Which description BEST captures this triad?
  52. In medico-legal cases involving alcohol, the Widmark formula is used to back-calculate blood alcohol concentration (BAC) at the time of driving. If a person has a current BAC of 0.06 g/dL, weighs 70 kg (r-factor = 0.68), consumed alcohol 3 hours ago, and metabolism rate is 0.015 g/dL/hour, what was the BAC at the time of alleged driving (3 hours ago)?
  53. A patient presents with acute poisoning: miosis (pinpoint pupils), respiratory depression, loss of consciousness, and decreased bowel sounds. Urine immunoassay is positive for opioids. When naloxone is administered, the patient awakens immediately but becomes extremely agitated. After 45 minutes, the patient again becomes unresponsive. What accounts for this recurrence?
  54. A farmer presents with excessive salivation, lacrimation, miosis, bradycardia, and profuse sweating after working with an organophosphate insecticide. The antidote that addresses BOTH the muscarinic and nicotinic effects of this poisoning is:
  55. A patient presents with cherry-pink mucous membranes, headache, confusion, and a SpO2 reading of 99% on pulse oximetry despite severe tissue hypoxia. The substance responsible is:
  56. A 25-year-old presents 18 hours after ingesting methanol. Arterial blood gas shows severe metabolic acidosis with high anion gap. The earliest specific vision-related symptom expected in methanol poisoning is:
  57. Which of the following correctly identifies the medico-legally important Schedule H1 drug category in India under the Drugs and Cosmetics Act, 1940?
  58. A 40-year-old presents with alopecia, transverse white bands on fingernails (Mees' lines), peripheral neuropathy, and hyper-pigmentation of palms. Urine turns brown on adding 5% AgNO3. The MOST likely toxin is:
  59. A farmer is brought to the emergency department with profuse salivation, lacrimation, miosis, bradycardia, and muscle fasciculations after accidental exposure to a pesticide. Which enzyme activity in red blood cells is most diagnostically relevant?
  60. At autopsy of a suspected morphine overdose, the characteristic postmortem finding in the brain is:
  61. A 35-year-old male is found dead with cherry-red discolouration of skin and lividity. The most likely toxic cause is:
  62. Mees' lines on the fingernails are a classic sign of chronic poisoning with which heavy metal?
  63. In medicolegal practice, the best specimen for detecting alcohol consumption at the time of death is:
  64. Cyanide poisoning causes cellular hypoxia. Unlike carbon monoxide, cyanide does NOT bind haemoglobin. The mechanism of cyanide toxicity at the cellular level is:
  65. A 22-year-old is brought unconscious with miosis, bradycardia, coma, and profound respiratory depression following injection of an unknown drug. Naloxone produces dramatic reversal of all symptoms within minutes. What is the mechanism of naloxone's action in opioid overdose?
  66. A 45-year-old woman ingests an unknown quantity of tablets. On presentation she has nausea, abdominal pain, tinnitus, and hyperventilation. ABG shows: pH 7.49, PaCO₂ 22 mmHg, HCO₃ 17 mEq/L. Later, the repeat ABG shows pH 7.28 with elevated lactate. This pattern is MOST consistent with poisoning by:
  67. A post-mortem blood alcohol concentration (BAC) of 120 mg/dL is reported. The forensic pathologist notes that the gastric mucosa shows submucosal haemorrhages and hyperaemia but the liver shows no fatty change. In post-mortem toxicology, which major confounding factor must be considered when interpreting blood ethanol levels?
  68. In a living person, blood alcohol concentration (BAC) is correlated with clinical features. A subject with a BAC of 300 mg/dL (0.30%) would MOST likely exhibit which clinical picture?
  69. A child presents with severe colicky abdominal pain, constipation, and a violaceous-grey gingival line (Burton's line). X-ray abdomen shows radio-opaque deposits in the large bowel. Blood smear shows basophilic stippling of RBCs. Which metal is responsible, and what is the pathomechanism of the gingival line?
  70. A forensic investigator is testing a suspected arsenic-containing beverage using the Marsh test. The glass apparatus produces a silver mirror deposit in the reduction tube when the sample is acidified and heated with zinc. The deposit dissolves in sodium hypochlorite but NOT in ammonium sulphide. Which substance has been deposited?
  71. A fire victim found in a smoke-filled room has COHb saturation of 65%. Autopsy shows soot in the trachea and bronchi, cherry-red lividity, and frothy exudate in the bronchi. Which finding MOST definitively establishes that the victim was alive during the fire (vital reaction)?
  72. A man presents with severe paraesthesiae (burning and tingling of lips, tongue, and extremities), profuse salivation, bradycardia, hypotension, and generalised weakness, progressing to ventricular arrhythmias. He consumed a herbal preparation. Post-mortem analysis identifies aconitine in the gastric contents. Aconitine causes toxicity primarily through which mechanism?
  73. A patient develops a dramatic convulsive death — consciousness is intact throughout, the body is arched in opisthotonus, the face shows a fixed grin (risus sardonicus), and convulsions are triggered by the slightest touch or sound. The responsible poison is:
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