Forensic Toxicology

Toxicology Intro - Poisons & Proof

• Toxicology: Scientific study of poisons, their effects, detection, and treatment.
• Poison: Any substance that, when introduced into or absorbed by a living organism, causes injury, illness, or death, typically by chemical means.
• Classification of Poisons:
  • Corrosives (e.g., Acids, Alkalis)
  • Irritants (e.g., Arsenic, Mercury)
  • Systemic (Neurotics, Cardiac, Asphyxiants)
  • Miscellaneous (e.g., Food additives, Pesticides)
• Proof of Poisoning (Medico-Legal):
  • Motive, opportunity, access to poison.
  • Symptoms observed before death.
  • Post-mortem appearances.
  • Chemical analysis of viscera, body fluids.
  • Detection of poison in food, medicine, or containers.
• Sample Collection & Preservation (Viscera):
  • Stomach & entire contents.
  • Small intestine (~50 cm) with contents, tied at both ends.
  • Liver (~500g), Spleen (half), Kidneys (both, halved).
  • Blood: 10-20 ml (Sodium Fluoride for alcohol; EDTA for others).
  • Urine: ~50 ml.
  • Vitreous humor: Especially for alcohol, drugs.
  • Preservative: Rectified spirit. Saturated saline if spirit unavailable. ⚠️ Formalin generally avoided as it interferes with tests.

⭐ Vitreous humor is often the best sample for estimating blood alcohol levels in decomposed bodies due to its resistance to putrefaction and microbial contamination.

Common Poisons - Deadly Dozen

• Organophosphates (OPC) & Carbamates:
  • Mechanism: Irreversible (OPC) / Reversible (Carbamates) AChE inhibition → cholinergic crisis.
  • Features: 📌 DUMBBELS (Diarrhea, Urination, Miosis, Bronchospasm/Bradycardia, Emesis, Lacrimation, Salivation/Sweating). Muscle fasciculations, paralysis.
  • Antidote: Atropine (muscarinic), Pralidoxime (PAM - for OPC, nicotinic).
• Paracetamol (Acetaminophen):
  • Mechanism: Toxic metabolite NAPQI depletes glutathione → liver necrosis.
  • Features: N/V, RUQ pain, jaundice, encephalopathy.
  • Antidote: N-acetylcysteine (NAC). Nomogram guided. Fatal dose: >15g.
• Salicylates (Aspirin):
  • Mechanism: Uncouples oxidative phosphorylation; respiratory alkalosis → metabolic acidosis.
  • Features: Tinnitus, hyperventilation, fever, AMS, coma.
  • Management: Alkalinization of urine, hemodialysis.
• Opioids (e.g., Morphine, Heroin):
  • Features: CNS depression, respiratory depression, miosis (pinpoint pupils).
  • Antidote: Naloxone.
• Cyanide:
  • Mechanism: Inhibits cytochrome oxidase → cellular hypoxia.
  • Features: Almond breath, cherry-red skin (late), rapid LOC, seizures.
  • Antidote: Hydroxocobalamin, Sodium thiosulfate + Sodium nitrite.
• Methanol:
  • Mechanism: Metabolized to formic acid → optic neuritis, metabolic acidosis.
  • Features: Visual disturbances ("snowstorm vision"), blindness, AGMA.
  • Antidote: Fomepizole, Ethanol.

⭐ In Organophosphate poisoning, atropinization is judged by dry mouth, ↓ secretions, ↑ Heart Rate (>80 bpm), and pupil dilation. Target signs indicate adequate muscarinic blockade.

Analytical Tox - Lab Detectives

• Goal: Detect, identify, quantify drugs/poisons in biological evidence.

• Specimens: Blood, urine, vitreous humor, bile, liver, brain, hair. Chain of Custody is vital.

• Process: Screening → Confirmation → Quantification → Interpretation.

• Screening: Rapid, sensitive.

  • Immunoassays (ELISA, EMIT).
  • Color tests, TLC.

• Confirmation: Specific, accurate.

  • GC-MS: Gold standard for volatiles (e.g., alcohol).
  • LC-MS/MS: Non-volatiles, thermolabile (e.g., opioids, benzodiazepines).
  • HPLC: Precise quantification.

⭐ Vitreous humor: Best for alcohol (ethanol) in decomposed bodies; resists putrefaction better than blood.

A visual of GC-MS and LC-MS machines in a lab setting would be appropriate here, perhaps with a label indicating "Analytical Instruments".

Medico-Legal Tox - Doctor's Duty

• Suspect poisoning: Based on history & clinical findings.
• Inform Police: Mandatory (CrPC Sec 39). Failure is punishable.
• Dying Declaration: Record if patient apprehends death (IEA Sec 32).
  • Magistrate ideal; doctor can if urgent.
• Prioritize Treatment: Save life first.
• Sample Collection: Crucial for viscera, blood, urine. Ensure proper labeling, sealing.
• Documentation: Detailed Medico-Legal Case (MLC) report.
• Confidentiality: Maintain, unless law requires disclosure.

⭐ Under CrPC Sec 39, a doctor must immediately report suspected poisoning to police/magistrate; failure is a legal offense.

High‑Yield Points - ⚡ Biggest Takeaways

• Ethanol: Zero-order kinetics for metabolism; Widmark's formula estimates BAC.
• Methanol: Causes metabolic acidosis, optic neuritis; antidote fomepizole or ethanol.
• Organophosphates: Induce cholinergic crisis (SLUDGE); treat with atropine and oximes.
• Carbon Monoxide (CO): High Hb affinity, cherry-red lividity, forms carboxyhemoglobin.
• Cyanide: Inhibits cytochrome oxidase causing histotoxic hypoxia; use nitrites, thiosulfate.
• Arsenic: Characteristic Aldrich-Mees lines, raindrop pigmentation, garlic odor.
• Opioids: Classic triad of pinpoint pupils, respiratory depression, coma; antidote naloxone.