Forensic Toxicology Practice Questions

Q: Nerve gas is:

Sarin. **Explanation:** **Correct Answer: D. Sarin** Sarin is a highly potent organophosphorus compound classified as a **nerve gas** (or nerve agent). These agents act by irreversibly inhibiting the enzyme **acetylcholinesterase**. This leads to an accumulation of acetylcholine at neuromuscular junctions and synapses, resulting in a "cholinergic crisis" characterized by miosis, salivation, bronchospasm, and paralysis. Other classic nerve gases include Soman, Tabun, and VX. **Analysis of Incorrect Options:** * **A. Methyl Isocyanate (MIC):** This is an intermediate chemical used in pesticide manufacturing. It is famous for the **Bhopal Gas Tragedy**. It is a severe mucosal and pulmonary irritant, not a nerve gas. * **B. Phosgene:** This is a **choking agent** (pulmonary irritant). It was used in WWI and causes delayed-onset pulmonary edema by damaging the alveolar-capillary membrane. * **C. Diphenylchloroarsine:** This is a **sneezing agent** (sternutator). It is a vomiting agent used historically in chemical warfare to irritate the upper respiratory tract. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote for Nerve Gas:** Atropine (to block muscarinic effects) and Pralidoxime/2-PAM (to reactivate cholinesterase, provided "aging" of the enzyme has not occurred). * **Most Potent Nerve Agent:** VX (Venomous Agent X) is considered the most lethal. * **Mnemonic for Cholinergic Crisis:** **DUMBELS** (Diarrhea, Urination, Miosis, Bronchospasm/Bradycardia, Emesis, Lacrimation, Salivation). * **War Gas Classification:** * *Vesicants:* Mustard gas, Lewisite. * *Blood agents:* Cyanogen chloride, Hydrogen cyanide.

Q: A severely depressed 32-year-old man commits suicide by running his car motor in his closed garage for several hours. What is the primary mechanism of death in this case of carbon monoxide poisoning?

Displacement of oxygen on hemoglobin by carbon monoxide. **Explanation:** **Mechanism of Carbon Monoxide (CO) Toxicity:** Carbon monoxide is a colorless, odorless gas that causes death primarily through **tissue hypoxia**. The correct answer is **A** because CO has an affinity for hemoglobin (Hb) that is **200–250 times greater** than that of oxygen. When inhaled, it binds to hemoglobin to form **Carboxyhemoglobin (COHb)**, effectively displacing oxygen and reducing the oxygen-carrying capacity of the blood. Furthermore, it causes a **leftward shift of the oxygen-dissociation curve**, meaning the remaining oxygen binds more tightly to hemoglobin and is not released to the tissues. **Analysis of Incorrect Options:** * **B. Hepatocellular necrosis:** This is characteristic of Paracetamol (Acetaminophen) poisoning or Carbon tetrachloride, not CO. * **C. Inhibition of protein synthesis:** This is the mechanism for toxins like Ricin or Diphtheria toxin. * **D. Inhibition of respiratory chain enzymes:** While CO does bind to Cytochrome c oxidase (Complex IV), this is a secondary mechanism. This option is the primary mechanism for **Cyanide poisoning**. In CO poisoning, the displacement of oxygen from hemoglobin is the dominant lethal factor. **High-Yield Clinical Pearls for NEET-PG:** * **Post-mortem finding:** The classic sign is **cherry-red discoloration** of the skin, mucous membranes, and blood. * **Brain Lesion:** Chronic or severe exposure often leads to bilateral necrosis of the **Globus Pallidus**. * **Diagnosis:** Measured via co-oximetry (Pulse oximetry is unreliable as it cannot distinguish between HbO2 and COHb). * **Treatment:** 100% Hyperbaric oxygen (HBO) to reduce the half-life of COHb.

Q: All of the following effects are seen with cocaine except?

Sympatholytic effect. **Explanation:** The correct answer is **D. Sympatholytic effect**. Cocaine is a potent **indirect-acting sympathomimetic** agent. It works by blocking the reuptake of catecholamines (dopamine, norepinephrine, and serotonin) at the synaptic cleft. This leads to an excess of norepinephrine, causing a "sympathomimetic toxidrome" characterized by tachycardia, hypertension, mydriasis, and diaphoresis. Therefore, it has a **sympathomimetic** effect, not a sympatholytic (blocking) one. **Analysis of other options:** * **A. Black pigmentation of the tongue:** Chronic cocaine smokers may develop a characteristic black coating on the dorsum of the tongue, often referred to as "cocaine tongue," likely due to the direct effects of the smoke or contaminants. * **B. Nasal septal perforation:** Cocaine is a powerful vasoconstrictor. When snorted (insufflation), it causes intense local ischemia in the nasal mucosa. Chronic use leads to necrosis of the cartilaginous septum, resulting in perforation. * **C. Freebasing:** This refers to the process of converting cocaine hydrochloride (powder) into a purified, smokable "freebase" form (like crack cocaine) to achieve a more rapid and intense high. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Inhibits reuptake of biogenic amines (Dopamine > NE > 5-HT). * **Cardiac Risk:** Cocaine-induced vasospasm can lead to Myocardial Infarction. **Beta-blockers are contraindicated** in management due to the risk of unopposed alpha-adrenergic stimulation. * **Formication:** A tactile hallucination known as "Cocaine bugs" (Magnan’s sign) where the patient feels insects crawling under the skin. * **Pupils:** Causes **Mydriasis** (dilated pupils), unlike opioids which cause Miosis.

Q: What is the active substance in Hashish?

TetraHydrocannabinol. **Explanation** **Correct Answer: D. TetraHydrocannabinol (THC)** Hashish (Charas) is a resinous extract obtained from the flowering tops of the plant *Cannabis sativa*. The primary psychoactive constituent responsible for the "high" and medicinal effects of all cannabis products is **Delta-9-TetraHydrocannabinol (THC)**. It acts predominantly on CB1 and CB2 receptors in the central nervous system. **Analysis of Incorrect Options:** * **A. Morphine:** This is the principal alkaloid derived from the Opium poppy (*Papaver somniferum*). It is a potent opioid analgesic, not a cannabinoid. * **B. LSD (Lysergic Acid Diethylamide):** A potent semisynthetic psychedelic drug derived from Ergot fungus (*Claviceps purpurea*). It acts primarily on serotonin receptors. * **C. Mescaline:** A naturally occurring hallucinogenic alkaloid found in the Peyote cactus (*Lophophora williamsii*). **High-Yield Clinical Pearls for NEET-PG:** * **Cannabis Products:** Ranked by potency (THC content): **Bhang** (leaves/lowest) < **Ganja** (flower tops) < **Charas/Hashish** (resin/highest). * **Hashish Oil:** The most concentrated form of cannabis. * **Clinical Signs:** Characterized by "Red eyes" (conjunctival injection), increased appetite (munchies), and tachycardia. * **Psychological Effects:** Can cause "Run Amok" (a state of homicidal mania) and "Amotivational Syndrome" (chronic use). * **Test:** The **Duquenois-Levine test** is the chemical screening test used to identify cannabis (shows a violet color in the chloroform layer).

Q: Rhabdomyolysis can be caused by which of the following?

Sea snake venom. **Explanation:** The correct answer is **Sea snake venom (Option A)**. **1. Why Sea Snake Venom is Correct:** Sea snake venom is primarily **myotoxic**. It contains phospholipase A2 and small-molecule toxins that directly damage skeletal muscle fibers, leading to extensive **rhabdomyolysis**. This process releases massive amounts of myoglobin into the bloodstream (myoglobinemia), which is then excreted in the urine (myoglobinuria), often causing acute kidney injury (AKI) due to tubular necrosis. Clinically, patients present with generalized muscle pain, stiffness, and "cola-colored" urine. **2. Why the Other Options are Incorrect:** * **Cobra (Option B) and Krait (Option D):** These are **elapids** whose venom is primarily **neurotoxic**. They act on the neuromuscular junction (Cobra: post-synaptic; Krait: pre-synaptic), leading to muscle paralysis and respiratory failure, but they do not typically cause direct muscle fiber breakdown (rhabdomyolysis). * **Viper (Option C):** Viper venom is primarily **vasculotoxic** and **hemotoxic**. It causes local tissue necrosis, coagulopathy (DIC), and hemorrhages. While severe swelling can occasionally lead to compartment syndrome, the primary mechanism of systemic toxicity is not rhabdomyolysis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Sea Snake Bite:** Characterized by a "painless" bite with a latent period (30 mins to several hours) before the onset of muscle aches and myoglobinuria. * **Diagnosis:** Elevated Serum Creatine Phosphokinase (CPK) levels are the most sensitive indicator of myotoxicity. * **Treatment:** Polyvalent Antisnake Venom (ASV) in India does **not** cover sea snake bites. Specific monovalent antivenom is required. * **Rule of Thumb:** * Elapids (Cobra/Krait) = Neurotoxic * Vipers = Vasculotoxic * Sea Snakes = Myotoxic

Q: Which of the following is true for kraits?

4th infralabial scale is large. To identify venomous snakes in forensic toxicology, specific morphological features of the scales are high-yield diagnostic markers. ### **Explanation of the Correct Answer** **Option C (4th infralabial scale is large)** is the characteristic feature of a **Krait** (*Bungarus* species). In Kraits, the 4th infralabial (lower lip) scale is significantly larger than the others. Additionally, Kraits are identified by a row of enlarged **hexagonal scales** along the mid-dorsal spine and undivided sub-caudal scales. ### **Analysis of Incorrect Options** * **Option A (Pit present near the nostrils):** This is a characteristic of **Vipers** (specifically Pit Vipers like the Crotalinae subfamily). The loreal pit is a thermo-receptive organ located between the eye and the nostril. Kraits are elapids and lack this pit. * **Option B (3rd supralabial scale is large):** This is the classic identification mark for a **Cobra** (*Naja naja*). In Cobras, the 3rd supralabial (upper lip) scale touches both the eye and the nostril. ### **Clinical Pearls for NEET-PG** * **Neurotoxicity:** Kraits are primarily **pre-synaptically neurotoxic**. They prevent the release of Acetylcholine, making their bite often unresponsive to Neostigmine (unlike Cobras, which are post-synaptic). * **The "Silent" Bite:** Krait bites often occur at night while the victim is sleeping. The bite is relatively painless with minimal local swelling, often leading to a "silent" death due to respiratory paralysis. * **Abdominal Pain:** A unique clinical presentation of Krait poisoning is severe abdominal pain, which can mimic an acute abdomen. * **Management:** Polyvalent Anti-Snake Venom (ASV) is the mainstay of treatment. In India, ASV covers the "Big Four": Cobra, Krait, Russell’s Viper, and Saw-scaled Viper.

Q: Acrodynia is also known as:

Both of the above.. **Explanation:** **Acrodynia**, also known as **Pink disease** or **Swift disease**, is a clinical syndrome resulting from chronic exposure to **mercury** (elemental or inorganic). It was historically common in infants exposed to mercurous chloride in teething powders and calomel lotions. 1. **Why the correct answer is right:** * **Pink disease:** This name is derived from the characteristic clinical presentation where the patient’s hands and feet become bright pink, swollen, and painful (erythromelalgia). * **Swift disease:** It is named after Dr. H. Swift, who first described the condition in detail in 1914. * Since both terms are synonymous with Acrodynia, **Option C** is the correct choice. 2. **Analysis of Options:** * **Option A & B:** While both are correct, selecting only one would be incomplete. * **Option D:** Incorrect, as the terminology is well-established in pediatric toxicology. 3. **High-Yield Clinical Pearls for NEET-PG:** * **Pathophysiology:** Mercury inhibits the enzyme *catechol-O-methyltransferase* (COMT), leading to an accumulation of epinephrine and norepinephrine. This causes the characteristic "sympathetic storm." * **Clinical Features (The 6 P’s):** **P**ink skin, **P**aresthesia, **P**uffiness (edema), **P**erspiration (profuse sweating), **P**hotophobia, and **P**ersonality changes (irritability). * **Other features:** Hypertension, hypotonia, and loss of teeth/nails. * **Diagnosis:** Elevated 24-hour urinary mercury levels. * **Treatment:** Removal of the source and chelation therapy using **Succimer (DMSA)** or **Dimercaprol (BAL)**.

Question 1

Nerve gas is:

Accepted Answer

Sarin

Answer

Methyl isocyanate

Answer

Phosgene

Answer

Diphenylchloroarsine

Question 2

Gastric lavage is indicated in all cases of acute poisoning ideally because of which of the following risks?

Accepted Answer

Fear of aspiration

Answer

Danger of cardiac arrest

Answer

Danger of respiratory arrest

Answer

Inadequate ventilation

Question 3

A severely depressed 32-year-old man commits suicide by running his car motor in his closed garage for several hours. What is the primary mechanism of death in this case of carbon monoxide poisoning?

Accepted Answer

Displacement of oxygen on hemoglobin by carbon monoxide

Answer

Hepatocellular necrosis

Answer

Inhibition of protein synthesis

Answer

Inhibition of the respiratory chain enzymes

Question 4

What amount of pressure should be applied to a limb to prevent venom migration in snake bite?

Accepted Answer

40-70 mm of Hg

Answer

Less than 10 mm of Hg

Answer

20-30 mm of Hg

Answer

Greater than 100 mm of Hg

Question 5

Preservation of brain tissue is NOT required in which of the following types of poisoning?

Accepted Answer

Heavy metal poisoning

Answer

Alkaloid poisoning

Answer

Organophosphorus poisoning

Answer

Volatile organic poisoning

Question 6

All of the following effects are seen with cocaine except?

Accepted Answer

Sympatholytic effect

Answer

Black pigmentation of the tongue

Answer

Nasal septal perforation

Answer

Freebasing

Question 7

What is the active substance in Hashish?

Accepted Answer

TetraHydrocannabinol

Answer

Morphine

Answer

LSD

Answer

Mescaline

Question 8

Rhabdomyolysis can be caused by which of the following?

Accepted Answer

Sea snake venom

Answer

Cobra venom

Answer

Viper venom

Answer

Krait venom

Question 9

Which of the following is true for kraits?

Accepted Answer

4th infralabial scale is large

Answer

Pit present near the nostrils

Answer

3rd supralabial scale is large

Answer

All of the above

Question 10

Acrodynia is also known as:

Accepted Answer

Both of the above.

Answer

Pink disease.

Answer

Swift disease.

Answer

None.

Forensic Toxicology — MCQs

Forensic Toxicology — MCQs

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