Toxicology and Overdose Management Practice Questions

Q: A patient presented with dry mouth, dry hot skin, and dilated pupils. What is the likely cause?

Anticholinergic poisoning. ### Explanation The clinical presentation of **dry mouth, dry hot skin, and dilated pupils** is the classic "Anticholinergic Toxidrome." This occurs due to the competitive inhibition of acetylcholine at muscarinic receptors [1] [2]. #### 1. Why Anticholinergic Poisoning is Correct Anticholinergic agents (e.g., Atropine, Datura, TCAs, Antihistamines) block the parasympathetic nervous system, leading to: * **Dry mouth (Xerostomia):** Decreased salivary secretions. * **Dry hot skin:** Inhibition of sweat glands (anhidrosis) leads to hyperthermia [2]. * **Dilated pupils (Mydriasis):** Paralysis of the pupillary sphincter muscle. * **Other signs:** Tachycardia, urinary retention, and "madness" (delirium/hallucinations) [1]. #### 2. Why Other Options are Incorrect * **Options B & C (Cholinesterase inhibitors/Organophosphates):** These cause a **Cholinergic Toxidrome** by increasing acetylcholine levels [4]. This presents with the opposite symptoms, often remembered by the mnemonic **DUMBELS**: Diarrhea, Urination, Miosis (constricted pupils), Bradycardia/Bronchospasm, Emesis, Lacrimation, and Salivation. The patient would have "wet" skin and pinpoint pupils, not dry skin and dilated pupils. #### 3. NEET-PG High-Yield Pearls * **Classic Mnemonic:** "Hot as a hare (hyperthermia), Red as a beet (flushing), Dry as a bone (anhidrosis), Blind as a bat (mydriasis/cycloplegia), and Mad as a hatter (delirium)." * **Antidote:** **Physostigmine** is the specific antidote for central anticholinergic toxicity (it crosses the blood-brain barrier) [3]. * **Common Culprit:** In the Indian context, **Datura poisoning** is a frequent cause of this toxidrome [1]. * **Management:** Primarily supportive care, cooling measures, and benzodiazepines for agitation [3]. Avoid phenothiazines as they have anticholinergic properties.

Q: Hemoperfusion with charcoal is useful in poisoning with which of the following substances?

Barbiturate poisoning. **Explanation:** **Hemoperfusion** is an extracorporeal technique where blood is passed through a column containing adsorbent material, typically **activated charcoal** or resin. It is superior to hemodialysis for substances that have high lipid solubility, high protein binding, or a large molecular weight, as these factors often limit the clearance of toxins through a standard dialysis membrane. 1. **Why Barbiturates are the correct answer:** Long-acting barbiturates (like Phenobarbital) and especially short-to-intermediate acting barbiturates are highly lipid-soluble and protein-bound. Charcoal hemoperfusion is highly effective at adsorbing these molecules directly from the blood, making it a preferred method for severe, life-threatening barbiturate toxicity when supportive care is insufficient. 2. **Why the other options are incorrect:** * **Methyl Alcohol & Ethylene Glycol:** These are small, water-soluble molecules with low protein binding. They are best removed by **Hemodialysis**, which also helps correct the severe anion-gap metabolic acidosis associated with these toxicities. * **Lithium:** Lithium is a small monovalent cation that does not bind to charcoal. It is effectively removed by **Hemodialysis** due to its small size and lack of protein binding. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hemoperfusion:** Remember **"CHIP"** (Chloramphenicol, Hydantoin/Phenytoin, Isopropyl alcohol/Isothiazides, Phenobarbital/Paraquat). * **Paraquat poisoning:** Hemoperfusion is the treatment of choice if initiated early (within 2-4 hours). * **Hemodialysis vs. Hemoperfusion:** If the toxin is small and water-soluble (Lithium, Alcohols, Salicylates), choose Hemodialysis. If the toxin is large, lipid-soluble, or protein-bound (Barbiturates, Carbamazepine, Theophylline), choose Hemoperfusion.

Q: Which of the following statements is FALSE regarding acute aluminum phosphide poisoning?

May lead to esophageal stricture. Aluminum phosphide (AlP) is a highly lethal fumigant commonly used in grain preservation. The correct answer is **D** because esophageal strictures are a classic complication of **corrosive poisoning** (strong acids or alkalis), not aluminum phosphide [2]. AlP causes systemic cellular toxicity rather than local corrosive tissue destruction. **Why the other options are correct (and thus incorrect choices for this question):** * **Mechanism (B & C):** Upon contact with moisture (water or gastric acid), AlP releases **phosphine gas (PH₃)** [1, 3]. This gas is a potent mitochondrial toxin that inhibits **cytochrome c oxidase**, leading to a total breakdown of the electron transport chain, cellular hypoxia, and multi-organ failure [1]. * **Cardiac Effects (A):** The heart is highly sensitive to phosphine [1]. It causes direct toxic myocarditis, arrhythmias, and **subendocardial infarction/hemorrhage**, even in patients with normal coronary arteries. This is a hallmark of fatal AlP poisoning. **High-Yield Clinical Pearls for NEET-PG:** * **Garlic Odor:** A characteristic garlic-like or decaying fish odor is often noted in the patient's breath or gastric aspirate [4]. * **Silver Nitrate Test:** A quick bedside test where gastric aspirate or exhaled air turns silver nitrate paper **black** (due to the formation of silver phosphide). * **Refractory Shock:** The primary cause of death is profound, treatment-resistant metabolic acidosis and cardiovascular collapse [1]. * **Management:** There is no specific antidote [3]. Management is supportive, often involving gastric lavage with **potassium permanganate (1:10,000)** to oxidize phosphine and the use of coconut oil to inhibit gas release.

Q: Basal ganglia calcification is associated with poisoning of which substance?

Carbon monoxide. Carbon monoxide (CO) poisoning is the correct answer because of its specific affinity for the basal ganglia, particularly the globus pallidus [1]. CO causes tissue hypoxia by forming carboxyhemoglobin (which displaces oxygen) and by directly inhibiting the mitochondrial cytochrome oxidase system [1]. The basal ganglia are highly metabolically active and have a unique vascular supply that makes them susceptible to ischemic-hypoxic injury. Following an acute or chronic exposure, necrotic areas in the globus pallidus can undergo dystrophic calcification, which is a classic neuroimaging finding on CT scans in survivors. [2] Analysis of Incorrect Options: * A. Carbon dioxide: High levels cause respiratory acidosis and narcosis but do not typically result in focal basal ganglia calcification. * C. Hydrogen sulfide: While it also inhibits cytochrome oxidase (similar to cyanide), it is more commonly associated with rapid respiratory failure and "knock-down" effects rather than delayed basal ganglia calcification. [4] * D. Sulfur dioxide: This is primarily a mucosal and respiratory irritant; it does not have a predilection for deep brain structures. High-Yield Clinical Pearls for NEET-PG: * MRI Finding: The most sensitive early sign of CO poisoning is bilateral hyperintensity of the globus pallidus on T2-weighted images. * Cherry-red skin: A classic (though often post-mortem) physical sign of CO poisoning. [3] * Treatment: 100% high-flow oxygen is the first line; Hyperbaric Oxygen (HBO) is indicated if carboxyhemoglobin levels are >25% or if there are neurological deficits/loss of consciousness. * Differential Diagnosis: Other causes of basal ganglia calcification include Fahr’s Syndrome, hypoparathyroidism, and lead poisoning. [5]

Q: A patient presented with vomiting, pain in abdomen, jaundice, and encephalopathy following an attempted suicide. Poisoning is suspected. What is the most likely offending agent?

Paracetamol. **Explanation:** The clinical presentation of **vomiting, abdominal pain, jaundice, and encephalopathy** is a classic description of **Acute Liver Failure (ALF)** [3]. Among the options provided, **Paracetamol (Acetaminophen)** is the most common cause of drug-induced fulminant hepatic failure. **Why Paracetamol is correct:** Paracetamol toxicity occurs when the metabolic pathway involving glutathione becomes saturated. This leads to the accumulation of the toxic metabolite **NAPQI** (*N-acetyl-p-benzoquinone imine*), which causes centrilobular hepatic necrosis [1]. The clinical course typically progresses from initial GI upset (Phase 1) to right upper quadrant pain and elevated transaminases (Phase 2), culminating in jaundice, coagulopathy, and hepatic encephalopathy (Phase 3) within 72–96 hours [1]. **Why the other options are incorrect:** * **Benzodiazepines:** Overdose typically presents with CNS depression (lethargy, coma) and respiratory depression, but does not cause hepatic failure [2]. * **Organophosphorus:** Presentation includes cholinergic crisis (miosis, salivation, lacrimation, bradycardia, and muscle fasciculations). It does not cause jaundice or ALF. * **Acetylsalicylic acid (Aspirin):** Toxicity presents with tinnitus, hyperventilation, metabolic acidosis, and respiratory alkalosis. While it can cause Reye’s syndrome in children, it is not a primary cause of acute hepatic encephalopathy in adults [4]. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote:** N-acetylcysteine (NAC) – most effective if given within 8 hours. * **Rumack-Matthew Nomogram:** Used to predict hepatotoxicity based on plasma paracetamol levels (only for single acute ingestions). * **King’s College Criteria:** Used to determine the need for a liver transplant in paracetamol-induced ALF (pH 100s, Cr >3.4 mg/dL, and Grade III/IV encephalopathy).

Q: Which enzyme is inhibited in cyanide poisoning?

Cytochrome oxidase. **Explanation:** **Cyanide poisoning** is a life-threatening condition that primarily affects cellular respiration. The correct answer is **Cytochrome oxidase** (specifically **Cytochrome a3**), which is a key component of the **Electron Transport Chain (ETC)** located in the inner mitochondrial membrane [1]. 1. **Mechanism of Action:** Cyanide ions ($CN^-$) have a high affinity for the **ferric ($Fe^{3+}$) state** of iron. They bind to the heme group of Cytochrome a3 (Complex IV), effectively halting the final step of the ETC [1]. This prevents the reduction of oxygen to water, leading to a total arrest of aerobic metabolism. The cell shifts to anaerobic glycolysis, resulting in profound **lactic acidosis** and a high venous oxygen saturation as tissues cannot extract oxygen from the blood [1]. 2. **Analysis of Incorrect Options:** * **Xanthine oxidase:** This enzyme is involved in the catabolism of purines (converting hypoxanthine to xanthine and then to uric acid). It is the target of drugs like Allopurinol, not cyanide. * **Glutathione oxidase:** While glutathione systems are vital for managing oxidative stress, they are not the primary target of cyanide. Cyanide does not directly inhibit these enzymes to cause its lethal effects. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** "Cherry-red" skin/mucosa, almond-like odor on the breath, and severe metabolic acidosis with an increased anion gap [1]. * **Antidote Protocol:** 1. **Amyl nitrite/Sodium nitrite:** Induces **methemoglobinemia**. Methemoglobin contains $Fe^{3+}$, which "lures" cyanide away from cytochrome oxidase to form cyanomethemoglobin [1]. 2. **Sodium thiosulfate:** Acts as a sulfur donor for the enzyme **rhodanase**, converting cyanide into the non-toxic thiocyanate [1]. 3. **Hydroxocobalamin (Preferred):** Binds cyanide to form Vitamin B12 (cyanocobalamin), which is excreted by the kidneys.

Question 1

A 30-year-old male presents with hyperkeratosis and transverse nail lines. What is the most likely cause?

Accepted Answer

Chronic arsenic poisoning

Answer

Chronic lead poisoning

Answer

Chronic mercury poisoning

Answer

Acute arsenic poisoning

Question 2

Which of the following statements is NOT true for lead poisoning?

Accepted Answer

Only inorganic lead compounds are absorbed through the skin.

Answer

Approximately 90% of ingested lead is excreted in feces.

Answer

Lead poisoning primarily causes central nervous system (CNS) toxicity.

Answer

Urine lead levels exceeding 0.8 mg/L are indicative of significant lead absorption.

Question 3

A 25-year-old patient presents with loss of consciousness following cocaine overdose. On examination, BP is 200/100 mmHg and GCS is 7/15. The right pupil is dilated and sluggish to light. Which of the following interventions is NOT recommended for this patient?

Accepted Answer

Initiate sodium nitroprusside to achieve MAP below 130 mmHg

Answer

Administer mannitol at 1 g/kg body weight

Answer

Administer hypertonic fluids to maintain sodium at 145 mEq/dL

Answer

Neuromuscular paralysis

Question 4

A patient presented with dry mouth, dry hot skin, and dilated pupils. What is the likely cause?

Accepted Answer

Anticholinergic poisoning

Answer

Cholinesterase inhibitor poisoning

Answer

Organophosphate poisoning

Answer

None of the above

Question 5

Hemoperfusion with charcoal is useful in poisoning with which of the following substances?

Accepted Answer

Barbiturate poisoning

Answer

Methyl alcohol

Answer

Lithium

Answer

Ethylene glycol

Question 6

Which of the following statements is FALSE regarding acute aluminum phosphide poisoning?

Accepted Answer

May lead to esophageal stricture

Answer

Can cause subendocardial infarct

Answer

The substance produces phosphine gas

Answer

Inhibits mitochondrial cytochrome oxidase

Question 7

Basal ganglia calcification is associated with poisoning of which substance?

Accepted Answer

Carbon monoxide

Answer

Carbon dioxide

Answer

Hydrogen sulfide

Answer

Sulfur dioxide

Question 8

A patient presented with vomiting, pain in abdomen, jaundice, and encephalopathy following an attempted suicide. Poisoning is suspected. What is the most likely offending agent?

Accepted Answer

Paracetamol

Answer

Benzodiazepines

Answer

Organophosphorus

Answer

Acetylsalicylic acid

Question 9

A 21-year-old woman attempted suicide by taking an overdose of barbiturates. On arrival in the emergency department, her blood pressure is 95/65 mmHg and her pulse is 105 beats per minute. Arterial blood gases are ordered. Which of the following values would you expect in this patient?

Accepted Answer

PO2 = 75 mmHg, PCO2 = 60 mmHg, pH = 7.30

Answer

PO2 = 45 mmHg, PCO2 = 45 mmHg, pH = 7.45

Answer

PO2 = 55 mmHg, PCO2 = 70 mmHg, pH = 7.50

Answer

PO2 = 65 mmHg, PCO2 = 35 mmHg, pH = 7.45

Question 10

Which enzyme is inhibited in cyanide poisoning?

Accepted Answer

Cytochrome oxidase

Answer

Xanthine oxidase

Answer

Glutathione oxidase

Answer

None of the above

Toxicology and Overdose Management — MCQs

Toxicology and Overdose Management — MCQs

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