Toxicology and Overdose Management Practice Questions

Q: Which of the following is the cause of this condition?

Digoxin toxicity. ***Digoxin toxicity*** - Characteristic ECG findings include **bidirectional ventricular tachycardia** and **scooped ST depression** (Salvador Dali mustache sign). - **Digitalis toxicity** commonly presents with **nausea**, **visual disturbances** (yellow halos), and dangerous **arrhythmias**. *Hypokalemia* - Typically causes **prominent U waves**, **flattened T waves**, and **prolonged QT interval** on ECG. - Does not produce the characteristic **bidirectional VT** or **scooped ST changes** seen with digoxin toxicity. *Hypercalcemia* - Results in **shortened QT interval** and **widened QRS complex** on ECG findings. - Does not cause the distinctive **arrhythmias** or **ST segment changes** associated with digitalis toxicity. *Beta blockers toxicity* - Primarily causes **bradycardia**, **heart blocks** (AV blocks), and **hypotension**. - Does not produce **ventricular tachycardia** or the **characteristic ST changes** seen in this condition.

Q: Heavy metal poisoning from mercury affects which part of the renal tubule?

Proximal Convoluted Tubule (PCT). The **Proximal Convoluted Tubule (PCT)** is the primary site of injury in acute mercury poisoning (specifically inorganic mercury salts like mercuric chloride). The underlying mechanism involves the high metabolic activity of PCT cells and their role in the transport and reabsorption of filtered metals. Mercury has a high affinity for **sulfhydryl (-SH) groups** on enzymes and proteins [1]. Once filtered or secreted into the tubular lumen, mercury is taken up by PCT cells, where it causes oxidative stress, mitochondrial dysfunction, and subsequent **Acute Tubular Necrosis (ATN)**. **Analysis of Incorrect Options:** * **Distal Convoluted Tubule (DCT) & Collecting Tubule (CT):** While these segments can be affected in severe, end-stage systemic toxicity, they are not the primary or initial targets. They have lower rates of solute transport and lower concentrations of the transport proteins that facilitate mercury entry compared to the PCT. * **Loop of Henle:** This segment is primarily involved in the concentration of urine and electrolyte balance (via the NKCC2 transporter). It is generally more susceptible to hypoxic injury rather than direct heavy metal nephrotoxicity. **Clinical Pearls for NEET-PG:** * **Triad of Mercury Poisoning:** Tremors (Danbury tremor), Neuropsychiatric symptoms (Erethism mercurialis/Mad Hatter syndrome), and Gingivostomatitis. * **Acrodynia (Pink Disease):** A specific pediatric presentation of mercury poisoning characterized by pinkish discoloration of hands/feet and hypertension. * **Antidote:** Dimercaprol (BAL) or Succimer (DMSA) are used for inorganic mercury; however, BAL is contraindicated in organic (methyl) mercury poisoning as it may increase brain levels. * **Other PCT Toxins:** Lead, Cadmium (causes Fanconi Syndrome), and Cisplatin also primarily target the PCT.

Q: A 50-year-old man is brought to the emergency department by ambulance. His respirations are shallow and infrequent, his pupils are constricted, and he is stuporous. He was noted to have suffered a grand mal seizure in the ambulance. Which drug is this man likely to have overdosed on?

Meperidine. ### Explanation **Correct Answer: C. Meperidine** The patient presents with the classic **Opioid Toxidrome**, characterized by the "triad" of CNS depression (stupor), respiratory depression (shallow/infrequent breathing), and miosis (constricted pupils) [1, 2]. While most opioids cause miosis and CNS depression, **Meperidine (Pethidine)** is unique because its metabolite, **normeperidine**, is a potent CNS stimulant with a long half-life. Accumulation of normeperidine—especially in cases of overdose or renal impairment—lowers the seizure threshold and leads to **grand mal seizures** [2]. This distinguishes it from other opioids like morphine or heroin, which typically do not cause convulsions. **Analysis of Incorrect Options:** * **A. Cocaine:** A sympathomimetic that causes **mydriasis** (dilated pupils), tachycardia, and hypertension. While it can cause seizures, it would not cause respiratory depression or miosis. * **B. LSD:** A hallucinogen that typically causes **mydriasis**, tachycardia, and perceptual distortions [3]. It does not cause the respiratory depression or stupor seen here. * **C. PCP (Phencyclidine):** Often causes nystagmus (horizontal or vertical), agitation, and violent behavior. While it can cause seizures, it is not associated with the classic opioid triad of miosis and respiratory depression. **NEET-PG High-Yield Pearls:** * **Meperidine & Pupils:** Unlike other opioids, Meperidine can sometimes cause **mydriasis** (due to its atropine-like structure), but in acute toxic overdose, miosis is still frequently observed. * **Normeperidine Toxicity:** Always suspect Meperidine in a patient with opioid signs + seizures or tremors. * **Drug Interaction:** Meperidine is contraindicated with **MAO Inhibitors** as it can precipitate a fatal **Serotonin Syndrome**. * **Antidote:** Naloxone reverses the respiratory depression but may not effectively reverse the seizure activity caused by the normeperidine metabolite.

Q: What is the management for a 10-year-old girl presenting with acute paracetamol overdose?

N-acetylcysteine. **Explanation:** **1. Why N-acetylcysteine (NAC) is the Correct Answer:** Paracetamol (Acetaminophen) toxicity occurs when the normal metabolic pathways (glucuronidation and sulfation) are saturated. This leads to the production of a highly reactive metabolite, **NAPQI**, via the cytochrome P450 system. Normally, NAPQI is detoxified by **Glutathione**. In overdose, glutathione stores are depleted, leading to hepatic necrosis. **N-acetylcysteine (NAC)** is the specific antidote because it acts as a precursor to glutathione, replenishing stores and directly detoxifying NAPQI [1]. It is most effective when administered within 8 hours of ingestion. **2. Why the Other Options are Incorrect:** * **B & C (PT monitoring and Hepatic enzymes):** While Prothrombin Time (PT/INR) and Liver Function Tests (ALT/AST) are essential for *monitoring* the severity of hepatotoxicity and prognosis, they are diagnostic/monitoring tools, not the primary *management* or treatment to prevent damage. * **D (Activated charcoal IV):** Activated charcoal is used for gastric decontamination to prevent absorption, but it is administered **orally**, never intravenously [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Rumack-Matthew Nomogram:** Used to determine the need for NAC based on serum paracetamol levels measured at or after **4 hours** post-ingestion. * **Toxic Dose:** In children, a dose >150 mg/kg is considered potentially hepatotoxic. * **Stages of Toxicity:** Hepatic necrosis typically manifests in Stage III (72–96 hours) with jaundice, encephalopathy, and coagulopathy. * **Best Prognostic Marker:** PT/INR is a more sensitive indicator of liver failure than transaminases in acute paracetamol poisoning.

Q: A 27-year-old, previously healthy man suddenly collapses at a party where both legal and illicit drugs are being used. En route to the hospital, he requires resuscitation with defibrillation to establish a normal cardiac rhythm. On physical examination, his temperature is 40°C; respirations, 30/min; heart rate, 110/min; and blood pressure, 175/90 mm Hg. He has dilated pupils, a perforated nasal septum, and a prominent callus on the right thumb. CT scan of the head shows an acute right frontal lobe hemorrhage. Which of the following substances is most likely responsible for these findings?

Cocaine. **Explanation:** The clinical presentation is classic for **Cocaine toxicity**, a potent sympathomimetic. Cocaine inhibits the reuptake of norepinephrine, dopamine, and serotonin, leading to excessive sympathetic stimulation [1]. **Why Cocaine is correct:** * **Sympathomimetic Toxidrome:** Tachycardia, hypertension, hyperthermia (40°C), and mydriasis (dilated pupils) are hallmark signs [1], [2]. * **Cardiovascular/Neurological Complications:** Cocaine causes coronary vasospasm and arrhythmias (explaining the collapse/defibrillation) and severe hypertension [2], which is a leading cause of **intracerebral hemorrhage** (the right frontal lobe bleed) in young adults. * **Physical Exam Clues:** A **perforated nasal septum** indicates chronic intranasal use ("snorting"). The **callus on the thumb** (from repeated use of a lighter) and the sudden collapse suggest smoking "crack" cocaine [3]. **Why other options are incorrect:** * **Amphetamines:** While they cause a similar sympathomimetic toxidrome [4], they are not typically associated with nasal septum perforation. * **Barbiturates & Ethanol:** Both are CNS depressants. Overdose typically presents with respiratory depression, bradycardia, hypotension, and pinpoint or normal pupils (miosis in severe barbiturate coma), rather than the hypertensive/hyperthermic state seen here [4]. **High-Yield Pearls for NEET-PG:** * **Management:** Benzodiazepines are the first-line treatment for cocaine toxicity to control agitation and hypertension. * **Contraindication:** **Beta-blockers** (like Propranolol) are strictly contraindicated in cocaine toxicity as they lead to "unopposed alpha-stimulation," worsening hypertension and coronary vasoconstriction. * **Differential:** Always consider cocaine in a young patient presenting with sudden MI, stroke, or aortic dissection.

Q: In organophosphorus compound poisoning, atropine can reverse all the following signs except?

Muscle weakness. In organophosphorus (OP) poisoning, the inhibition of acetylcholinesterase leads to an accumulation of acetylcholine at both **muscarinic** and **nicotinic** receptors [1]. **1. Why Muscle Weakness is the Correct Answer:** Atropine is a competitive **antimuscarinic** agent. It specifically blocks acetylcholine at muscarinic receptor sites (parasympathetic postganglionic endings). However, muscle weakness and paralysis in OP poisoning are mediated by **nicotinic receptors** at the neuromuscular junction (NMJ) [1]. Since atropine has no effect on nicotinic receptors, it cannot reverse muscle weakness, fasciculations, or respiratory muscle paralysis. These symptoms require **Oximes** (like Pralidoxime) to reactivate the enzyme [1]. **2. Why the other options are incorrect:** * **Lacrimation, Diaphoresis, and Diarrhea** are all classic "SLUDGE" symptoms caused by overstimulation of muscarinic receptors [1]. * **Lacrimation** (tearing) and **Diarrhea** (increased GI motility) are parasympathetic effects easily reversed by the anticholinergic action of atropine. * **Diaphoresis** (sweating) is unique because sweat glands are innervated by sympathetic fibers that are **cholinergic** (muscarinic). Therefore, atropine effectively stops the excessive sweating seen in OP poisoning. **NEET-PG High-Yield Pearls:** * **Mnemonic for Muscarinic effects:** **DUMBELS** (Diarrhea, Urination, Miosis, Bradycardia/Bronchospasm, Emesis, Lacrimation, Salivation/Sweating). * **Atropinization Endpoint:** The goal of therapy is not "normal" pupils, but rather **clearing of lung crepitations** (drying of secretions) and a heart rate >80 bpm. * **Oximes** must be given early (before "aging" of the enzyme-toxin bond) and are the specific treatment for nicotinic symptoms [1].

Q: An ECG of a patient with snake bite is shown below. What is the abnormality seen?

Hyperkalemia. ***Hyperkalemia*** - Snake bite, particularly **viper envenomation**, causes **rhabdomyolysis** leading to **acute kidney injury** and subsequent **hyperkalemia**. - Classic ECG features include **peaked T waves**, **widened QRS complexes**, and **prolonged PR intervals** as potassium levels rise. *Hypokalemia* - ECG shows **flattened T waves**, **prominent U waves**, and **ST depression**, which are opposite to hyperkalemia findings. - Snake bite typically causes **hyperkalemia** due to muscle breakdown and kidney dysfunction, not potassium loss. *Myocarditis* - ECG typically shows **ST elevation**, **T wave inversions**, and **arrhythmias** resembling myocardial infarction patterns. - While snake venom can cause **direct cardiotoxicity**, the predominant ECG abnormality is related to **electrolyte imbalance**. *Bigeminy* - Refers to **alternating normal and premature beats** creating a coupled rhythm pattern on ECG. - Snake bite-induced ECG changes are primarily due to **hyperkalemia** affecting cardiac conduction, not ectopic beat patterns.

Q: A rubber industry worker presents with abdominal colic and severe anemia. His blood examination reveals basophilic stippling of RBCs and microcytic anemia. What is the likely diagnosis?

Lead poisoning. **Explanation:** The clinical presentation of abdominal colic, severe anemia, and **basophilic stippling** in a worker from the rubber industry (where lead is used as a vulcanizing agent) is a classic description of **Lead Poisoning (Plumbism)**. **1. Why Lead Poisoning is correct:** Lead inhibits two key enzymes in the heme synthesis pathway: **Delta-aminolevulinic acid dehydratase (ALAD)** and **Ferrochelatase**. This leads to microcytic hypochromic anemia. The characteristic **basophilic stippling** occurs because lead inhibits the enzyme **5'-nucleotidase**, resulting in the degradation failure and subsequent aggregation of ribosomal RNA within erythrocytes. Abdominal colic ("Lead colic") is a common systemic manifestation. **2. Why other options are incorrect:** * **Radiation effects:** Typically present with bone marrow suppression leading to pancytopenia (aplastic anemia), not isolated microcytic anemia with stippling. * **Benzene poisoning:** Primarily associated with the rubber/solvent industry but typically causes **Aplastic Anemia** or **Acute Myeloid Leukemia (AML)**. * **Sideroblastic anemia:** While it also shows basophilic stippling and microcytosis, the occupational history and specific symptom of abdominal colic point definitively toward lead toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Burton’s Line:** A bluish-purple line on the gums (gingival lead line). * **Wrist Drop/Foot Drop:** Due to peripheral neuropathy (radial/peroneal nerve damage). * **Diagnosis:** Best screening test is **Blood Lead Levels**; most sensitive indicator of recent exposure is **Zinc Protoporphyrin (ZPP)**. * **Treatment:** Chelation therapy with **Succimer** (oral), **Ca-EDTA**, or **British Anti-Lewisite (BAL/Dimercaprol)**. * **Radiology:** "Lead lines" (increased density) at the metaphyses of long bones in children.

Q: A 30-year-old patient presents with nausea, weakness, headache, impaired vision, and high anion gap metabolic acidosis. What is the most likely cause?

Methanol. ### Explanation The clinical presentation of **High Anion Gap Metabolic Acidosis (HAGMA)** combined with **visual disturbances** is a classic hallmark of **Methanol poisoning** [1], [3]. **1. Why Methanol is Correct:** Methanol is metabolized by alcohol dehydrogenase into **formaldehyde** and then by aldehyde dehydrogenase into **formic acid** [2]. Formic acid is the toxic metabolite responsible for the HAGMA [1]. Crucially, formic acid has a predilection for the optic nerve and retina, leading to symptoms ranging from "seeing a snowstorm" to blurred vision and permanent blindness (optic atrophy) [1], [2], [3]. **2. Why the Other Options are Incorrect:** * **Ethanol:** While it can cause a mild metabolic acidosis (ketoacidosis) in chronic users, it does not typically cause a significant HAGMA or the specific visual impairment seen here. * **Ethylene Glycol:** This also causes HAGMA and an osmolar gap. However, its toxicity primarily targets the **kidneys** (acute tubular necrosis due to calcium oxalate crystals) rather than the eyes [3]. Patients often present with flank pain and hematuria. * **Amphetamine:** Toxicity presents with a sympathomimetic toxidrome (tachycardia, hypertension, mydriasis, and agitation). It does not typically cause HAGMA unless complicated by rhabdomyolysis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Antidote:** Fomepizole (inhibits alcohol dehydrogenase) is the first-line treatment [1]. Ethanol is an alternative if fomepizole is unavailable. * **Fundoscopy:** May show optic disc hyperemia or edema in early stages [3]. * **Imaging:** Methanol poisoning can characteristically cause **bilateral putaminal necrosis** on a CT/MRI of the brain. * **Mnemonic for HAGMA:** MUDPILES (Methanol, Uremia, DKA, Propylene glycol, Iron/INH, Lactic acidosis, Ethylene glycol, Salicylates).

Question 1

A 20-year-old fireman presents with headache and dizziness after extinguishing a garage fire. He denies shortness of breath, and his arterial blood gas shows a normal PO2. There is no cyanosis. What is the best initial management step for this patient?

Accepted Answer

Obtain a carboxyhemoglobin level

Answer

Assess for methemoglobinemia

Answer

Obtain an electrocardiogram (ECG)

Answer

Obtain a computed tomography (CT) scan of the head

Question 2

Which of the following is the cause of this condition?

Accepted Answer

Digoxin toxicity

Answer

Hypokalemia

Answer

Hypercalcemia

Answer

Beta blockers toxicity

Question 3

Heavy metal poisoning from mercury affects which part of the renal tubule?

Accepted Answer

Proximal Convoluted Tubule (PCT)

Answer

Distal Convoluted Tubule (DCT)

Answer

Collecting Tubule (CT)

Answer

Loop of Henle

Question 4

A 50-year-old man is brought to the emergency department by ambulance. His respirations are shallow and infrequent, his pupils are constricted, and he is stuporous. He was noted to have suffered a grand mal seizure in the ambulance. Which drug is this man likely to have overdosed on?

Accepted Answer

Meperidine

Answer

Cocaine

Answer

LSD

Answer

PCP

Question 5

What is the management for a 10-year-old girl presenting with acute paracetamol overdose?

Accepted Answer

N-acetylcysteine

Answer

PT monitoring

Answer

Measurement of hepatic enzymes

Answer

Activated charcoal IV, given

Question 6

A 27-year-old, previously healthy man suddenly collapses at a party where both legal and illicit drugs are being used. En route to the hospital, he requires resuscitation with defibrillation to establish a normal cardiac rhythm. On physical examination, his temperature is 40°C; respirations, 30/min; heart rate, 110/min; and blood pressure, 175/90 mm Hg. He has dilated pupils, a perforated nasal septum, and a prominent callus on the right thumb. CT scan of the head shows an acute right frontal lobe hemorrhage. Which of the following substances is most likely responsible for these findings?

Accepted Answer

Cocaine

Answer

Amphetamine

Answer

Barbiturate

Answer

Ethanol

Question 7

In organophosphorus compound poisoning, atropine can reverse all the following signs except?

Accepted Answer

Muscle weakness

Answer

Lacrimation

Answer

Diaphoresis

Answer

Diarrhea

Question 8

An ECG of a patient with snake bite is shown below. What is the abnormality seen?

Accepted Answer

Hyperkalemia

Answer

Hypokalemia

Answer

Myocarditis

Answer

Bigemini

Question 9

A rubber industry worker presents with abdominal colic and severe anemia. His blood examination reveals basophilic stippling of RBCs and microcytic anemia. What is the likely diagnosis?

Accepted Answer

Lead poisoning

Answer

Radiation effects

Answer

Benzene poisoning

Answer

Sideroblastic anemia

Question 10

A 30-year-old patient presents with nausea, weakness, headache, impaired vision, and high anion gap metabolic acidosis. What is the most likely cause?

Accepted Answer

Methanol

Answer

Ethanol

Answer

Ethylene glycol

Answer

Amphetamine

Toxicology and Overdose Management — MCQs

Toxicology and Overdose Management — MCQs

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