Toxicology and Overdose Management Practice Questions

Q: Carbon monoxide poisoning causes which type of hypoxia?

Anemic hypoxia. **Explanation:** **Carbon Monoxide (CO) poisoning** causes **Anemic Hypoxia** through a dual mechanism that impairs oxygen delivery despite a normal partial pressure of arterial oxygen ($PaO_2$) [1][3]. 1. **Reduced Oxygen Carrying Capacity:** CO has an affinity for hemoglobin (Hb) that is **200–250 times greater** than that of oxygen [1][3]. It binds to Hb to form **Carboxyhemoglobin (COHb)**, effectively reducing the amount of functional hemoglobin available to transport oxygen—mimicking a state of anemia. 2. **Left Shift of the Dissociation Curve:** The binding of CO to one of the four heme sites increases the oxygen affinity of the remaining three sites. This shifts the **Oxygen-Dissociation Curve to the left**, preventing the release of oxygen to the tissues [1][3]. **Analysis of Incorrect Options:** * **Histotoxic Hypoxia:** Occurs when cells cannot utilize oxygen despite adequate delivery (e.g., **Cyanide poisoning**, which inhibits Cytochrome Oxidase). * **Anoxic (Hypoxic) Hypoxia:** Characterized by low arterial $PaO_2$ due to external factors like high altitude, hypoventilation, or V/Q mismatch [2]. In CO poisoning, $PaO_2$ remains normal. * **Stagnant (Ischemic) Hypoxia:** Results from inadequate blood flow/circulation to tissues (e.g., Heart failure, Shock, or localized embolism) [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Sign:** "Cherry-red" skin/mucosa (usually a post-mortem finding; rarely seen in living patients). * **Diagnosis:** Measured via **Co-oximetry**. Standard pulse oximetry is unreliable as it cannot distinguish between Oxy-Hb and CO-Hb. * **Treatment:** 100% Hyperbaric Oxygen (HBO) is the gold standard to reduce the half-life of COHb and prevent delayed neuropsychiatric sequelae.

Q: All of the following are used in the management of heroin poisoning EXCEPT:

Haloperidol. **Explanation:** The management of heroin (opioid) poisoning and withdrawal focuses on reversing respiratory depression, managing autonomic hyperactivity, and substitution therapy. **Why Haloperidol is the correct answer:** Haloperidol is a typical antipsychotic that **lowers the seizure threshold**. In the context of opioid withdrawal or toxicity, the patient is already physiologically unstable. Using Haloperidol can precipitate seizures and may worsen the QTc prolongation sometimes seen in polydrug abuse. It has no role in the specific reversal or symptomatic management of opioid toxidromes. **Analysis of Incorrect Options:** * **Clonidine:** This is a centrally acting $\alpha_2$-agonist used to treat the **autonomic symptoms** of opioid withdrawal (tachycardia, hypertension, sweating, and lacrimation). It reduces the sympathetic "storm" associated with stopping heroin. * **Buprenorphine:** A **partial $\mu$-opioid agonist**. It is used in opioid replacement therapy (ORT) because its high affinity displaces heroin from receptors while its partial agonist activity prevents severe withdrawal symptoms without causing significant euphoria. * **Pentazocine:** While rarely a first-line choice today, it is an **opioid agonist-antagonist**. In certain clinical protocols, it has been used to manage withdrawal, though it must be used cautiously as it can precipitate acute withdrawal in highly dependent individuals. **Clinical Pearls for NEET-PG:** 1. **Drug of Choice (Acute):** Naloxone (pure opioid antagonist) is the gold standard for reversing respiratory depression. 2. **Triad of Opioid Poisoning:** Pinpoint pupils (miosis), respiratory depression, and altered mental status (coma) [1]. 3. **Exception to Miosis:** Pethidine (Meperidine) poisoning causes **mydriasis** (dilated pupils) due to its atropine-like action. 4. **Maintenance:** Methadone (long-acting agonist) and Buprenorphine are the mainstays for long-term rehabilitation.

Q: Dialysis is not effective in which of the following poisonings?

Digoxin poisoning. To determine if a toxin can be removed by hemodialysis, we look at the mnemonic **"V-M-P"**: **V**olume of distribution (Vd), **M**olecular weight, and **P**rotein binding. For dialysis to be effective, a toxin must have a **low Vd**, low molecular weight, and low protein binding. [1] ### Why Digoxin is the Correct Answer **Digoxin** has an extremely **high Volume of Distribution (Vd > 5-7 L/kg)**. It is highly lipid-soluble and binds extensively to peripheral tissues (especially cardiac and skeletal muscle). Since only a tiny fraction of the drug remains in the plasma, hemodialysis cannot access or remove it effectively. * **Management Pearl:** The definitive treatment for life-threatening digoxin toxicity is **Digoxin-specific antibody fragments (DigiFab).** ### Why the Other Options are Incorrect * **A. Salicylates (Aspirin):** These have a low Vd and are highly dialyzable. Hemodialysis is the treatment of choice in severe cases (levels >100 mg/dL) as it also corrects the associated metabolic acidosis. [1], [2] * **C. Barbiturates:** Long-acting barbiturates (like Phenobarbital) have low protein binding and low Vd, making them amenable to dialysis or hemoperfusion. * **D. Methanol:** This is a small, water-soluble molecule. Dialysis is life-saving as it removes both the parent alcohol and its toxic metabolite (formic acid). ### NEET-PG High-Yield Pearls: * **Mnemonic for Dialyzable drugs (BLAST-M):** **B**arbiturates, **L**ithium, **A**lcohol (Methanol/Ethylene glycol), **S**alicylates, **T**heophylline. [2] * **Drugs NOT dialyzable:** Digoxin, Benzodiazepines, Tricyclic Antidepressants (TCAs), and Organophosphates (due to high Vd or high protein binding). * **Volume of Distribution Rule:** If Vd > 1 L/kg, dialysis is generally ineffective.

Q: What is the drug of choice in theophylline poisoning?

Phenobarbitone. ### **Explanation: Management of Theophylline Poisoning** Theophylline is a methylxanthine used in airway diseases, but it has a narrow therapeutic index. In cases of toxicity, the drug of choice for managing specific complications is **Phenobarbitone**. #### **Why Phenobarbitone is the Correct Answer** Theophylline toxicity leads to severe CNS excitation, most notably **refractory seizures**. These seizures are often resistant to standard benzodiazepines (like Diazepam). Phenobarbitone is the preferred agent because [1]: 1. It acts as a potent anticonvulsant by enhancing GABAergic inhibition. 2. It is a known **enzyme inducer** (CYP1A2 and CYP3A4), which can theoretically accelerate the metabolism and clearance of theophylline from the body. --- #### **Analysis of Incorrect Options** * **A. Cimetidine:** This is an enzyme inhibitor. It **increases** theophylline levels by inhibiting its metabolism, which would worsen the toxicity. * **B. Propranolol:** While beta-blockers can treat theophylline-induced tachyarrhythmias, they are generally **contraindicated** because theophylline is often used in patients with asthma or COPD; propranolol can trigger life-threatening bronchospasm. (Esmolol is a safer, short-acting alternative). * **C. Thyroxine:** This has no role in theophylline management and may exacerbate tachycardia. --- #### **High-Yield Clinical Pearls for NEET-PG** * **Mechanism of Toxicity:** Inhibition of phosphodiesterase (increasing cAMP) and antagonism of adenosine receptors. * **Clinical Presentation:** "Coffee-ground" emesis (due to gastritis), intractable seizures, and hypokalemia (due to beta-adrenergic stimulation). * **Definitive Treatment:** For severe toxicity (serum levels >60–100 mg/L), **Hemoperfusion** (charcoal) is the gold standard for rapid removal of the drug. * **MDAC:** Multiple Dose Activated Charcoal is highly effective in enhancing the "gut-dialysis" of theophylline.

Q: Which of the following is a recommended step in the management of salicylate poisoning?

Alkaline diuresis. **Explanation:** Salicylate poisoning (e.g., Aspirin overdose) is a classic NEET-PG topic. The management focuses on enhancing elimination and correcting acid-base disturbances. **Why Alkaline Diuresis is Correct:** Salicylates are weak acids. According to the principle of **ion trapping**, when the urine is alkalinized (using IV Sodium Bicarbonate), the salicylic acid molecules become ionized ($COO^-$) [2]. Ionized molecules are lipid-insoluble and cannot be reabsorbed across the renal tubule back into the blood [2]. This "traps" the salicylate in the urine, significantly increasing its excretion [2][4]. The goal is a urinary pH of 7.5–8.5 [4]. **Why Other Options are Incorrect:** * **Chelating agents:** These are used for heavy metal poisoning (e.g., EDTA for lead, Desferrioxamine for iron), not for salicylates [3]. * **Atropine:** This is the antidote for organophosphate poisoning or symptomatic bradycardia; it has no role in salicylate toxicity. * **Observation:** Salicylate poisoning is potentially fatal due to metabolic acidosis, respiratory alkalosis, and cerebral edema [1]. Active intervention (decontamination, alkalinization, or hemodialysis) is required for symptomatic patients [5]. **High-Yield Clinical Pearls for NEET-PG:** * **Acid-Base Pattern:** The earliest sign is **Respiratory Alkalosis** (due to direct stimulation of the respiratory center), followed by **High Anion Gap Metabolic Acidosis** (HAGMA) [1]. * **Tinnitus:** A classic early symptom of toxicity [1]. * **Potassium Management:** Hypokalemia must be corrected for alkaline diuresis to be effective; if $K^+$ is low, the kidneys will reabsorb $K^+$ in exchange for $H^+$, making the urine acidic. * **Hemodialysis:** The definitive treatment for severe cases (serum levels >100 mg/dL, refractory acidosis, or altered mental status) [5].

Q: Theophylline overdose causes which of the following?

Seizures. Theophylline is a methylxanthine derivative used in the treatment of asthma and COPD. It has a narrow therapeutic index (10–20 μg/mL), making toxicity a common clinical scenario in NEET-PG questions. **Why Seizures is the Correct Answer:** Theophylline toxicity leads to excessive stimulation of the central nervous system (CNS). The primary mechanisms include **adenosine receptor antagonism** and **phosphodiesterase inhibition**, which increases intracellular cAMP. Adenosine normally acts as an inhibitory neurotransmitter; by blocking it, theophylline lowers the seizure threshold. Seizures in theophylline overdose are often refractory to standard treatment and are a major cause of mortality. **Analysis of Incorrect Options:** * **A. Bradycardia:** Theophylline causes **tachycardia** (sinus, SVT, or ventricular arrhythmias) due to increased catecholamine release and direct positive chronotropic effects. * **C. Drowsiness:** Theophylline is a CNS stimulant (similar to caffeine). Toxicity presents with agitation, restlessness, and insomnia, rather than drowsiness. * **D. Bronchospasm:** Theophylline is a **bronchodilator**. It is used therapeutically to treat bronchospasm; therefore, an overdose would not cause it. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolic Abnormalities:** Toxicity characteristically causes **Hypokalemia**, hyperglycemia, and metabolic acidosis. * **Gastrointestinal:** Intractable vomiting is a hallmark sign of acute toxicity. * **Management:** Activated charcoal is used for gastric decontamination. In severe cases (serum levels >60-100 μg/mL or refractory seizures), **hemodialysis** is the treatment of choice. * **Drug Interactions:** Ciprofloxacin and Erythromycin inhibit Cytochrome P450 (CYP1A2), raising theophylline levels and precipitating toxicity.

Q: Hemodialysis is useful in poisoning with which of the following agents, EXCEPT?

Diazepam. The effectiveness of hemodialysis (HD) in removing a toxin depends on specific pharmacokinetic properties: **low molecular weight, low protein binding, small volume of distribution (Vd < 1 L/kg), and high water solubility.** **Why Diazepam is the correct answer:** Diazepam (a Benzodiazepine) is **not** dialyzable because it has a **very high volume of distribution** and is **highly protein-bound** [2]. It is extensively distributed into peripheral tissues (fat), making it inaccessible to the dialysis membrane [2]. Furthermore, the clinical management of benzodiazepine overdose is primarily supportive, with Flumazenil reserved for specific cases. **Why the other options are incorrect:** * **Salicylates (A):** HD is the treatment of choice for severe aspirin poisoning [1]. Salicylates have a small Vd and are easily cleared when blood pH is corrected [1]. * **Methyl alcohol (B):** Methanol and its toxic metabolites (formic acid) are small, water-soluble molecules. HD is indicated if there are visual changes, severe metabolic acidosis, or high serum levels. * **Barbiturates (D):** Specifically, long-acting barbiturates like **Phenobarbital** are effectively removed by HD (and hemoperfusion) due to lower protein binding compared to short-acting ones. **NEET-PG High-Yield Pearls:** * **Mnemonic for Dialyzable toxins (I STUMBLE):** **I**sopropanol, **S**alicylates, **T**heophylline, **U**remia, **M**ethanol, **B**arbiturates (long-acting), **L**ithium, **E**thylene glycol. * **Non-dialyzable drugs:** Digoxin, Benzodiazepines, Tricyclic Antidepressants (TCAs), and Calcium Channel Blockers (due to high Vd or high protein binding). * **Hemoperfusion** is generally superior to HD for **Theophylline** and **Barbiturates** but does not correct acid-base disturbances.

Question 1

A 23-year-old homeless man is found to have consumed alcohol adulterated with methanol. He is started on treatment effective for minimizing the toxicity to methanol. Which of the following is the most likely explanation for the benefit of this treatment?

Accepted Answer

Prevents biotransformation of methanol

Answer

Enhances renal excretion of methanol

Answer

Combines to form a nontoxic polymer

Answer

Changes the toxin's volume of distribution

Question 2

Carbon monoxide poisoning causes which type of hypoxia?

Accepted Answer

Anemic hypoxia

Answer

Histotoxic hypoxia

Answer

Anoxic hypoxia

Answer

Stagnant hypoxia

Question 3

Which of the following is caused by arsenic poisoning?

Accepted Answer

Extrahepatic portal vein obstruction

Answer

Hepatic carcinoma

Answer

Portal hypertension

Answer

Cirrhosis

Question 4

All of the following are used in the management of heroin poisoning EXCEPT:

Accepted Answer

Haloperidol

Answer

Clonidine

Answer

Buprenorphine

Answer

Pentazocine

Question 5

Dialysis is not effective in which of the following poisonings?

Accepted Answer

Digoxin poisoning

Answer

Salicylate poisoning

Answer

Barbiturate poisoning

Answer

Methanol poisoning

Question 6

What is the drug of choice in theophylline poisoning?

Accepted Answer

Phenobarbitone

Answer

Cimetidine

Answer

Propranolol

Answer

Thyroxine

Question 7

Which of the following is a recommended step in the management of salicylate poisoning?

Accepted Answer

Alkaline diuresis

Answer

Chelating agents

Answer

Atropine

Answer

Observation

Question 8

Theophylline overdose causes which of the following?

Accepted Answer

Seizures

Answer

Bradycardia

Answer

Drowsiness

Answer

Bronchospasm

Question 9

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 10

Hemodialysis is useful in poisoning with which of the following agents, EXCEPT?

Accepted Answer

Diazepam

Answer

Salicylates

Answer

Methyl alcohol

Answer

Barbiturates

Toxicology and Overdose Management — MCQs

Toxicology and Overdose Management — MCQs

On this page

Practice by Chapter

Want unlimited practice?