Antidotes in Emergency Medicine — MCQs
In case of cyanide poisoning, antidote of amyl nitrite is given. This is an example of:
Acetaminophen [Paracetamol] induced liver toxicity is due to which metabolite?
What is the antidote for acetaminophen overdose?
Which of the following statements about flumazenil is correct?
A patient presented to the emergency department with an overdose of a drug, exhibiting increased salivation and increased bronchial secretions. On examination, the blood pressure was 88/60 mmHg, and the RBC cholinesterase level was reduced to 50% of normal. What should be the treatment for this individual?
A 5-year-old child who has taken 10 iron tablets presents with nausea and abdominal pain. What is the antidote of iron poisoning?
What is the dose of ulipristal acetate when used for emergency contraception?
Drug of choice for beta antagonist toxicity is?
Which of these is the best for management of methanol poisoning?
A 1-year-old child with moderate VSD is scheduled for surgery next month. For control of symptoms of CHF, a drug $X$ was given. The uneducated parents gave double the dose of drug resulting in the child developing listlessness and poor feeding. Based on the ECG shown, what is the drug prescribed and its side effect?
Antidotes in Emergency Medicine Indian Medical PG Practice Questions and MCQs
Question 1: In case of cyanide poisoning, antidote of amyl nitrite is given. This is an example of:
- A. Receptor antagonism
- B. Chemical antagonism (Correct Answer)
- C. Physical antagonism
- D. Physiological antagonism
Explanation: ***Chemical antagonism*** - Amyl nitrite functions by inducing the formation of **methemoglobin**, which has a higher affinity for **cyanide ions** than cytochrome c oxidase. - This effectively sequesters cyanide, rendering it unable to bind to and inhibit the **cytochrome oxidase enzyme**, thus preventing its toxic effects [3]. *Receptor antagonism* - This involves a drug binding to a **receptor** and blocking the action of an **agonist**, without activating the receptor itself [1], [2]. - Amyl nitrite does not exert its effect by binding to a specific receptor and blocking cyanide's action; instead, it directly interacts with cyanide itself. *Physical antagonism* - This type of antagonism involves a drug preventing another drug's action through a **physical property**, such as adsorption or chelation. - While there is an interaction, the formation of methemoglobin and its subsequent binding to cyanide is more precisely described as a chemical reaction rather than a simple physical interaction or adsorption. *Physiological antagonism* - This occurs when two drugs act on **different receptors** or pathways to produce **opposite physiological effects**. - Amyl nitrite does not produce an opposite physiological effect by acting on a different pathway; rather, it directly counteracts the chemical nature of cyanide.
Question 2: Acetaminophen [Paracetamol] induced liver toxicity is due to which metabolite?
- A. Co-Q
- B. Cytochrome 'C'
- C. NAPQI (Correct Answer)
- D. N-acetylcysteine
Explanation: ***NAPQI*** - **N-acetyl-p-benzoquinone imine (NAPQI)** is a highly reactive and toxic metabolite produced during acetaminophen metabolism, especially in overdose situations [1, 3]. - When glutathione stores are depleted due to excessive NAPQI formation, this metabolite covalently binds to hepatic macromolecules, causing **hepatocellular damage and necrosis** [1, 3].*N-acetylcysteine* - **N-acetylcysteine (NAC)** is the antidote for acetaminophen overdose, not the toxic metabolite itself [2, 3]. - NAC works by replenishing hepatic **glutathione stores**, which helps detoxify NAPQI and prevent liver injury [2, 3].*Co-Q* - **Coenzyme Q10 (CoQ10)** is an endogenous antioxidant and electron carrier in the mitochondrial respiratory chain. - It is not a metabolite of acetaminophen and plays no direct role in acetaminophen-induced liver toxicity.*Cytochrome 'C'* - **Cytochrome c** is a protein involved in the electron transport chain in mitochondria and plays a critical role in apoptosis. - While cellular damage from NAPQI can eventually lead to cytochrome c release and apoptosis, cytochrome c itself is not a metabolite of acetaminophen or the direct cause of toxicity.
Question 3: What is the antidote for acetaminophen overdose?
- A. N-acetylcysteine (NAC) (Correct Answer)
- B. Heparin
- C. Morphine
- D. Benzodiazepine
Explanation: ***N-acetylcysteine (NAC)*** - **N-acetylcysteine (NAC)** is the specific antidote for acetaminophen overdose, working by replenishing **glutathione** stores in the liver. - Glutathione is crucial for detoxifying the toxic metabolite of acetaminophen, **N-acetyl-p-benzoquinone imine (NAPQI)**, thus preventing **hepatic damage**. *Heparin* - **Heparin** is an **anticoagulant** used to prevent and treat various thrombotic events by inhibiting coagulation. - It has no role in the treatment or detoxification of acetaminophen overdose. *Morphine* - **Morphine** is an **opioid analgesic** primarily used for pain management, acting on opioid receptors in the central nervous system. - It is not an antidote for any specific overdose and would exacerbate respiratory depression if given in an opioid overdose. *Benzodiazepine* - **Benzodiazepines** are a class of drugs with **sedative, anxiolytic, muscle relaxant, and anticonvulsant** properties, commonly used for anxiety, insomnia, or seizures. - They are not an antidote for acetaminophen overdose and would not counteract its hepatotoxic effects.
Question 4: Which of the following statements about flumazenil is correct?
- A. Can be used in barbiturate poisoning
- B. Specific antidote for opiate overdose
- C. Can be used in benzodiazepine overdose (Correct Answer)
- D. None of the options
Explanation: ***Can be used in benzodiazepine overdose*** - **Flumazenil** is a **competitive antagonist** at the **GABA-A receptor**, specifically designed to reverse the effects of **benzodiazepines**. - It binds to the same receptor site as benzodiazepines, effectively blocking their sedative and anxiolytic actions, making it useful in emergent overdose situations. *Can be used in barbiturate poisoning* - **Flumazenil** is **ineffective** in **barbiturate overdose** because barbiturates bind to a different site on the GABA-A receptor than benzodiazepines. - Barbiturates enhance **GABAergic activity** through a distinct mechanism, which flumazenil does not antagonize. *Specific antidote for opiate overdose* - The **specific antidote for opiate overdose** is **naloxone**, which acts as an opioid receptor antagonist. - **Flumazenil** has **no affinity** for opioid receptors and thus no role in reversing opiate toxicity. *None of the options* - This option is incorrect because **flumazenil** is indeed used for **benzodiazepine overdose**, as described above. - Its specific mechanism of action targets benzodiazepine-induced central nervous system depression.
Question 5: A patient presented to the emergency department with an overdose of a drug, exhibiting increased salivation and increased bronchial secretions. On examination, the blood pressure was 88/60 mmHg, and the RBC cholinesterase level was reduced to 50% of normal. What should be the treatment for this individual?
- A. Atropine (Correct Answer)
- B. Physostigmine
- C. Flumazenil
- D. Neostigmine
Explanation: ***Atropine*** - The patient exhibits symptoms of **cholinergic crisis** (increased salivation, bronchial secretions, hypotension) and reduced RBC esterase, strongly indicative of **organophosphate poisoning**. - **Atropine** is the primary antidote, as it competitively blocks muscarinic acetylcholine receptors, reversing the parasympathetic effects. *Neostigmine* - **Neostigmine** is an **acetylcholinesterase inhibitor**, meaning it would worsen the cholinergic crisis by increasing acetylcholine levels further. - It is used in conditions like **myasthenia gravis** to improve muscle strength, not in organophosphate poisoning. *Flumazenil* - **Flumazenil** is an **antagonist of benzodiazepine receptors** and is used to reverse benzodiazepine overdose. - It has no role in treating organophosphate poisoning or cholinergic symptoms. *Physostigmine* - **Physostigmine** is also an **acetylcholinesterase inhibitor** that can cross the blood-brain barrier. - While it has some ophthalmic uses, it would exacerbate the cholinergic symptoms of organophosphate poisoning due to increased acetylcholine.
Question 6: A 5-year-old child who has taken 10 iron tablets presents with nausea and abdominal pain. What is the antidote of iron poisoning?
- A. EDTA
- B. British Anti Lewisite
- C. Deferoxamine (Correct Answer)
- D. Penicillamine
Explanation: ***Deferoxamine*** - **Deferoxamine** is the chelating agent of choice for **iron poisoning**, forming a non-toxic complex that is excreted in urine. - It is indicated in patients with significant iron overdose, often presenting with **gastrointestinal symptoms** (nausea, abdominal pain), metabolic acidosis, or evidence of end-organ damage. *EDTA* - **EDTA (Calcium Disodium Versenate)** is primarily used to treat **lead poisoning** and sometimes other heavy metal intoxications [1]. - It is not effective for iron poisoning and can potentially worsen symptoms due to its affinity for calcium [1]. *British Anti Lewisite* - **British Anti Lewisite (BAL), or dimercaprol**, is an antidote for **arsenic, mercury, and gold poisoning** [2]. - It is not used for iron overdose and has a high incidence of side effects. *Penicillamine* - **Penicillamine** is another chelating agent used to treat **copper poisoning (Wilson's disease)** and sometimes lead or mercury poisoning. - It is not the primary antidote for iron poisoning and has a slower onset of action compared to deferoxamine.
Question 7: What is the dose of ulipristal acetate when used for emergency contraception?
- A. 30mg (Correct Answer)
- B. 300 mg
- C. 300 µg
- D. 30 µg
Explanation: ***30mg*** - The standard dose of **ulipristal acetate** for emergency contraception is a single 30 mg tablet. - This dosage effectively delays or inhibits **ovulation**, making it an effective post-coital contraceptive method. - Ulipristal acetate can be used up to **120 hours (5 days)** after unprotected intercourse, though it is most effective when taken as soon as possible. *300 mg* - A dose of 300 mg of **ulipristal acetate** is significantly higher than the standard therapeutic dose for emergency contraception. - Such a high dose would likely lead to increased side effects and is not recommended for this indication. *300 µg* - A dose of 300 µg (0.3 mg) of **ulipristal acetate** is too low to be effective for emergency contraception. - This dose would not provide sufficient **hormonal inhibition** to prevent ovulation or implantation. *30 µg* - A dose of 30 µg (0.03 mg) of **ulipristal acetate** is also too low for effective emergency contraception. - The efficacy of emergency contraception relies on specific hormonal levels, which this dose would not achieve.
Question 8: Drug of choice for beta antagonist toxicity is?
- A. Adrenaline
- B. Glucagon (Correct Answer)
- C. ACE inhibitors
- D. Dopamine
Explanation: ***Glucagon*** - **Glucagon** is the drug of choice for **beta-blocker overdose** because it bypasses the beta-adrenergic receptors and directly activates **adenylate cyclase** to increase intracellular cAMP [1]. - This action leads to increased heart rate and myocardial contractility, counteracting the cardiac depression caused by beta-blockers [1]. *Adrenaline* - **Adrenaline** (epinephrine) is a beta-agonist, but its effects are blunted in severe **beta-blocker overdose** due to **competitive antagonism** at beta receptors. - While it can be used for its alpha-agonist effects to increase blood pressure, its efficacy in reversing profound bradycardia and myocardial depression may be limited. *ACE inhibitors* - **ACE inhibitors** are used in the management of hypertension and heart failure, primarily by reducing **angiotensin II** formation and inhibiting **bradykinin** degradation. - They have no direct role in reversing the immediate cardiovascular effects of **beta-antagonist toxicity**. *Dopamine* - **Dopamine** is a **catecholamine** with dose-dependent effects, including positive inotropy and chronotropy at higher doses, but it relies on **adrenergic receptor activation**. - Its effects can be attenuated in **beta-blocker overdose**, similar to adrenaline, making it less effective than glucagon as first-line therapy.
Question 9: Which of these is the best for management of methanol poisoning?
- A. Fomepizole (Correct Answer)
- B. Naltrexone
- C. Disulfiram
- D. Acamprosate
Explanation: ***Fomepizole*** - **Fomepizole** is a competitive inhibitor of **alcohol dehydrogenase**, the enzyme responsible for metabolizing methanol into toxic metabolites like formic acid. - By inhibiting this enzyme, it prevents the formation of these toxic metabolites, thereby reducing organ damage and metabolic acidosis in methanol poisoning. *Naltrexone* - **Naltrexone** is an **opioid receptor antagonist** used in the treatment of alcohol and opioid dependence. - It does not have any direct action on the metabolism of methanol or its toxic byproducts. *Disulfiram* - **Disulfiram** inhibits **aldehyde dehydrogenase**, leading to an unpleasant reaction when alcohol is consumed (flushing, nausea, vomiting). - It is used for alcohol cessation and has no role in the management of methanol poisoning. *Acamprosate* - **Acamprosate** is a medication used to reduce alcohol cravings in individuals recovering from alcohol dependence, possibly by modulating **glutamate neurotransmission**. - It does not directly affect the metabolism of methanol or mitigate its toxic effects.
Question 10: A 1-year-old child with moderate VSD is scheduled for surgery next month. For control of symptoms of CHF, a drug $X$ was given. The uneducated parents gave double the dose of drug resulting in the child developing listlessness and poor feeding. Based on the ECG shown, what is the drug prescribed and its side effect?
- A. Spironolactone, hypokalemia
- B. Digoxin toxicity, ventricular bigeminy (Correct Answer)
- C. Furosemide, hypokalemia
- D. Beta blocker, third-degree heart block
Explanation: ***Digoxin toxicity, ventricular bigeminy*** - The ECG shows a regular rhythm with alternating normal sinus beats and **premature ventricular contractions (PVCs)**, indicating **ventricular bigeminy**. This is a classic arrhythmia associated with **digoxin toxicity**, especially in a child being treated for CHF. - **Digoxin** is commonly used in pediatric CHF to improve myocardial contractility, and overdose (as suggested by double dosing) can lead to symptoms like **listlessness and poor feeding** due to its narrow therapeutic window and central nervous system effects. *Spironolactone, hypokalemia* - **Spironolactone** is a potassium-sparing diuretic and would primarily cause **hyperkalemia**, not hypokalemia. - While used in CHF, it primarily acts on renal electrolyte balance and would not directly cause ventricular arrhythmias like bigeminy. *Furosemide, hypokalemia* - **Furosemide** is a loop diuretic that can cause **hypokalemia**, which is indeed a risk factor for arrhythmias, but the ECG pattern of **bigeminy** is more specific to **digoxin toxicity**. - While hypokalemia *can* predispose to arrhythmias, furosemide itself is not directly indicated by the bigeminy pattern; the symptoms of toxicity (listlessness, poor feeding) for furosemide overdose would primarily involve dehydration and electrolyte imbalances, not specifically cardiac rhythm disturbances like bigeminy. *Beta blocker, third-degree heart block* - **Beta-blockers** are used in some forms of CHF but an overdose typically causes **bradycardia** and **varying degrees of AV block**, potentially a third-degree heart block, but not **ventricular bigeminy**. - The ECG does not show dissociated P waves and QRS complexes characteristic of third-degree heart block; instead, it shows a patterned alternation of normal and ectopic beats.
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