Clinical Pharmacology and Drug Toxicity — MCQs

Clinical Pharmacology and Drug Toxicity Indian Medical PG Practice Questions and MCQs

Question 421: Which of the following drugs should be avoided in G6PD deficiency?

A. Chloroquine (Correct Answer)
B. Vancomycin
C. Nicorandil
D. Hydralazine

Explanation: **Explanation:** **G6PD deficiency** is an X-linked recessive disorder where the lack of glucose-6-phosphate dehydrogenase leads to decreased production of NADPH. This results in a failure to maintain reduced glutathione levels, leaving red blood cells vulnerable to **oxidative stress**. When exposed to certain drugs, hemoglobin denatures into **Heinz bodies**, leading to hemolysis. **Why Chloroquine is the correct answer:** **Chloroquine** is a 4-aminoquinoline antimalarial that can induce oxidative stress. While its cousin, Primaquine, is the most notorious trigger for hemolysis in G6PD deficiency, Chloroquine is also classified as a high-risk drug (though the risk is lower than with Primaquine). In the context of NEET-PG, antimalarials as a class are the most frequently tested triggers for G6PD-related hemolysis. **Why the other options are incorrect:** * **Vancomycin:** A glycopeptide antibiotic primarily associated with "Red Man Syndrome" (histamine release) and nephrotoxicity, but it does not cause oxidative stress in RBCs. * **Nicorandil:** A potassium channel opener used in angina; its main side effect is mucosal ulceration (anal/oral). * **Hydralazine:** A direct vasodilator used in hypertension; its classic high-yield side effect is Drug-Induced Lupus Erythematosus (DILE) in slow acetylators. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for G6PD triggers:** "**S**ell **P**ale **A**ntimalarials **N**ow" (**S**ulfonamides, **P**rimaquine/Chloroquine, **A**spirin/NSAIDs, **N**itrofurantoin). * **Dapsone** is another extremely high-yield trigger often tested. * **Diagnosis:** Look for "Bite cells" (degmacytes) and "Heinz bodies" on a peripheral smear. * **Acute Phase:** Never test G6PD enzyme levels during an acute hemolytic episode, as young reticulocytes have normal enzyme levels and can give a **false-negative** result.

Question 422: A 19-year-old male complains of shortness of breath associated with wheezing after taking aspirin for a headache. In cases of aspirin hypersensitivity, which of the following mediators is responsible for this condition?

A. Leukotriene LTC4 (Correct Answer)
B. PGE2
C. Prostacyclin
D. Thromboxane

Explanation: ### Explanation **Mechanism of Aspirin-Exacerbated Respiratory Disease (AERD)** Aspirin and other NSAIDs work by inhibiting the enzyme **Cyclooxygenase (COX)**. In susceptible individuals, the inhibition of the COX pathway prevents the conversion of Arachidonic acid into Prostaglandins. This leads to a "shunting" of Arachidonic acid metabolism toward the **Lipoxygenase (LOX) pathway**. This results in the overproduction of **Cysteinyl Leukotrienes (LTC4, LTD4, and LTE4)**. **LTC4** is a potent bronchoconstrictor that increases vascular permeability and mucus secretion, leading to the clinical presentation of wheezing and shortness of breath (Aspirin-induced asthma). **Analysis of Options:** * **Option A (LTC4):** Correct. It is the primary mediator responsible for bronchospasm in aspirin hypersensitivity. * **Option B (PGE2):** Incorrect. PGE2 actually has a protective effect on the airways. Aspirin-induced depletion of PGE2 (which normally inhibits the LOX enzyme) further contributes to the overproduction of leukotrienes. * **Option C (Prostacyclin):** Incorrect. Prostacyclin (PGI2) is a vasodilator and inhibitor of platelet aggregation; its levels decrease with aspirin use but it does not cause bronchoconstriction. * **Option D (Thromboxane):** Incorrect. Thromboxane (TXA2) is involved in platelet aggregation. Aspirin inhibits its synthesis, which is the basis for its antiplatelet effect, not hypersensitivity. **High-Yield Clinical Pearls for NEET-PG:** * **Samter’s Triad:** Aspirin sensitivity, Bronchial Asthma, and Nasal Polyps. * **Management:** The drug of choice for treating aspirin-induced asthma is **Leukotriene Receptor Antagonists (LTRAs)** like **Montelukast** or **Zafirlukast**. * **Safe Alternative:** Acetaminophen (Paracetamol) is generally safe in low doses for patients with aspirin-induced asthma as it is a weak COX-1 inhibitor.

Question 423: What is the drug of choice for warfarin toxicity?

A. Protamine sulfate
B. Vitamin K (Correct Answer)
C. Dipyridamole
D. Ticlopidine

Explanation: **Explanation:** **Warfarin** is an oral anticoagulant that acts as a competitive inhibitor of the enzyme **Vitamin K Epoxide Reductase (VKORC1)**. This inhibition prevents the regeneration of active Vitamin K, thereby halting the synthesis of Vitamin K-dependent clotting factors (**II, VII, IX, and X**). **Why Vitamin K is the Correct Answer:** In cases of warfarin toxicity or over-dosage, the physiological antidote is **Vitamin K1 (Phytonadione)**. It bypasses the inhibited VKORC1 enzyme to provide a source for the gamma-carboxylation of clotting factors. * **Clinical Note:** While Vitamin K is the specific antidote, its effect is delayed (6–24 hours) as it requires the synthesis of new proteins. In cases of life-threatening bleeding, **Prothrombin Complex Concentrate (PCC)** or **Fresh Frozen Plasma (FFP)** is administered for immediate replacement of factors. **Why Other Options are Incorrect:** * **A. Protamine sulfate:** This is the specific antidote for **Heparin** toxicity. It is a basic protein that neutralizes the acidic heparin molecule via ionic bonding. * **C. Dipyridamole:** This is a phosphodiesterase inhibitor used as an **antiplatelet** agent, often in combination with aspirin or for cardiac stress testing. * **D. Ticlopidine:** This is a P2Y12 receptor antagonist (thienopyridine class) used as an **antiplatelet** drug. **High-Yield Pearls for NEET-PG:** 1. **Monitoring:** Warfarin therapy is monitored using **PT/INR** (extrinsic pathway). 2. **Teratogenicity:** Warfarin is contraindicated in pregnancy (causes **Fetal Warfarin Syndrome**); Heparin is the preferred anticoagulant for pregnant women. 3. **Skin Necrosis:** Occurs due to a rapid decline in Protein C levels; prevented by "bridging" with Heparin. 4. **Metabolism:** Warfarin is metabolized by **CYP2C9**; watch for interactions with enzyme inhibitors (e.g., Amiodarone) which increase bleeding risk.

Question 424: A patient receives a toxic dose of lignocaine intravenously. What are the likely symptoms the patient will exhibit?

A. Excessive salivation
B. Mydriasis and diarrhea
C. Respiratory paralysis
D. Seizures and coma (Correct Answer)

Explanation: **Explanation:** Lignocaine (Lidocaine) is an amide-linked local anesthetic that acts by blocking voltage-gated sodium channels. When administered intravenously in toxic doses, it primarily affects the **Central Nervous System (CNS)** and the Cardiovascular System. **Why D is correct:** CNS toxicity follows a predictable pattern of excitation followed by depression. Initially, lignocaine inhibits cortical inhibitory pathways, leading to excitatory symptoms like perioral numbness, tinnitus, tremors, and **seizures**. As plasma levels rise further, generalized CNS depression occurs, resulting in **coma** and respiratory arrest. **Why the other options are incorrect:** * **A & B:** Excessive salivation, diarrhea, and miosis (not mydriasis) are features of **cholinergic toxicity** (e.g., Organophosphate poisoning). Lignocaine does not have significant autonomic effects at these sites. * **C:** While respiratory arrest can occur in the terminal stages of lignocaine toxicity due to medullary depression, **seizures and coma** are the hallmark clinical presentation of systemic toxicity (LAST - Local Anesthetic Systemic Toxicity) that precedes or accompanies respiratory failure. **High-Yield NEET-PG Pearls:** 1. **Early Signs:** Perioral tingling and a metallic taste are often the earliest warning signs of lignocaine toxicity. 2. **Antidote:** The specific treatment for systemic local anesthetic toxicity (LAST) is **Intravenous Lipid Emulsion (20% Intralipid)**, which acts as a "lipid sink" to sequester the drug. 3. **Bupivacaine vs. Lignocaine:** Bupivacaine is significantly more **cardiotoxic** than lignocaine, often causing refractory arrhythmias. 4. **Metabolism:** Lignocaine is metabolized in the liver; hence, toxicity is more likely in patients with hepatic failure or reduced hepatic blood flow (e.g., CHF).

Question 425: All are important hypersensitivity-related side effects of high-dose sulfasalazine therapy, EXCEPT?

A. Hepatitis
B. Agranulocytosis
C. Pancreatitis
D. Thrombocytopenia (Correct Answer)

Explanation: <h3>Explanation</h3><p><strong>Sulfasalazine</strong> is a prodrug composed of <strong>5-aminosalicylic acid (5-ASA)</strong> and <strong>sulfapyridine</strong>, linked by a diazo bond. While 5-ASA provides the therapeutic effect in Ulcerative Colitis, the sulfapyridine moiety is responsible for most systemic side effects, which are categorized into dose-dependent (pharmacological) and dose-independent (hypersensitivity) reactions [2].</p><h4>Why Thrombocytopenia is the Correct Answer</h4><p><strong>Thrombocytopenia</strong> in the context of sulfasalazine is typically a <strong>dose-dependent</strong> (Type A) adverse effect related to bone marrow suppression, rather than a pure hypersensitivity (Type B) reaction. While sulfasalazine can cause various blood dyscrasias, aplastic anemia, which includes thrombocytopenia, is an extremely rare occurrence with sulfonamide therapy [1]. Thrombocytopenia is less frequently associated with the classic "hypersensitivity syndrome" compared to the other options listed.</p><h4>Analysis of Incorrect Options (Hypersensitivity Reactions)</h4><ul><li><strong>Hepatitis:</strong> This is a well-documented idiosyncratic hypersensitivity reaction to the sulfonamide component. It often presents with fever, rash, and elevated transaminases within the first few weeks of therapy.</li><li><strong>Agranulocytosis:</strong> This is a severe, life-threatening idiosyncratic (hypersensitivity) reaction. Agranulocytosis occurs in ~0.1% of patients who receive sulfadiazine and can follow the use of other sulfonamides [1]. It occurs unpredictably and is not strictly related to the serum concentration of the drug.</li><li><strong>Pancreatitis:</strong> Acute pancreatitis is a recognized hypersensitivity reaction to sulfasalazine. It is rare but occurs independently of the dose, often necessitating immediate and permanent discontinuation of the drug.</li></ul><h4>NEET-PG High-Yield Pearls</h4><ul><li><strong>Metabolism:</strong> Sulfasalazine is cleaved by <strong>bacterial azoreductase</strong> in the colon [2].</li><li><strong>Acetylation Status:</strong> Slow acetylators are at a higher risk of sulfapyridine-induced toxicity (nausea, vomiting, headache) [2].</li><li><strong>Male Infertility:</strong> Sulfasalazine causes <strong>reversible oligospermia</strong> (a common NEET-PG question).</li><li><strong>Supplementation:</strong> It inhibits folate absorption; hence, <strong>folic acid supplementation</strong> is mandatory.</li><li><strong>Hypersensitivity Syndrome:</strong> Often presents as a triad of fever, skin rash, and internal organ involvement (Hepatitis/Pneumonitis).</li></ul>

Question 426: Which of the following is NOT a correct antidote-toxin pair?

A. Deferoxamine - Iron
B. Flumazenil - Benzodiazepines
C. Dimercaprol - Arsenic
D. Naloxone - Dhatura (Correct Answer)

Explanation: **Explanation:** The correct answer is **D (Naloxone - Dhatura)** because Naloxone is a specific opioid antagonist used to reverse respiratory depression in **Opioid poisoning**, not Dhatura poisoning. **Dhatura** contains tropane alkaloids (Atropine, Hyoscine, and Scopolamine) which cause anticholinergic toxicity. The specific antidote for Dhatura (anticholinergic) poisoning is **Physostigmine**, a reversible acetylcholinesterase inhibitor that crosses the blood-brain barrier to reverse both central and peripheral symptoms. **Analysis of Incorrect Options:** * **A. Deferoxamine - Iron:** Correct pair. Deferoxamine is a specific chelating agent used in acute iron toxicity; it binds systemic iron to form ferrioxamine, which is excreted in the urine (often causing "vin-rose" colored urine). * **B. Flumazenil - Benzodiazepines:** Correct pair. Flumazenil is a competitive antagonist at the GABA-A receptor benzodiazepine binding site. *Note: Use with caution in chronic users as it can precipitate seizures.* * **C. Dimercaprol (BAL) - Arsenic:** Correct pair. Dimercaprol is a traditional chelating agent used for heavy metals like Arsenic, Mercury, and Lead. **NEET-PG High-Yield Pearls:** * **Dhatura Poisoning:** Remember the mnemonic "Mad as a hatter, dry as a bone, red as a beet, hot as a hare, blind as a bat." * **Specific Antidotes:** * Acetaminophen: **N-acetylcysteine** * Organophosphates: **Atropine and Pralidoxime (PAM)** * Methanol: **Fomepizole** (preferred) or Ethanol * Copper/Wilson's Disease: **Penicillamine** * Beta-blockers: **Glucagon**

Question 427: What is the mechanism of action of sodium nitrite in cyanide poisoning?

A. Produces methemoglobinemia (Correct Answer)
B. Increased blood flow to the liver
C. Increased blood flow to the heart
D. Increased blood flow to the kidney

Explanation: ### Explanation **Mechanism of Action (Correct Answer: A)** Cyanide is highly toxic because it binds to the **ferric (Fe³⁺) iron** in mitochondrial **cytochrome oxidase (Complex IV)**, halting aerobic respiration and causing cellular hypoxia. Sodium nitrite acts by oxidizing the ferrous (Fe²⁺) iron in hemoglobin to **methemoglobin (Fe³⁺)**. Methemoglobin has a higher affinity for cyanide than cytochrome oxidase does. Consequently, methemoglobin "traps" the cyanide, pulling it away from the mitochondria to form **cyanmethemoglobin**. This restores mitochondrial function. Subsequently, sodium thiosulfate is administered to convert cyanmethemoglobin into non-toxic **thiocyanate**, which is excreted by the kidneys. **Analysis of Incorrect Options** * **Options B, C, and D:** While nitrites are vasodilators and can alter regional blood flow, their therapeutic effect in cyanide poisoning is purely biochemical (methemoglobin induction), not hemodynamic. Increased blood flow to the liver, heart, or kidneys does not neutralize the cyanide ion or reverse its binding to cytochrome oxidase. **Clinical Pearls for NEET-PG** * **The Cyanide Antidote Kit (CAK):** Consists of Amyl nitrite (inhaled), Sodium nitrite (IV), and Sodium thiosulfate (IV). * **Hydroxocobalamin (Vitamin B12a):** Now preferred over nitrites in many settings (especially fire victims) because it binds cyanide to form **cyanocobalamin** without inducing methemoglobinemia, which can be dangerous in patients with concomitant carbon monoxide poisoning. * **Side Effect:** Excessive methemoglobinemia reduces the oxygen-carrying capacity of blood; levels should be monitored and kept below 30%. * **Classic Sign:** "Cherry-red" skin/mucosa and a bitter almond odor on the breath.

Question 428: Which of the following is associated with the highest risk of anaphylaxis?

A. Irondextran (Correct Answer)
B. Iron sucrose
C. Ferumoxytol
D. Iron gluconate

Explanation: **Explanation:** **1. Why Iron Dextran is the Correct Answer:** Iron dextran is a high-molecular-weight complex that carries a significantly higher risk of **Type I hypersensitivity reactions (anaphylaxis)** compared to other parenteral iron formulations. The primary mechanism involves the presence of the **dextran polymer**, which can trigger the production of anti-dextran antibodies (IgE-mediated) or cause non-immunological mast cell degranulation. Due to this risk, a **mandatory test dose** (25 mg) is required before administering the full therapeutic dose of iron dextran. **2. Why Other Options are Incorrect:** * **Iron Sucrose (B) and Iron Gluconate (D):** These are non-dextran-containing formulations. They are much safer and have a negligible risk of true anaphylaxis. They are generally preferred in clinical practice for patients with chronic kidney disease (CKD) or those intolerant to oral iron. * **Ferumoxytol (C):** This is a superparamagnetic iron oxide nanoparticle coated with a carbohydrate shell. While it carries a "Black Box Warning" for hypersensitivity, the statistical risk remains lower than that of traditional high-molecular-weight iron dextran. **3. High-Yield Clinical Pearls for NEET-PG:** * **Test Dose:** Only Iron Dextran strictly requires a test dose. However, clinicians should monitor patients for at least 30 minutes after any IV iron infusion. * **Newer Agents:** Ferric carboxymaltose and Ferumoxytol allow for rapid infusion of large doses (1g) in a single sitting, unlike sucrose or gluconate. * **Adverse Effect:** Apart from anaphylaxis, a common side effect of IV iron is a transient metallic taste and arthralgia. * **Contraindication:** Avoid IV iron in patients with active systemic infections, as iron can promote bacterial growth (siderophilic bacteria).

Question 429: In the treatment of which of the following poisonings is a cholinesterase reactivator used?

A. Curare poisoning
B. Organophosphorus compound poisoning (Correct Answer)
C. Amanita muscaria poisoning
D. All of the above

Explanation: **Explanation:** **1. Why Organophosphorus (OP) poisoning is correct:** Organophosphorus compounds (like Malathion or Parathion) act by irreversibly binding to the active site of the enzyme **Acetylcholinesterase (AChE)** through phosphorylation. This leads to a "cholinergic crisis" due to the accumulation of acetylcholine. **Cholinesterase reactivators**, such as **Pralidoxime (PAM)** and Obidoxime, belong to the chemical class of Oximes. They work by dephosphorylating the enzyme, thereby restoring its activity. However, they must be administered before "aging" of the enzyme occurs (the permanent strengthening of the phosphorus-enzyme bond). **2. Why other options are incorrect:** * **Curare poisoning:** Curare is a non-depolarizing neuromuscular blocker that competes with acetylcholine at nicotinic receptors. Treatment involves **Neostigmine** (an AChE inhibitor) to increase acetylcholine levels, not a reactivator. * **Amanita muscaria poisoning:** This mushroom contains muscarine, which directly stimulates muscarinic receptors. The treatment is a pharmacological antagonist like **Atropine**, not an enzyme reactivator. **3. NEET-PG High-Yield Pearls:** * **The "Aging" Phenomenon:** Once the OP-enzyme complex ages (usually within 24–48 hours), oximes become ineffective. * **Atropine vs. PAM:** Atropine is the drug of choice for symptomatic relief (antagonizes muscarinic effects), but it does **not** reactivate the enzyme or treat muscle paralysis. PAM is specific for reversing nicotinic effects (muscle weakness/paralysis). * **Contraindication:** Oximes are generally **not** recommended in Carbamate poisoning (e.g., Carbaryl) because the carbamylated enzyme dissociates spontaneously and rapidly; in some cases, PAM may even worsen carbamate toxicity.

Question 430: Which of the following drugs are associated with bland cholestasis?

A. Oral contraceptive pills (Correct Answer)
B. Androgens
C. Chlorpromazine
D. Erythromycin

Explanation: **Explanation:** Drug-induced liver injury (DILI) can present as various forms of cholestasis. **Bland cholestasis** is characterized by bile stasis in the canaliculi with minimal or no hepatocellular inflammation or necrosis. **1. Why Oral Contraceptive Pills (OCPs) are correct:** OCPs (specifically the estrogen component) and **Anabolic Steroids** (C-17 alkylated androgens) are the classic causes of bland cholestasis. Estrogens interfere with the bile salt export pump (BSEP) and increase the permeability of tight junctions, leading to decreased bile flow without significant inflammatory cell infiltration. Patients typically present with pruritus and jaundice, but liver enzymes (ALT/AST) remain near normal. **2. Why the other options are incorrect:** * **Androgens:** While C-17 alkylated androgens cause bland cholestasis, the option "Androgens" is less specific than OCPs in this context. However, in many textbooks, both are grouped together. In a single-best-answer format, OCPs are the prototypical example. * **Chlorpromazine:** Causes **inflammatory cholestasis** (cholestatic hepatitis). It is associated with a "portal triad" inflammatory infiltrate (eosinophils and lymphocytes) and elevated alkaline phosphatase. * **Erythromycin:** Specifically the estolate salt causes **cholestatic hepatitis** (inflammatory), often presenting with fever and abdominal pain mimicking cholecystitis. **High-Yield NEET-PG Pearls:** * **Bland Cholestasis:** OCPs, Anabolic steroids (Methyltestosterone). * **Inflammatory Cholestasis:** Chlorpromazine, Erythromycin, Amoxicillin-Clavulanate. * **Zone 3 Necrosis:** Paracetamol (Acetaminophen) toxicity. * **Microvesicular Steatosis:** Valproate, Tetracyclines, Salicylates (Reye’s Syndrome). * **Granulomatous Hepatitis:** Phenylbutazone, Allopurinol, Hydralazine.

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