Clinical Pharmacology and Drug Toxicity — MCQs

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

Question 151: What is the treatment of choice in acute hyperkalemia that is life-threatening to cardiac myocytes?

A. Infusion of calcium gluconate (Correct Answer)
B. Oral resins
C. Intravenous infusion of insulin
D. Beta-blocker

Explanation: ### Explanation In the management of acute hyperkalemia, the priority is determined by the presence of ECG changes or life-threatening arrhythmias. **1. Why Calcium Gluconate is the Correct Answer:** Hyperkalemia increases the resting membrane potential of cardiac myocytes, bringing it closer to the threshold potential. This leads to myocardial excitability and potential cardiac arrest. **Intravenous Calcium Gluconate (10%)** is the "membrane stabilizer" of choice. It does not lower serum potassium levels; instead, it antagonizes the cardiotoxic effects of potassium by stabilizing the myocardial membrane. It acts within 1–3 minutes, making it the first-line treatment in emergencies. **2. Why the Other Options are Incorrect:** * **Oral Resins (e.g., Sodium Polystyrene Sulfonate):** These remove potassium from the body via the GI tract. However, they have a slow onset of action (hours to days) and are unsuitable for life-threatening situations. * **Intravenous Insulin (with Dextrose):** This is a highly effective method to shift potassium from the extracellular to the intracellular compartment. While it lowers serum potassium, it does not provide immediate protection to the cardiac membrane. It is usually the second step after calcium administration. * **Beta-blockers:** These are contraindicated. Beta-2 agonists (like Albuterol) help shift potassium into cells, but **Beta-blockers** can actually worsen hyperkalemia by preventing this shift. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "C-BIG-K" Mnemonic for Hyperkalemia:** **C**alcium gluconate (Stabilize), **B**icarbonate/Beta-agonists (Shift), **I**nsulin + **G**lucose (Shift), **K**ayexalate/Resins (Remove), and **D**ialysis (Remove). * **Calcium Chloride vs. Gluconate:** Calcium chloride contains 3x more elemental calcium but is more irritating to peripheral veins; thus, Calcium Gluconate is preferred unless central venous access is available. * **ECG Progression:** Tall peaked T-waves → Prolonged PR interval → Loss of P-wave → Widened QRS (Sine wave pattern) → V-Fib.

Question 152: All of the following are known to cause Lupus-like syndrome, except?

A. Isoniazid (INH)
B. Penicillin (Correct Answer)
C. Procainamide
D. Sulfonamides

Explanation: **Explanation:** **Drug-Induced Lupus Erythematosus (DILE)** is an autoimmune phenomenon where certain drugs trigger clinical and serological features similar to Systemic Lupus Erythematosus (SLE). **Why Penicillin is the correct answer:** Penicillin is primarily associated with **Type I (Anaphylactic)** and **Type II (Cytotoxic)** hypersensitivity reactions. While it can cause various skin rashes and serum sickness, it is **not** a recognized cause of Lupus-like syndrome. **Analysis of Incorrect Options:** * **Procainamide (Option C):** This anti-arrhythmic has the **highest risk** of inducing DILE. Approximately 80% of patients develop Anti-Nuclear Antibodies (ANA), and 20% develop clinical symptoms. * **Isoniazid (Option A):** A key anti-tubercular drug known to cause DILE, especially in patients who are **slow acetylators** of the drug. * **Sulfonamides (Option D):** These are well-documented triggers for drug-induced lupus, along with other hypersensitivity reactions like Stevens-Johnson Syndrome. **High-Yield Clinical Pearls for NEET-PG:** 1. **Hallmark Antibody:** The most specific marker for DILE is **Anti-Histone Antibodies** (>95% cases). Unlike idiopathic SLE, Anti-dsDNA antibodies are usually absent. 2. **Metabolism Link:** Most drugs causing DILE (like Procainamide and Hydralazine) are metabolized by **Acetylation**. "Slow acetylators" are at a significantly higher risk. 3. **Common Culprits (Mnemonic - SHIP):** **S**ulfonamides, **H**ydralazine, **I**soniazid, **P**rocainamide. (Others include Phenytoin and Minocycline). 4. **Clinical Presentation:** DILE typically presents with pleuritis, pericarditis, fever, and arthralgia. Notably, **CNS and Renal involvement are rare** compared to idiopathic SLE. 5. **Management:** Symptoms usually resolve spontaneously within weeks of **discontinuing the offending drug**.

Question 153: Which of the following drugs can cause aplastic anemia?

A. Chlorpromazine
B. Allopurinol
C. Diclofenac
D. All of the above (Correct Answer)

Explanation: **Explanation:** Aplastic anemia is a life-threatening condition characterized by pancytopenia (reduction in RBCs, WBCs, and platelets) resulting from bone marrow suppression. In clinical pharmacology, drug-induced aplastic anemia is often an **idiosyncratic type B reaction**, meaning it is unpredictable, not dose-dependent, and carries high mortality [1]. **Analysis of Options:** * **Chlorpromazine:** This typical antipsychotic is a well-documented cause of blood dyscrasias. While agranulocytosis is more common, it can rarely progress to full bone marrow failure (aplastic anemia) [1]. * **Allopurinol:** Used for chronic gout, this xanthine oxidase inhibitor is associated with severe hypersensitivity reactions (DRESS syndrome) and rare instances of bone marrow suppression leading to aplastic anemia. * **Diclofenac:** Among NSAIDs, while phenylbutazone is the most notorious for aplastic anemia, diclofenac and indomethacin are also recognized triggers for idiosyncratic marrow suppression. Since all three drugs are clinically recognized causes of this condition, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Trigger:** **Chloramphenicol** is the most frequently asked drug associated with aplastic anemia (occurs in 1 in 20,000–40,000 patients). * **Other Key Culprits:** Carbamazepine, Phenytoin, Gold salts, Penicillamine, and Sulfonamides. * **Mechanism:** Most drug-induced aplastic anemias are immune-mediated, where the drug or its metabolite acts as a hapten, triggering T-cell-mediated destruction of hematopoietic stem cells. * **Management:** Immediate withdrawal of the offending drug; definitive treatment may require Bone Marrow Transplantation or immunosuppressants (Antithymocyte globulin + Cyclosporine).

Question 154: Which of the following drugs does not cause nephrotoxicity?

A. Cisplatin
B. Cyclophosphamide
C. Cyclosporine
D. Sirolimus (Correct Answer)

Explanation: **Explanation:** The correct answer is **Sirolimus (Option D)**. **Why Sirolimus is the correct answer:** Sirolimus (Rapamycin) is an mTOR inhibitor used as an immunosuppressant. Unlike Calcineurin inhibitors (CNIs), it is notably **non-nephrotoxic** [1]. In clinical practice, it is often used as an alternative to switch patients who develop renal impairment while on drugs like Cyclosporine or Tacrolimus [1], [2]. Its primary side effects are hyperlipidemia, thrombocytopenia, and impaired wound healing [1]. **Why the other options are incorrect:** * **Cisplatin (Option A):** A platinum-based chemotherapeutic agent notorious for causing **Acute Tubular Necrosis (ATN)**. It is the most nephrotoxic drug in its class. Nephrotoxicity is dose-limiting and can be mitigated by aggressive hydration and Amifostine. * **Cyclophosphamide (Option B):** While primarily known for causing **Hemorrhagic Cystitis** (due to the metabolite Acrolein), it can cause nephrotoxicity in the form of SIADH (water retention) and, at high doses, direct tubular damage [3]. * **Cyclosporine (Option C):** A Calcineurin inhibitor that causes nephrotoxicity via **afferent arteriolar vasoconstriction** [4], [5]. This leads to decreased GFR and, with chronic use, interstitial fibrosis (striped fibrosis). **High-Yield Clinical Pearls for NEET-PG:** 1. **Amifostine** is a cytoprotective agent used specifically to reduce Cisplatin-induced nephrotoxicity. 2. **Mesna** (2-Mercaptoethane sulfonate) is used to prevent Hemorrhagic Cystitis caused by Cyclophosphamide/Ifosfamide. 3. **Tacrolimus vs. Sirolimus:** Both bind to FKBP-12, but Tacrolimus inhibits Calcineurin (nephrotoxic), while Sirolimus inhibits mTOR (non-nephrotoxic) [1]. 4. **Drug of choice** for reversing CNI-induced renal vasoconstriction: Calcium Channel Blocks (CCBs).

Question 155: What is the specific antidote for poisoning due to metoprolol?

A. Atropine
B. Isoproterenol
C. Glucagon (Correct Answer)
D. Verapamil

Explanation: ### Explanation **Correct Answer: C. Glucagon** **Mechanism of Action:** Metoprolol is a selective $\beta_1$-blocker. In cases of severe overdose, $\beta$-receptors are occupied, leading to bradycardia and hypotension. **Glucagon** is the drug of choice because it bypasses the blocked $\beta$-adrenergic receptors. It acts on specific **G-protein coupled glucagon receptors** on the myocardium, which stimulates **adenylyl cyclase**. This increases intracellular **cAMP** levels, leading to positive inotropic (increased contractility) and chronotropic (increased heart rate) effects, effectively reversing the cardiac depression caused by the blocker. **Why other options are incorrect:** * **Atropine (A):** While it is an anticholinergic used for symptomatic bradycardia, it is often ineffective in severe $\beta$-blocker toxicity because it cannot overcome the profound suppression of the conduction system. * **Isoproterenol (B):** This is a non-selective $\beta$-agonist. In the presence of a massive $\beta$-blocker overdose, the receptors are competitively occupied; extremely high doses of isoproterenol would be required, which can lead to severe peripheral vasodilation and worsening hypotension. * **Verapamil (D):** This is a Calcium Channel Blocker (CCB). Administering Verapamil would be contraindicated as it would exacerbate the bradycardia and myocardial depression. **High-Yield Clinical Pearls for NEET-PG:** 1. **First-line management:** Initial steps include IV fluids and Atropine, but **Glucagon** is the specific antidote for refractory cases. 2. **Other treatments:** If Glucagon fails, **High-dose Insulin Euglycemic Therapy (HIET)** and IV lipid emulsion are considered. 3. **Key distinction:** Glucagon is also the antidote for **Calcium Channel Blocker** poisoning, though HIET is often preferred there. 4. **Side effect:** A common side effect of high-dose Glucagon administration is **vomiting**; ensure airway protection.

Question 156: Bleomycin toxicity is characterized by destruction of?

A. Endothelial cells
B. Type I pneumocytes (Correct Answer)
C. Type II pneumocytes
D. Alveolar macrophages

Explanation: **Explanation:** Bleomycin is a glycopeptide antibiotic used as a chemotherapeutic agent. Its most serious dose-limiting toxicity is **pulmonary fibrosis**. **Why Type I Pneumocytes are the correct answer:** Bleomycin acts by producing reactive oxygen species (free radicals) that cause DNA strand breaks. The lung is particularly susceptible because it lacks the enzyme **bleomycin hydrolase**, which normally inactivates the drug. The primary site of injury is the **Type I pneumocyte**. Destruction of these cells leads to an inflammatory response, recruitment of fibroblasts, and subsequent collagen deposition, resulting in irreversible interstitial pulmonary fibrosis. **Analysis of Incorrect Options:** * **A. Endothelial cells:** While bleomycin can cause some initial microvascular damage, the hallmark of its toxicity is the specific destruction of the alveolar epithelium (Type I cells). * **C. Type II pneumocytes:** These cells actually undergo **hyperplasia** and proliferation in an attempt to repair the alveolar basement membrane after Type I cells are destroyed. They do not undergo primary destruction. * **D. Alveolar macrophages:** These cells remain functional and are involved in the inflammatory cascade by releasing cytokines (like TGF-beta) that promote fibrosis, rather than being the primary target of destruction. **High-Yield Clinical Pearls for NEET-PG:** * **Dose-limiting toxicity:** Pulmonary fibrosis occurs typically when the cumulative dose exceeds **400 units**. * **Monitoring:** Serial **DLCO (Diffusion Capacity of the Lung for Carbon Monoxide)** is the most sensitive test to detect early toxicity. * **Risk Factor:** Administration of high concentrations of **supplemental oxygen** (e.g., during surgery) can exacerbate bleomycin-induced lung injury due to increased free radical formation. * **Other Side Effect:** Flagellate hyperpigmentation of the skin.

Question 157: Which of the following drugs does NOT cause gynecomastia?

A. Cimetidine
B. Spironolactone
C. Pyrazinamide (Correct Answer)
D. Ketoconazole

Explanation: **Explanation:** Gynecomastia is the benign proliferation of glandular breast tissue in males, typically caused by an imbalance between estrogen and androgen action [1]. **Why Pyrazinamide is the correct answer:** Pyrazinamide is a first-line antitubercular drug (part of RIPE therapy) [2]. Its primary side effects include **hyperuricemia** (leading to gout) and **hepatotoxicity** [2]. It does not interfere with sex hormone synthesis or receptors and, therefore, does not cause gynecomastia. Among antitubercular drugs, **Isoniazid (INH)** is the one classically associated with gynecomastia (likely due to its effect on hepatic metabolism of hormones). **Analysis of incorrect options:** * **Cimetidine:** An H2-receptor antagonist that causes gynecomastia by two mechanisms: it acts as a weak androgen receptor antagonist and inhibits the cytochrome P450-mediated hydroxylation of estradiol, leading to increased estrogen levels. * **Spironolactone:** A potassium-sparing diuretic that is a common cause of gynecomastia. It blocks androgen receptors and increases the peripheral conversion of testosterone to estradiol [1]. * **Ketoconazole:** An antifungal that inhibits the enzyme **17,20-desmolase** (CYP17), which is essential for steroid and testosterone synthesis [1]. Decreased testosterone leads to a relative increase in estrogen. **High-Yield Clinical Pearls for NEET-PG:** To remember the common drugs causing gynecomastia, use the mnemonic **"DISCO"**: * **D**igoxin * **I**soniazid * **S**pironolactone * **C**imetidine * **O**estrogens / **K**etoconazole (often added as DISCO-K) Other notable causes include **Finasteride** (5-alpha reductase inhibitor) and **Risperidone** (via hyperprolactinemia).

Question 158: Lithium is used in a pregnant woman. Which of the following congenital anomalies occurs in the fetus?

A. Tetralogy of Fallot's
B. Tricuspid atresia
C. Ebstein anomaly (Correct Answer)
D. Pulmonary stenosis

Explanation: **Explanation:** **Lithium** is a mood stabilizer primarily used for Bipolar Affective Disorder. It is a known **teratogen** (Category D), and its use during the first trimester of pregnancy is classically associated with **Ebstein anomaly**. **Why Ebstein Anomaly is the correct answer:** Ebstein anomaly is a rare congenital heart defect characterized by the **downward displacement of the tricuspid valve leaflets** into the right ventricle. This "atrializes" the right ventricle, leading to severe tricuspid regurgitation and right-sided heart failure. While the absolute risk of this anomaly in lithium-exposed pregnancies is low (approx. 1 in 1,000), it represents a 10–20 fold increase compared to the general population, making it the most specific association for the exam. **Why other options are incorrect:** * **Tetralogy of Fallot (A), Tricuspid Atresia (B), and Pulmonary Stenosis (D):** While these are common congenital cyanotic heart diseases, they are not specifically linked to Lithium exposure. They are more commonly associated with genetic syndromes (like Down syndrome or DiGeorge syndrome) or other environmental factors. **High-Yield Clinical Pearls for NEET-PG:** * **Timing:** The risk is highest during the **first trimester** (organogenesis). * **Management:** If a pregnant woman must take Lithium, fetal echocardiography is recommended at 18–20 weeks. * **Other Lithium Side Effects:** In neonates, Lithium can cause **"Floppy Infant Syndrome"** (hypotonia, cyanosis, and lethargy) and neonatal goiter. * **Excretion:** Lithium is excreted in breast milk; hence, breastfeeding is generally discouraged while on high-dose therapy.

Question 159: Which drug used for the common cold can cause stroke?

A. Phenylpropanolamine (Correct Answer)
B. Oxymetazoline
C. Phenylephrine
D. None of the above

Explanation: **Explanation:** **Phenylpropanolamine (PPA)** is the correct answer because of its strong association with an increased risk of **hemorrhagic stroke**, particularly in young women. PPA is a sympathomimetic drug formerly used as a nasal decongestant and appetite suppressant. Its mechanism involves the release of norepinephrine, leading to potent vasoconstriction. In 2000, the FDA requested its withdrawal from the market after a landmark study (the Hemorrhagic Stroke Project) demonstrated that PPA could cause sudden, severe hypertension and cerebral vasculitis, leading to intracranial hemorrhage. **Analysis of Incorrect Options:** * **Oxymetazoline:** This is a selective $\alpha_1$ and partial $\alpha_2$ agonist used primarily as a **topical** nasal spray. Because it is applied locally, systemic absorption is minimal at therapeutic doses, making the risk of systemic complications like stroke extremely low compared to oral PPA. * **Phenylephrine:** Following the withdrawal of PPA, phenylephrine became the standard oral and topical decongestant. While it is a sympathomimetic, it has a shorter half-life and lower potency regarding systemic hypertensive crises when used at recommended doses, and it has not been epidemiologically linked to stroke [1], [2]. **Clinical Pearls for NEET-PG:** * **Drug of Choice for Decongestant-induced Rhinitis (Rhinitis Medicamentosa):** This condition occurs with prolonged use of topical decongestants (like Oxymetazoline) for >3-5 days. Treatment involves stopping the spray and starting topical nasal steroids. * **PPA Toxicity:** Apart from stroke, PPA was known to cause "amphetamine-like" CNS stimulation, including insomnia and restlessness. * **Safe Alternatives:** Pseudoephedrine is another oral alternative, though it is strictly regulated in many regions due to its potential use in the illicit manufacture of methamphetamine.

Question 160: Therapeutic drug monitoring is required for which of the following medications?

A. Prodrugs
B. Levodopa
C. Lithium carbonate (Correct Answer)
D. MAO inhibitors

Explanation: **Explanation:** Therapeutic Drug Monitoring (TDM) is essential for drugs where the **therapeutic index is narrow**, meaning the dose required for efficacy is very close to the dose that causes toxicity. **1. Why Lithium Carbonate is Correct:** Lithium is the classic example of a drug requiring TDM. It has a very narrow therapeutic window (0.6–1.2 mEq/L). Levels above 1.5 mEq/L can lead to severe toxicity (tremors, ataxia, seizures), while levels below 0.6 mEq/L are often ineffective for treating bipolar disorder. Additionally, its pharmacokinetics are highly influenced by renal function and sodium balance, making regular monitoring mandatory for safety. **2. Why the Other Options are Incorrect:** * **Prodrugs (A):** TDM measures the active drug concentration. Monitoring the inactive parent prodrug provides no clinical utility regarding efficacy or toxicity. * **Levodopa (B):** The clinical response to Levodopa (improvement in motor symptoms) is easily observable. We titrate the dose based on the patient’s physical signs rather than plasma levels. * **MAO Inhibitors (D):** These drugs often cause irreversible enzyme inhibition. The plasma concentration of the drug does not correlate well with the degree of enzyme inhibition or the clinical effect. **High-Yield Clinical Pearls for NEET-PG:** * **Criteria for TDM:** Narrow therapeutic index, poor correlation between dose and plasma concentration, and lack of an easily measurable clinical endpoint (e.g., BP or heart rate). * **Other Drugs requiring TDM:** Digoxin, Phenytoin, Theophylline, Aminoglycosides (Gentamicin), Cyclosporine, and Tricyclic Antidepressants (TCAs). * **Lithium Sampling:** Blood should be drawn **12 hours after the last dose** (trough level) to ensure steady-state accuracy.

Practice by Chapter

Principles of Clinical Pharmacology

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Therapeutic Drug Monitoring

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Drug Toxicity and Overdose

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Antidotes and Their Applications

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Management of Drug Poisoning

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Drug-Induced Liver Injury

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Drug-Induced Kidney Injury

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Drug-Induced Blood Dyscrasias

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Drug-Induced QT Prolongation

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Pharmacovigilance

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