Clinical Pharmacology and Drug Toxicity — MCQs

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

Question 211: All of the following antibodies require dose adjustment in renal failure except?

A. Ceftriaxone
B. Isoniazid
C. Erythromycin (Correct Answer)
D. Gentamicin

Explanation: **Explanation:** The primary factor determining whether a drug requires dose adjustment in renal failure is its **route of elimination**. [1] Drugs that are primarily excreted unchanged by the kidneys or have active metabolites cleared renally require dose modification to prevent toxicity. [1] **Why Erythromycin is the Correct Answer:** Erythromycin is a macrolide antibiotic that is primarily metabolized by the liver and excreted via the **bile and feces**. Only a small fraction (approx. 2–5%) is excreted unchanged in the urine. Therefore, its clearance is not significantly affected by declining renal function, making it safe to use without dose adjustment in renal failure. **Analysis of Incorrect Options:** * **Gentamicin:** This aminoglycoside is eliminated almost entirely by glomerular filtration. It is highly nephrotoxic; dose adjustment (based on creatinine clearance) is mandatory to prevent further renal damage and ototoxicity. [2] * **Ceftriaxone:** Although it has dual elimination (biliary and renal), it still requires monitoring and potential adjustment in patients with combined renal and hepatic impairment. [2] In isolated severe renal failure, while often considered safer than other cephalosporins, most guidelines still suggest caution or minor adjustments at maximum doses. * **Isoniazid:** While primarily metabolized by the liver (acetylation), its metabolites are excreted renally. In end-stage renal disease (ESRD), dose reduction is often recommended to prevent neurotoxicity. **NEET-PG High-Yield Pearls:** * **Mnemonic for drugs NOT requiring dose adjustment in renal failure:** "**D**o **C**areful **L**iver **M**etabolism" (**D**oxycycline, **C**eftriaxone/Cefoperazone, **L**inezolid, **M**acrolides/Metronidazole). * **Doxycycline** is the tetracycline of choice in renal failure because it is excreted via the gut. [2] * **Aminoglycosides and Vancomycin** always require Therapeutic Drug Monitoring (TDM) in renal impairment.

Question 212: Desferrioxamine is a drug used for:

A. Kala-azar
B. Pernicious anaemia
C. Pain control
D. Thalassemia (Correct Answer)

Explanation: **Explanation:** **Desferrioxamine** is a potent **iron-chelating agent** used primarily to treat chronic iron overload. **Why Thalassemia is correct:** Patients with **Thalassemia Major** require lifelong, regular blood transfusions to manage severe anemia. Each unit of transfused blood contains approximately 200–250 mg of iron. Since the human body lacks an active physiological mechanism to excrete excess iron, it deposits in vital organs (heart, liver, endocrine glands), leading to **secondary hemochromatosis**. Desferrioxamine binds to ferric iron ($Fe^{3+}$) to form **ferrioxamine**, a water-soluble complex excreted by the kidneys, thereby preventing organ damage. **Why other options are incorrect:** * **Kala-azar:** Treated with Sodium Stibogluconate, Amphotericin B, or Miltefosine. * **Pernicious Anaemia:** Caused by Vitamin B12 deficiency due to lack of intrinsic factor; treated with parenteral Cyanocobalamin or Methylcobalamin. * **Pain control:** Managed with NSAIDs, Opioids, or adjuvant analgesics, not chelating agents. **High-Yield Clinical Pearls for NEET-PG:** * **Route of Administration:** Desferrioxamine is poorly absorbed orally; it is administered via slow subcutaneous or intravenous infusion. * **Oral Alternatives:** **Deferasirox** (once-daily oral drug) and **Deferiprone** are preferred for better patient compliance. * **Acute Toxicity:** It is also the drug of choice for **acute iron poisoning** (often seen in children). * **Side Effects:** Rapid IV injection can cause histamine release and hypotension. Long-term use may lead to visual and auditory neurotoxicity.

Question 213: N-acetylcysteine replenishes intracellular levels of which of the following?

A. Sodium
B. Potassium
C. Glutathione (Correct Answer)
D. None of the above

Explanation: **Explanation:** **Mechanism of Action:** N-acetylcysteine (NAC) is the specific antidote for **Paracetamol (Acetaminophen) poisoning**. Under normal conditions, a small portion of paracetamol is metabolized by the Cytochrome P450 system into a highly reactive and toxic metabolite called **NAPQI** (*N-acetyl-p-benzoquinone imine*). In therapeutic doses, NAPQI is immediately detoxified by conjugation with **Glutathione**. However, in an overdose, glutathione stores are depleted, leading to hepatic necrosis. NAC acts as a precursor for cysteine, which is the rate-limiting substrate for the synthesis of **Glutathione**, thereby replenishing its intracellular levels and facilitating the detoxification of NAPQI. **Analysis of Options:** * **Option A (Sodium) & Option B (Potassium):** These are primary extracellular and intracellular electrolytes, respectively. NAC does not play a role in the synthesis or regulation of these ions. Their levels are typically managed via intravenous fluids or specific ion-exchange resins. * **Option D:** Incorrect, as Glutathione is the well-established target of NAC therapy. **High-Yield Clinical Pearls for NEET-PG:** * **The "Golden Period":** NAC is most effective when administered within **8–10 hours** of paracetamol ingestion. * **Rumack-Matthew Nomogram:** This is used to determine the risk of hepatotoxicity based on plasma paracetamol levels vs. time since ingestion. * **Other Uses of NAC:** 1. **Mucolytic:** Breaks disulfide bonds in mucus (used in COPD/Cystic Fibrosis). 2. **Prevention of Contrast-Induced Nephropathy:** Though evidence is now debated, it is a classic exam fact. * **Route:** Can be given Orally (smells like rotten eggs due to sulfur) or Intravenously.

Question 214: Which drug is not banned for athletes by the World Anti-Doping Agency (WADA)?

A. Salbutamol
B. Sodium chromoglycate (Correct Answer)
C. Erythropoietin
D. Spironolactone

Explanation: **Explanation:** The World Anti-Doping Agency (WADA) maintains a list of prohibited substances to ensure fair play and athlete safety. **Why Sodium Chromoglycate is the correct answer:** Sodium chromoglycate is a **mast cell stabilizer** used primarily for the prophylaxis of bronchial asthma and allergic rhinitis. It does not possess any performance-enhancing properties, stimulant effects, or masking capabilities. Therefore, it is **not prohibited** by WADA and can be used by athletes without a Therapeutic Use Exemption (TUE). **Analysis of Incorrect Options:** * **Salbutamol (Option A):** This is a Beta-2 agonist. While inhaled salbutamol is permitted under specific dosage thresholds (max 1600 mcg over 24 hours), it is technically a **restricted/prohibited substance** if levels exceed the limit, as systemic doses can have anabolic effects. * **Erythropoietin (Option B):** Classified under "Peptide Hormones and Growth Factors." It increases red blood cell production (erythropoiesis), enhancing oxygen-carrying capacity and aerobic endurance. It is strictly prohibited at all times. * **Spironolactone (Option D):** This is a diuretic. Diuretics are banned because they act as **masking agents** by diluting urine (making it harder to detect other performance-enhancing drugs) and are used for rapid weight loss in sports with weight categories. **High-Yield Clinical Pearls for NEET-PG:** * **Masking Agents:** Diuretics (e.g., Furosemide, Spironolactone) and Probenecid are classic examples. * **Glucocorticoids:** Prohibited **in-competition** when administered by oral, intravenous, intramuscular, or rectal routes. * **Beta-blockers:** These are prohibited only in specific sports that require steady hands and precision, such as Archery, Shooting, and Golf.

Question 215: Gynaecomastia is an adverse effect of all of the following drugs except:

A. Spironolactone
B. Finasteride
C. Cortisol (Correct Answer)
D. Cimetidine

Explanation: **Explanation:** Gynaecomastia (enlargement of male breast tissue) occurs due to an imbalance between estrogenic and androgenic effects on breast tissue. It is a high-yield side effect in pharmacology. **Why Cortisol is the correct answer:** Cortisol is a glucocorticoid. While chronic excess of glucocorticoids (Cushing’s syndrome) can lead to fat redistribution (buffalo hump, supraclavicular fat pads), it **does not** directly cause glandular proliferation of breast tissue. In fact, some steroids like Danazol or Dihydrotestosterone are used to treat gynaecomastia. **Why the other options are incorrect:** * **Spironolactone:** The most common drug-induced cause. It acts by blocking androgen receptors and inhibiting testosterone synthesis. * **Finasteride:** A 5-alpha reductase inhibitor that prevents the conversion of Testosterone to the more potent Dihydrotestosterone (DHT), leading to a relative increase in estrogen levels. * **Cimetidine:** An H2 blocker that also possesses anti-androgenic properties and increases serum prolactin levels. **NEET-PG High-Yield Pearls: "DISCO" Mnemonic** To remember common drugs causing gynaecomastia, use the mnemonic **DISCO**: * **D:** Digoxin (estrogenic activity) * **I:** Isoniazid (INH) * **S:** Spironolactone * **C:** Cimetidine / Calcium Channel Blockers (rarely) * **O:** Oestrogens **Other notable causes:** Ketoconazole (inhibits steroid synthesis), Marijuana, and Methyldopa.

Question 216: Sparfloxacin and astemizole can cause which of the following?

A. Ventricular arrhythmia (Correct Answer)
B. Myopathy
C. Electrolyte imbalance
D. Nephropathy

Explanation: The correct answer is **Ventricular arrhythmia**. Both Sparfloxacin and Astemizole are notorious for causing **QT interval prolongation**, which can lead to a life-threatening polymorphic ventricular tachycardia known as **Torsades de Pointes (TdP)** [1, 3]. 1. **Mechanism:** These drugs block the delayed rectifier potassium channels ($I_{Kr}$) in the cardiac myocytes. This delays ventricular repolarization, lengthening the action potential duration and the QT interval on an ECG [1, 2]. 2. **Sparfloxacin:** A fluoroquinolone antibiotic. Among its class, sparfloxacin and grepafloxacin (now withdrawn) carry the highest risk of QT prolongation and phototoxicity. 3. **Astemizole:** A second-generation H1-antihistamine. It was withdrawn from many markets because it blocks cardiac $K^+$ channels, especially when its metabolism is inhibited by CYP3A4 inhibitors (like erythromycin or ketoconazole), leading to fatal arrhythmias [2]. **Analysis of Incorrect Options:** * **B. Myopathy:** Commonly associated with Statins, Fibrates, or Zidovudine, but not typically with these two drugs. * **C. Electrolyte imbalance:** While hypokalemia or hypomagnesemia can *predispose* a patient to QT prolongation, these drugs do not inherently cause electrolyte shifts. * **D. Nephropathy:** Associated with drugs like Aminoglycosides, Amphotericin B, or NSAIDs. **NEET-PG High-Yield Pearls:** * **Mnemonic for QT Prolonging Drugs:** "**ABCDE**" – **A**ntiarrhythmics (Class IA, III), **B**iotics (Macrolides, Quinolones), **C**ypsychotics (Haloperidol), **D**epressants (TCAs), **E**metics (Ondansetron). * **Terfenadine** is another antihistamine (like Astemizole) withdrawn due to Torsades de Pointes. Its active metabolite, **Fexofenadine**, is safe and does not cause arrhythmias.

Question 217: Megaloblastic anemia is caused by all of the following EXCEPT:

A. Aspirin (Correct Answer)
B. Primidone
C. Methotrexate
D. Nitrous oxide

Explanation: Megaloblastic anemia is characterized by impaired DNA synthesis, leading to the formation of large, immature red blood cell precursors. This is most commonly due to a deficiency or interference in the metabolism of Vitamin B12 or Folic acid [1, 2, 3]. **Why Aspirin is the Correct Answer:** **Aspirin** is a non-steroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX) enzymes. While chronic aspirin use can lead to **iron deficiency anemia** due to occult gastrointestinal bleeding, it does not interfere with DNA synthesis or folate/B12 metabolism. Therefore, it does not cause megaloblastic anemia. **Why the other options are incorrect:** * **Primidone:** This is an antiepileptic (metabolized to phenobarbital) that causes megaloblastic anemia by interfering with intestinal folate absorption and increasing its catabolism. * **Methotrexate:** A potent dihydrofolate reductase (DHFR) inhibitor. It prevents the conversion of dihydrofolate to tetrahydrofolate, directly halting DNA synthesis. * **Nitrous oxide:** Known as "laughing gas," it oxidizes the cobalt atom of Vitamin B12, rendering the enzyme methionine synthase inactive. This leads to a functional B12 deficiency. **High-Yield Clinical Pearls for NEET-PG:** * **Drugs causing Folate deficiency:** Phenytoin, Primidone, Phenobarbital, Methotrexate, Trimethoprim, and Pyrimethamine. * **Drugs causing B12 deficiency:** Metformin (decreases absorption in the terminal ileum), Proton Pump Inhibitors (PPIs), and Nitrous oxide. * **Zidovudine (AZT):** A common cause of macrocytosis/megaloblastic changes in HIV patients. * **Rescue Therapy:** Leucovorin (folinic acid) is used to "rescue" bone marrow from Methotrexate toxicity.

Question 218: What is relcovaptan?

A. Angiotensin antagonist
B. Renin inhibitor
C. Vasopressin antagonist (Correct Answer)
D. ACE inhibitor

Explanation: **Explanation:** **Relcovaptan** is a selective, non-peptide **Vasopressin V1a receptor antagonist**. Vasopressin (Antidiuretic Hormone) acts on three main receptors: V1a (vasoconstriction and uterine contraction), V1b (ACTH release), and V2 (water reabsorption in renal collecting ducts). By blocking the V1a receptor, relcovaptan has been investigated for its potential in treating conditions like Raynaud’s disease, dysmenorrhea, and to delay preterm labor by inhibiting uterine contractions. **Analysis of Options:** * **Option A (Angiotensin antagonist):** These are Angiotensin Receptor Blockers (ARBs) like Losartan or Valsartan. They block the AT1 receptor to treat hypertension and heart failure. * **Option B (Renin inhibitor):** Aliskiren is the prototype drug in this class. It directly inhibits renin, preventing the conversion of angiotensinogen to angiotensin I. * **Option D (ACE inhibitor):** These drugs (e.g., Enalapril, Lisinopril) inhibit the Angiotensin-Converting Enzyme, preventing the formation of Angiotensin II and the breakdown of bradykinin. **High-Yield NEET-PG Pearls:** * **The "Vaptans":** This class consists of vasopressin antagonists. * **Conivaptan:** Non-selective (V1a + V2 blocker), administered IV. * **Tolvaptan:** Selective V2 blocker, administered orally; used in SIADH and autosomal dominant polycystic kidney disease (ADPKD). * **Clinical Use:** Vaptans are primarily used to treat **euvolemic and hypervolemic hyponatremia**. * **Mnemonic:** Relcovaptan starts with **"R"**—think **R**elaxation of the uterus (V1a effect) or **R**aynaud’s.

Question 219: All of the following drugs are used as immunosuppressants EXCEPT?

A. Glucocorticoids
B. Cyclosporin
C. Cephalosporin (Correct Answer)
D. Azathioprine

Explanation: **Explanation:** The correct answer is **Cephalosporin** because it is a class of **β-lactam antibiotics**, not an immunosuppressant. Cephalosporins work by inhibiting bacterial cell wall synthesis (binding to Penicillin-Binding Proteins) and are used to treat bacterial infections. **Analysis of Options:** * **Glucocorticoids (Option A):** These are the most commonly used immunosuppressants. They act by inhibiting the transcription of pro-inflammatory cytokines (like IL-1, IL-2, and TNF-α) and inducing apoptosis in T-cells. * **Cyclosporin (Option B):** A potent **Calcineurin Inhibitor**. It binds to cyclophilin to inhibit calcineurin, preventing the dephosphorylation of NFAT (Nuclear Factor of Activated T-cells), which ultimately stops the production of IL-2. It is a cornerstone drug in organ transplantation. * **Azathioprine (Option C):** A **Purine Antimetabolite** (prodrug of 6-Mercaptopurine). It inhibits DNA synthesis, thereby suppressing the proliferation of rapidly dividing B and T lymphocytes. **High-Yield Clinical Pearls for NEET-PG:** 1. **Cyclosporin Side Effects:** Remember the "5 H’s"—**H**ypertension, **H**yperplasia (Gingival), **H**irsutism, **H**yperlipidemia, and **H**epatotoxicity. It is also notably **Nephrotoxic**. 2. **Azathioprine Interaction:** It is metabolized by **Xanthine Oxidase**. Concurrent use with **Allopurinol** (a xanthine oxidase inhibitor) leads to toxic levels of azathioprine, necessitating a dose reduction by 75%. 3. **Tacrolimus vs. Cyclosporin:** Both are calcineurin inhibitors, but Tacrolimus binds to **FKBP-12** instead of cyclophilin. Tacrolimus is more potent and does not cause gingival hyperplasia or hirsutism.

Question 220: A patient on warfarin presents with major bleeding and has a PT INR of 1.5. What is the recommended dose of fresh frozen plasma for treatment?

A. 15 ml/kg (Correct Answer)
B. 10 ml/kg
C. 5 ml/kg
D. 20 ml/kg

Explanation: ### Explanation **1. Why Option A is Correct:** In the management of warfarin-induced major bleeding, the goal is to rapidly replace vitamin K-dependent clotting factors (II, VII, IX, and X). Fresh Frozen Plasma (FFP) is a standard treatment when Prothrombin Complex Concentrate (PCC) is unavailable. The standard therapeutic dose of FFP required to achieve a significant rise in clotting factor levels (approximately 10-15%) and reverse coagulopathy is **15 ml/kg**. This dose provides a sufficient volume of plasma to neutralize the effect of warfarin and achieve hemostasis. **2. Analysis of Incorrect Options:** * **Option B (10 ml/kg):** This dose is generally considered sub-therapeutic for major bleeding. While it may slightly improve the INR, it often fails to provide enough clotting factors to stop life-threatening hemorrhage. * **Option C (5 ml/kg):** This is an inadequate dose for reversal. Such low volumes are insufficient to replace the depleted factors and will not significantly impact the PT/INR. * **Option D (20 ml/kg):** While effective, this higher dose increases the risk of **Transfusion-Associated Circulatory Overload (TACO)**, especially in elderly patients or those with underlying cardiac/renal disease. 15 ml/kg is the preferred balance between efficacy and safety. **3. Clinical Pearls for NEET-PG:** * **Drug of Choice:** For immediate reversal of warfarin in major bleeding, **4-factor PCC** is superior to FFP because it works faster and avoids volume overload. * **Vitamin K:** Always co-administer **Intravenous Vitamin K (5–10 mg)** with FFP/PCC to ensure sustained synthesis of new clotting factors, as the effect of FFP is transient. * **INR Paradox:** In cases of major bleeding, clinical management (reversal) is required regardless of the INR value (even if it is near normal, as seen in this question). * **Monitoring:** One unit of FFP is approximately 200–250 ml. For a 70 kg adult, a 15 ml/kg dose equals roughly 4–5 units of FFP.

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