Clinical Pharmacology and Drug Toxicity — MCQs

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

Question 881: Which of the following vitamins, when taken at higher doses, can cause cystoid macular edema?

A. Niacin (Correct Answer)
B. Vitamin A
C. Vitamin D
D. Vitamin E

Explanation: ***Niacin*** - High doses of **niacin (nicotinic acid)**, particularly the extended-release forms used for lipid management, are known to cause **cystoid macular edema (CME)**. - The mechanism is thought to involve **vasodilation** and metabolic changes in the retinal pigment epithelium. *Vitamin A* - While essential for vision, **excessive vitamin A** intake (hypervitaminosis A) can lead to symptoms like **headache**, **blurred vision**, and skin changes, but not typically cystoid macular edema. - Deficiency of vitamin A can cause **night blindness** and xerophthalmia. *Vitamin D* - High doses of vitamin D can lead to **hypercalcemia**, causing symptoms such as nausea, vomiting, and kidney stones. - It does not directly cause **cystoid macular edema**. *Vitamin E* - **Excessive vitamin E** intake can interfere with **blood clotting** and increase the risk of bleeding, especially in individuals on anticoagulants. - There is no established link between high-dose vitamin E and **cystoid macular edema**.

Question 882: MgSO4 has no role in the prevention of...

A. Bradycardia (Correct Answer)
B. Seizures in severe pre-eclampsia
C. Recurrent seizures in eclampsia
D. Respiratory Distress Syndrome (RDS) in premature baby

Explanation: ***Bradycardia*** - Magnesium sulfate has **no role in preventing bradycardia**; in fact, it can **cause or worsen bradycardia** as a significant side effect. - MgSO4 acts as a **calcium channel blocker** and CNS depressant, which can lead to cardiac conduction depression and bradycardia. - Its administration requires careful monitoring for cardiorespiratory depression, including bradycardia. *Seizures in severe pre-eclampsia* - Magnesium sulfate is the **drug of choice** for prevention of eclamptic seizures in women with severe pre-eclampsia (Magpie Trial). - It acts as a **CNS depressant** by reducing acetylcholine release at the neuromuscular junction and inhibiting neuronal excitability. - Clear established role in seizure prophylaxis. *Recurrent seizures in eclampsia* - Magnesium sulfate is the **gold standard** for treatment of active eclamptic seizures and prevention of their recurrence. - Its **anticonvulsant properties** make it the first-line agent in managing this life-threatening complication of pregnancy. - Superior to other anticonvulsants like diazepam or phenytoin in this context. *Respiratory Distress Syndrome (RDS) in premature baby* - **Antenatal corticosteroids** (betamethasone/dexamethasone), NOT magnesium sulfate, are used for **prevention of RDS** in premature babies. - While MgSO4 given antenatally does provide **neuroprotection** and reduces risk of cerebral palsy in preterm infants, this is distinct from RDS prevention. - MgSO4 has no established role in preventing respiratory distress syndrome itself.

Question 883: A patient presents to the emergency department with a history of ingestion of ten tablets of paracetamol. He has developed oliguria and liver function tests show deranged values. In the context of paracetamol overdose, which of the following can be used in the management of this condition?

A. N-acetylcysteine (Correct Answer)
B. Dopamine
C. Ursodeoxycholic acid
D. Furosemide

Explanation: **Correct: N-acetylcysteine** - **N-acetylcysteine (NAC)** is the specific antidote for **paracetamol overdose**, working by replenishing **glutathione** stores in the liver. - Replenishing **glutathione** helps detoxify the toxic metabolite **N-acetyl-p-benzoquinone imine (NAPQI)**, preventing further **hepatic damage** and facilitating recovery in cases of **liver failure** and potential **renal damage** (oliguria). - Most effective when given within **8 hours** of ingestion, but remains beneficial even with **established hepatotoxicity** (as in this case with deranged LFTs). *Incorrect: Dopamine* - **Dopamine** is a **vasopressor** primarily used to increase **blood pressure** and **cardiac output** in conditions like **shock**. - While it might be used to support circulation in severe overdose complications, it does not directly treat the **paracetamol toxicity** itself. *Incorrect: Ursodeoxycholic acid* - **Ursodeoxycholic acid (UDCA)** is a **cholagogue** used in the management of **cholestatic liver diseases** (e.g., primary biliary cholangitis) by improving bile flow. - It has no role in the direct management of **acute liver failure** due to **paracetamol overdose**. *Incorrect: Furosemide* - **Furosemide** is a **loop diuretic** used to increase **urine output** in conditions like **fluid overload** or **heart failure**. - While **oliguria** is present, it is often a sign of **acute kidney injury** requiring supportive care, and furosemide would not address the underlying **toxic mechanism** of paracetamol.

Question 884: What is the drug of choice for preventing chemotherapy-induced vomiting?

A. Granisetron (Correct Answer)
B. Prazosin
C. Clonidine
D. Dimenhydrinate

Explanation: ***Granisetron*** - As a **5-HT3 receptor antagonist**, granisetron is highly effective in blocking serotonin-mediated nausea and vomiting caused by chemotherapy. - It works by blocking serotonin receptors in the **chemoreceptor trigger zone** and the **gastrointestinal tract**, which are key sites for chemotherapy-induced emesis. *Prazosin* - This drug is an **alpha-1 adrenergic blocker** primarily used for hypertension and benign prostatic hypertrophy. - It has no significant antiemetic properties and is not indicated for preventing chemotherapy-induced vomiting. *Clonidine* - **Clonidine** is an **alpha-2 adrenergic agonist** typically used for hypertension, ADHD, and withdrawal syndromes. - It does not act on the pathways responsible for chemotherapy-induced nausea and vomiting. *Dimenhydrinate* - **Dimenhydrinate** is an **antihistamine** with antiemetic properties primarily used for motion sickness and mild nausea. - While it can help with some forms of nausea, it is generally not potent enough to prevent the severe vomiting induced by highly emetogenic chemotherapy.

Question 885: 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 886: Which drug decreases the bone resorption in osteoporosis?

A. Teriparatide
B. Risedronate (Correct Answer)
C. Cortisone
D. Cimetidine

Explanation: ***Risedronate*** - **Risedronate** is a **bisphosphonate**, a class of drugs that inhibits osteoclast activity, thereby decreasing **bone resorption**. - By reducing the rate at which bone is broken down, it helps to preserve **bone mineral density** in patients with osteoporosis. *Teriparatide* - **Teriparatide** is a **parathyroid hormone analog** that primarily works by stimulating **osteoblast activity** to promote new bone formation. - While it treats osteoporosis, its primary mechanism is **anabolic** (bone building), not directly decreasing bone resorption as its main effect. *Cortisone* - **Cortisone** is a **glucocorticoid** that can actually *worsen* osteoporosis by increasing **bone resorption** and decreasing **bone formation** with long-term use. - It is used to treat inflammatory conditions, not to decrease bone resorption for osteoporosis. *Cimetidine* - **Cimetidine** is an **H2-receptor antagonist** used to reduce stomach acid production, commonly for conditions like GERD or ulcers. - It has no known effect on **bone metabolism** or **osteoporosis**.

Question 887: Which of the following drugs can lead to pemphigus?

A. Carbamazepine
B. Penicillamine (Correct Answer)
C. Isoniazid
D. Furosemide

Explanation: ***Penicillamine*** - **Penicillamine** is a well-known drug that can induce **pemphigus**, often through mechanisms involving alterations in **desmosome structure** or function. - The drug's sulfhydryl groups are thought to interfere with the integrity of **desmoglein proteins**, leading to blister formation. *Isoniazid* - **Isoniazid** is a first-line antituberculosis drug primarily associated with **hepatotoxicity** and **peripheral neuropathy**. - It is not typically implicated in the development of **pemphigus**. *Carbamazepine* - **Carbamazepine** is an anticonvulsant that can cause various cutaneous reactions, most notably **Stevens-Johnson syndrome (SJS)** and **toxic epidermal necrolysis (TEN)**. - While it can cause severe skin reactions, **pemphigus** is not a common side effect of carbamazepine. *Furosemide* - **Furosemide** is a loop diuretic that can cause **photosensitivity**, rashes, and rarely, severe skin reactions like **erythema multiforme**. - It is not recognized as a drug that induces **pemphigus**.

Question 888: Which of the following methods can reduce flushing caused by niacin?

A. All of the options (Correct Answer)
B. Tachyphylaxis
C. Laropiprant
D. Premedication with aspirin

Explanation: ***All of the options*** - **All three methods** (tachyphylaxis, laropiprant, and premedication with aspirin) are effective strategies for reducing niacin-induced flushing. - This demonstrates that multiple pharmacological and physiological approaches can mitigate this common side effect of niacin therapy. **Why each method works:** **Tachyphylaxis:** - Refers to the rapid decrease in response to a drug after repeated administration - With continued niacin use, tolerance develops and flushing intensity decreases over time - This is a natural adaptive response, though not an immediate solution for initial flushing episodes **Laropiprant:** - A selective antagonist of the **prostaglandin D2 receptor 1 (DP1)** - Specifically developed to reduce niacin-induced flushing by blocking prostaglandin D2-mediated vasodilation - Was marketed in combination with niacin (though later withdrawn due to other safety concerns) **Premedication with aspirin:** - **Aspirin** or other NSAIDs taken approximately 30 minutes before niacin administration - Reduces flushing by inhibiting **prostaglandin synthesis**, particularly prostaglandin D2 - Prostaglandins are key mediators of the cutaneous vasodilation that causes flushing

Question 889: Which vitamin/nutrient toxicity is associated with excessive sweating?

A. Choline (Correct Answer)
B. Biotin
C. Folic acid
D. Niacin (Vitamin B3)

Explanation: ***Choline*** - **Excessive sweating** is a recognized symptom of choline toxicity, often accompanied by a **fishy body odor**, hypotension, and gastrointestinal distress. - Choline plays a role in various metabolic pathways, and high doses can overwhelm these systems, leading to adverse effects. *Biotin* - **Biotin toxicity** is extremely rare, even at very high doses; there are no well-documented cases of adverse effects from excessive intake. - Symptoms like excessive sweating are not associated with biotin overdose. *Folic acid* - While high doses of **folic acid** can mask a **vitamin B12 deficiency**, side effects like gastrointestinal upset or sleep disturbances are rare. - Excessive sweating is **not a characteristic symptom** of folic acid toxicity. *Niacin (Vitamin B3)* - High doses of niacin, especially its nicotinic acid form, are well-known to cause **flushing, itching, and liver toxicity**. - While skin effects are common with niacin toxicity, **excessive sweating** as a primary symptom is not typically reported.

Question 890: Intracranial pressure may be increased by all of the following drugs except -

A. Quinolones
B. Aminoglycosides (Correct Answer)
C. Vitamin A
D. Corticosteroids

Explanation: ***Aminoglycosides*** - **Aminoglycosides** are not typically associated with increasing intracranial pressure. Their primary toxicities include **ototoxicity** and **nephrotoxicity**. - There is no established physiological mechanism by which aminoglycosides directly elevate ICP. *Vitamin A* - **Vitamin A toxicity**, particularly the chronic form of hypervitaminosis A, is a known cause of **idiopathic intracranial hypertension (pseudotumor cerebri)**, which directly increases ICP. - This occurs due to an unknown mechanism that leads to impaired CSF absorption or increased CSF production. *Corticosteroids* - While corticosteroids are often used to reduce cerebral edema and ICP, their **withdrawal**, particularly after prolonged use, can lead to rebound increases in ICP. - In certain susceptible individuals, or with paradoxical reactions, corticosteroids can also induce **pseudotumor cerebri**, leading to elevated ICP. *Quinolones* - **Quinolones** (fluoroquinolones) have been implicated in cases of **drug-induced intracranial hypertension (pseudotumor cerebri)**. - The mechanism is not fully understood but is thought to involve effects on **cerebrospinal fluid dynamics**.

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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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Pharmacovigilance

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