Clinical Pharmacology and Drug Toxicity — MCQs

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

Question 791: A patient presents with painful oral ulcers and target lesions on extremities. Which drug is MOST likely to cause this condition?

A. Metformin
B. Allopurinol (Correct Answer)
C. Atorvastatin
D. Amlodipine

Explanation: ***Allopurinol*** - **Allopurinol** is a well-known cause of drug-induced **Stevens-Johnson Syndrome (SJS)** or **Toxic Epidermal Necrolysis (TEN)**, which presents with typical mucocutaneous lesions like painful oral ulcers and target lesions on the skin. - The drug is frequently implicated, especially in patients with **renal impairment** or those started on high doses, making it the most likely choice given the severe symptoms. *Metformin* - **Metformin** is a common medication for type 2 diabetes, primarily causing **gastrointestinal side effects** like nausea, diarrhea, and abdominal discomfort. - It is **rarely associated** with severe cutaneous adverse reactions like SJS/TEN. *Atorvastatin* - **Atorvastatin** is a statin commonly used for hyperlipidemia, and its most common side effects include **myalgia**, headache, and gastrointestinal issues. - While it can rarely cause *rashes*, it is **not a typical or frequent cause** of severe mucocutaneous reactions such as target lesions or painful oral ulcers characteristic of SJS/TEN. *Amlodipine* - **Amlodipine**, a calcium channel blocker, is typically associated with side effects such as **edema**, headache, and flushing. - Although drug eruptions can occur with amlodipine, **severe mucocutaneous reactions** like SJS/TEN presenting with target lesions and oral ulcers are **exceedingly rare** and not characteristic of this drug.

Question 792: A patient with TB on DOTS develops orange-red discoloration of urine and tears. Which drug is responsible?

A. Ethambutol
B. Rifampicin (Correct Answer)
C. Pyrazinamide
D. Isoniazid

Explanation: ***Rifampicin*** - **Rifampicin** is well-known for causing **orange-red discoloration** of urine, sweat, tears, and other body fluids due to its intrinsic color. - This side effect is benign and does not indicate liver damage or other serious toxicity, but patients should be informed about it. *Ethambutol* - **Ethambutol** is primarily associated with **optic neuritis**, leading to decreased visual acuity and red-green color blindness. - It does not cause discoloration of body fluids. *Pyrazinamide* - **Pyrazinamide** is commonly associated with **hepatotoxicity** and **hyperuricemia**, which can lead to gout. - It does not cause discoloration of body fluids. *Isoniazid* - **Isoniazid** is known to cause **peripheral neuropathy** (prevented by pyridoxine supplementation) and **hepatotoxicity**. - It does not cause discoloration of body fluids.

Question 793: A 68-year-old with depression and chronic pain is on amitriptyline. What side effect may arise if given oxybutynin for overactive bladder?

A. Severe dry mouth (Correct Answer)
B. Bradycardia
C. Increased sweating
D. Urinary incontinence

Explanation: ***Severe dry mouth*** - Both **amitriptyline** (a tricyclic antidepressant) and **oxybutynin** (an anticholinergic for overactive bladder) have significant anticholinergic effects. - The combination of these two drugs can lead to an additive effect, causing pronounced anticholinergic side effects such as **severe dry mouth**, blurred vision, constipation, and cognitive impairment. *Bradycardia* - **Anticholinergic drugs** typically cause **tachycardia** (increased heart rate) by blocking the parasympathetic nervous system's muscarinic receptors on the heart, rather than bradycardia. - While amitriptyline can affect cardiac conduction, severe bradycardia is not a typical **additive anticholinergic side effect** in this context. *Increased sweating* - **Anticholinergic drugs** like amitriptyline and oxybutynin inhibit the activity of sweat glands, which are primarily innervated by cholinergic nerves. - Therefore, the combination of these drugs would likely lead to **decreased sweating** (anhidrosis) rather than increased sweating. *Urinary incontinence* - **Oxybutynin** is prescribed specifically to treat **overactive bladder** and reduce urinary incontinence by relaxing the detrusor muscle. - Therefore, it would improve rather than worsen urinary incontinence; however, it can cause **urinary retention** due to its anticholinergic effect, especially in older male patients.

Question 794: A diabetic patient with history of heart failure is prescribed pioglitazone. What complication may arise?

A. Hepatotoxicity
B. Pulmonary fibrosis
C. Fluid retention (Correct Answer)
D. Hypokalemia

Explanation: ***Fluid retention***- **Pioglitazone**, a thiazolidinedione (TZD), commonly causes **fluid retention** or edema [1].- This fluid retention can **exacerbate heart failure** symptoms and lead to cardiac decompensation, especially in patients with pre-existing heart conditions [1].*Hepatotoxicity*- While TZDs like pioglitazone have been associated with **liver dysfunction** in some cases, significant hepatotoxicity is rare and usually not the primary concern or most common serious side effect [1].- **Regular monitoring of liver enzymes** is recommended, but fluid retention leading to heart failure exacerbation is a more immediate and severe risk in this patient profile.*Pulmonary fibrosis*- **Pulmonary fibrosis** is not a known or common complication directly associated with pioglitazone use.- This complication is typically linked to other medications or systemic diseases.*Hypokalemia*- **Hypokalemia**, or low potassium levels, is generally not a direct side effect of pioglitazone.- Electrolyte imbalances associated with heart failure or diuretic use, rather than pioglitazone itself, are more likely causes of hypokalemia.

Question 795: Which drug is the primary treatment for Wilson’s disease?

A. Activated charcoal
B. Penicillamine (Correct Answer)
C. Deferoxamine
D. Zinc acetate

Explanation: ***Penicillamine*** - **Penicillamine** is a **chelating agent** that binds to copper, forming a complex that is then excreted in the urine. - **Historically considered first-line**, but now generally reserved as an **alternative chelator** due to: - High **side effect profile** (20-30% discontinuation rate) - Risk of **neurological worsening** (up to 50% in neurologically presenting patients) - **Hypersensitivity reactions**, bone marrow suppression, and nephrotic syndrome - **Trientine** has largely replaced penicillamine as the preferred chelator in current practice. *Activated charcoal* - **Activated charcoal** is used to treat **acute toxic ingestions** by adsorbing toxins in the gastrointestinal tract, preventing their absorption. - It is **not effective** for the chronic management of copper overload in Wilson's disease. - Has **no role** in Wilson's disease treatment. *Deferoxamine* - **Deferoxamine** is a **chelating agent** primarily used to treat **iron overload**, particularly in patients with hemochromatosis or those receiving multiple transfusions. - It has **no role** in the treatment of copper accumulation in Wilson's disease. - **Not effective** for copper chelation. *Zinc acetate* - **Zinc acetate** is an important treatment option for Wilson's disease. - **First-line therapy** for **presymptomatic/asymptomatic patients**. - Used for **maintenance therapy** after initial chelation. - Zinc works by **blocking copper absorption** from the gut and promoting metallothionein synthesis (which binds copper intracellularly). - **Does not chelate existing copper stores**, making it less suitable for symptomatic patients with significant copper burden requiring rapid removal.

Question 796: Which immunosuppressant blocks IL-2 production?

A. Sirolimus
B. Methotrexate
C. Tacrolimus (Correct Answer)
D. Mycophenolate

Explanation: ***Tacrolimus*** - Tacrolimus is a **calcineurin inhibitor** that works by binding to **FKBP-12**, forming a complex that inhibits calcineurin. - This inhibition prevents the dephosphorylation of **NFAT**, thereby blocking its translocation to the nucleus and subsequent **IL-2 gene transcription**. *Sirolimus* - Sirolimus is an **mTOR inhibitor** that works downstream from the IL-2 receptor, blocking **T-cell proliferation** in response to IL-2, rather than blocking IL-2 production itself. - It binds to **FKBP-12** but targets the **mTOR complex**, which is crucial for cell growth and division. *Methotrexate* - Methotrexate is an **antimetabolite** that inhibits **dihydrofolate reductase**, interfering with **DNA synthesis** and thus suppressing the proliferation of rapidly dividing cells, including lymphocytes. - Its primary action is not directly blocking IL-2 production but rather reducing the overall immune cell expansion. *Mycophenolate* - Mycophenolate mofetil is a **reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH)**, an enzyme critical for the *de novo* synthesis of guanosine nucleotides. - This preferentially inhibits the proliferation of **lymphocytes**, which are highly dependent on the *de novo* pathway for purine synthesis, but does not directly block IL-2 production.

Question 797: Which sedative is most appropriate in a patient with hepatic impairment?

A. Midazolam
B. Lorazepam (Correct Answer)
C. Zolpidem
D. Diazepam

Explanation: ***Lorazepam*** - **Lorazepam** is primarily metabolized by **glucuronidation**, a phase II metabolic pathway that is relatively preserved in most forms of hepatic impairment - This makes it a safer choice in patients with **liver disease** compared to other benzodiazepines that rely heavily on oxidative metabolism - Preferred sedative in cirrhosis and acute liver failure *Midazolam* - **Midazolam** is primarily metabolized by the **cytochrome P450 3A4 (CYP3A4)** enzyme system in the liver - Hepatic impairment can significantly reduce **CYP3A4 activity**, leading to prolonged half-life, increased sedative effects, and accumulation of the drug - Should be avoided or dose-reduced in hepatic impairment *Zolpidem* - **Zolpidem** is extensively metabolized by **hepatic cytochrome P450 enzymes**, particularly CYP3A4 and CYP2C9 - In patients with **hepatic impairment**, its clearance is significantly reduced, necessitating dose reduction to avoid excessive sedation and adverse effects - Maximum dose should be limited to 5 mg in hepatic dysfunction *Diazepam* - **Diazepam** undergoes extensive **hepatic oxidative metabolism** via CYP2C19 and CYP3A4 to active metabolites such as **desmethyldiazepam**, which also have long half-lives - In patients with **liver disease**, this metabolism is impaired, leading to prolonged drug action, increased sedation, and accumulation of the parent drug and active metabolites - Active metabolites can accumulate for days to weeks in hepatic impairment

Question 798: Atropine is not an antidote in:

A. Baygon
B. Parathion
C. Endrin (Correct Answer)
D. Tik 20

Explanation: ***Endrin*** - Endrin is an **organochlorine insecticide**, and its toxicity is primarily mediated through the central nervous system, causing seizures and neurological symptoms. - Atropine is an **anticholinergic drug** and is ineffective because organochlorines do not act on cholinergic receptors; therefore, it is not an antidote for endrin poisoning. *Baygon* - Baygon is a **carbamate insecticide**, which inhibits acetylcholinesterase, leading to cholinergic crisis. - Atropine is an appropriate antidote for Baygon poisoning, as it blocks the effects of excess acetylcholine at muscarinic receptors. *Parathion* - Parathion is an **organophosphate insecticide**, known for irreversible inhibition of acetylcholinesterase, resulting in severe cholinergic toxicity. - Atropine is a crucial antidote for parathion poisoning, used to counteract the muscarinic effects of acetylcholine accumulation. *Tik 20* - Tik 20 typically contains **organophosphate compounds** such as malathion or parathion, which are acetylcholinesterase inhibitors. - As an effective anticholinergic, atropine is indicated in the treatment of poisoning by organophosphates found in products like Tik 20.

Question 799: A patient on anti-tubercular therapy develops tingling sensation in the limbs. Which of the following when supplemented can result in improvement of symptoms?

A. Folic acid
B. Thiamine
C. Pyridoxine (Correct Answer)
D. Methylcobalamine

Explanation: ***Pyridoxine*** - **Isoniazid**, a key anti-tubercular drug, can cause **peripheral neuropathy** due to its interference with **pyridoxine (vitamin B6)** metabolism. - Supplementation with **pyridoxine** is crucial to prevent and treat this neurological side effect, leading to an improvement in tingling sensations. *Folic acid* - **Folic acid** (vitamin B9) deficiency can cause **megaloblastic anemia** and some neurological symptoms, but it is not directly related to isoniazid-induced peripheral neuropathy. - While beneficial for overall health, it would not specifically address the tingling caused by anti-tubercular therapy. *Thiamine* - **Thiamine (vitamin B1)** deficiency can cause **beriberi**, leading to peripheral neuropathy, but it is not the primary vitamin implicated in isoniazid-induced neuropathy. - Substituting thiamine would not effectively reverse the specific mechanism of nerve damage caused by isoniazid. *Methylcobalamine* - **Methylcobalamine** (Mecobalamin) is a form of **vitamin B12** and is used to treat **vitamin B12 deficiency**, which can also cause neuropathy. - However, the neuropathy associated with anti-tubercular therapy, specifically isoniazid, is primarily linked to **pyridoxine deficiency**, not B12 deficiency.

Question 800: 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.

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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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Drug-Induced QT Prolongation

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Pharmacovigilance

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