Clinical Pharmacology and Drug Toxicity — MCQs

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

Question 981: Bleomycin toxicity affects which organ predominantly?

A. Bone marrow
B. Lungs (Correct Answer)
C. Liver
D. RBC

Explanation: ***Lungs*** - **Bleomycin** is well-known for causing **pulmonary fibrosis**, an irreversible scarring of the lungs, as its most significant and dose-limiting toxicity. - This toxicity is thought to be due to an inability of the lungs to adequately inactivate bleomycin, leading to oxidative damage. *Bone marrow* - While many chemotherapeutic agents cause **bone marrow suppression**, bleomycin is notable for causing **minimal myelosuppression** compared to other cytotoxic drugs. - Therefore, bone marrow is not the predominantly affected organ for toxicity with bleomycin. *Liver* - **Hepatotoxicity** (liver damage) can occur with some chemotherapy agents, but it is **not a primary or prominent toxicity associated with bleomycin**. - Other drugs are much more frequently associated with liver damage. *RBC* - Bleomycin does not directly target **red blood cells (RBCs)** for toxicity. - While severe bone marrow suppression from other drugs can lead to anemia, bleomycin's effect on RBCs is indirect and not its predominant toxicity profile.

Question 982: Which of the following drugs causes pseudotumour cerebri?

A. Sparfloxacin
B. Gentamicin
C. Clofazimine
D. Tetracycline (Correct Answer)

Explanation: ***Tetracycline*** - **Tetracyclines** are a well-known cause of **pseudotumor cerebri**, also called idiopathic intracranial hypertension. - This condition involves increased **intracranial pressure**, leading to symptoms like headaches, visual disturbances, and papilledema. *Sparfloxacin* - **Sparfloxacin** is a **fluoroquinolone antibiotic** primarily associated with phototoxicity and QTc prolongation. - It is not typically linked to the development of **pseudotumor cerebri**. *Gentamicin* - **Gentamicin** is an **aminoglycoside antibiotic** known for its ototoxicity and nephrotoxicity. - It does not cause **pseudotumor cerebri**. *Clofazimine* - **Clofazimine** is an **antimycobacterial drug** used in leprosy, and its primary side effects include skin discoloration and gastrointestinal issues. - It is not associated with **pseudotumor cerebri**.

Question 983: Digoxin toxicity is increased by all except:

A. Hypercalcemia
B. Hypomagnesemia
C. Hyperkalemia (Correct Answer)
D. Renal impairment

Explanation: ***Hyperkalemia*** - **Hyperkalemia** actually *reduces* the binding of digoxin to the Na+/K+ ATPase, thereby **decreasing** its pharmacological effect and the risk of toxicity. - While it can cause cardiac arrhythmias on its own, it does not increase the specific risk of digoxin toxicity. *Renal impairment* - **Digoxin** is primarily excreted by the **kidneys**, so **renal impairment** leads to reduced clearance and accumulation of the drug. - This increased drug concentration in the body significantly raises the risk of **digoxin toxicity**. *Hypercalcemia* - **Hypercalcemia** potentiates the effects of digoxin by increasing the intracellular calcium concentration, which can lead to enhanced contractility and increased risk of **arrhythmias**. - High calcium levels can exacerbate the cardiac side effects of digoxin toxicity, such as **AV blocks** and **ventricular arrhythmias**. *Hypomagnesemia* - **Hypomagnesemia** increases the binding of digoxin to the Na+/K+ ATPase, making the heart more sensitive to digoxin's effects. - Along with **hypokalemia**, **hypomagnesemia** is a common electrolyte imbalance that can precipitate or worsen digoxin toxicity, promoting **arrhythmias**.

Question 984: Which of these drugs can be given safely to a patient with renal disease?

A. Aminoglycoside
B. Phenacetin
C. Tetracycline
D. Morphine (Correct Answer)

Explanation: ***Morphine*** - Morphine is primarily metabolized in the **liver** and excreted as glucuronide conjugates, making it generally safer in patients with **renal impairment**. - While careful dosing and monitoring are still needed, its elimination is less dependent on **kidney function** compared to other drugs listed. *Phenacetin* - Phenacetin is an **NSAID** that is known to cause **analgesic nephropathy**, leading to chronic interstitial nephritis and papillary necrosis. - Its use is contraindicated in patients with existing **renal disease** due to the high risk of further kidney damage. *Tetracycline* - Tetracyclines can accumulate in patients with **renal impairment**, leading to increased side effects such as **nephrotoxicity** and increased **blood urea nitrogen (BUN)**. - Specifically, some tetracyclines (e.g., outdated tetracycline) can cause a **Fanconi-like syndrome** in susceptible individuals. *Aminoglycoside* - Aminoglycosides are extensively excreted by the kidneys and are highly **nephrotoxic**, causing acute tubular necrosis. - Their use in **renal disease** requires significant dose adjustments and careful monitoring of plasma levels to prevent further kidney damage and ototoxicity.

Question 985: During a malaria outbreak, some patients treated with quinine developed blackwater fever, characterized by kidney damage due to hemolysis. What role does quinine play in this context?

A. An autoantigen
B. A hapten (Correct Answer)
C. An immunogen
D. A carrier

Explanation: ***A hapten*** - Quinine, when bound to red blood cells, can act as a **hapten**, forming a hapten-carrier complex that induces an immune response. - This immune response leads to the production of **anti-quinine antibodies** which then bind to red blood cells, causing their destruction (hemolysis) observed in blackwater fever. *An autoantigen* - An **autoantigen** is a normal body component that is mistakenly recognized as foreign by the immune system, leading to autoimmune disease. Quinine is an exogenous drug, not a normal body component. - While quinine leads to destruction of self cells (red blood cells), the initial trigger is the drug itself, not a misidentification of a self-protein as foreign. *An immunogen* - An **immunogen** is a substance that can directly elicit an adaptive immune response on its own. - Quinine is generally too small to be immunogenic by itself; it requires binding to a larger molecule (like a protein on red blood cells) to become antigenic and provoke an immune response. *A carrier* - A **carrier protein** is a large molecule that, when bound to a hapten, makes the hapten immunogenic. In the case of blackwater fever, quinine acts as the hapten, and a protein on the red blood cell surface acts as the carrier. - The carrier itself is not the substance that causes the allergic reaction; it merely facilitates the immune recognition of the hapten.

Question 986: Which of the following statements is incorrect about morphine use?

A. It can be used in Hypotension but with caution
B. It can be used in diabetes mellitus
C. It can be used in Head injury (Correct Answer)
D. It can be used for severe pain management in selected patients

Explanation: ***It can be used in Head injury*** - Morphine is generally **contraindicated** in patients with **head injuries** due to its potential to **increase intracranial pressure**, mask neurological signs, and cause respiratory depression. - The elevated CO2 levels from respiratory depression can lead to cerebral vasodilation, further exacerbating intracranial pressure. *It can be used in Hypotension but with caution* - Morphine can cause **histamine release** and **vasodilation**, potentially worsening existing hypotension. - While possible, it requires careful monitoring and often necessitates concomitant use of **vasopressors** in hypotensive patients. *It can be used in diabetes mellitus* - Morphine use is generally considered safe in patients with **diabetes mellitus**, as it does not directly interfere with glucose metabolism or insulin sensitivity. - However, **renal impairment**, common in long-standing diabetes, can affect morphine excretion and necessitate dose adjustments. *It can be used for severe pain management in selected patients* - Morphine is a potent **opioid analgesic** and is highly effective for managing severe pain in various clinical settings. - Its use is indicated when other less potent analgesics are insufficient, and it is crucial to select patients carefully based on their overall health and potential for adverse effects.

Question 987: Which of the following antidepressants is least likely to have sexual side effects?

A. Amitriptyline
B. Fluoxetine
C. Venlafaxine
D. Mirtazapine (Correct Answer)

Explanation: ***Mirtazapine*** - **Mirtazapine** is an atypical antidepressant (NaSSA - Noradrenergic and Specific Serotonergic Antidepressant) that works by blocking alpha-2 adrenergic receptors, enhancing serotonin and norepinephrine release [1]. - It has the **lowest incidence of sexual side effects** among antidepressants because it blocks 5-HT2 and 5-HT3 receptors while avoiding significant 5-HT1A stimulation, which is responsible for sexual dysfunction with SSRIs [1]. - It may even **improve libido** in some cases due to its unique receptor profile and histamine antagonism that can enhance sleep quality. *Amitriptyline* - **Amitriptyline** is a tricyclic antidepressant (TCA) with broad receptor actions, including anticholinergic and antihistaminic effects. - TCAs like amitriptyline can cause **sexual dysfunction** (including erectile dysfunction and decreased libido) due to their anticholinergic properties and effects on multiple neurotransmitter systems, though typically less severe than SSRIs. *Fluoxetine* - **Fluoxetine** is a selective serotonin reuptake inhibitor (SSRI), and while effective for depression, it is associated with a **high incidence of sexual side effects** (30-70% of patients) [2]. - These side effects include **decreased libido**, **anorgasmia**, and **erectile dysfunction**, caused by increased serotonergic activity at 5-HT2 receptors in areas regulating sexual function [2]. *Venlafaxine* - **Venlafaxine** is a serotonin-norepinephrine reuptake inhibitor (SNRI), increasing both serotonin and norepinephrine levels in the brain [1]. - Like SSRIs, SNRIs such as venlafaxine frequently cause **sexual dysfunction**, with common complaints including reduced libido and difficulty achieving orgasm due to enhanced serotonergic neurotransmission [1].

Question 988: A middle-aged man with chronic renal failure, diagnosed with sputum-positive pulmonary tuberculosis, has a creatinine clearance of 25 ml/min. All of the following drugs require modification in doses except:

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

Explanation: ***Rifampicin*** - **Rifampicin** is primarily metabolized by the **liver** and excreted in bile, making dose adjustment largely unnecessary in renal impairment [1]. - Its elimination is minimally affected by **creatinine clearance** values as low as 25 ml/min, unlike extensively renally excreted drugs. *Isoniazid* - **Isoniazid** undergoes significant **renal excretion** of its active metabolites, requiring dose adjustment in severe renal impairment. - Accumulation of metabolites can lead to increased risk of **peripheral neuropathy** and other toxicities. *Streptomycin* - **Streptomycin** is almost entirely eliminated by the **kidneys** and is highly dependent on renal function. - In a patient with a creatinine clearance of 25 ml/min, the dose must be significantly reduced to avoid **ototoxicity** and **nephrotoxicity**. *Ethambutol* - **Ethambutol** is mainly eliminated by the **kidneys**, and its plasma levels can rise significantly with reduced renal function. - Dose adjustment is crucial to prevent dose-dependent **optic neuritis**, a severe side effect.

Question 989: Methemoglobinemia is seen with which of the following agents?

A. Tetracaine
B. Prilocaine (Correct Answer)
C. Bupivacaine
D. Procaine

Explanation: ***Correct: Prilocaine*** - **Prilocaine** is a local anesthetic known to cause **methemoglobinemia**, especially at higher doses or in susceptible individuals - It metabolizes into **ortho-toluidine**, which oxidizes hemoglobin to methemoglobin - This is a well-recognized adverse effect, particularly when doses exceed 600 mg or in susceptible populations *Incorrect: Tetracaine* - While a local anesthetic, **tetracaine** is not typically associated with causing **methemoglobinemia** - Its primary concern is often related to **systemic toxicity** if absorbed in large quantities *Incorrect: Bupivacaine* - **Bupivacaine** is a widely used local anesthetic, but it is not a common cause of **methemoglobinemia** - It is more famously associated with **cardiotoxicity** at high systemic concentrations *Incorrect: Procaine* - **Procaine** is an ester-type local anesthetic with a lower incidence of systemic toxicity and is not known to cause **methemoglobinemia** - It is more often associated with **allergic reactions** due to its metabolite, **para-aminobenzoic acid (PABA)**

Question 990: Which agent is associated with pseudoeschar formation?

A. Silver Nitrate
B. Silver sulfadiazine (Correct Answer)
C. Mafenide acetate
D. Povidone iodine

Explanation: ***Silver sulfadiazine*** - **Silver sulfadiazine** reacts with wound exudate to form a black precipitate, which can be mistaken for an eschar and is thus called **pseudoeschar**. - This characteristic pseudoeschar formation is an important consideration when assessing wound healing in patients treated with this agent. *Silver Nitrate* - While it has antimicrobial properties and can stain tissues, it is not primarily known for causing a widespread **pseudoeschar** formation like silver sulfadiazine. - Its mechanism often involves acting as a caustic agent, forming a crust, but not typically a pseudoeschar from its interaction with exudate. *Povidone iodine* - **Povidone iodine** is an antiseptic that can cause temporary staining of the skin to a brownish color, but it does not form a black, leathery **pseudoeschar**. - Its antiseptic action is due to the slow release of iodine, which denatures proteins and oxidizes cell components. *Mafenide acetate* - **Mafenide acetate** is a carbonic anhydrase inhibitor that can cause metabolic acidosis and pain upon application but does not typically lead to the formation of a **pseudoeschar**. - It penetrates the eschar effectively and is known for its broad-spectrum antimicrobial activity.

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