Clinical Pharmacology and Drug Toxicity — MCQs

An 8-year-old child is brought to the emergency department after accidentally swallowing multiple tablets of a drug. The child developed severe diarrhea, polyuria, sweating, and respiratory difficulty. On examination, the pupil was constricted, and crepitations were heard on lung auscultation in the lower lobes of both lungs. There were no vascular or CNS effects. Which drug can cause these types of effects?

Q975

A patient with multidrug-resistant tuberculosis, who is receiving antitubercular drugs, develops an inability to distinguish between red and green colors after a few months. Which antitubercular drug is most likely causing these symptoms?

Q976

Which of the following drugs is MOST classically associated with hypomagnesemia?

Q977

Drug-induced myopathy can be caused by all of the following except:

Q978

The choice of drug for hyperthyroidism in the first trimester of pregnancy is?

Q979

What is the primary metabolite of methanol that contributes to its toxicity and potential visual disturbances?

Q980

Most common anomaly seen in a fetus of a mother taking lithium carbonate is:

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

Question 971: What is the commonly used concentration of tetracaine for topical anesthesia in minor ophthalmic procedures?

A. 1%
B. 0.5% (Correct Answer)
C. 2%
D. 0.25%

Explanation: ***0.5%*** - **Tetracaine 0.5%** is the standard and most commonly used concentration for **topical ocular anesthesia** in minor ophthalmic procedures. - This concentration provides effective and rapid onset topical anesthesia for procedures like tonometry, foreign body removal, and gonioscopy with minimal side effects. *1%* - **Tetracaine 1%** is a higher concentration not typically used for routine topical ophthalmic anesthesia due to an increased risk of **epithelial toxicity** and other side effects. - While it would provide more potent anesthesia, its use is generally limited to specific cases where stronger anesthesia is needed and the benefits outweigh the risks. *2%* - **Tetracaine 2%** is an even higher concentration, rarely used in ophthalmology because of a significantly increased risk of **corneal damage** and other ocular surface complications. - This concentration is considered too strong for topical use in the eye and could lead to prolonged epithelial defects. *0.25%* - **Tetracaine 0.25%** is a lower concentration that may not provide sufficient depth or duration of anesthesia for most minor ophthalmic procedures. - While it would have a lower risk of toxicity, its **suboptimal anesthetic effect** makes it less commonly used than 0.5%.

Question 972: What is the first-line drug used for painful diabetic neuropathy?

A. Venlafaxine
B. EMLA cream
C. Carbamazepine
D. Duloxetine (Correct Answer)

Explanation: ***Duloxetine*** - **Duloxetine**, a serotonin-norepinephrine reuptake inhibitor (SNRI), is recommended as a **first-line agent** for the management of **painful diabetic neuropathy**. - Its efficacy in reducing neuropathic pain has been demonstrated in multiple clinical trials, leading to its approval for this indication. *Carbamazepine* - **Carbamazepine** is an **antiepileptic drug** primarily used for seizure disorders and trigeminal neuralgia, but it is not a first-line treatment for painful diabetic neuropathy. - While it can be used for neuropathic pain, its efficacy in diabetic neuropathy is **limited**, and it has a narrower therapeutic index with potential for significant adverse effects. *Venlafaxine* - **Venlafaxine** is another SNRI, similar to duloxetine, and can be used for neuropathic pain. However, **duloxetine** is generally preferred as a first-line agent specifically for **diabetic neuropathy** due to more robust evidence and specific FDA approval for this indication. - While it has similar mechanisms of action, it is often considered a **second-line** or alternative agent for painful diabetic neuropathy. *EMLA cream* - **EMLA cream** (eutectic mixture of local anesthetics) contains lidocaine and prilocaine and is a **topical agent** used for localized pain or before minor procedures. - It is **not suitable for diffuse or widespread neuropathic pain**, such as that seen in painful diabetic neuropathy, and would not be considered a first-line systemic treatment.

Question 973: In a post-renal transplant patient already on triple therapy with Cyclosporine, Azathioprine, and Prednisolone, which of the following drugs would NOT be added to this regimen?

A. Cyclosporine
B. Prednisolone
C. Azathioprine
D. FK 506 (Correct Answer)

Explanation: ***FK 506 (Tacrolimus)***- **FK 506** is tacrolimus, which is a calcineurin inhibitor like cyclosporine and should **NOT be added** to a regimen already containing cyclosporine due to overlapping mechanisms of action and increased toxicity risk [2].- Both tacrolimus and cyclosporine inhibit calcineurin, preventing T-cell activation. Using both simultaneously would provide no additional benefit but significantly increase nephrotoxicity and neurotoxicity [2, 3].- In clinical practice, tacrolimus may **replace** cyclosporine in triple therapy but is never used **concurrently** with it [2].*Cyclosporine*- **Cyclosporine** is already part of the described triple therapy regimen as the calcineurin inhibitor component.- It inhibits calcineurin phosphatase activity, preventing NF-AT dephosphorylation and subsequent IL-2 gene transcription, thereby suppressing T-cell activation [1].*Azathioprine*- **Azathioprine** is already part of the described triple therapy regimen as the antimetabolite component.- It is converted to 6-mercaptopurine, which inhibits purine synthesis and suppresses lymphocyte proliferation.*Prednisolone*- **Prednisolone** is already part of the described triple therapy regimen as the corticosteroid component.- It provides broad immunosuppression through anti-inflammatory effects and lymphocyte apoptosis.

Question 974: An 8-year-old child is brought to the emergency department after accidentally swallowing multiple tablets of a drug. The child developed severe diarrhea, polyuria, sweating, and respiratory difficulty. On examination, the pupil was constricted, and crepitations were heard on lung auscultation in the lower lobes of both lungs. There were no vascular or CNS effects. Which drug can cause these types of effects?

A. Physostigmine
B. Acetylcholine
C. Neostigmine (Correct Answer)
D. Bethanechol

Explanation: ***Neostigmine***- **Neostigmine** is an **acetylcholinesterase inhibitor** that increases acetylcholine levels, leading to widespread **cholinergic effects** as observed (diarrhea, polyuria, sweating, constricted pupils, respiratory difficulty, and crepitations) [2].- **Key distinguishing feature:** Neostigmine is a **quaternary ammonium compound** that **does not cross the blood-brain barrier** [1], explaining the **absence of CNS effects** despite severe peripheral cholinergic toxicity.- This matches the clinical presentation perfectly: severe peripheral cholinergic symptoms without CNS involvement.*Physostigmine*- **Physostigmine** is a **tertiary amine** acetylcholinesterase inhibitor that **readily crosses the blood-brain barrier**, causing significant **CNS effects** (seizures, confusion, coma) [1].- The **absence of CNS symptoms** in this case definitively rules out physostigmine poisoning.- While it causes similar peripheral cholinergic effects, the lack of neurological symptoms is the critical differentiator.*Acetylcholine*- **Acetylcholine** itself is rapidly metabolized by acetylcholinesterase and cholinesterase enzymes, so it would not produce such **prolonged and severe effects** even if ingested.- Has **poor oral bioavailability** and would be broken down quickly in the GI tract.- As a direct agonist, any effects would be transient due to rapid **enzymatic breakdown**.*Bethanechol*- **Bethanechol** is a **direct muscarinic agonist** (quaternary ammonium) primarily used to stimulate bladder and bowel function [1].- While it can cause some peripheral cholinergic effects, it would not typically produce the **severe respiratory distress with crepitations** seen here.- The severity and widespread nature of symptoms are more characteristic of **acetylcholinesterase inhibitor toxicity** rather than direct muscarinic agonism [2].

Question 975: A patient with multidrug-resistant tuberculosis, who is receiving antitubercular drugs, develops an inability to distinguish between red and green colors after a few months. Which antitubercular drug is most likely causing these symptoms?

A. Ethambutol (Correct Answer)
B. Rifampicin
C. Ethionamide
D. Cycloserine

Explanation: ***Ethambutol*** - **Ethambutol** is known to cause **optic neuritis**, which can manifest as **red-green color blindness** and decreased visual acuity [1]. - This adverse effect is typically dose-dependent and reversible upon discontinuation of the drug [1].*Rifampicin* - **Rifampicin** is associated with a variety of side effects including **hepatotoxicity**, **orange discoloration of body fluids**, and gastrointestinal upset, but not typically optic neuritis or color blindness. - While it is a potent antitubercular drug, its adverse effect profile does not include ophthalmological issues like those described.*Ethionamide* - **Ethionamide** is known for side effects such as **gastrointestinal disturbance**, **hepatotoxicity**, and **hypothyroidism**. - It can also cause psychiatric side effects and peripheral neuropathy, but not specifically red-green color vision impairment.*Cycloserine* - **Cycloserine** is primarily associated with **neuropsychiatric side effects**, including psychosis, depression, seizures, and peripheral neuropathy [2]. - It does not typically cause optic neuritis or color vision disturbances like those seen with ethambutol.

Question 976: Which of the following drugs is MOST classically associated with hypomagnesemia?

A. Cisplatin (Correct Answer)
B. Valproate
C. Foscarnet
D. Cetuximab

Explanation: ***Cisplatin*** - **Cisplatin** is a platinum-based chemotherapy drug **most classically and severely** associated with **hypomagnesemia** due to **direct renal tubular damage** - Causes significant **magnesium wasting** in the urine through damage to the distal convoluted tubule - This **renal magnesium loss** is a common and often **dose-limiting side effect** of cisplatin therapy - Can persist for **months to years** after treatment and may be **irreversible** *Valproate* - **Valproate** is primarily associated with hepatotoxicity, hyperammonemia, pancreatitis, and teratogenicity - **Not associated** with hypomagnesemia - Its mechanism involves enhancing GABAergic transmission with limited direct renal effects on electrolyte balance *Foscarnet* - **Foscarnet** is an antiviral agent that can cause multiple electrolyte abnormalities including hypocalcemia, hypomagnesemia, and hypokalemia - However, it is **more characteristically associated with hypocalcemia** rather than hypomagnesemia - Works by inhibiting viral DNA polymerase and can chelate divalent cations *Cetuximab* - **Cetuximab**, an EGFR inhibitor, does cause **hypomagnesemia** through increased renal excretion of magnesium (occurs in 10-15% of patients) - However, **cisplatin** is the **more classic and severe** cause due to: - Direct nephrotoxic tubular damage (vs. EGFR-mediated mechanism) - Higher incidence and severity of hypomagnesemia - Longer duration and potential irreversibility - More established in medical literature as the prototypical drug causing this side effect

Question 977: Drug-induced myopathy can be caused by all of the following except:

A. d-penicillamine
B. ciprofloxacin (Correct Answer)
C. chloroquine
D. atorvastatin

Explanation: ***Ciprofloxacin*** - **Ciprofloxacin**, a fluoroquinolone antibiotic, is primarily associated with **tendonitis and tendon rupture**, particularly the Achilles tendon. - While it can cause some musculoskeletal pain, it is **not a common cause of myopathy** or muscle damage with elevated muscle enzymes. *Atorvastatin* - **Statins** like atorvastatin are well-known causes of **drug-induced myopathy**, ranging from myalgia to severe rhabdomyolysis. - This effect is due to inhibition of **HMG-CoA reductase**, which can disrupt muscle cell membrane integrity. *D-penicillamine* - **D-penicillamine** can induce a variety of autoimmune phenomena, including muscle disorders resembling **myasthenia gravis** or **polymyositis**. - Its mechanism involves interfering with **collagen and elastin cross-linking**, and potentially promoting autoimmune responses against muscle components. *Chloroquine* - **Chloroquine** (and hydroxychloroquine) can cause a dose-dependent myopathy, characterized by **proximal muscle weakness** and elevated creatine kinase. - The medication accumulates in lysosomes, leading to **lysosomal vacuolar myopathy** and muscle fiber degeneration.

Question 978: The choice of drug for hyperthyroidism in the first trimester of pregnancy is?

A. Methimazole
B. Carbimazole
C. Perchlorate
D. Propylthiouracil (Correct Answer)

Explanation: ***Propylthiouracil*** - **Propylthiouracil (PTU)** is the preferred treatment for hyperthyroidism during the **first trimester of pregnancy** due to a lower risk of teratogenicity compared to methimazole [1]. [2] - While PTU can cause **liver toxicity**, the risk of birth defects with methimazole in the first trimester is generally considered greater [2]. *Methimazole* - **Methimazole** is generally avoided in the first trimester because it is associated with a higher risk of **congenital anomalies**, specifically **aplasia cutis** and **esophageal atresia**. - It becomes the preferred choice in the **second and third trimesters**, as its side effect profile for the mother is often more favorable [1]. *Carbimazole* - **Carbimazole** is a prodrug that is converted to **methimazole** in the body, and therefore shares the same teratogenic risks as methimazole in the first trimester [2]. - It is also generally avoided during early pregnancy due to the risk of **fetal malformations**. *Perchlorate* - **Perchlorate** can be used to treat hyperthyroidism, but it is not typically a first-line drug, especially in pregnancy. - Its mechanism involves blocking **iodide uptake** into the thyroid gland, but it is associated with potential side effects and other treatment options are generally preferred due to their better-established safety profiles in pregnancy.

Question 979: What is the primary metabolite of methanol that contributes to its toxicity and potential visual disturbances?

A. Formic acid (Correct Answer)
B. Uric acid
C. Lactic acid
D. Pyruvic acid

Explanation: ***Formic acid*** - Methanol is metabolized by **alcohol dehydrogenase** to formaldehyde, which is then rapidly converted to **formic acid** by aldehyde dehydrogenase. - Formic acid is directly responsible for the **metabolic acidosis** and specific toxicity, including **retinal damage** leading to visual disturbances and blindness. *Uric acid* - **Uric acid** is a waste product of purine metabolism and is associated with gout, not methanol poisoning. - Its accumulation in the body is not due to methanol metabolism. *Lactic acid* - **Lactic acid** accumulates during anaerobic metabolism or in conditions like shock or severe hypoxia. - While methanol poisoning can cause **lactic acidosis**, lactic acid is not a primary metabolite of methanol itself. *Pyruvic acid* - **Pyruvic acid** is an intermediate in glycolysis and gluconeogenesis, and its metabolism is usually affected by various metabolic derangements. - It is not a direct metabolite of methanol responsible for its specific toxicity.

Question 980: Most common anomaly seen in a fetus of a mother taking lithium carbonate is:

A. Limb reduction
B. Neural tube defect
C. Cardiac deformities (Correct Answer)
D. Genitourinary deformity

Explanation: Detailed assessment of fetal risk indicates that the most significant and well-known teratogenic effect of **lithium carbonate** in utero is congenital **cardiac deformities**, particularly **Ebstein's anomaly** [2]. **Ebstein's anomaly** involves the downward displacement of the tricuspid valve, leading to tricuspid regurgitation and right heart failure [2]. *Limb reduction* - **Limb reduction defects** are typically associated with medications like **thalidomide** or vascular disruptions, not commonly with lithium exposure. - While various drug exposures can cause limb abnormalities, lithium's primary teratogenic risk lies elsewhere. *Neural tube defect* - **Neural tube defects (NTDs)** like spina bifida and anencephaly are most commonly associated with **folate deficiency** and certain antiepileptic drugs like valproic acid [1]. - Lithium has no established association with an increased risk of neural tube defects. *Genitourinary deformity* - While some medications can affect genitourinary development, **lithium carbonate** is not primarily linked to genitourinary deformities. - Its teratogenic effects are predominantly on the cardiovascular system.

Practice by Chapter

Principles of Clinical Pharmacology

Practice Questions

Therapeutic Drug Monitoring

Practice Questions

Drug Toxicity and Overdose

Practice Questions

Antidotes and Their Applications

Practice Questions

Management of Drug Poisoning

Practice Questions

Drug-Induced Liver Injury

Practice Questions

Drug-Induced Kidney Injury

Practice Questions

Drug-Induced Blood Dyscrasias

Practice Questions

Drug-Induced QT Prolongation

Practice Questions

Pharmacovigilance

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free