Clinical Pharmacology and Drug Toxicity — MCQs

A 23-year-old female underwent kidney transplantation and developed acute humoral rejection after 8 days, which was successfully managed with tacrolimus and another drug that suppresses both B and T lymphocytes. What is the drug that targets both B and T lymphocytes by inhibiting de novo synthesis of purines?

Q968

All of the following drugs cause hirsutism except:

Q969

Which of the following drugs is a corticosteroid and not used for treating glaucoma?

Q970

For chemotherapy-induced vomiting, which 5-HT3 antagonist has the maximum potency?

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

Question 961: What is the antidote for acetaminophen overdose?

A. N-acetylcysteine (NAC) (Correct Answer)
B. Heparin
C. Morphine
D. Benzodiazepine

Explanation: ***N-acetylcysteine (NAC)*** - **N-acetylcysteine (NAC)** is the specific antidote for acetaminophen overdose, working by replenishing **glutathione** stores in the liver. - Glutathione is crucial for detoxifying the toxic metabolite of acetaminophen, **N-acetyl-p-benzoquinone imine (NAPQI)**, thus preventing **hepatic damage**. *Heparin* - **Heparin** is an **anticoagulant** used to prevent and treat various thrombotic events by inhibiting coagulation. - It has no role in the treatment or detoxification of acetaminophen overdose. *Morphine* - **Morphine** is an **opioid analgesic** primarily used for pain management, acting on opioid receptors in the central nervous system. - It is not an antidote for any specific overdose and would exacerbate respiratory depression if given in an opioid overdose. *Benzodiazepine* - **Benzodiazepines** are a class of drugs with **sedative, anxiolytic, muscle relaxant, and anticonvulsant** properties, commonly used for anxiety, insomnia, or seizures. - They are not an antidote for acetaminophen overdose and would not counteract its hepatotoxic effects.

Question 962: Most sensitive test for organophosphate poisoning is which one?

A. OP level in blood
B. OP level in urine
C. OP level in lavage
D. RBC acetylcholinesterase (Correct Answer)

Explanation: ***RBC acetylcholinesterase*** - Organophosphates primarily exert their toxic effects by **inhibiting acetylcholinesterase** enzymes, leading to accumulation of acetylcholine. - The **RBC acetylcholinesterase** level directly reflects the extent of this enzymatic inhibition in the body and thus the severity of organophosphate poisoning. *OP level in blood* - Measuring organophosphate levels in the blood can confirm exposure, but it does not directly correlate with the **degree of enzyme inhibition** or clinical toxicity. - The blood OP level decreases rapidly as the substance is metabolized or distributed, making it less sensitive for assessing the clinical impact. *OP level in urine* - Organophosphate metabolites are excreted in the urine, and their detection can indicate exposure, especially if the parent compound is not found in blood. - However, urine levels are primarily useful for **biomonitoring exposure** and do not provide an immediate or sensitive measure of acetylcholinesterase inhibition. *OP level in lavage* - Gastric lavage fluid might contain organophosphates if ingested, making it useful for identifying the poison in cases of recent oral exposure. - This method is more for identifying the presence of a toxin rather than assessing the **physiological impact** or severity of the poisoning.

Question 963: Which of the following is not an adverse effect of cyclosporine?

A. Hirsutism
B. Nephrotoxicity
C. Hypoglycemia (Correct Answer)
D. Hypertension

Explanation: ***Hypoglycemia*** - Cyclosporine is known to cause **hyperglycemia** rather than hypoglycemia, due to its inhibitory effects on insulin secretion and increased insulin resistance. - While it can affect glucose metabolism, causing high blood sugar is the more common and established adverse effect. *Hirsutism* - **Hirsutism**, or excessive hair growth, is a well-known and common adverse effect of cyclosporine, particularly noticeable on the face and body. - This effect is often dose-dependent and can be a significant cosmetic concern for patients. *Nephrotoxicity* - **Nephrotoxicity** is a major and dose-limiting adverse effect of cyclosporine, leading to impaired kidney function. - It can manifest as acute or chronic interstitial nephritis and is a primary reason for careful monitoring of renal parameters. *Hypertension* - **Hypertension** is a frequent adverse effect of cyclosporine, contributing to cardiovascular risk in transplant patients. - The drug's effects on vasoconstriction and fluid retention contribute to increased blood pressure.

Question 964: Bulls-eye retinopathy is seen in toxicity of:

A. Quinine
B. Tobacco
C. Ethanol
D. Chloroquine (Correct Answer)

Explanation: ***Chloroquine*** - **Bulls-eye maculopathy** is a classic and severe manifestation of retinal toxicity associated with **chloroquine** and **hydroxychloroquine** use. - This pattern involves central macular damage with a surrounding ring of preserved photoreceptors, affecting **visual acuity** and **color vision**. *Quinine* - Quinine toxicity primarily affects the **optic nerve** and **retinal vessels**, leading to **vasoconstriction** and **ischemia**, which can cause **optic neuropathy** and **sudden vision loss**. - It does not typically cause the characteristic bulls-eye maculopathy pattern. *Tobacco* - **Tobacco amblyopia** is a form of **toxic optic neuropathy** associated with chronic tobacco use, particularly smoking or chewing. - It is characterized by **progressive, painless vision loss**, often with **central or centrocecal scotomas**, and typically affects the **optic nerve** rather than the macula in a bulls-eye pattern. *Ethanol* - **Ethanol** (alcohol abuse) can lead to **nutritional optic neuropathy**, especially when combined with poor diet and vitamin deficiencies (e.g., **B vitamins**). - This condition affects the **optic nerve** and causes **gradual vision loss** and **central scotomas**, but not the specific bulls-eye retinopathy seen with chloroquine.

Question 965: Pancreatitis is a common complication of which one of the following?

A. Zidovudine
B. Zalcitabine
C. Stavudine
D. Didanosine (ddI) (Correct Answer)

Explanation: ***Didanosine (ddI)*** - **Didanosine (ddI)** is a nucleoside reverse transcriptase inhibitor (NRTI) known for causing dose-dependent **pancreatitis** as a significant adverse effect. - Patients on didanosine require monitoring for symptoms and elevated **amylase/lipase** levels. *Zidovudine* - **Zidovudine** (AZT) is an NRTI primarily associated with **bone marrow suppression** (anemia, neutropenia) and myopathy. - While it can cause lactic acidosis, **pancreatitis** is not its most common or dose-limiting side effect. *Zalcitabine* - **Zalcitabine** (ddC) is an NRTI whose primary dose-limiting toxicity is **peripheral neuropathy**, particularly in the extremities. - **Pancreatitis** is a less common adverse effect compared to didanosine. *Stavudine* - **Stavudine** (d4T) is an NRTI frequently associated with **peripheral neuropathy** and **lipoatrophy** (loss of subcutaneous fat). - Although it can also contribute to lactic acidosis, **pancreatitis** is not its characteristic or most common side effect.

Question 966: Which of the following treatment options for nicotine dependence is considered the least effective?

A. Nicotine tablets
B. Nicotine patches
C. Nicotine gums (Correct Answer)
D. Varenicline

Explanation: **Nicotine gums** - Among nicotine replacement therapies, **nicotine gums** often show **lower real-world effectiveness** due to adherence challenges and technique requirements. - They require a **specific chewing technique** (chew-and-park method) which is frequently done incorrectly, reducing nicotine absorption and efficacy. - **Adherence rates** are typically lower compared to patches due to taste issues, jaw discomfort, and the need for frequent dosing throughout the day. - Real-world quit rates with gum tend to be **lower than patches** despite similar pharmacological potential when used correctly. *Nicotine patches* - **Nicotine patches** provide **steady-state nicotine delivery** over 16-24 hours with once-daily application. - They have **superior adherence** compared to other NRTs due to convenience and ease of use. - Consistently demonstrate **higher real-world quit rates** among NRTs, making them a first-line option. *Varenicline* - **Varenicline** is a **partial agonist at α4β2 nicotinic receptors**, reducing cravings while blocking rewarding effects of smoking. - It is the **most effective pharmacological treatment** for smoking cessation (quit rates 30-35% vs 15-20% for NRTs). - Superior efficacy compared to all NRTs in multiple meta-analyses and clinical trials. *Nicotine tablets* - **Nicotine lozenges/tablets** dissolve slowly in the mouth, providing **rapid nicotine absorption** through oral mucosa. - They offer **better discretion and convenience** than gum without the chewing technique requirement. - **Adherence and efficacy** are generally comparable to or slightly better than nicotine gum in clinical studies.

Question 967: A 23-year-old female underwent kidney transplantation and developed acute humoral rejection after 8 days, which was successfully managed with tacrolimus and another drug that suppresses both B and T lymphocytes. What is the drug that targets both B and T lymphocytes by inhibiting de novo synthesis of purines?

A. Prednisone
B. Methotrexate
C. Mycophenolate mofetil (Correct Answer)
D. Cyclophosphamide

Explanation: ***Mycophenolate mofetil*** - This drug inhibits **inosine monophosphate dehydrogenase**, an enzyme crucial for the **de novo synthesis of guanine nucleotides** in lymphocytes. - This selective inhibition effectively suppresses the proliferation and function of both **B and T lymphocytes**, making it a cornerstone in preventing transplant rejection. *Methotrexate* - **Methotrexate** is an **antimetabolite** that primarily inhibits **dihydrofolate reductase**, interfering with DNA synthesis and cell proliferation. - While it has immunosuppressive effects, its primary mechanism in inhibiting purine synthesis is not de novo synthesis in the same manner as mycophenolate mofetil. *Prednisone* - **Prednisone** is a **corticosteroid** that exerts its immunosuppressive effects through broad anti-inflammatory actions, genomic and non-genomic effects, affecting the function of various immune cells. - It does not specifically target **de novo purine synthesis** as its primary mechanism of immunosuppression. *Cyclophosphamide* - **Cyclophosphamide** is an **alkylating agent** that cross-links DNA strands, leading to cell cycle arrest and apoptosis, particularly in rapidly dividing cells like lymphocytes. - While it is a potent immunosuppressant affecting both B and T cells, its mechanism does not involve the inhibition of **de novo purine synthesis**.

Question 968: All of the following drugs cause hirsutism except:

A. Phenytoin
B. Minoxidil
C. Corticosteroids
D. Heparin (Correct Answer)

Explanation: ***Heparin*** - Heparin is an **anticoagulant** medication used to prevent blood clots. - Its primary side effects include **bleeding**, **thrombocytopenia**, and **osteoporosis** with long-term use, but not hirsutism. *Phenytoin* - **Phenytoin** is an anticonvulsant commonly associated with **hirsutism** as a side effect. - It can cause excessive hair growth on the face, trunk, and extremities due to its effects on **hair follicles**. *Minoxidil* - **Minoxidil** is a vasodilator primarily used to treat **androgenetic alopecia** (hair loss), but it can cause **hirsutism** as a side effect, especially when used systemically. - When applied topically for hair regrowth, it can still lead to unwanted hair growth in other areas. *Corticosteroids* - Long-term or high-dose use of **corticosteroids** (e.g., prednisone) can cause a range of side effects, including **hirsutism**. - This is often part of a broader spectrum of **Cushingoid features**, such as moon facies and central obesity.

Question 969: Which of the following drugs is a corticosteroid and not used for treating glaucoma?

A. Prednisolone (Correct Answer)
B. Dorzolamide
C. Timolol
D. Brimonidine

Explanation: ***Prednisolone*** - **Prednisolone** is a potent **corticosteroid** used to reduce inflammation. - While it has various therapeutic uses, **corticosteroids** can cause or worsen **glaucoma** by increasing intraocular pressure and are therefore generally avoided in its treatment. *Brimonidine* - **Brimonidine** is an **alpha-2 adrenergic agonist** used to treat **glaucoma** by reducing aqueous humor production and increasing uveoscleral outflow. - It is not a corticosteroid and directly targets **intraocular pressure (IOP)** reduction. *Dorzolamide* - **Dorzolamide** is a **carbonic anhydrase inhibitor** that effectively treats **glaucoma** by decreasing aqueous humor secretion. - It works by inhibiting the enzyme **carbonic anhydrase** in the ciliary body, and it is not a corticosteroid. *Timolol* - **Timolol** is a **non-selective beta-blocker** that lowers **intraocular pressure** by reducing the production of aqueous humor. - It is one of the most commonly prescribed drugs for **glaucoma** and is not a corticosteroid.

Question 970: For chemotherapy-induced vomiting, which 5-HT3 antagonist has the maximum potency?

A. Ondansetron
B. Granisetron
C. Dolasetron
D. Palonosetron (Correct Answer)

Explanation: ***Palonosetron*** - Palonosetron is a **second-generation 5-HT3 antagonist** [1], [2] known for its **highest potency** and longer duration of action compared to first-generation agents [2]. - Its high affinity for the **5-HT3 receptor** and extended half-life make it particularly effective for both acute and delayed **chemotherapy-induced nausea and vomiting (CINV)** [3]. *Ondansetron* - Ondansetron is a **first-generation 5-HT3 antagonist** [1], [2] that is widely used, but it has a shorter half-life and lower receptor affinity than palonosetron [2]. - While effective for acute CINV, it is generally considered less potent for **delayed-phase CINV**. *Granisetron* - Granisetron is another **first-generation 5-HT3 antagonist** [1], [2] with a potency and duration of action comparable to ondansetron [3]. - It is effective for **acute CINV**, but its efficacy for delayed CINV is similar to other first-generation agents [2]. *Dolasetron* - Dolasetron is also a **first-generation 5-HT3 antagonist** [1], [2] that is available in intravenous and oral forms. - While effective for acute CINV, it does not demonstrate the same high potency or extended duration of action as palonosetron.

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