General Pharmacology — MCQs

General Pharmacology Indian Medical PG Practice Questions and MCQs

Question 561: What is the mechanism of action of tacrolimus?

A. Inhibition of calcineurin (Correct Answer)
B. Antimetabolite
C. mTOR inhibitor
D. Inhibition of DNA synthesis

Explanation: ***Inhibition of calcineurin*** - **Tacrolimus** is a macrolide lactone that functions as a potent **calcineurin inhibitor**. - By inhibiting calcineurin, it prevents the dephosphorylation of **NFAT (Nuclear Factor of Activated T-cells)**, thereby blocking the transcription of genes encoding various pro-inflammatory cytokines, especially **IL-2**, crucial for T-cell proliferation and activation. *Antimetabolite* - **Antimetabolites** interfere with DNA and RNA synthesis, usually by mimicking natural metabolites required for these processes. - Examples include azathioprine or mycophenolate mofetil, which are distinct from the action of tacrolimus. *mTOR inhibitor* - **mTOR inhibitors** (e.g., sirolimus, everolimus) block the mammalian target of rapamycin, a serine/threonine kinase involved in cell growth and proliferation. - While also immunosuppressive, their mechanism is distinct from calcineurin inhibition. *Inhibition of DNA synthesis* - Inhibition of DNA synthesis is a hallmark of **cytotoxic immunosuppressants** or antimetabolites, leading to impaired cell division. - This mechanism is characteristic of drugs like cyclophosphamide or methotrexate, not tacrolimus.

Question 562: Which of the following is a long-acting corticosteroid?

A. Triamcinolone
B. Betamethasone (Correct Answer)
C. Hydrocortisone
D. Prednisolone

Explanation: **Betamethasone** - **Betamethasone** is classified as a **long-acting corticosteroid** with a duration of action greater than 36 hours. - Its prolonged action is due to its chemical structure, which allows for slower metabolism and excretion. *Triamcinolone* - **Triamcinolone** is an **intermediate-acting corticosteroid** with a duration of action typically between 12 to 36 hours. - It is often used for conditions requiring an effect longer than hydrocortisone but shorter than the ultra-long acting corticosteroids. *Hydrocortisone* - **Hydrocortisone** is a **short-acting corticosteroid**, with a duration of action of 8-12 hours. - It is equivalent to the natural hormone **cortisol** and is primarily used for replacement therapy or conditions requiring a rapid, short-term effect. *Prednisolone* - **Prednisolone** is an **intermediate-acting corticosteroid**, similar to triamcinolone, with a duration of action between 12 to 36 hours [1]. - It is frequently used for inflammatory and autoimmune conditions due to its potent anti-inflammatory effects.

Question 563: What is the primary reason for hepatic involvement in oral contraceptives?

A. Estrogen (Correct Answer)
B. Progesterone
C. Mixed trace elements
D. Estrogen + Progesterone

Explanation: ***Estrogen*** - **Estrogen** components of oral contraceptives are primarily responsible for potential hepatic side effects, including some cases of **cholestasis** and **hepatocellular adenomas**. - High doses of estrogen can alter **liver enzyme metabolism** and affect bile flow. *Progesterone* - **Progesterone** components alone are generally not associated with significant hepatic dysfunction. - While synthetic progestins are metabolized by the liver, they typically do not induce the same level of hepatic risk as estrogen. *Estrogen + Progesterone* - While both hormones are present in combined oral contraceptives, the **estrogenic component** is the main driver of hepatic involvement. - The liver effects are primarily attributed to estrogen's influence on **hepatic synthesis** and metabolism, with progesterone playing a less direct role in adverse hepatic events. *Mixed trace elements* - **Oral contraceptives** do not contain significant amounts of mixed trace elements that would account for hepatic involvement. - Hepatic issues related to trace elements are usually associated with **toxicity** or deficiency states not relevant to oral contraceptive use.

Question 564: Most effective agent to prevent motion sickness is?

A. Ephedrine
B. Nedocromil
C. Cyproheptidine
D. Hyoscine (Correct Answer)

Explanation: ***Hyoscine*** - **Hyoscine (scopolamine)** is an anticholinergic drug that works by blocking muscarinic receptors in the **vestibular system** and **vomiting center**, making it highly effective for preventing motion sickness [1], [2]. - It is often administered as a **transdermal patch** for sustained release, providing convenience and prolonged efficacy [1], [2]. *Ephedrine* - **Ephedrine** is a sympathomimetic drug primarily used as a decongestant and bronchodilator. - While it has some central nervous system effects, it is **not considered a primary or effective agent** for preventing motion sickness. *Nedocromil* - **Nedocromil** is a mast cell stabilizer used in the treatment of asthma and allergic conjunctivitis. - Its mechanism of action involves **inhibiting the release of inflammatory mediators**, which is unrelated to the physiological pathways of motion sickness. *Cyproheptidine* - **Cyproheptidine** is a first-generation antihistamine with anticholinergic and antiserotonergic properties. - While some antihistamines can relieve motion sickness, cyproheptidine is mainly used for **allergic conditions** and as an **appetite stimulant**, and is not the most effective choice for motion sickness prevention [3].

Question 565: Which of the following actions are associated with Danazol?

A. Weak androgenic
B. Progestational
C. Anabolic
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - **Danazol** is a synthetic steroid with a variety of hormonal activities, including **weak androgenic**, **anabolic**, and **progestational** effects. - Its diverse pharmacological profile contributes to its therapeutic uses, particularly in conditions like **endometriosis** and **fibrocystic breast disease**, where it suppresses gonadotropin release and ovarian function. - All three properties listed (androgenic, progestational, and anabolic) are characteristics of Danazol. **Weak androgenic activity:** - Danazol possesses **weak androgenic activity**, meaning it can bind to androgen receptors and exert effects similar to, but less potent than, testosterone. - This can lead to side effects such as **hirsutism**, **acne**, and **voice deepening** in some patients. **Progestational activity:** - While not its primary action, Danazol has some **progestational properties** due to its steroid structure, contributing to its ability to suppress the hypothalamic-pituitary-ovarian axis. - This activity helps in creating a **hypoestrogenic state**, which is beneficial in treating conditions like endometriosis. **Anabolic activity:** - Danazol has **anabolic effects**, promoting protein synthesis and muscle growth, similar to other anabolic steroids. - This property is utilized in treating **hereditary angioedema** by increasing C1 esterase inhibitor levels. - This can lead to side effects like **weight gain** and changes in **lipid profiles**.

Question 566: What is the drug of choice (DOC) for prophylaxis of motion sickness?

A. Promethazine (Correct Answer)
B. Prochlorperazine
C. Metoclopramide
D. Itopride

Explanation: ***Promethazine*** - **Promethazine** is an antihistamine with significant anticholinergic properties, making it highly effective for preventing **motion sickness**. - It acts by blocking **H1 histamine receptors** and **muscarinic acetylcholine receptors** in the brainstem and vestibular pathways. *Prochlorperazine* - **Prochlorperazine** is a **dopamine D2 receptor antagonist** primarily used for severe nausea and vomiting. - While it has some efficacy against nausea, it is generally **less effective** than anticholinergics or antihistamines for motion sickness prophylaxis. *Metoclopramide* - **Metoclopramide** is a **dopamine D2 receptor antagonist** and a **serotonin 5-HT4 receptor agonist**, which primarily increases gastrointestinal motility. - Its antiemetic action is mainly confined to conditions like **gastroparesis** and chemotherapy-induced nausea, and it is largely ineffective for **motion sickness**. *Itopride* - **Itopride** is a **dopamine D2 receptor antagonist** and an **acetylcholinesterase inhibitor**, used to treat functional dyspepsia by enhancing gastric motility. - It has **no significant role** in the prevention or treatment of **motion sickness**.

Question 567: Theophylline by what mechanism causes diuresis?

A. Adenosine A1 receptor antagonism (Correct Answer)
B. Phosphodiesterase 3 inhibition
C. Phosphodiesterase 4 inhibition
D. Beta-2 adrenergic agonist action

Explanation: ***Adenosine A1 receptor antagonism*** - Theophylline is an **adenosine receptor antagonist**, primarily blocking A1 and A2A receptors at therapeutic concentrations. - **Adenosine A1 receptor antagonism** in the kidney leads to increased renal blood flow and glomerular filtration rate, resulting in a diuretic effect. *Phosphodiesterase 3 inhibition* - While theophylline is a **non-specific phosphodiesterase inhibitor**, its diuretic effect is not primarily mediated by PDE3 inhibition at clinical concentrations. - PDE3 inhibition is more commonly associated with **cardiac contractility** and **vasodilation**, but not direct diuresis. *Phosphodiesterase 4 inhibition* - **PDE4 inhibition** is a mechanism shared by some other bronchodilators (e.g., roflumilast) but is not the primary mechanism by which theophylline exerts its diuretic action. - PDE4 inhibition mainly affects **inflammatory cells** and smooth muscle, contributing to bronchodilation and anti-inflammatory effects. *Beta-2 adrenergic agonist action* - Theophylline has **no significant direct beta-2 adrenergic agonist action**; it primarily works through adenosine receptor antagonism and phosphodiesterase inhibition. - Beta-2 agonists (e.g., albuterol) act by stimulating beta-2 receptors, leading to **bronchodilation**, not diuresis.

Question 568: Which among the following is most probable reason for preference of Cisatracurium over atracurium?

A. Decreased histamine release (Correct Answer)
B. Increased histamine release
C. Decreased CNS toxicity
D. Due to elimination by non-specific plasma esterases

Explanation: ***Decreased histamine release*** - **Cisatracurium** is preferred over atracurium primarily due to its significantly **lower potential for histamine release**, which can cause undesirable side effects like **hypotension**, **tachycardia**, and **bronchospasm**. - This reduced histamine release contributes to a **more stable hemodynamic profile** and **fewer allergic-type reactions**, especially in critically ill or hemodynamically unstable patients. *Increased histamine release* - This is incorrect because **atracurium** is known to cause **more histamine release** compared to cisatracurium, which is why cisatracurium is often preferred. - Increased histamine release is an **undesirable effect** that can lead to adverse cardiovascular and respiratory reactions. *Decreased CNS toxicity* - While both drugs are **quaternary ammonium compounds** and do not readily cross the blood-brain barrier, **CNS toxicity** is not a primary concern or differentiating factor between atracurium and cisatracurium in clinical practice. - The potential for CNS effects from their metabolites (like **laudanosine**) is generally low with standard dosing, and **cisatracurium produces less laudanosine**. *Due to elimination by non-specific plasma esterases* - Both cisatracurium and atracurium are eliminated primarily by **Hofmann elimination** and **non-specific plasma esterases**. This is a shared characteristic, not a reason for cisatracurium's preference over atracurium. - **Hofmann elimination** is a non-enzymatic chemical degradation process that occurs at physiological pH and temperature, making their elimination **independent of renal or hepatic function**.

Question 569: What is mechanism of action of colchicine in acute gout?

A. Inhibition of purine metabolism
B. Inhibition of uric acid conversion
C. Migration of leukocytes
D. Inhibition of leukocyte migration and microtubule function (Correct Answer)

Explanation: ***Inhibition of leukocyte migration and microtubule function*** - Colchicine works by disrupting **microtubule polymerization**, which interferes with the **motility and activity of neutrophils and other inflammatory cells** [1]. - Its anti-inflammatory effect in acute gout is primarily due to the inhibition of **leukocyte migration and phagocytosis of urate crystals**, thereby reducing the inflammatory response [1]. - The mechanism involves binding to **tubulin**, preventing microtubule assembly, which affects multiple cellular processes including chemotaxis and cell division [1]. *Inhibition of purine metabolism* - This mechanism is associated with drugs like **allopurinol**, which inhibit **xanthine oxidase** to reduce uric acid production [2]. - Colchicine does not directly inhibit **purine metabolism** or uric acid synthesis; its effect is on the inflammatory response, not uric acid formation [1]. *Inhibition of uric acid conversion* - This mechanism refers to **uricosuric agents** like probenecid that increase renal excretion of uric acid. - Colchicine's action is primarily anti-inflammatory, not related to uric acid metabolism or excretion [1]. *Migration of leukocytes* - While this is partially correct, as colchicine does inhibit **leukocyte migration**, this option is incomplete. - The complete mechanism must include its action as a **microtubule inhibitor**, which is the underlying basis for all its cellular effects including inhibition of migration, phagocytosis, and inflammatory mediator release [1].

Question 570: What is the mechanism of action of Basiliximab?

A. IL-1 receptor antagonist
B. Anti-CD3 antibody
C. IL-2 receptor antagonist (Correct Answer)
D. TNF inhibitor

Explanation: ***IL-2 receptor antagonist*** - **Basiliximab** is a **monoclonal antibody** that specifically targets and blocks the **CD25 alpha subunit** of the **interleukin-2 (IL-2) receptor** on activated T lymphocytes. - By blocking IL-2 binding, it prevents **T-cell proliferation** and differentiation, thereby suppressing the immune response and preventing **organ transplant rejection**. *IL-1 receptor antagonist* - An **IL-1 receptor antagonist** (e.g., **anakinra**) blocks the action of **interleukin-1**, a potent pro-inflammatory cytokine. - This mechanism is primarily used in inflammatory conditions like **rheumatoid arthritis** and CAPS, not directly for transplant immunosuppression in the same manner as Basiliximab. *Anti-CD3 antibody* - **Anti-CD3 antibodies** (e.g., **muromonab-CD3**) bind to the **CD3 complex** on the surface of T lymphocytes, leading to their depletion or functional inactivation. - While also used for **immunosuppression** in transplant, their mechanism of action and side effect profile are distinct from Basiliximab. *TNF inhibitor* - **TNF inhibitors** (e.g., **infliximab**, **etanercept**) block the activity of **tumor necrosis factor-alpha**, another major pro-inflammatory cytokine. - These agents are primarily used in **autoimmune diseases** such as rheumatoid arthritis, Crohn's disease, and psoriasis, not as a primary immunosuppressant for organ transplantation in the way Basiliximab is used.

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