NEET-PG 2012 — Pharmacology
93 Previous Year Questions with Answers & Explanations
What is considered a toxic serum level of lithium?
Which of the following drugs is known to cross the blood-brain barrier?
What is the mechanism of action of Clopidogrel?
What is the primary mechanism by which epinephrine reduces insulin secretion?
Which of the following is a guanosine analogue?
Which of the following is the MOST CRITICAL indication for Acyclovir use during pregnancy?
Which of the following drugs acts directly to induce an erection without the need for sexual stimulation?
Desmopressin is preferred over vasopressin because it:
Which of the following has the least glucocorticoid activity?
Which of the following potassium-sparing diuretics was the first to be shown to reduce cardiac mortality in chronic heart failure patients?
NEET-PG 2012 - Pharmacology NEET-PG Practice Questions and MCQs
Question 1: What is considered a toxic serum level of lithium?
- A. 0.6
- B. 12
- C. 2.6 (Correct Answer)
- D. <0.6
Explanation: **2.6 mEq/L** - **Lithium toxicity** is generally considered to occur when serum lithium levels are above **1.5 mEq/L** with severe toxicity typically seen at levels above **2.5 mEq/L**. - At a level of **2.6 mEq/L**, patients are at high risk for significant neurological symptoms such as seizures, coma, and even death. *0.6 mEq/L* - A serum lithium level of **0.6 mEq/L** is within the normal therapeutic range, which is typically between **0.6 and 1.2 mEq/L**. - At this concentration, lithium is generally effective for bipolar disorder and other conditions with minimal risk of toxicity. *12 mEq/L* - A serum lithium level of **12 mEq/L** would represent an **extremely severe and likely fatal level of toxicity**, far beyond typical therapeutic or even severely toxic ranges. - Survival at such a high concentration would be highly improbable, as it would cause irreversible organ damage and profound central nervous system depression. *<0.6 mEq/L* - A serum lithium level of **less than 0.6 mEq/L** is considered subtherapeutic, meaning it is unlikely to be effective in treating bipolar disorder or other conditions. - While not toxic, such a low level would indicate a lack of therapeutic benefit and potential for symptom recurrence.
Question 2: Which of the following drugs is known to cross the blood-brain barrier?
- A. Glycopyrrolate
- B. Neostigmine
- C. Physostigmine (Correct Answer)
- D. All of the options
Explanation: ***Physostigmine*** - **Physostigmine** is a **tertiary amine** that is uncharged at physiological pH, allowing it to readily cross the **lipophilic blood-brain barrier**. - Its ability to enter the central nervous system makes it useful for treating **central anticholinergic toxicity**, as it can inhibit acetylcholinesterase in the brain. *Glycopyrrolate* - **Glycopyrrolate** is a **quaternary ammonium compound**, meaning it carries a permanent positive charge. - This charge prevents it from crossing the **blood-brain barrier** effectively, limiting its effects to the peripheral nervous system. *Neostigmine* - **Neostigmine** is also a **quaternary ammonium compound**, similar to glycopyrrolate, making it highly ionized. - Due to its poor lipid solubility and charge, **neostigmine** has very limited penetration into the **central nervous system**. *All of the options* - This option is incorrect because both **glycopyrrolate** and **neostigmine** are charged molecules that do not readily cross the **blood-brain barrier**. - Only **physostigmine** among the listed drugs possesses the necessary lipophilicity to enter the central nervous system.
Question 3: What is the mechanism of action of Clopidogrel?
- A. Inhibition of Thromboxane A2
- B. Inhibition of GP IIb/IIIa receptors
- C. No effect on platelet activation
- D. Inhibition of ADP-mediated platelet activation (Correct Answer)
Explanation: ***Inhibition of ADP-mediated platelet activation*** - Clopidogrel is an **antiplatelet agent** that works by a direct antagonistic action at the **P2Y12 receptor** on the surface of platelets. - This binding prevents adenosine diphosphate (ADP) from binding to its receptor, thereby inhibiting the activation of the **GP IIb/IIIa receptor complex** and subsequent platelet aggregation. *Inhibition of Thromboxane A2* - This mechanism of action is characteristic of **aspirin**, which inhibits the enzyme **cyclooxygenase-1 (COX-1)**. - COX-1 inhibition leads to reduced production of **Thromboxane A2**, a potent platelet aggregator and vasoconstrictor. *Inhibition of GP IIb/IIIa receptors* - While Clopidogrel ultimately affects the activation of **GP IIb/IIIa receptors**, it does not directly inhibit them. - Drugs like **abciximab**, **eptifibatide**, and **tirofiban** are direct inhibitors of the GP IIb/IIIa receptors, preventing fibrinogen binding and platelet aggregation. *No effect on platelet activation* - This statement is incorrect as Clopidogrel is a well-established **antiplatelet drug**. - Its therapeutic effect is specifically to **reduce platelet activation** and aggregation, thus preventing thrombotic events.
Question 4: What is the primary mechanism by which epinephrine reduces insulin secretion?
- A. Predominantly through beta action
- B. Through both alpha and beta actions
- C. Through muscarinic receptors
- D. Predominantly through alpha action (Correct Answer)
Explanation: ***Predominantly through alpha action*** - **Epinephrine** primarily reduces insulin secretion by stimulating **alpha-2 adrenergic receptors** on pancreatic beta cells. - Activation of these receptors leads to a decrease in **cAMP levels** and an inhibition of insulin release. *Predominantly through beta action* - **Beta-2 adrenergic receptor activation** on pancreatic beta cells typically **stimulates** insulin secretion, which is opposite to epinephrine's overall effect. - While epinephrine has both alpha and beta effects, the **alpha-2 inhibition** of insulin release predominates in this context. *Through both alpha and beta actions* - Although epinephrine exerts both alpha and beta effects, the **alpha-2 receptor-mediated inhibition** of insulin secretion is the dominant mechanism. - The **beta-2 receptor-mediated stimulation** of insulin release is overridden by the stronger inhibitory alpha-2 effect. *Through muscarinic receptors* - Muscarinic receptors are part of the **parasympathetic nervous system** and are involved in stimulating insulin secretion. - **Epinephrine** acts on adrenergic receptors, not muscarinic receptors, to influence insulin release.
Question 5: Which of the following is a guanosine analogue?
- A. Abacavir (Correct Answer)
- B. Bromodeoxyuridine
- C. Allopurinol
- D. Acyclovir
Explanation: ***Abacavir*** - **Abacavir** is a nucleoside reverse transcriptase inhibitor (NRTI) used in HIV treatment. - It is a **carbocyclic analogue of guanosine** (specifically, a 2'-deoxyguanosine analogue). - Structurally, it contains a modified cyclopentane ring instead of the ribose sugar, but retains the guanine base, making it a guanosine analogue. *Acyclovir* - **Acyclovir** is also a **guanosine analogue** - specifically an acyclic guanosine analogue. - It is an antiviral drug used to treat herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. - Note: Both Abacavir and Acyclovir are technically guanosine analogues; in this PYQ context, Abacavir is the expected answer. *Bromodeoxyuridine* - **Bromodeoxyuridine** is a **pyrimidine analogue**, specifically a thymidine analogue. - It is incorporated into DNA during replication and is used in research and as a radiosensitizer. *Allopurinol* - **Allopurinol** is a purine analogue (hypoxanthine analogue) that inhibits xanthine oxidase. - It is primarily used to treat **gout** and prevent kidney stones by reducing uric acid production. - While it's a purine derivative, it is not specifically a guanosine analogue.
Question 6: Which of the following is the MOST CRITICAL indication for Acyclovir use during pregnancy?
- A. Treatment of disseminated herpes (Correct Answer)
- B. Treatment of chickenpox in the first trimester
- C. Prophylaxis for recurrent herpes during pregnancy
- D. Prevention of cytomegalovirus infection in pregnancy
Explanation: ***Treatment of disseminated herpes*** - **Disseminated herpes** in pregnancy is a severe, life-threatening condition for both the mother and the fetus, making acyclovir use critically indicated. - This systemic infection can lead to **visceral organ involvement**, **encephalitis**, and significantly increased maternal and fetal morbidity and mortality. - Immediate treatment with intravenous acyclovir is essential to prevent **multi-organ failure** and death. *Treatment of chickenpox in the first trimester* - While chickenpox in the first trimester can be serious, leading to **congenital varicella syndrome**, acyclovir's role here is primarily to mitigate maternal illness, not as critical as disseminated herpes. - The risk of congenital varicella syndrome for the fetus is relatively low (around 0.4%) after maternal infection in the first trimester. *Prophylaxis for recurrent herpes during pregnancy* - **Prophylactic acyclovir** in the third trimester is commonly used to prevent recurrent genital herpes and reduce the risk of **neonatal herpes**, but it is not as acutely critical as treating disseminated disease. - This intervention aims to prevent transmission during delivery rather than managing an immediate, life-threatening maternal or fetal condition. *Prevention of cytomegalovirus infection in pregnancy* - Acyclovir has **minimal activity against CMV** and is not indicated for CMV prevention or treatment. - **Ganciclovir** or **valganciclovir** are the antivirals used for CMV, not acyclovir.
Question 7: Which of the following drugs acts directly to induce an erection without the need for sexual stimulation?
- A. Sildenafil
- B. Tadalafil
- C. Alprostadil (Correct Answer)
- D. Testosterone
Explanation: ***Alprostadil***- **Alprostadil** is a **prostaglandin E1** analog that can directly induce vasodilation in the penile arteries, leading to an erection without sexual stimulation [1].- It is typically administered via **intracavernosal injection** or as a **urethral suppository**.*Sildenafil*- **Sildenafil** is a **PDE5 inhibitor** that works by enhancing the effects of **nitric oxide**, which is released in response to sexual stimulation [2, 3].- It requires **sexual arousal** to be effective, as it doesn't directly initiate the erectile process [2, 3].*Tadalafil*- Similar to sildenafil, **tadalafil** is also a **PDE5 inhibitor** that works by increasing cGMP levels and promoting smooth muscle relaxation [2, 3].- Its action is dependent on the release of **nitric oxide** triggered by sexual stimulation [2, 3].*Testosterone*- **Testosterone** is a hormone involved in sex drive and overall erectile function over time, but it does not directly or acutely induce an erection.- Its primary role in erectile dysfunction is in cases of **hypogonadism**, and it requires sexual stimulation for its effects on erection.
Question 8: Desmopressin is preferred over vasopressin because it:
- A. Is more potent and has little vasoconstrictor activity (Correct Answer)
- B. Is more potent than vasopressin
- C. Has little vasoconstrictor activity
- D. Is more selective for V2 receptors than vasopressin
Explanation: **Is more potent and has little vasoconstrictor activity** - **Desmopressin** is a synthetic analog of **vasopressin** (ADH) that is modified to have much higher selectivity for **V2 receptors** in the renal collecting ducts, leading to potent **antidiuretic effects** [1], [3]. - This selective action results in significantly **reduced vasoconstrictor activity** (mediated by V1 receptors) compared to natural vasopressin, making it safer for clinical use to manage water balance without significant cardiovascular side effects [1], [3]. *Is more potent than vasopressin* - While desmopressin is indeed more potent in its **antidiuretic effect** due to increased affinity for **V2 receptors**, this option alone doesn't specify the critical advantage of *reduced vasoconstrictor activity* [3]. - Its superior potency alone doesn't fully explain its preference over vasopressin, as the **side-effect profile** is a major consideration. *Has little vasoconstrictor activity* - This statement is true and highlights a key advantage of desmopressin, but it omits the fact that **desmopressin is also more potent** in its desired antidiuretic effect compared to natural vasopressin [1]. - Both the **potency** and **reduced vasoconstrictor activity** contribute to its superior clinical profile [3]. *Is more selective for V2 receptors than vasopressin* - **Desmopressin's increased selectivity** for **V2 receptors** is the mechanistic basis for its preferred properties, leading to both greater antidiuretic potency and reduced vasoconstriction [1], [4]. - However, the option "Is more potent and has little vasoconstrictor activity" describes the *clinical consequences* of this selectivity, which are the direct reasons for its preferred use [2].
Question 9: Which of the following has the least glucocorticoid activity?
- A. Fludrocortisone
- B. Cortisone (Correct Answer)
- C. Dexamethasone
- D. Betamethasone
Explanation: ***Cortisone*** - **Cortisone has the LEAST glucocorticoid activity** among the options listed. - It is a **prodrug** that must be converted to **hydrocortisone (cortisol)** by 11β-hydroxysteroid dehydrogenase in the liver to become active. - Its glucocorticoid potency is approximately **0.8** relative to hydrocortisone (when hydrocortisone = 1). - Due to variable hepatic conversion, it has **lower and less predictable glucocorticoid effects** compared to other agents. *Fludrocortisone* - Primarily used for its **potent mineralocorticoid activity** (125× that of hydrocortisone). - However, it retains **significant glucocorticoid activity** approximately **10-15 times** that of hydrocortisone. - Despite being marketed as a mineralocorticoid, its glucocorticoid potency is **considerably higher than cortisone**. *Dexamethasone* - **Highly potent synthetic glucocorticoid** with negligible mineralocorticoid activity. - Glucocorticoid potency is approximately **25-30 times** that of hydrocortisone. - Long duration of action (36-72 hours) and excellent CNS penetration. *Betamethasone* - **Highly potent synthetic glucocorticoid**, structurally similar to dexamethasone (differs only in stereochemistry at C-16). - Glucocorticoid potency is approximately **25-30 times** that of hydrocortisone. - Minimal mineralocorticoid activity, with similar clinical applications to dexamethasone.
Question 10: Which of the following potassium-sparing diuretics was the first to be shown to reduce cardiac mortality in chronic heart failure patients?
- A. Spironolactone (Correct Answer)
- B. Amiloride
- C. Triamterene
- D. Eplerenone
Explanation: ***Spironolactone*** - **Spironolactone** was the first potassium-sparing diuretic shown to reduce **cardiac mortality** in patients with **chronic heart failure** in the **RALES trial** (Randomized Aldactone Evaluation Study). - Its beneficial effects in heart failure are primarily attributed to its **aldosterone receptor antagonist** properties, which counteract the harmful effects of aldosterone on the myocardium and vasculature, rather than just its diuretic effect. *Amiloride* - **Amiloride** is a potassium-sparing diuretic that works by directly inhibiting **epithelial sodium channels (ENaC)** in the collecting duct. - While it helps in potassium conservation, it has not been shown to significantly reduce cardiac mortality in chronic heart failure patients in clinical trials. *Triamterene* - **Triamterene** is another potassium-sparing diuretic that also directly inhibits **ENaC** in the collecting duct, similar to amiloride. - Like amiloride, it is used to prevent hypokalemia but lacks evidence for significant **cardiac mortality reduction** in chronic heart failure. *Eplerenone* - **Eplerenone** is a selective **aldosterone receptor antagonist**, similar to spironolactone, with fewer hormonal side effects. - While it has been shown to reduce **cardiac mortality** in chronic heart failure (e.g., in the EMPHASIS-HF trial), it was introduced later than spironolactone and was not the *first* to demonstrate this benefit.