NEET-PG 2012 — Pharmacology

Q: What is considered a toxic serum level of lithium?

2.6. **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. [Practice more Pharmacology PYQs on OnCourse]

Q: Which of the following drugs is known to cross the blood-brain barrier?

Physostigmine. ***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. [Practice more Pharmacology PYQs on OnCourse]

Q: What is the mechanism of action of Clopidogrel?

Inhibition of ADP-mediated platelet activation. ***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. [Practice more Pharmacology PYQs on OnCourse]

Q: Which of the following is a guanosine analogue?

Abacavir. ***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. [Practice more Pharmacology PYQs on OnCourse]

Q: What is the primary mechanism by which epinephrine reduces insulin secretion?

Predominantly through alpha action. ***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. [Practice more Pharmacology PYQs on OnCourse]

93 Previous Year Questions with Answers & Explanations

Questions

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?

Which of the following is a guanosine analogue?

What is the primary mechanism by which epinephrine reduces insulin secretion?

Which of the following is not an alpha-blocker?

Which enzyme is irreversibly inhibited by aspirin?

Side effects of thiazide diuretics include all of the following except?

What is the primary therapeutic use of 5-HT1B/1D agonists?

Q10

Long-term steroid ingestion leads to all of the following except:

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: 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 5: 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 6: Which of the following is not an alpha-blocker?

A. Atenolol (Correct Answer)
B. Indoramine
C. Idazoxan
D. Prazosin

Explanation: ***Atenolol*** - Atenolol is a **selective beta-1 adrenergic receptor blocker**, primarily used to treat hypertension, angina, and certain arrhythmias. - Its mechanism of action involves **blocking the effects of adrenaline** on the heart, leading to decreased heart rate and blood pressure, rather than affecting alpha receptors. *Indoramine* - Indoramine is an **alpha-1 adrenergic receptor blocker** used historically for hypertension. - It specifically **antagonizes alpha-1 receptors** in vascular smooth muscle, causing vasodilation. *Idazoxan* - Idazoxan is an **alpha-2 adrenergic receptor antagonist**, primarily used in research contexts. - It **blocks presynaptic alpha-2 receptors**, which can lead to an increase in norepinephrine release. *Prazosin* - Prazosin is a well-known **alpha-1 adrenergic receptor blocker** used to treat hypertension and benign prostatic hyperplasia (BPH). - It causes **vasodilation** by relaxing vascular smooth muscle, thus lowering blood pressure.

Question 7: Which enzyme is irreversibly inhibited by aspirin?

A. Lipooxygenase
B. Cyclooxygenase (Correct Answer)
C. Thromboxane synthase
D. Phospholipase

Explanation: ***Cyclooxygenase*** - **Aspirin** irreversibly inhibits **cyclooxygenase (COX-1 and COX-2)** by acetylating a serine residue in the enzyme's active site. - This irreversible inhibition prevents the production of **prostaglandins, thromboxane**, and **prostacyclin**, thereby reducing inflammation, pain, fever, and platelet aggregation. *Lipooxygenase* - **Lipooxygenase** is involved in the synthesis of **leukotrienes**, which are mediators of inflammation and allergic responses. - Aspirin does not directly inhibit lipooxygenase; rather, it primarily targets the COX pathway. *Thromboxane synthase* - **Thromboxane synthase** is an enzyme downstream of COX, responsible for converting prostaglandin H2 into **thromboxane A2**. - While aspirin's effect on platelet aggregation is due to reduced thromboxane A2 synthesis via COX inhibition, it does not directly inhibit thromboxane synthase itself. *Phospholipase* - **Phospholipase A2** is responsible for releasing **arachidonic acid** from cell membrane phospholipids, which is the initial step in both the cyclooxygenase and lipooxygenase pathways. - Aspirin does not directly inhibit phospholipase A2; its action occurs later in the cascade.

Question 8: Side effects of thiazide diuretics include all of the following except?

A. Hypokalemia
B. Erectile dysfunction
C. Hyponatremia
D. Hypocalcemia (Correct Answer)

Explanation: ***Hypocalcemia*** - Thiazide diuretics are known to cause **hypercalcemia** (increased calcium reabsorption), NOT hypocalcemia, due to their action on the distal convoluted tubule. - This property makes them useful in treating conditions like **idiopathic hypercalciuria** and **calcium-containing kidney stones**. - The mechanism involves enhanced passive calcium reabsorption in the proximal tubule and active reabsorption in the distal tubule. *Hyponatremia* - Thiazide diuretics impair the kidney's ability to dilute urine and reabsorb sodium in the distal tubule, leading to **increased sodium excretion** and potential hyponatremia. - This effect is more pronounced in **elderly patients** and those with increased free water intake. - Hyponatremia is one of the most common electrolyte disturbances with thiazides. *Hypokalemia* - Thiazides increase the delivery of sodium and water to the collecting duct, leading to increased activity of the **renin-angiotensin-aldosterone system** and enhanced potassium secretion. - This results in **potassium wasting** and hypokalemia, which may require potassium supplementation or combination with potassium-sparing diuretics. *Erectile dysfunction* - Thiazide diuretics can cause **erectile dysfunction** through mechanisms including effects on vascular smooth muscle, reduced blood flow, and possible hormonal effects. - This is a common side effect reported in male patients using these medications for hypertension and may affect compliance.

Question 9: What is the primary therapeutic use of 5-HT1B/1D agonists?

A. Anti-anxiety medications
B. Acute migraine treatment (Correct Answer)
C. Anti-nausea medications for chemotherapy
D. Drugs for gastroesophageal reflux disease (GERD)

Explanation: ***Acute migraine treatment*** - 5-HT1B/1D agonists, such as **triptans**, primarily work by causing **vasoconstriction of intracranial blood vessels** and inhibiting the release of pro-inflammatory neuropeptides. - This action directly alleviates the pain and associated symptoms of **acute migraine attacks**. *Anti-anxiety medications* - Anti-anxiety medications typically target neurotransmitter systems like **GABA** (e.g., benzodiazepines) or **serotonin reuptake** (e.g., SSRIs), not the 5-HT1B/1D receptors in this context. - While serotonin plays a role in anxiety, specific 5-HT1B/1D agonism does not lead to anxiolytic effects. *Anti-nausea medications for chemotherapy* - Anti-nausea medications used for chemotherapy-induced nausea and vomiting often target **5-HT3 receptors** (e.g., ondansetron) to block their pro-emetic effects. - 5-HT1B/1D agonists do not have primary anti-emetic properties useful in this setting. *Drugs for gastroesophageal reflux disease (GERD)* - GERD medications primarily focus on reducing stomach acid production (e.g., **proton pump inhibitors**, H2 blockers) or neutralizing it (antacids). - 5-HT1B/1D agonists do not directly influence gastric acid secretion or esophageal motility in a way beneficial for GERD.

Question 10: Long-term steroid ingestion leads to all of the following except:

A. Avascular necrosis of head of femur
B. Growth retardation
C. Hypoglycemia (Correct Answer)
D. Cataract

Explanation: ***Hypoglycemia*** - Chronic steroid use primarily leads to **hyperglycemia** due to increased **gluconeogenesis** and **insulin resistance**, not hypoglycemia. - Steroids raise blood glucose levels, potentially inducing or worsening **diabetes mellitus**. *Avascular necrosis of head of femur* - Long-term steroid use is a well-established risk factor for **avascular necrosis**, particularly affecting the **femoral head**. - This occurs due to impaired blood supply to the bone, leading to its death. *Cataract* - **Posterior subcapsular cataracts** are a known ocular complication of prolonged systemic corticosteroid therapy. - The mechanism involves direct effects of steroids on lens metabolism and protein aggregation. *Growth retardation* - In children, chronic corticosteroid therapy can suppress growth, leading to **growth retardation**. - This is due to interference with **growth hormone secretion** and direct effects on bone formation.