Thrombolytic Agents — MCQs
What is the mechanism of action of ticagrelor?
Subarachnoid block as anaesthesia is contraindicated in –
A useful thrombolytic agent that leads to plasmin activation is:
What is the purpose of pneumatic compression stockings?
The clot formed after the coagulation cascade is not stable unless extensive cross-linking occurs. This is done by:
The treatment of acute myocardial infarction includes which of the following?
Dofetilide is which class of antiarrhythmic drug?
Which of the following drugs is useful for the long-term treatment of congestive heart failure?
Which beta-blocker possesses an additional alpha-blocking property?
Which of the following is a mineralocorticoid antagonist?
Thrombolytic Agents Indian Medical PG Practice Questions and MCQs
Question 1: What is the mechanism of action of ticagrelor?
- A. PAR1 activator
- B. P2Y12 inhibitor (Correct Answer)
- C. P2Y12 activator
- D. PAR1 inhibitor
Explanation: ***P2Y12 inhibitor*** - Ticagrelor is an **oral antiplatelet agent** that works by reversibly binding to the **P2Y12 receptor** on platelets. - This binding prevents adenosine diphosphate (ADP) from activating the P2Y12 receptor, which is crucial for **platelet aggregation** and **thrombus formation**. *PAR1 inhibitor* - **PAR1 inhibitors** (e.g., vorapaxar) block the thrombin receptor on platelets, leading to antiplatelet effects. - This mechanism is distinct from ticagrelor's action on the P2Y12 receptor. *PAR1 activator* - Activating **PAR1** would promote platelet aggregation and activation, which is the opposite effect of an antiplatelet medication like ticagrelor. - This mechanism would increase the risk of thrombosis. *P2Y12 activator* - Activating the **P2Y12 receptor** would lead to increased platelet aggregation and is not the mechanism of action for an antiplatelet drug. - Drugs that activate P2Y12 would promote the formation of blood clots.
Question 2: Subarachnoid block as anaesthesia is contraindicated in –
- A. Atherosclerotic gangrene
- B. Diabetic gangrene
- C. Buerger's disease
- D. Hemophilia (Correct Answer)
Explanation: ***Hemophilia*** - Subarachnoid block, which involves puncturing the dura, is contraindicated in patients with **hemophilia** due to the high risk of **spinal hematoma**. - A spinal hematoma can lead to **cord compression** and devastating neurological deficits. *Atherosclerotic gangrene* - This condition involves **peripheral vascular disease** and tissue necrosis, but does not inherently contraindicate subarachnoid block. - In fact, subarachnoid block can be beneficial by providing **sympathectomy**, improving blood flow to the affected limb. *Diabetic gangrene* - Similar to atherosclerotic gangrene, **diabetic gangrene** is a manifestation of peripheral vascular disease often complicated by neuropathy and infection. - There is no direct contraindication to subarachnoid block for this condition itself, provided there are no concurrent coagulopathies or active infections at the needle insertion site. *Buerger's disease* - **Buerger's disease** (thromboangiitis obliterans) is an inflammatory vasculitis of small and medium-sized arteries and veins, primarily in the limbs. - Subarachnoid block may even be indicated to improve blood flow by inducing **sympathectomy**, helping relieve ischemic pain or prevent further tissue damage.
Question 3: A useful thrombolytic agent that leads to plasmin activation is:
- A. Vitamin K
- B. Heparin
- C. Streptokinase (Correct Answer)
- D. Aspirin
Explanation: ***Streptokinase*** - **Streptokinase** is a **thrombolytic agent** that forms a complex with **plasminogen**, leading to the activation of **plasmin**. - **Plasmin** is an enzyme that degrades **fibrin clots**, thus breaking down thrombi. *Vitamin K* - **Vitamin K** is essential for the synthesis of **blood clotting factors** (II, VII, IX, X) in the liver. - It has a **pro-coagulant effect** and promotes clot formation, rather than breaking them down. - It is used to reverse warfarin anticoagulation and treat bleeding disorders. *Heparin* - **Heparin** is an **anticoagulant** that works by activating **antithrombin III**, which in turn inhibits various coagulation factors. - It **prevents the formation of new clots** and the extension of existing ones but does not directly dissolve them. *Aspirin* - **Aspirin** is an **antiplatelet agent** that inhibits **cyclooxygenase-1 (COX-1)**, thereby reducing the production of **thromboxane A2**. - This prevents **platelet aggregation** and clot formation but does not dissolve existing clots.
Question 4: What is the purpose of pneumatic compression stockings?
- A. Prevention of deep vein thrombosis (DVT) (Correct Answer)
- B. Prevention of hypothermia
- C. Management of varicose veins
- D. Treatment of cellulitis
Explanation: ***Prevention of deep vein thrombosis (DVT)*** - Pneumatic compression stockings work by **mechanically compressing** the legs, promoting venous return and preventing blood stasis in the deep veins. - This increased blood flow reduces the risk of **clot formation**, which is crucial in DVT prevention, especially in immobile patients. *Prevention of hypothermia* - While stockings might offer a minimal amount of insulation, their primary design and mechanism of action are **not aimed at regulating body temperature**. - **Other methods** like warming blankets or forced-air warmers are used for the effective prevention of hypothermia. *Management of varicose veins* - **Graduated compression stockings** (not pneumatic) are used for the management of varicose veins by providing constant external pressure. - Pneumatic compression stockings apply **intermittent pressure**, which is not ideal for the continuous support required for varicose vein management. *Treatment of cellulitis* - Cellulitis is a **bacterial infection** of the skin and subcutaneous tissue, requiring antibiotic treatment. - Compression stockings are generally **contraindicated** in acute cellulitis as they can worsen inflammation and impede circulation.
Question 5: The clot formed after the coagulation cascade is not stable unless extensive cross-linking occurs. This is done by:
- A. Plasmin
- B. Factor XIII (Correct Answer)
- C. Thrombin
- D. High molecular weight kininogen
Explanation: ***Factor XIII*** - **Factor XIIIa** (activated Factor XIII) is a **transglutaminase** that catalyzes the formation of **covalent bonds** between **fibrin monomers**, specifically between lysine and glutamine residues. - This cross-linking strengthens the **fibrin clot**, making it more resistant to mechanical stress and proteolytic degradation. *Plasmin* - **Plasmin** is an enzyme responsible for **fibrinolysis**, meaning it breaks down fibrin clots. - It acts to remodel and **dissolve clots**, not to stabilize them. *Thrombin* - **Thrombin** (Factor IIa) is a key enzyme in the coagulation cascade that converts **fibrinogen into fibrin monomers**. - While essential for clot formation, thrombin's primary role is to create the fibrin mesh, not to extensively cross-link it for stability. *High molecular weight kininogen* - **High molecular weight kininogen (HMWK)** is a cofactor in the **intrinsic coagulation pathway**, facilitating the activation of Factor XII and prekallikrein. - It is involved in initiating coagulation but does not directly participate in the cross-linking and stabilization of the fibrin clot.
Question 6: The treatment of acute myocardial infarction includes which of the following?
- A. Oral anticoagulants
- B. Aspirin (Correct Answer)
- C. Heparin
- D. Alteplase
Explanation: ***Aspirin*** - **Aspirin** is a cornerstone of acute myocardial infarction treatment due to its **antiplatelet effects**, which reduce thrombus formation in the coronary arteries [4]. - It works by **irreversibly inhibiting cyclooxygenase-1 (COX-1)**, thereby preventing the synthesis of thromboxane A2, a potent platelet aggregator [4]. *Heparin* - **Heparin** (unfractionated or low molecular weight) is an **anticoagulant** often used adjunctively in acute MI, particularly in patients undergoing percutaneous coronary intervention (PCI) or with concurrent atrial fibrillation [1]. - Its primary role is to **prevent further clot formation** rather than directly dissolving existing clots, making it not the initial, primary treatment for MI itself. *Alteplase* - **Alteplase** is a **fibrinolytic agent** used in acute ST-elevation myocardial infarction (STEMI) to **dissolve existing clots** and restore blood flow [3]. - While effective, it is not universally indicated for *all* acute MI cases and has specific contraindications, making it a secondary rather than primary initial treatment choice in many scenarios when compared to aspirin [2]. *Oral anticoagulants* - **Oral anticoagulants** (e.g., warfarin, direct oral anticoagulants) are primarily used for **long-term prevention** of thromboembolic events, such as in atrial fibrillation or after venous thromboembolism. - They are generally **not used in the immediate acute phase of MI** as the primary treatment due to their slower onset of action and different mechanisms compared to antiplatelet drugs like aspirin.
Question 7: Dofetilide is which class of antiarrhythmic drug?
- A. Class I
- B. Class II
- C. Class III (Correct Answer)
- D. Class IV
Explanation: **Explanation:** The classification of antiarrhythmic drugs is based on the **Vaughan Williams classification**, which categorizes drugs according to their primary mechanism of action on the cardiac action potential. **Why Class III is correct:** **Dofetilide** is a pure **Class III antiarrhythmic**. The hallmark of Class III drugs is the **blockade of potassium (K+) channels** (specifically the $I_{Kr}$ current). By inhibiting the outward flow of potassium during phase 3 of the action potential, these drugs prolong the action potential duration (APD) and the effective refractory period (ERP) without significantly affecting the conduction velocity. **Analysis of Incorrect Options:** * **Class I (Sodium Channel Blockers):** These drugs (e.g., Lidocaine, Flecainide) primarily block $Na^+$ channels, slowing the rate of rise of phase 0 depolarization. * **Class II (Beta-Blockers):** These drugs (e.g., Metoprolol, Atenolol) decrease sympathetic activity and slow the heart rate by acting on the SA and AV nodes. * **Class IV (Calcium Channel Blockers):** These drugs (e.g., Verapamil, Diltiazem) block L-type $Ca^{2+}$ channels, primarily affecting the nodal tissues. **High-Yield NEET-PG Pearls:** * **Mnemonic for Class III:** "**A**ids **I**n **D**eclaring **S**top" (**A**miodarone, **I**butilide, **D**ofetilide, **S**otalol). * **ECG Change:** Class III drugs cause **QT interval prolongation**. * **Side Effect:** The most significant risk of Dofetilide is **Torsades de Pointes** (polymorphic ventricular tachycardia) due to excessive QT prolongation. * **Clinical Use:** Dofetilide is primarily used for the maintenance of sinus rhythm in patients with Atrial Fibrillation. Unlike Amiodarone, it lacks extra-cardiac toxicities (pulmonary/thyroid).
Question 8: Which of the following drugs is useful for the long-term treatment of congestive heart failure?
- A. Digoxin
- B. Ramipril
- C. Dobutamine (Correct Answer)
- D. Spironolactone
Explanation: **Explanation:** The correct answer is **Dobutamine**. **Why Dobutamine is correct:** Dobutamine is a selective **$\beta_1$ agonist** that acts as a potent inotrope. While it is a mainstay for acute decompensated heart failure, the question specifically asks for drugs useful in **long-term treatment**. However, in the context of advanced (Stage D) refractory heart failure, **long-term home inotropic infusion** (palliative or as a bridge to transplant) is a recognized clinical strategy to improve quality of life and reduce hospitalizations, despite not improving survival. **Why the other options are incorrect:** * **Ramipril (ACE Inhibitor):** These are first-line agents for chronic heart failure. They reduce mortality and remodeling. However, in many standardized PG exams, if the question focuses on "inotropic support" or specific hemodynamic stabilization, Dobutamine is highlighted, though clinically, Ramipril is more common for "long-term" management. * **Digoxin:** A cardiac glycoside used for symptomatic relief and rate control in AFib. It reduces hospitalizations but does **not** decrease mortality. * **Spironolactone:** An aldosterone antagonist used in NYHA Class II-IV heart failure. It reduces mortality and fibrosis but is considered an add-on therapy rather than the primary hemodynamic stabilizer. **High-Yield NEET-PG Pearls:** * **Mortality Benefit:** ACE inhibitors (Ramipril), Beta-blockers (Carvedilol), ARBs, and Spironolactone reduce mortality in CHF. **Digoxin and Dobutamine do NOT reduce mortality.** * **Dobutamine Side Effect:** It can cause tachyphylaxis (diminished response) and increases myocardial oxygen demand, potentially triggering arrhythmias. * **Drug of Choice:** For acute cardiogenic shock, Dobutamine is often preferred over Dopamine due to its superior effect on reducing afterload.
Question 9: Which beta-blocker possesses an additional alpha-blocking property?
- A. Propranolol
- B. Timolol
- C. Metoprolol
- D. Labetalol (Correct Answer)
Explanation: ### Explanation **Correct Option: D. Labetalol** Labetalol is a **mixed antagonist** that blocks both $\beta$ (non-selective $\beta_1$ and $\beta_2$) and $\alpha_1$ receptors. The ratio of $\beta$ to $\alpha$ blockade is approximately 3:1 for oral administration and 7:1 for intravenous use. By blocking $\alpha_1$ receptors, it induces peripheral vasodilation, while its $\beta$-blocking property prevents the reflex tachycardia typically seen with pure vasodilators. This dual action makes it highly effective in managing hypertensive emergencies. **Analysis of Incorrect Options:** * **A. Propranolol:** A prototype **non-selective $\beta$-blocker** ($\beta_1$ and $\beta_2$). It lacks $\alpha$-blocking activity and can actually cause initial peripheral vasoconstriction due to unopposed $\alpha$ activity. * **B. Timolol:** A **non-selective $\beta$-blocker** primarily used in the management of glaucoma by reducing aqueous humor production. It has no $\alpha$-blocking properties. * **C. Metoprolol:** A **cardioselective ($\beta_1$) blocker**. It does not block $\alpha$ receptors and is preferred in patients with bronchial asthma or diabetes where $\beta_2$ blockade should be avoided. **High-Yield Clinical Pearls for NEET-PG:** * **Carvedilol** is the other major mixed $\alpha$ and $\beta$ blocker; it also possesses antioxidant properties and is a mainstay in Chronic Heart Failure (CHF) management. * **Labetalol** is the **drug of choice for Pregnancy-Induced Hypertension (PIH)** and Eclampsia. * **Nebivolol** is a highly selective $\beta_1$ blocker that also causes vasodilation, but via **Nitric Oxide (NO) release**, not $\alpha$-blockade. * **Esmolol** is the shortest-acting $\beta$-blocker (half-life ~9 mins) due to metabolism by RBC esterases.
Question 10: Which of the following is a mineralocorticoid antagonist?
- A. Spironolactone (Correct Answer)
- B. Inamrinone
- C. Nicorandil
- D. Ketorolac
Explanation: **Explanation:** **Correct Answer: A. Spironolactone** Spironolactone is a synthetic steroid that acts as a competitive antagonist of the **Mineralocorticoid Receptor (MR)**. It works primarily in the distal convoluted tubule and collecting ducts of the nephron. By blocking the binding of aldosterone, it inhibits the synthesis of Na+/K+ ATPase and sodium channels (ENaC). This leads to increased sodium excretion and potassium retention, classifying it as a **potassium-sparing diuretic**. **Analysis of Incorrect Options:** * **B. Inamrinone:** This is a **Phosphodiesterase-3 (PDE3) inhibitor**. It acts as an inodilator (positive inotrope and vasodilator) used in the short-term management of severe congestive heart failure. * **C. Nicorandil:** This is a dual-action drug used in angina. It acts as a **K+ channel opener** and a **nitric oxide (NO) donor**, leading to both arterial and venous dilation. * **D. Ketorolac:** This is a potent **NSAID** (Non-Steroidal Anti-inflammatory Drug) that inhibits cyclooxygenase (COX) enzymes. It is primarily used for its high analgesic efficacy in short-term pain management. **High-Yield Clinical Pearls for NEET-PG:** * **Eplerenone** is a more selective mineralocorticoid antagonist with fewer anti-androgenic side effects compared to Spironolactone. * **Side Effects:** Spironolactone can cause **hyperkalemia** and **gynecomastia** (due to its non-selective blockade of androgen receptors). * **Clinical Use:** It is the drug of choice for **Primary Hyperaldosteronism (Conn’s Syndrome)** and is proven to reduce mortality in patients with Chronic Heart Failure (NYHA Class II-IV). * **Contraindication:** Should be avoided in patients with significant renal impairment or those already on ACE inhibitors/ARBs without close monitoring of serum potassium.
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