Drugs Affecting Blood and Blood Formation — MCQs

Drugs Affecting Blood and Blood Formation Indian Medical PG Practice Questions and MCQs

Question 121: Low doses of aspirin prolong bleeding time by selectively inhibiting synthesis of the following mediator in the platelets?

A. Thromboxane A2 (Correct Answer)
B. 5-Hydroxytryptamine
C. Platelet activating factor
D. Prostacyclin

Explanation: ### Explanation **Correct Option: A. Thromboxane A2 (TXA2)** Aspirin (Acetylsalicylic acid) acts by **irreversibly inhibiting the enzyme Cyclooxygenase-1 (COX-1)** via acetylation of a serine residue. In platelets, COX-1 is responsible for converting arachidonic acid into **Thromboxane A2 (TXA2)**, a potent vasoconstrictor and platelet aggregator. * **Mechanism of Selectivity:** Platelets are anuclear and cannot synthesize new enzymes. Therefore, a low dose of aspirin (75–150 mg) permanently disables COX-1 for the entire lifespan of the platelet (8–11 days), leading to a prolonged bleeding time. **Incorrect Options:** * **B. 5-Hydroxytryptamine (Serotonin):** While released from platelet dense granules during activation to promote aggregation, its synthesis is not the primary target of aspirin. * **C. Platelet Activating Factor (PAF):** This is a phospholipid mediator of inflammation and aggregation; its pathway is independent of the COX-1 enzyme inhibited by aspirin. * **D. Prostacyclin (PGI2):** PGI2 is a vasodilator and anti-aggregatory mediator produced by **vascular endothelial cells**. Unlike platelets, endothelial cells have nuclei and can regenerate COX enzymes. Low-dose aspirin spares PGI2 production while inhibiting TXA2, maintaining a favorable antithrombotic balance. **High-Yield Clinical Pearls for NEET-PG:** * **Irreversibility:** Aspirin is the only NSAID that binds irreversibly to COX. * **Bleeding Time (BT) vs. Clotting Time (CT):** Aspirin increases BT (platelet function) but has no effect on CT (coagulation cascade). * **Primary Prevention:** Low-dose aspirin is used for prophylaxis in Ischemic Heart Disease (IHD) and Stroke. * **Aspirin Resistance:** Can occur in patients with high platelet turnover.

Question 122: Abciximab is:

A. An antibody against Ilb/Illa receptors (Correct Answer)
B. An antibody against Ib/IX receptors
C. A topoisomerase inhibitor
D. An adenosine inhibitor

Explanation: **Explanation:** **Abciximab** is a potent antiplatelet agent classified as a **Glycoprotein (GP) IIb/IIIa receptor antagonist**. It is a chimeric monoclonal antibody (Fab fragment) that binds irreversibly to the GP IIb/IIIa receptors on the surface of activated platelets. Since these receptors are the "final common pathway" for platelet aggregation—serving as the binding site for fibrinogen and von Willebrand factor to cross-link platelets—blocking them effectively prevents thrombus formation regardless of the initial stimulus (ADP, Thromboxane A2, or Collagen). **Analysis of Options:** * **Option A (Correct):** Abciximab is a monoclonal antibody specifically targeting the GP IIb/IIIa receptor. * **Option B (Incorrect):** GP Ib/IX is the receptor for von Willebrand factor involved in platelet *adhesion* to the subendothelium, not the target of Abciximab. * **Option C (Incorrect):** Topoisomerase inhibitors (e.g., Etoposide, Irinotecan) are cytotoxic chemotherapy agents used in cancer treatment, not antiplatelets. * **Option D (Incorrect):** Adenosine inhibitors are not a standard class for this context; however, Dipyridamole is an adenosine *reuptake* inhibitor used as an antiplatelet. **High-Yield Clinical Pearls for NEET-PG:** * **Route:** Administered only via **Intravenous (IV)** route. * **Clinical Use:** Primarily used in patients undergoing **Percutaneous Coronary Intervention (PCI)** to prevent ischemic complications. * **Other GP IIb/IIIa Inhibitors:** **Eptifibatide** (a cyclic peptide) and **Tirofiban** (a non-peptide small molecule). Unlike Abciximab, these are reversible inhibitors. * **Side Effects:** The most significant risk is **bleeding** and **thrombocytopenia**. * **Monitoring:** Platelet counts should be monitored closely after administration.

Question 123: Ferrous sulfate is a hydrated salt containing what percentage of Iron?

A. 20% (Correct Answer)
B. 25%
C. 30%
D. 35%

Explanation: **Explanation:** The correct answer is **20% (Option A)**. In pharmacology, it is crucial to distinguish between the total weight of an iron salt and its **elemental iron** content, as the latter determines the therapeutic efficacy and potential toxicity. **1. Why 20% is correct:** Ferrous sulfate is commonly administered as the hydrated salt ($FeSO_4 \cdot 7H_2O$) or the dried salt. The standard hydrated form contains approximately **20% elemental iron** by weight. For example, a standard 300 mg tablet of ferrous sulfate provides roughly 60 mg of elemental iron ($300 \times 0.20 = 60$). This is the "gold standard" for oral iron therapy due to its high bioavailability and low cost. **2. Why other options are incorrect:** * **Options B, C, and D:** These percentages do not correspond to Ferrous sulfate. However, they may be confused with other iron salts. For instance, **Ferrous fumarate** contains about **33%** elemental iron (closest to Option C/D), while **Ferrous gluconate** contains only **12%**. **High-Yield Clinical Pearls for NEET-PG:** * **Elemental Iron Content:** Remember the "Rule of Iron Salts": * Ferrous Gluconate: 12% * Ferrous Sulfate: 20% * Ferrous Fumarate: 33% (Highest among common oral salts). * **Absorption:** Oral iron is best absorbed in the **ferrous ($Fe^{2+}$)** state and in an **acidic medium**. Vitamin C (Ascorbic acid) enhances absorption, while antacids, tea, and tetracyclines inhibit it. * **Side Effects:** Epigastric pain, constipation, and black stools (must be differentiated from melena). * **Treatment Duration:** In Iron Deficiency Anemia, treatment should continue for **3–6 months** after hemoglobin normalizes to replenish depleted iron stores (ferritin).

Question 124: Which of the following drugs is not used for thromboprophylaxis?

A. Heparin
B. Warfarin
C. Antithrombin III (Correct Answer)
D. Aspirin

Explanation: **Explanation:** The core concept in this question is distinguishing between **antithrombotic agents** (used for prophylaxis) and **replacement therapies** (used for deficiency states). **Why Antithrombin III is the correct answer:** Antithrombin III (ATIII) is a natural endogenous anticoagulant that inactivates thrombin and Factor Xa. While it is used as a **replacement therapy** in patients with hereditary ATIII deficiency (especially during surgery or childbirth) to prevent clots, it is **not** used as a standard pharmacological agent for routine thromboprophylaxis in the general population. Its clinical use is highly specific and restricted to correcting a deficiency rather than actively inhibiting the coagulation cascade in a normal individual. **Analysis of Incorrect Options:** * **Heparin (Unfractionated & LMWH):** The gold standard for parenteral thromboprophylaxis. It acts by accelerating the activity of ATIII, primarily inhibiting Factor Xa and Thrombin. * **Warfarin:** The most common oral anticoagulant used for long-term thromboprophylaxis, especially in patients with atrial fibrillation or prosthetic heart valves. It inhibits Vitamin K Epoxide Reductase (VKOR). * **Aspirin:** An antiplatelet drug used for arterial thromboprophylaxis to prevent myocardial infarction and stroke by irreversibly inhibiting COX-1. **NEET-PG High-Yield Pearls:** * **Heparin Resistance:** If a patient does not respond to heparin (activated partial thromboplastin time - aPTT does not prolong), suspect **Antithrombin III deficiency**. * **LMWH vs. Heparin:** LMWH (e.g., Enoxaparin) is preferred for prophylaxis due to a longer half-life, more predictable response, and lower risk of Heparin-Induced Thrombocytopenia (HIT). * **Bridge Therapy:** Warfarin requires "bridging" with Heparin initially because it induces a transient prothrombotic state by depleting Protein C and S before affecting clotting factors.

Question 125: What is the mode of action of warfarin?

A. Factor Xa inhibitor
B. Vitamin K antagonist (Correct Answer)
C. Activates antithrombin III
D. Activates factor IX

Explanation: **Explanation:** **Mechanism of Action:** Warfarin is a **Vitamin K Antagonist (VKA)**. It acts by inhibiting the enzyme **Vitamin K Epoxide Reductase (VKORC1)**. This enzyme is responsible for converting inactive vitamin K epoxide back into its active form (hydroquinone). Active vitamin K is a necessary cofactor for the **gamma-carboxylation** of glutamate residues on certain clotting factors. Without this post-translational modification, **Factors II, VII, IX, and X**, as well as **Proteins C and S**, remain inactive (PIVKA—Proteins Induced by Vitamin K Absence). **Analysis of Incorrect Options:** * **Option A (Factor Xa inhibitor):** This describes the mechanism of Direct Oral Anticoagulants (DOACs) like **Rivaroxaban** and **Apixaban**, or indirect inhibitors like Fondaparinux. * **Option C (Activates antithrombin III):** This is the mechanism of **Heparin** and Low Molecular Weight Heparins (LMWH). They bind to antithrombin III, accelerating its inactivation of Thrombin (IIa) and Factor Xa. * **Option D (Activates factor IX):** This is incorrect; anticoagulants aim to inhibit, not activate, clotting factors. **NEET-PG High-Yield Pearls:** * **Monitoring:** Warfarin therapy is monitored using **PT/INR** (Prothrombin Time/International Normalized Ratio). * **Teratogenicity:** Warfarin is contraindicated in pregnancy (causes **Fetal Warfarin Syndrome**—chondrodysplasia punctata); LMWH is the drug of choice. * **Skin Necrosis:** Occurs due to the rapid depletion of Protein C (short half-life) causing a transient hypercoagulable state. This is why "Heparin bridging" is required. * **Antidote:** For immediate reversal, use **Fresh Frozen Plasma (FFP)** or Prothrombin Complex Concentrate (PCC). For non-emergency reversal, use **Vitamin K1 (Phytonadione)**.

Question 126: Arrange the following drugs in decreasing order of their antiplatelet potency: Clopidogrel, Prasugrel, Aspirin, Abciximab?

A. Prasugrel > Abciximab > Aspirin > Clopidogrel
B. Aspirin > Abciximab > Clopidogrel > Prasugrel
C. Abciximab > Prasugrel > Clopidogrel > Aspirin (Correct Answer)
D. Clopidogrel > Abciximab > Aspirin > Prasugrel

Explanation: The potency of antiplatelet drugs is determined by their mechanism of action and the specific step of platelet activation they inhibit. ### **Mechanism and Hierarchy of Potency** 1. **Abciximab (GP IIb/IIIa Inhibitor):** This is the **most potent** class. GP IIb/IIIa is the "final common pathway" for platelet aggregation. By blocking this receptor, Abciximab prevents the binding of fibrinogen regardless of which agonist (ADP, Thromboxane, or Collagen) initiated the activation. 2. **Prasugrel (3rd Gen P2Y12 Inhibitor):** A thienopyridine that irreversibly blocks ADP receptors. It is a pro-drug but is converted more efficiently and rapidly into its active metabolite than clopidogrel, leading to more predictable and higher levels of platelet inhibition. 3. **Clopidogrel (2nd Gen P2Y12 Inhibitor):** Also an irreversible ADP receptor blocker, but it requires a complex two-step hepatic metabolism (CYP2C19). This results in slower onset and lower potency compared to Prasugrel, with significant "resistance" seen in some patients. 4. **Aspirin (COX Inhibitor):** The **least potent** in this list. It irreversibly inhibits Cyclooxygenase-1, preventing the synthesis of Thromboxane A2. While effective, it only blocks one minor pathway of activation, leaving ADP and Thrombin pathways intact. ### **Analysis of Options** * **Option C is correct** because it follows the hierarchy: Final Common Pathway (Abciximab) > Potent ADP blocker (Prasugrel) > Standard ADP blocker (Clopidogrel) > TXA2 inhibitor (Aspirin). * **Options A, B, and D** are incorrect as they misplace the GP IIb/IIIa inhibitor or fail to recognize that Prasugrel is superior to Clopidogrel and Aspirin in terms of raw antiplatelet effect. ### **High-Yield Clinical Pearls for NEET-PG** * **Abciximab:** A chimeric monoclonal antibody; its effect lasts 24–48 hours despite a short plasma half-life. * **Prasugrel:** Contraindicated in patients with a history of **Stroke or TIA** due to increased bleeding risk. * **Clopidogrel:** Effectiveness is reduced by **Omeprazole** (inhibits CYP2C19). * **Aspirin:** Low doses (75–150 mg) are preferred for antiplatelet effects to avoid inhibiting PGI2 (prostacyclin) in endothelial cells.

Question 127: Ticlopidine is which of the following types of drugs?

A. Antiplatelet drug (Correct Answer)
B. Antiarrhythmic drug
C. Anticoagulant drug
D. Antifibrinolytic drug

Explanation: **Explanation:** **Ticlopidine** is a first-generation **P2Y12 receptor antagonist**, belonging to the thienopyridine class of **antiplatelet drugs**. Its primary mechanism involves the irreversible inhibition of the P2Y12 subtype of ADP receptors on the platelet surface. This prevents the activation of the GPIIb/IIIa receptor complex, thereby inhibiting platelet aggregation and thrombus formation. **Analysis of Options:** * **Option A (Correct):** Ticlopidine inhibits ADP-induced platelet aggregation, making it a classic antiplatelet agent used to prevent thromboembolic events like stroke or MI. * **Option B (Incorrect):** Antiarrhythmic drugs (e.g., Amiodarone, Lidocaine) act on ion channels (Na+, K+, Ca2+) of the myocardium to treat rhythm disorders; they do not affect platelet function. * **Option C (Incorrect):** Anticoagulants (e.g., Heparin, Warfarin) interfere with the coagulation cascade and fibrin formation. While both prevent clots, antiplatelets specifically target platelet activation. * **Option D (Incorrect):** Antifibrinolytics (e.g., Tranexamic acid) inhibit the breakdown of fibrin to promote clotting; Ticlopidine does the opposite by preventing clot initiation. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Irreversible P2Y12 inhibition (similar to Clopidogrel and Prasugrel). * **Adverse Effects:** Ticlopidine is notorious for causing **severe neutropenia/agranulocytosis** and **Thrombotic Thrombocytopenic Purpura (TTP)**. Due to these hematological toxicities, it has largely been replaced by Clopidogrel in clinical practice. * **Monitoring:** If used, frequent CBC monitoring is mandatory during the first 3 months of therapy. * **Prodrug Status:** Like Clopidogrel, Ticlopidine is a prodrug requiring hepatic activation.

Question 128: Low molecular weight heparin therapy is associated with all of the following except:

A. Less chances of bleeding
B. Single dose per day
C. Easy filterability by glomerular capillaries
D. High biological interaction to plasma proteins (Correct Answer)

Explanation: ### Explanation The correct answer is **D. High biological interaction to plasma proteins.** Low Molecular Weight Heparins (LMWHs), such as Enoxaparin and Dalteparin, are derived from Unfractionated Heparin (UFH) through depolymerization. This process significantly alters their pharmacokinetic profile. **1. Why Option D is the correct (incorrect statement):** Unlike UFH, LMWHs have **low affinity for plasma proteins**, vascular endothelial cells, and macrophages. This lack of protein binding results in a highly **predictable dose-response relationship**, eliminating the need for routine laboratory monitoring (like aPTT). UFH, conversely, binds extensively to plasma proteins, leading to variable bioavailability. **2. Analysis of Incorrect Options:** * **A. Less chances of bleeding:** LMWHs have a higher ratio of Anti-Xa to Anti-IIa activity. They do not inhibit thrombin as strongly as UFH and have less effect on platelet function and vascular permeability, leading to a lower risk of major bleeding and Heparin-Induced Thrombocytopenia (HIT). * **B. Single dose per day:** LMWHs have a longer half-life (3–6 hours) compared to UFH (1–2 hours) and better subcutaneous bioavailability. This allows for convenient once or twice-daily dosing. * **C. Easy filterability by glomerular capillaries:** Due to their smaller molecular size (~5000 Da), LMWHs are primarily excreted by the kidneys. This makes them "easily filterable" but also necessitates dose adjustment or avoidance in patients with renal failure (CrCl <30 ml/min). **Clinical Pearls for NEET-PG:** * **Monitoring:** While UFH is monitored by **aPTT**, LMWH monitoring (if required, e.g., in pregnancy or obesity) is done via **Factor Xa assay**. * **Antidote:** Protamine sulfate completely neutralizes UFH but only **partially** neutralizes LMWH. * **Drug of Choice:** LMWH is the preferred anticoagulant in **pregnancy** as it does not cross the placenta.

Question 129: What is the target International Normalized Ratio (INR) for a patient receiving warfarin therapy?

A. 1.5
B. 2.5 (Correct Answer)
C. 3.5
D. 4.5

Explanation: **Explanation:** Warfarin is an oral anticoagulant that acts as a Vitamin K epoxide reductase (VKOR) inhibitor, preventing the synthesis of clotting factors II, VII, IX, and X. The intensity of warfarin therapy is monitored using the **International Normalized Ratio (INR)**, which standardizes Prothrombin Time (PT) results across different laboratories. **1. Why Option B is Correct:** For most clinical indications—including the treatment and prevention of Deep Vein Thrombosis (DVT), Pulmonary Embolism (PE), and prevention of systemic embolism in patients with Atrial Fibrillation—the recommended **therapeutic target INR is 2.5** (with a typical range of **2.0 to 3.0**). This range provides an optimal balance between preventing thromboembolic events and minimizing the risk of spontaneous hemorrhage. **2. Why Other Options are Incorrect:** * **Option A (1.5):** This is sub-therapeutic. An INR below 2.0 significantly increases the risk of clot formation and stroke. * **Option C (3.5):** While a higher target (range 2.5–3.5) is used for high-risk patients, such as those with **mechanical prosthetic heart valves**, it is not the standard target for general warfarin therapy. * **Option D (4.5):** This is supra-therapeutic. An INR above 4.0 exponentially increases the risk of major bleeding, including intracranial hemorrhage. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Inhibits $\gamma$-carboxylation of glutamate residues on clotting factors. * **Antidote:** For immediate reversal, use **Fresh Frozen Plasma (FFP)** or Prothrombin Complex Concentrate (PCC). For non-emergency reversal, use **Vitamin K1 (Phytonadione)**. * **Teratogenicity:** Warfarin is contraindicated in pregnancy (causes Fetal Warfarin Syndrome); **Heparin** is the anticoagulant of choice for pregnant women. * **Skin Necrosis:** Occurs due to a rapid decline in Protein C levels; prevented by "bridging" with Heparin.

Question 130: All of the following are parenteral Direct Thrombin Inhibitors except?

A. Lepirudin
B. Bivalirudin
C. Argatroban
D. Dabigatran (Correct Answer)

Explanation: **Explanation:** Direct Thrombin Inhibitors (DTIs) are anticoagulants that bind directly to thrombin (Factor IIa), inhibiting its ability to convert fibrinogen into fibrin. They are classified based on their route of administration into parenteral and oral agents. **1. Why Dabigatran is the correct answer:** Dabigatran (specifically Dabigatran etexilate) is the only **oral** Direct Thrombin Inhibitor among the options. It is a prodrug and belongs to the class of Non-vitamin K antagonist Oral Anticoagulants (NOACs/DOACs). It is primarily used for stroke prevention in non-valvular atrial fibrillation and the treatment of DVT/PE. **2. Why the other options are incorrect:** * **Lepirudin & Bivalirudin:** These are recombinant derivatives of hirudin (found in leech saliva). They are **parenteral** (IV) bivalent DTIs, meaning they bind to both the active site and the exosite of thrombin. * **Argatroban:** This is a synthetic small molecule and a **parenteral** (IV) univalent DTI, binding only to the active site of thrombin. It is the preferred agent for patients with Heparin-Induced Thrombocytopenia (HIT) who also have hepatic impairment (though it is primarily metabolized by the liver, unlike Lepirudin which is renal). **High-Yield Clinical Pearls for NEET-PG:** * **Antidote:** The specific reversal agent for Dabigatran is **Idarucizumab** (a monoclonal antibody fragment). * **Monitoring:** Unlike Heparin (aPTT) or Warfarin (PT/INR), DTIs generally do not require routine monitoring. However, if needed, **Ecarin Clotting Time (ECT)** is the most sensitive test for DTIs. * **Drug of Choice:** Argatroban and Bivalirudin are the drugs of choice for managing **Heparin-Induced Thrombocytopenia (HIT)**.

Practice by Chapter

Hematopoietic Growth Factors

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Iron Preparations and Management of Iron Deficiency

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Vitamin B12 and Folic Acid

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Anticoagulants: Heparins and Direct Inhibitors

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Oral Anticoagulants

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Antiplatelet Drugs

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Thrombolytic Agents

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Hemostatic Drugs

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Plasma Expanders

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Blood Transfusion and Alternatives

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