Drugs Affecting Blood and Blood Formation — MCQs

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

Question 191: A 54-year-old bed-bound woman in a nursing home developed swelling of her left leg. Doppler ultrasound confirmed deep vein thrombosis. Which chemical should be administered to prevent the clot from enlarging?

A. Digitalis
B. Ouabain
C. Heparin (Correct Answer)
D. Heparan sulfate

Explanation: **Explanation:** The clinical presentation of a bed-bound patient with unilateral leg swelling and a positive Doppler ultrasound is diagnostic of **Deep Vein Thrombosis (DVT)**. The primary goal in managing acute DVT is to prevent the extension of the thrombus and the occurrence of pulmonary embolism. **Why Heparin is correct:** Heparin is a rapid-acting parenteral anticoagulant. It works by binding to **Antithrombin III (AT-III)**, inducing a conformational change that accelerates the inactivation of thrombin (Factor IIa) and Factor Xa. By inhibiting these key proteases in the coagulation cascade, heparin prevents the conversion of fibrinogen to fibrin, thereby stopping the clot from enlarging. It is the drug of choice for the immediate anticoagulation of DVT. **Why the other options are incorrect:** * **Digitalis & Ouabain:** These are cardiac glycosides used to treat heart failure and certain arrhythmias (like atrial fibrillation). They inhibit the Na+/K+-ATPase pump and have no effect on the coagulation cascade. * **Heparan sulfate:** While structurally related to heparin, heparan sulfate is a glycosaminoglycan found naturally on the surface of endothelial cells and in the extracellular matrix. It has much weaker anticoagulant activity compared to pharmacological heparin and is not used as a therapeutic agent for DVT. **High-Yield NEET-PG Pearls:** * **Antidote:** The specific antagonist for heparin overdose is **Protamine sulfate** (1 mg neutralizes ~100 units of heparin). * **Monitoring:** Unfractionated Heparin (UFH) is monitored using **aPTT** (activated Partial Thromboplastin Time). * **Side Effect:** Watch for **Heparin-Induced Thrombocytopenia (HIT)**, caused by antibodies against the Heparin-Platelet Factor 4 complex. * **LMWH:** Low Molecular Weight Heparins (e.g., Enoxaparin) primarily inhibit Factor Xa and do not require routine lab monitoring.

Question 192: Quinine-induced thrombocytopenia is a type of?

A. Antibody-mediated reaction (Correct Answer)
B. Dose-related toxicity
C. Idiosyncratic reaction
D. Inhibition of platelet production

Explanation: **Explanation:** **Correct Answer: A. Antibody-mediated reaction** Quinine-induced thrombocytopenia (QITP) is a classic example of **drug-induced immune thrombocytopenia (DITP)**. The underlying mechanism is a **Type II Hypersensitivity reaction**. Quinine acts as a hapten or alters platelet surface glycoproteins (specifically GPIb/IX or GPIIb/IIIa), making them antigenic. This triggers the production of drug-dependent antibodies (usually IgG) that bind to platelets only in the presence of the drug. These antibody-coated platelets are then rapidly cleared by the splenic macrophages, leading to a profound drop in platelet count. **Why other options are incorrect:** * **B. Dose-related toxicity:** QITP is not related to the plasma concentration of the drug. Even minute amounts (e.g., quinine in tonic water) can trigger a severe reaction in sensitized individuals. * **C. Idiosyncratic reaction:** While the reaction occurs in a small subset of patients, "Idiosyncratic" is a broad term for unpredictable reactions. "Antibody-mediated" is the specific, more accurate immunologic mechanism required for NEET-PG. * **D. Inhibition of platelet production:** This refers to bone marrow suppression (e.g., by chemotherapy or thiazides). Quinine causes peripheral destruction of mature platelets, not a failure of megakaryocytes in the marrow. **NEET-PG High-Yield Pearls:** * **Common Culprits of DITP:** Quinine, Quinidine, Sulfonamides, Heparin (HIT), and Vancomycin. * **Clinical Presentation:** Sudden onset of petechiae, mucosal bleeding, or "wet purpura" within hours of drug ingestion. * **Diagnosis:** Platelet count often drops severely (<20,000/µL). * **Management:** Immediate discontinuation of the drug is the most critical step. Recovery usually occurs within 7–10 days as the drug is cleared from the system.

Question 193: All are antiplatelet drugs except?

A. Aspirin
B. Clopidogrel
C. Dipyridamole
D. Warfarin (Correct Answer)

Explanation: ### Explanation The fundamental distinction in this question lies between **antiplatelet drugs** and **anticoagulants**. While both are "blood thinners," they target different stages of the hemostatic process. **Why Warfarin is the correct answer:** Warfarin is an **oral anticoagulant**, not an antiplatelet drug. Its mechanism involves the inhibition of **Vitamin K Epoxide Reductase (VKOR)**, which prevents the γ-carboxylation of Vitamin K-dependent clotting factors (**II, VII, IX, and X**) and proteins C and S. It acts on the coagulation cascade to prevent fibrin formation, making it effective for venous thromboembolism and atrial fibrillation, rather than primary arterial platelet aggregation. **Why the other options are incorrect:** * **Aspirin:** An irreversible inhibitor of **COX-1**, preventing the synthesis of **Thromboxane A2 (TXA2)**, a potent platelet aggregator. * **Clopidogrel:** A P2Y12 receptor antagonist (ADP receptor blocker). It is a prodrug activated by CYP2C19 that prevents ADP-induced platelet aggregation. * **Dipyridamole:** A phosphodiesterase (PDE) inhibitor that increases intra-platelet cAMP levels, thereby inhibiting aggregation. It also inhibits adenosine uptake. **High-Yield Clinical Pearls for NEET-PG:** * **Monitoring:** Warfarin is monitored using **PT/INR**, whereas Heparin is monitored via **aPTT**. * **Teratogenicity:** Warfarin is contraindicated in pregnancy (causes **Fetal Warfarin Syndrome**); Heparin is the drug of choice as it does not cross the placenta. * **GP IIb/IIIa Inhibitors:** Remember Abciximab, Eptifibatide, and Tirofiban as the "most potent" antiplatelet drugs (the final common pathway). * **Aspirin Resistance:** Can occur in patients with high platelet turnover or genetic polymorphisms.

Question 194: All of the following statements about ticlopidine are true, EXCEPT:

A. It has a delayed onset of action.
B. It has a long duration of action.
C. It directly interacts with platelet membrane GpIIb/IIIa receptors. (Correct Answer)
D. It is used as an alternative to aspirin in patients with cerebrovascular disease.

Explanation: **Explanation:** Ticlopidine belongs to the **Thienopyridine** class of antiplatelet drugs. Its mechanism of action involves the **irreversible inhibition of P2Y12 (ADP) receptors** on the platelet surface. This inhibition prevents the activation of the GpIIb/IIIa receptor complex indirectly. It does **not** interact directly with GpIIb/IIIa receptors; drugs that do so include Abciximab, Eptifibatide, and Tirofiban. **Analysis of Options:** * **Option C (Correct):** As stated, Ticlopidine inhibits the ADP pathway. It is an indirect inhibitor of GpIIb/IIIa activation, making this statement false and the correct answer. * **Option A:** Ticlopidine is a prodrug that requires hepatic conversion to an active metabolite. Consequently, it has a **delayed onset of action** (maximal effect takes 3–5 days), unlike newer agents like Ticagrelor. * **Option B:** Because it binds **irreversibly** to the P2Y12 receptor, its effects persist for the entire lifespan of the platelet (7–10 days), resulting in a **long duration of action**. * **Option D:** It is clinically indicated for the secondary prevention of stroke and TIAs in patients who are intolerant to aspirin or where aspirin therapy has failed. **High-Yield Clinical Pearls for NEET-PG:** * **Adverse Effects:** Ticlopidine is rarely used today due to severe hematological toxicities, specifically **Neutropenia/Agranulocytosis** (requires CBC monitoring) and **Thrombotic Thrombocytopenic Purpura (TTP)**. * **Successors:** Clopidogrel and Prasugrel are preferred thienopyridines due to better safety profiles. * **Mechanism Summary:** Thienopyridines = P2Y12 (ADP) blockers; Abciximab = GpIIb/IIIa blockers; Aspirin = COX-1 inhibitor.

Question 195: A patient on aspirin will have an increase in which of the following parameters?

A. Bleeding time (Correct Answer)
B. Clotting time
C. Prothrombin time
D. Activated partial thromboplastin time

Explanation: **Mechanism of Action** Aspirin (Acetylsalicylic acid) is an irreversible inhibitor of the enzyme **Cyclooxygenase-1 (COX-1)**. By acetylating the serine residue of COX-1, it prevents the synthesis of **Thromboxane A2 (TXA2)** in platelets. Since TXA2 is a potent platelet aggregator and vasoconstrictor, its inhibition leads to impaired platelet aggregation. **Why Bleeding Time (BT) increases:** Bleeding time is a clinical measure of **platelet function** and vascular integrity. Because aspirin causes an irreversible defect in platelet aggregation that lasts for the lifetime of the platelet (approx. 7–10 days), the formation of the "primary platelet plug" is delayed, leading to an **increase in Bleeding Time**. **Why other options are incorrect:** * **Clotting Time (CT):** Measures the intrinsic pathway and the overall ability of blood to clot. It is primarily affected by coagulation factor deficiencies, not platelet function. * **Prothrombin Time (PT):** Assesses the **Extrinsic** and common pathways. It is used to monitor Warfarin therapy, not aspirin. * **Activated Partial Thromboplastin Time (aPTT):** Assesses the **Intrinsic** and common pathways. It is used to monitor Unfractionated Heparin therapy. **NEET-PG High-Yield Pearls:** * **Low-dose aspirin (75–150 mg)** is selective for COX-1 (anti-platelet), while higher doses inhibit both COX-1 and COX-2 (anti-inflammatory). * Aspirin is the only NSAID that inhibits COX **irreversibly**. * **Surgery protocol:** Aspirin should ideally be stopped **7 days** prior to elective surgery to allow for the generation of new, functional platelets. * **Triad of Aspirin Intolerance:** Asthma, Nasal polyps, and Aspirin sensitivity (Samter’s Triad).

Question 196: Pegylated Filgrastim is used for the treatment of:

A. Anaemia
B. Neutropenia (Correct Answer)
C. Thrombocytopenia
D. Pancytopenia

Explanation: **Filgrastim** is a recombinant **Granulocyte Colony-Stimulating Factor (G-CSF)** [1]. It acts by binding to specific receptors on myeloid progenitor cells in the bone marrow, stimulating the proliferation, differentiation, and activation of **neutrophils** [1]. **Pegylated Filgrastim (Pegfilgrastim)** is the long-acting version of Filgrastim, created by attaching a polyethylene glycol (PEG) molecule [2]. This modification decreases renal clearance and increases the half-life, allowing for once-per-chemotherapy-cycle dosing instead of daily injections [2]. It is primarily used to reduce the duration and incidence of febrile **neutropenia** in patients receiving myelosuppressive anticancer drugs [3]. **Why other options are incorrect:** * **Anaemia:** This is a deficiency of red blood cells (RBCs). It is treated with Erythropoiesis-Stimulating Agents (ESAs) like **Erythropoietin** or Darbepoetin. * **Thrombocytopenia:** This is a low platelet count. It is managed with Thrombopoietin (TPO) receptor agonists like **Romiplostim** or **Eltrombopag**, or IL-11 (Oprelvekin) [2]. * **Pancytopenia:** This refers to a deficiency of all three blood cell lines (RBCs, WBCs, and platelets). While Filgrastim may help the neutrophil component, it does not treat the underlying cause or the other cell deficiencies. **High-Yield NEET-PG Pearls:** * **Side Effect:** The most common side effect of Filgrastim/Pegfilgrastim is **medullary bone pain** (due to marrow expansion). * **Sargramostim:** This is a recombinant **GM-CSF** (Granulocyte-Macrophage CSF) which stimulates both neutrophils and macrophages [3]. * **Timing:** G-CSFs should not be administered within 24 hours before or after chemotherapy to avoid "killing" the rapidly dividing stimulated cells.

Question 197: Which of the following drugs inhibits plasminogen activation?

A. Aspirin
B. Tranexamic acid (Correct Answer)
C. Alteplase
D. Streptokinase

Explanation: **Explanation:** The question tests your understanding of the fibrinolytic system and its inhibitors. To prevent clot dissolution (fibrinolysis), a drug must inhibit the conversion of plasminogen to plasmin. **Correct Option: B. Tranexamic acid** Tranexamic acid is an **antifibrinolytic agent**. It works by competitively inhibiting the activation of plasminogen to plasmin. It binds to the lysine-binding sites on plasminogen molecules, preventing them from binding to fibrin. This stabilizes the clot and reduces bleeding. It is commonly used in menorrhagia, trauma, and post-extraction bleeding in hemophiliacs. **Incorrect Options:** * **A. Aspirin:** This is an antiplatelet drug. It irreversibly inhibits the **COX-1 enzyme**, reducing the synthesis of Thromboxane A2 (TXA2), thereby inhibiting platelet aggregation. It has no direct effect on plasminogen. * **C. Alteplase:** This is a recombinant **Tissue Plasminogen Activator (tPA)**. Instead of inhibiting activation, it directly *promotes* the conversion of plasminogen to plasmin. It is used as a "clot buster" in ischemic stroke and MI. * **D. Streptokinase:** This is a fibrinolytic agent derived from beta-hemolytic streptococci. It forms a complex with plasminogen to **activate** it into plasmin. Like Alteplase, it promotes fibrinolysis rather than inhibiting it. **High-Yield NEET-PG Pearls:** * **Epsilon-aminocaproic acid (EACA)** works via a similar mechanism to Tranexamic acid but is less potent. * **Aprotinin** is another antifibrinolytic that directly inhibits the enzyme plasmin (rather than just activation). * **Antidote for Fibrinolytics:** If a patient bleeds due to Streptokinase or Alteplase overdose, **Tranexamic acid** is the specific pharmacological antagonist.

Question 198: Rivaroxaban is an anticoagulant belonging to which category?

A. Factor Xa inhibitor (Correct Answer)
B. Direct thrombin inhibitor
C. Vitamin K antagonist
D. Low molecular weight heparin

Explanation: **Explanation:** **Rivaroxaban** belongs to a class of drugs known as **Direct Oral Anticoagulants (DOACs)**. Its mechanism of action involves the direct, competitive, and highly selective inhibition of **Factor Xa**. Factor Xa is a critical component of the "common pathway" in the coagulation cascade; it converts prothrombin (Factor II) to thrombin (Factor IIa). By inhibiting Factor Xa, Rivaroxaban prevents thrombin generation and subsequent fibrin clot formation. **Analysis of Incorrect Options:** * **B. Direct Thrombin Inhibitors (DTIs):** These drugs (e.g., **Dabigatran**, Argatroban, Bivalirudin) inhibit Factor IIa directly. Unlike Rivaroxaban, they act one step further down the cascade. * **C. Vitamin K Antagonists:** This category refers to **Warfarin**. It acts by inhibiting the enzyme Vitamin K Epoxide Reductase (VKOR), preventing the γ-carboxylation of Factors II, VII, IX, and X. * **D. Low Molecular Weight Heparin (LMWH):** Drugs like **Enoxaparin** act primarily by accelerating the activity of Antithrombin III, which then inactivates Factor Xa (and to a lesser extent, Factor IIa). They are administered parenterally, not orally. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** Drugs with **"xa"** in their name (Riva**roxa**ban, Api**xa**ban, Edo**xa**ban) are Factor **Xa** inhibitors. * **Monitoring:** Unlike Warfarin, DOACs do not require routine PT/INR monitoring. * **Reversal Agent:** The specific antidote for Rivaroxaban and Apixaban is **Andexanet alfa**. * **Clinical Use:** Preferred for stroke prevention in non-valvular atrial fibrillation and treatment of DVT/PE.

Question 199: Regarding streptokinase, which of the following statements is false?

A. It is a protein produced by streptococci.
B. Its complex with plasminogen is inhibited by alpha2-antiplasmin. (Correct Answer)
C. It may rarely produce anaphylaxis.
D. It is initially given as a loading dose.

Explanation: **Explanation:** **Why Option B is False (The Correct Answer):** Streptokinase is a non-enzymatic protein that forms a 1:1 stoichiometric complex with plasminogen. This **Streptokinase-Plasminogen complex** is an active enzyme that converts free plasminogen into plasmin. Crucially, this complex is **resistant to inhibition by $\alpha_2$-antiplasmin**, allowing it to circulate and activate plasminogen throughout the plasma. This lack of inhibition is precisely why streptokinase causes a "systemic lytic state," leading to the depletion of fibrinogen and increasing the risk of bleeding. **Analysis of Other Options:** * **Option A:** Streptokinase is indeed a protein (exotoxin) produced by **Group C $\beta$-hemolytic streptococci** [2]. It is not an enzyme itself but a co-factor. * **Option C:** Because it is a foreign bacterial protein, it is antigenic. It can cause hypersensitivity reactions ranging from rashes and fever to **rare but life-threatening anaphylaxis**. * **Option D:** Most patients have pre-existing antibodies due to prior streptococcal infections. Therefore, a **loading dose** is required to neutralize these antibodies before a therapeutic effect can be achieved. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** It is a **non-fibrin specific** thrombolytic (unlike Alteplase/Reteplase) [2]. * **Half-life:** Approximately 20–30 minutes. * **Contraindication:** It should not be repeated within 6–12 months of the first dose due to high titers of neutralizing antibodies (risk of failure and allergy). * **Antidote:** Epsilon-aminocaproic acid (EACA) or Tranexamic acid can be used to manage overdose/bleeding [1].

Question 200: Warm antibody hemolytic anemia is seen in patients taking which of the following medications?

A. Methyldopa (Correct Answer)
B. Penicillin
C. Quinine
D. Stibophen

Explanation: **Explanation:** Drug-induced immune hemolytic anemia (DIIHA) occurs via different mechanisms. **Methyldopa** is the classic example of the **Autoimmune (True Autoantibody) Mechanism**. **1. Why Methyldopa is correct:** Methyldopa interferes with T-suppressor cell function, leading to the production of true autoantibodies (usually IgG) directed against the patient’s own Rh antigens on the RBC surface. This is termed **"Warm" antibody hemolytic anemia** because IgG binds optimally at 37°C. A key feature is that the Direct Antiglobulin Test (Coombs test) remains positive even in the absence of the drug, as the antibodies are directed against the RBC itself, not the drug. **2. Why other options are incorrect:** * **Penicillin (Hapten/Drug-Adsorption Mechanism):** Penicillin binds to the RBC membrane. Antibodies (IgG) are then formed against the penicillin-RBC complex. Hemolysis only occurs with high-dose intravenous penicillin. * **Quinine & Stibophen (Immune Complex/Bystander Mechanism):** These drugs form a complex with IgM antibodies in the plasma. This "drug-antibody" complex then sits loosely on the RBC, activates the complement system, and causes rapid intravascular hemolysis. This is often called the "innocent bystander" mechanism. **High-Yield Clinical Pearls for NEET-PG:** * **Methyldopa:** 15% of patients develop a positive Coombs test, but <1% develop actual hemolysis. * **Warm vs. Cold:** Warm antibodies are **IgG** (extravascular hemolysis in the spleen); Cold antibodies are **IgM** (intravascular hemolysis, seen in Mycoplasma or Mononucleosis). * **Other drugs causing Warm AIHA:** L-Dopa, Procainamide, and Cephalosporins (can act via multiple mechanisms).

Practice by Chapter

Hematopoietic Growth Factors

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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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