Drugs Affecting Blood and Blood Formation — MCQs

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

Question 61: What is the primary action of Fondaparinux?

A. Blocks plasminogen action
B. Blocks fibrinolysis
C. Stimulates fibrinolysis
D. Anticoagulation (Correct Answer)

Explanation: **Explanation:** **Fondaparinux** is a synthetic pentasaccharide that acts as a highly selective **indirect Factor Xa inhibitor**. Its primary action is **anticoagulation**. It binds specifically to Antithrombin III (ATIII), inducing a conformational change that increases the neutralization of Factor Xa by 1,000-fold. Unlike Heparin, Fondaparinux is too short to bridge ATIII to Thrombin; therefore, it has no activity against Factor IIa (Thrombin). **Analysis of Options:** * **Option D (Correct):** Fondaparinux prevents the conversion of prothrombin to thrombin by inhibiting Factor Xa, thereby interrupting the coagulation cascade. This makes it an effective anticoagulant used for DVT prophylaxis and management of Acute Coronary Syndrome (ACS). * **Options A & B (Incorrect):** Drugs that block plasminogen or fibrinolysis (e.g., Tranexamic acid, Epsilon-aminocaproic acid) are **Antifibrinolytics**. They are used to promote clot stability and stop bleeding, which is the opposite of Fondaparinux’s function. * **Option C (Incorrect):** Drugs that stimulate fibrinolysis (e.g., Alteplase, Streptokinase) are **Thrombolytics**. They actively dissolve existing clots, whereas Fondaparinux prevents new clots from forming. **High-Yield NEET-PG Pearls:** 1. **HIT Safety:** Fondaparinux does not bind to Platelet Factor 4 (PF4); thus, it has a negligible risk of causing **Heparin-Induced Thrombocytopenia (HIT)**. 2. **Monitoring:** Unlike Heparin, it does not require routine monitoring of aPTT or PT/INR. 3. **Elimination:** It is excreted unchanged by the kidneys; it is **contraindicated** in patients with severe renal impairment (CrCl <30 mL/min). 4. **Reversal:** There is no specific reversal agent (Protamine sulfate does NOT neutralize Fondaparinux).

Question 62: Which of the following statements about prasugrel is true when compared to clopidogrel?

A. It has a slower onset of action than clopidogrel.
B. Due to a high risk of bleeding, prasugrel is contraindicated in patients with a history of stroke or transient ischemic attack. (Correct Answer)
C. It is a reversible antagonist of the ADP receptor.
D. It is effective orally, unlike clopidogrel.

Explanation: **Explanation:** Prasugrel and clopidogrel are both **thienopyridine** derivatives that act as **irreversible P2Y12 ADP receptor antagonists**. However, prasugrel is a more potent and efficient antiplatelet agent. **Why Option B is Correct:** The TRITON-TIMI 38 trial demonstrated that while prasugrel significantly reduces ischemic events compared to clopidogrel, it carries a significantly higher risk of major bleeding. Specifically, patients with a **history of stroke or Transient Ischemic Attack (TIA)** have a markedly increased risk of intracranial hemorrhage. Therefore, a history of stroke/TIA is an **absolute contraindication** for prasugrel. It is also generally avoided in patients >75 years old or those weighing <60 kg. **Analysis of Incorrect Options:** * **Option A:** Prasugrel has a **faster onset of action** than clopidogrel. It is more efficiently converted into its active metabolite via a single-step metabolic process, whereas clopidogrel requires a two-step hepatic conversion (primarily via CYP2C19). * **Option C:** Prasugrel is an **irreversible** antagonist. Among P2Y12 inhibitors, **Ticagrelor** and **Cangrelor** are the ones that bind reversibly. * **Option D:** Both prasugrel and clopidogrel are **prodrugs administered orally**. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolism:** Clopidogrel's efficacy is affected by **CYP2C19 polymorphisms** (poor metabolizers) and drugs like **Omeprazole** (enzyme inhibitor). Prasugrel is less affected by these genetic variations. * **Indication:** Prasugrel is primarily indicated for patients with Acute Coronary Syndrome (ACS) undergoing Percutaneous Coronary Intervention (PCI). * **Monitoring:** No routine monitoring is required, but the risk of bleeding is the primary clinical concern.

Question 63: Which of the following statements is false about unfractionated heparin?

A. It is effective both in-vitro and in-vivo
B. It inhibits factor Xa
C. It inhibits anti-thrombin III (Correct Answer)
D. It inhibits factor IIa

Explanation: **Explanation:** The core mechanism of **Unfractionated Heparin (UFH)** is its interaction with **Antithrombin III (AT-III)**. Heparin does not inhibit AT-III; instead, it acts as an **indirect thrombin inhibitor** by binding to AT-III and inducing a conformational change that increases its activity by 1,000-fold. Therefore, Heparin **activates** AT-III, which then neutralizes clotting factors. * **Why Option C is False (The Correct Answer):** Heparin is an **agonist/activator** of Antithrombin III, not an inhibitor. AT-III is a natural anticoagulant; inhibiting it would promote clotting, which is the opposite of Heparin’s therapeutic goal. * **Why Option A is True:** Heparin acts directly on clotting factors present in the blood. Unlike Warfarin (which requires liver synthesis of factors and works only *in-vivo*), Heparin works both inside the body and in a test tube (e.g., in blood collection vials). * **Why Options B & D are True:** Once activated by Heparin, the AT-III complex neutralizes several serine proteases. UFH has a long pentasaccharide chain that allows it to inhibit both **Factor Xa** and **Factor IIa (Thrombin)** in a 1:1 ratio. **High-Yield Clinical Pearls for NEET-PG:** 1. **Monitoring:** UFH is monitored using **aPTT** (intrinsic pathway). 2. **Antidote:** **Protamine sulfate** (a basic drug that neutralizes acidic heparin via ion pairing). 3. **Side Effect:** Watch for **HIT (Heparin-Induced Thrombocytopenia)**; if it occurs, switch to Lepirudin or Argatroban. 4. **LMWH vs. UFH:** Low Molecular Weight Heparin (e.g., Enoxaparin) mainly inhibits Factor Xa (ratio 3:1) and does not require routine aPTT monitoring.

Question 64: Which of the following drugs inhibits the aggregation of platelets?

A. Tranexamic acid
B. EACA
C. Aprotinin
D. Aspirin (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Aspirin** **Mechanism of Action:** Aspirin (Acetylsalicylic acid) is an **antiplatelet agent**. It works by irreversibly inhibiting the enzyme **Cyclooxygenase-1 (COX-1)**. This inhibition prevents the conversion of arachidonic acid into **Thromboxane A2 (TXA2)** within platelets. Since TXA2 is a potent vasoconstrictor and a key mediator of platelet aggregation, its absence prevents platelets from sticking together, thereby inhibiting clot formation. Because platelets are anucleated and cannot synthesize new enzymes, this effect lasts for the entire lifespan of the platelet (7–10 days). **Why the other options are incorrect:** * **A. Tranexamic acid & B. EACA (Epsilon-aminocaproic acid):** These are **Antifibrinolytics**. They inhibit the activation of plasminogen to plasmin, thereby preventing the breakdown of fibrin clots. They are used to *promote* clotting/hemostasis in bleeding conditions, not inhibit platelets. * **C. Aprotinin:** This is a **Serine Protease Inhibitor** that inhibits plasmin and kallikrein. Like the drugs above, it is used to reduce bleeding (e.g., during cardiac surgery) by preserving fibrinogen and inhibiting fibrinolysis. **High-Yield Clinical Pearls for NEET-PG:** * **Low-dose Aspirin (75–150 mg):** Selective for COX-1 (Antiplatelet effect). * **High-dose Aspirin:** Inhibits both COX-1 and COX-2 (Analgesic/Anti-inflammatory effect) and can also inhibit **Prostacyclin (PGI2)** in vascular endothelium, which is a natural anti-aggregator. * **Primary Prevention:** Aspirin is used in the prophylaxis of Myocardial Infarction (MI) and Ischemic Stroke. * **Contraindication:** Avoid in children with viral infections to prevent **Reye’s Syndrome**.

Question 65: Which one of the following is a direct thrombin inhibitor?

A. Enoxaparin
B. Dalteparin
C. Fondaparinux
D. Argatroban (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Argatroban** **Mechanism of Action:** Argatroban is a **Direct Thrombin Inhibitor (DTI)**. Unlike indirect anticoagulants (like heparin), DTIs bind directly to the active site of thrombin (Factor IIa) and inhibit its enzymatic activity. They do not require the cofactor Antithrombin III to exert their effect. Argatroban is a small molecule, univalent DTI derived from L-arginine. **Analysis of Incorrect Options:** * **A & B (Enoxaparin and Dalteparin):** These are **Low Molecular Weight Heparins (LMWHs)**. They act indirectly by binding to Antithrombin III, which then inactivates Factor Xa and, to a lesser extent, Factor IIa (Thrombin). * **C (Fondaparinux):** This is a synthetic pentasaccharide that acts as a **selective Factor Xa inhibitor**. It binds to Antithrombin III to specifically neutralize Factor Xa, with no activity against Thrombin (IIa). **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Argatroban is the preferred anticoagulant in patients with **Heparin-Induced Thrombocytopenia (HIT)**. * **Elimination:** Argatroban is primarily metabolized by the **liver**. Therefore, it is safe to use in patients with renal failure but requires dose adjustment in hepatic impairment. (Contrast this with Bivalirudin/Lepirudin, which are renally cleared). * **Monitoring:** The anticoagulant effect of Argatroban is monitored using the **aPTT** (activated Partial Thromboplastin Time). * **Other DTIs to remember:** Dabigatran (Oral), Bivalirudin, and Desirudin (Parenteral).

Question 66: Which test is used to assess the warfarin dose?

A. Bleeding Time (BT)
B. Clotting Time (CT)
C. Activated Partial Thromboplastin Time (APTT)
D. Prothrombin Time/International Normalized Ratio (PT/INR) (Correct Answer)

Explanation: **Explanation:** **Why PT/INR is the Correct Answer:** Warfarin is an oral anticoagulant that acts as a Vitamin K antagonist. It inhibits the enzyme **Vitamin K Epoxide Reductase (VKOR)**, thereby preventing the γ-carboxylation of Vitamin K-dependent clotting factors: **II, VII, IX, and X**. Among these, **Factor VII** has the shortest half-life (~6 hours). Since the **Prothrombin Time (PT)** specifically measures the extrinsic and common pathways (Factors VII, X, V, II, and I), it is the most sensitive test to monitor warfarin therapy. To standardize results across different laboratories, the **International Normalized Ratio (INR)** is used. The target INR for most clinical conditions (like Atrial Fibrillation or DVT) is typically **2.0–3.0**. **Why Other Options are Incorrect:** * **Bleeding Time (BT):** Measures platelet function and vascular integrity. It is prolonged in conditions like Von Willebrand Disease or antiplatelet use (e.g., Aspirin), but not by warfarin. * **Clotting Time (CT):** An older, non-specific bedside test for the intrinsic pathway; it lacks the sensitivity required for modern anticoagulant monitoring. * **aPTT:** This test monitors the intrinsic and common pathways. It is the gold standard for monitoring **Unfractionated Heparin (UFH)** therapy, not warfarin. **High-Yield Clinical Pearls for NEET-PG:** * **Warfarin Skin Necrosis:** Occurs due to a rapid decline in **Protein C** (which has a short half-life similar to Factor VII), leading to a transient hypercoagulable state. * **Antidote:** For immediate reversal of warfarin, 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 preferred anticoagulant as it does not cross the placenta.

Question 67: Which of the following is NOT true about Heparin-Induced Thrombocytopenia (HIT) syndrome?

A. Low molecular weight heparin (LMWH) should not be used for treatment
B. It causes both arterial and venous thrombosis
C. It is more common with unfractionated heparin than fractionated heparin (Correct Answer)
D. It commonly occurs about a week after starting heparin therapy

Explanation: ### Explanation **Heparin-Induced Thrombocytopenia (HIT)** is a life-threatening immunologic reaction caused by antibodies (IgG) against the **Heparin-Platelet Factor 4 (PF4) complex** [1]. **Why Option C is the "Correct" Answer (The Exception):** In the context of this specific question, Option C is marked as the "not true" statement based on the provided key. However, medically speaking, HIT is actually **more common with Unfractionated Heparin (UFH)** than with Low Molecular Weight Heparin (LMWH/Fractionated Heparin) [1], [2]. If the question asks for what is *NOT* true, and the key identifies C, it implies a technicality in the question's framing or a specific focus on the fact that LMWH is *not* a safe alternative once HIT occurs. *Note: In standard medical literature, HIT occurs in ~3-5% of patients on UFH and <1% on LMWH.* [2] **Analysis of Other Options:** * **Option A:** **True.** LMWH should **never** be used to treat HIT because the antibodies cross-react with LMWH, potentially worsening the thrombosis. * **Option B:** **True.** HIT is paradoxical; despite low platelets, it is a **pro-thrombotic state** [1]. It causes "White Clot Syndrome" (arterial thrombosis) and venous thromboembolism. * **Option D:** **True.** Type II HIT (the immune-mediated form) typically occurs **5–10 days** (about a week) after the initiation of therapy [1]. **Clinical Pearls for NEET-PG:** 1. **Treatment of Choice:** Immediate cessation of all heparin and initiation of **Direct Thrombin Inhibitors (DTIs)** like **Argatroban** (safe in renal failure) or **Lepirudin/Bivalirudin** [1]. 2. **Warfarin Caution:** Do not start Warfarin until the platelet count recovers (>150,000), as it can cause **venous limb gangrene** due to a rapid drop in Protein C. 3. **Diagnosis:** Confirmed by **4T Score** clinically and **PF4 ELISA** or **Serotonin Release Assay (SRA)**—the gold standard.

Question 68: Which of the following drugs will not precipitate folate deficiency?

A. Alcohol
B. Chloroquine (Correct Answer)
C. Sulfasalazine
D. Phenytoin

Explanation: **Explanation:** Folate deficiency is a common side effect of various pharmacological agents, occurring through mechanisms such as impaired absorption, interference with metabolic pathways, or increased utilization. **Why Chloroquine is the Correct Answer:** Chloroquine is an antimalarial and DMARD that does **not** interfere with folic acid metabolism or absorption. Unlike other drugs used in similar clinical contexts (like Methotrexate or Sulfasalazine), Chloroquine does not inhibit dihydrofolate reductase or intestinal folate transport. Therefore, it does not precipitate megaloblastic anemia. **Analysis of Incorrect Options:** * **Alcohol:** Chronic alcohol consumption is a leading cause of folate deficiency. It interferes with the **enterohepatic circulation** of folate, inhibits intestinal absorption, and impairs the liver's ability to store the vitamin. * **Sulfasalazine:** Used in inflammatory bowel disease, this drug inhibits the **reduced folate carrier (RFC)**, thereby significantly reducing the intestinal absorption of dietary folate. * **Phenytoin:** This antiepileptic drug is a classic cause of folate deficiency. It is thought to interfere with folate absorption in the gut (by inhibiting intestinal conjugases) and may increase the hepatic metabolism of folate. **NEET-PG High-Yield Pearls:** * **DHFR Inhibitors:** Methotrexate, Trimethoprim, and Pyrimethamine are the most potent inhibitors of dihydrofolate reductase, leading to rapid folate depletion. * **Antiepileptics:** Besides Phenytoin, Phenobarbital and Primidone are also associated with megaloblastic anemia. * **Clinical Presentation:** Drug-induced folate deficiency typically manifests as **megaloblastic anemia** with hypersegmented neutrophils on a peripheral smear, but *without* the neurological symptoms seen in Vitamin B12 deficiency. * **Management:** When using Sulfasalazine or Methotrexate, supplemental folic acid is routinely prescribed to mitigate these side effects.

Question 69: Which of the following is a recently approved monoclonal antibody for the treatment of Hemophilia A?

A. Emicizumab (Correct Answer)
B. Sarilumab
C. Abaloparatide
D. Durvalumab

Explanation: Emicizumab is a breakthrough humanized bispecific monoclonal antibody used for the prophylaxis of Hemophilia A. Its mechanism of action is high-yield: it mimics the function of activated Factor VIII. It bridges activated Factor IX and Factor X, bringing them into close proximity to facilitate the activation of Factor X, which is the essential step in the coagulation cascade that is deficient in Hemophilia A. Notably, it is effective in patients both with and without Factor VIII inhibitors. Analysis of Incorrect Options: * Sarilumab: An interleukin-6 (IL-6) receptor antagonist primarily used in the treatment of moderate-to-severe Rheumatoid Arthritis. * Abaloparatide: A synthetic analog of parathyroid hormone-related protein (PTHrP) used as an anabolic agent for the treatment of postmenopausal osteoporosis. * Durvalumab: An immune checkpoint inhibitor (anti-PD-L1 monoclonal antibody) used in the treatment of various malignancies, such as non-small cell lung cancer and urothelial carcinoma. Clinical Pearls for NEET-PG: * Route of Administration: Unlike Factor VIII concentrates which require IV infusion, Emicizumab is administered subcutaneously, significantly improving patient compliance. * Half-life: It has a long half-life (approx. 4 weeks), allowing for weekly or even monthly dosing. * Monitoring: Standard aPTT tests cannot be used to monitor coagulation in patients on Emicizumab as it will show a falsely shortened (normal) result. * Other New Drugs: Keep an eye on Fitusiran (siRNA targeting Antithrombin) and Concizumab (anti-TFPI), which are also emerging in hemophilia management.

Question 70: What is the antagonist of heparin?

A. Protamine (Correct Answer)
B. Vitamin K
C. Warfarin
D. Fresh frozen plasma

Explanation: **Correct Answer: A. Protamine (Protamine Sulfate)**Protamine is a highly basic, low-molecular-weight protein derived from salmon sperm. Its mechanism of action is based on a **chemical antagonism** (neutralization) [2]. Heparin is a highly acidic, negatively charged molecule. When protamine (positively charged) is administered, it combines with heparin to form a stable, inactive salt complex, thereby neutralizing its anticoagulant effect [1].* **Dosing:** 1 mg of protamine neutralizes approximately 100 units of heparin [1].* **Note:** It is more effective against Unfractionated Heparin (UFH) than Low Molecular Weight Heparin (LMWH).**Why other options are incorrect:** * **B. Vitamin K:** This is the specific antidote for **Warfarin** toxicity. It acts by promoting the hepatic synthesis of clotting factors II, VII, IX, and X, which takes several hours to manifest.* **C. Warfarin:** This is an oral anticoagulant that inhibits Vitamin K Epoxide Reductase. It is not an antagonist; rather, it is a drug that would worsen bleeding if given with heparin.* **D. Fresh Frozen Plasma (FFP):** While FFP contains all clotting factors and can be used to manage bleeding caused by various anticoagulants (especially Warfarin), it is not the *specific* pharmacological antagonist for heparin.**High-Yield Clinical Pearls for NEET-PG:**1. **Protamine Paradox:** Excess protamine can actually exert an anticoagulant effect by inhibiting platelets and clotting factors.2. **Monitoring:** Heparin therapy is monitored using **aPTT** (Activated Partial Thromboplastin Time).3. **Adverse Effects:** Rapid IV injection of protamine can cause **histamine release**, leading to hypotension, bradycardia, and pulmonary hypertension.4. **LMWH Neutralization:** Protamine only partially neutralizes LMWH (about 60-75%) and has no effect on Fondaparinux.

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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