Drugs Affecting Blood and Blood Formation — MCQs

A 40-year-old male presented to the ER with bleeding diathesis and was diagnosed with Glanzmann thrombasthenia. This disorder is believed to be due to the absence of a particular platelet receptor protein. Which of the following drugs acts as an anti-platelet agent by inhibiting the same platelet receptor protein?

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

Question 181: Which mucopolysaccharide possesses anticoagulant action?

A. Heparin (Correct Answer)
B. Phenindione
C. Rivoroxaban
D. Dabigatran

Explanation: ### Explanation **Correct Answer: A. Heparin** **Mechanism and Rationale:** Heparin is a naturally occurring **sulfated glycosaminoglycan (mucopolysaccharide)** found in the secretory granules of mast cells. It acts as an indirect anticoagulant by binding to **Antithrombin III (AT-III)**. This binding induces a conformational change in AT-III, accelerating its ability to inactivate clotting factors, primarily **Thrombin (IIa) and Factor Xa**. Because of its highly acidic and large molecular structure, it must be administered parenterally. **Analysis of Incorrect Options:** * **B. Phenindione:** This is an **indanedione derivative** (oral anticoagulant). While it acts similarly to Warfarin by inhibiting Vitamin K epoxide reductase, it is rarely used today due to high toxicity (e.g., agranulocytosis). * **C. Rivaroxaban:** This is a **Direct Factor Xa inhibitor** (DOAC). Chemically, it is a small molecule oxazolidinone derivative, not a mucopolysaccharide. * **D. Dabigatran:** This is a **Direct Thrombin Inhibitor (DTI)**. It is a peptidomimetic prodrug administered orally, lacking the complex carbohydrate structure of heparin. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote:** Heparin overdose is neutralized by **Protamine Sulfate** (a basic protein derived from fish sperm) via a chemical neutralization reaction. * **Monitoring:** The efficacy of Unfractionated Heparin (UFH) is monitored using **aPTT** (activated Partial Thromboplastin Time). * **LMWH vs. UFH:** Low Molecular Weight Heparins (e.g., Enoxaparin) mainly inhibit Factor Xa and do not require routine aPTT monitoring. * **Side Effect:** Watch for **HIT (Heparin-Induced Thrombocytopenia)**, caused by IgG antibodies against the Heparin-Platelet Factor 4 complex.

Question 182: Dicumarol interferes with which of the following?

A. Vitamin K (Correct Answer)
B. Antithrombin
C. Platelets
D. Plasminogen

Explanation: **Explanation:** **Dicumarol** is a naturally occurring oral anticoagulant and a derivative of coumarin. Its mechanism of action is identical to that of Warfarin. **1. Why Vitamin K is correct:** Dicumarol acts as a **competitive inhibitor of Vitamin K epoxide reductase (VKORC1)**. This enzyme is responsible for regenerating the active (reduced) form of Vitamin K from its inactive epoxide form. Active Vitamin K is a mandatory cofactor for the enzyme **gamma-glutamyl carboxylase**, which performs the post-translational modification (gamma-carboxylation) of glutamic acid residues on **Factors II, VII, IX, and X**, as well as Protein C and S. By interfering with Vitamin K recycling, Dicumarol leads to the production of biologically inactive clotting factors. **2. Why other options are incorrect:** * **Antithrombin:** This is the target for **Heparin**. Heparin binds to Antithrombin III, accelerating its ability to inactivate Thrombin (IIa) and Factor Xa. * **Platelets:** Drugs like Aspirin (COX inhibitor) or Clopidogrel (P2Y12 inhibitor) interfere with platelet function. Dicumarol affects the coagulation cascade, not primary hemostasis. * **Plasminogen:** This is the target for **Thrombolytics** (e.g., Streptokinase, Alteplase), which convert plasminogen to plasmin to dissolve existing clots. **High-Yield Clinical Pearls for NEET-PG:** * **Historical Significance:** Dicumarol was discovered as the cause of "Sweet Clover Disease" (hemorrhagic tendency) in cattle. * **Monitoring:** Like Warfarin, the effect of Dicumarol is monitored using **PT/INR**. * **Antidote:** For immediate reversal, use **Fresh Frozen Plasma (FFP)** or Prothrombin Complex Concentrate (PCC). For non-emergent reversal, use **Vitamin K1 (Phytonadione)**. * **Teratogenicity:** Coumarin derivatives are teratogenic (Fetal Warfarin Syndrome) and are contraindicated in pregnancy.

Question 183: Which of the following iron therapies is associated with the highest risk of anaphylaxis?

A. Ferric carboxymaltose
B. Iron dextran (Correct Answer)
C. Ferrous sulfate
D. Ferrous fumarate

Explanation: The correct answer is **Iron dextran**. Among parenteral iron preparations, **Iron dextran** (specifically the high-molecular-weight formulation) carries the highest risk of severe Type I hypersensitivity reactions and anaphylaxis [2]. This is primarily due to the formation of antibodies against the **dextran polymer** component. Because of this risk, a **test dose** (usually 25 mg) is mandatory before administering the full therapeutic dose [2]. Patients must be monitored closely for at least an hour for signs of bronchospasm, hypotension, or urticaria [2]. **2. Why the other options are incorrect:** * **Ferric carboxymaltose (Option A):** This is a newer parenteral iron preparation designed with a non-dextran carbohydrate shell. It has a significantly lower risk of anaphylaxis compared to iron dextran and does not require a test dose [1]. It is preferred for rapid, high-dose replacement. * **Ferrous sulfate (Option C) and Ferrous fumarate (Option D):** These are **oral** iron salts. Anaphylaxis is a systemic reaction associated with intravenous administration; oral iron preparations typically cause gastrointestinal side effects rather than life-threatening allergic reactions [3]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Test Dose Requirement:** Iron dextran is the only iron preparation that strictly requires a test dose [2]. * **Iron Sucrose:** Another common IV option; it has a lower risk of allergy than dextran but can cause "free iron" toxicity if infused too rapidly. * **Management of Toxicity:** Acute iron poisoning is treated with **Deferoxamine** (IV/IM), while chronic iron overload (hemosiderosis) is managed with **Deferiprone** or **Deferasirox** (oral).

Question 184: Which of the following is NOT a GIIb/IIIa antagonist?

A. Abciximab
B. Clopidogrel (Correct Answer)
C. Tirofiban
D. Eptifibatide

Explanation: **Explanation:** The correct answer is **Clopidogrel** because it belongs to a different class of antiplatelet agents known as **P2Y12 receptor antagonists** (ADP receptor blockers). **1. Why Clopidogrel is the correct answer:** Clopidogrel is a thienopyridine prodrug that irreversibly inhibits the P2Y12 subtype of ADP receptors on the platelet surface. This prevents the activation of the GP IIb/IIIa receptor complex, thereby inhibiting platelet aggregation. It does not bind directly to the GP IIb/IIIa receptor itself. **2. Why the other options are incorrect:** The remaining options are all direct **Glycoprotein (GP) IIb/IIIa inhibitors**, which represent the "final common pathway" of platelet aggregation by preventing fibrinogen from binding to platelets. * **Abciximab (Option A):** A chimeric monoclonal antibody fragment that binds irreversibly to GP IIb/IIIa receptors. * **Tirofiban (Option C):** A non-peptide, small-molecule reversible antagonist of the GP IIb/IIIa receptor. * **Eptifibatide (Option D):** A cyclic heptapeptide that reversibly inhibits the GP IIb/IIIa receptor (derived from rattlesnake venom). **High-Yield NEET-PG Pearls:** * **Mechanism:** GP IIb/IIIa inhibitors are the most potent antiplatelet agents because they block the final step of aggregation regardless of the stimulus (ADP, Thrombin, or TXA2). * **Route:** All GP IIb/IIIa inhibitors are administered **intravenously** (IV), whereas Clopidogrel is administered **orally**. * **Clinical Use:** Primarily used in Acute Coronary Syndrome (ACS) and during Percutaneous Coronary Intervention (PCI). * **Side Effect:** The most significant side effect for this entire class is bleeding and acute thrombocytopenia.

Question 185: Which of the following drugs may cause thrombocytopenia?

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

Explanation: **Explanation:** **Ticlopidine** is the correct answer because it is notorious for causing severe hematological adverse effects. It is a first-generation P2Y12 receptor antagonist that inhibits ADP-induced platelet aggregation. Its clinical use has been largely superseded by newer agents due to its association with **neutropenia, agranulocytosis, and thrombocytopenia**. Most critically, it can cause **Thrombotic Thrombocytopenic Purpura (TTP)**, necessitating frequent blood count monitoring (CBC) during the first three months of therapy. **Analysis of Incorrect Options:** * **Clopidogrel:** While also a P2Y12 inhibitor, it is a second-generation drug designed to be safer than Ticlopidine. Although rare cases of TTP have been reported, it does not typically cause the significant bone marrow suppression or routine thrombocytopenia seen with Ticlopidine. * **Abciximab:** This is a Glycoprotein IIb/IIIa inhibitor. While it can cause *acute* immune-mediated thrombocytopenia in a small percentage of patients, it is not the classic "textbook" association for drug-induced hematological toxicity in the same category as Ticlopidine for NEET-PG purposes. * **Aspirin:** Aspirin inhibits COX-1, leading to decreased Thromboxane A2. It affects platelet *function* (irreversible inhibition) rather than platelet *count*. It does not cause thrombocytopenia. **High-Yield NEET-PG Pearls:** * **Ticlopidine Side Effects:** Neutropenia (most common), TTP, and Diarrhea. * **Monitoring:** Patients on Ticlopidine require a CBC every 2 weeks for the first 3 months. * **Prasugrel/Ticagrelor:** Newer P2Y12 inhibitors; Prasugrel is contraindicated in patients with a history of stroke/TIA, and Ticagrelor can cause transient dyspnea and hyperuricemia.

Question 186: What is the anticoagulant of choice for prophylaxis of pulmonary thromboembolism?

A. Heparan sulfate
B. Protamine sulfate
C. Low molecular weight heparin (Correct Answer)
D. Warfarin

Explanation: **Explanation:** The correct answer is **Low Molecular Weight Heparin (LMWH)**. **1. Why LMWH is the Correct Choice:** For the prophylaxis of pulmonary thromboembolism (PTE) and Deep Vein Thrombosis (DVT), LMWHs (e.g., Enoxaparin, Dalteparin) are preferred over Unfractionated Heparin (UFH). This is due to their **superior pharmacokinetic profile**: * **Higher Bioavailability:** Better absorption after subcutaneous injection. * **Longer Half-life:** Allows for once or twice-daily dosing. * **Predictable Response:** Eliminates the need for routine laboratory monitoring (aPTT). * **Safety:** Lower risk of Heparin-Induced Thrombocytopenia (HIT) and osteoporosis compared to UFH. **2. Analysis of Incorrect Options:** * **A. Heparan Sulfate:** This is a naturally occurring glycosaminoglycan found on the cell surface and extracellular matrix. While it has minor anticoagulant properties, it is not used clinically as a drug for prophylaxis. * **B. Protamine Sulfate:** This is the **antidote** (chemical antagonist) used to reverse the effects of Heparin in cases of overdose. It is not an anticoagulant. * **D. Warfarin:** While used for long-term maintenance, it is not the first choice for acute prophylaxis because it has a **slow onset of action** (requires 3-5 days to achieve therapeutic effect) and carries a risk of initial skin necrosis. **High-Yield NEET-PG Pearls:** * **Mechanism:** LMWH mainly inhibits **Factor Xa** (Ratio of Xa:IIa activity is 3:1), whereas UFH inhibits both Xa and IIa (1:1). * **Monitoring:** If monitoring is required (e.g., in renal failure or pregnancy), **Anti-Factor Xa levels** are measured, not aPTT. * **Excretion:** LMWHs are primarily excreted by the **kidneys**; therefore, they must be used with caution or dose-adjusted in patients with renal impairment.

Question 187: What is the drug of choice for Heparin-induced thrombocytopenia?

A. Argatroban (Correct Answer)
B. Warfarin
C. Low molecular weight heparin
D. Dabigatran

Explanation: **Explanation:** **Heparin-induced thrombocytopenia (HIT)** is a life-threatening prothrombotic condition caused by IgG antibodies against the Heparin-Platelet Factor 4 (PF4) complex. The primary goal of management is the immediate cessation of all heparin products and the initiation of a non-heparin anticoagulant. **Why Argatroban is the Correct Answer:** Argatroban is a parenteral **Direct Thrombin Inhibitor (DTI)**. It is the drug of choice because it does not cross-react with HIT antibodies. It directly binds to the active site of both free and clot-bound thrombin. It is particularly preferred in patients with renal impairment as it is **metabolized by the liver**, though it requires monitoring via aPTT. **Why Other Options are Incorrect:** * **Warfarin:** It is **contraindicated** in the acute phase of HIT. Starting warfarin alone can lead to a rapid depletion of Protein C, creating a hypercoagulable state that results in **venous limb gangrene** or skin necrosis. * **Low Molecular Weight Heparin (LMWH):** These are strictly contraindicated because they show high cross-reactivity with HIT antibodies and will worsen the condition. * **Dabigatran:** While it is an oral DTI, it is not the standard of care for the *acute* management of HIT, which typically requires titratable parenteral anticoagulation. **High-Yield NEET-PG Pearls:** 1. **Alternative in Renal Failure:** Use Argatroban (Hepaticaly cleared). 2. **Alternative in Hepatic Failure:** Use **Danaparoid** or **Bivalirudin** (Renally cleared). 3. **Diagnosis:** Suspect HIT if platelet count drops by >50% after 5–10 days of heparin therapy. Use the **4T Score** for clinical probability. 4. **Transition:** Only start Warfarin once the platelet count has recovered to >150,000/µL, overlapping with a DTI for at least 5 days.

Question 188: Clopidogrel inhibits platelet aggregation by:

A. Inhibiting the gp IIb/IIIa receptor
B. Inhibiting phosphodiesterase
C. Inhibiting ADP-mediated signaling (Correct Answer)
D. Inhibiting cyclooxygenase

Explanation: **Explanation:** **Clopidogrel** is a thienopyridine derivative that acts as an antiplatelet agent. Its mechanism of action involves the **irreversible inhibition of the P2Y12 receptor**, which is a subtype of the purinergic **ADP (Adenosine Diphosphate) receptor** on the platelet surface. Under normal physiological conditions, ADP binds to this receptor to activate the Gp IIb/IIIa complex, leading to platelet cross-linking via fibrinogen. By blocking ADP-mediated signaling, Clopidogrel prevents platelet activation and subsequent aggregation for the remainder of the platelet's lifespan (7–10 days). **Analysis of Incorrect Options:** * **Option A (Gp IIb/IIIa inhibitors):** These include drugs like **Abciximab, Eptifibatide, and Tirofiban**. They block the "final common pathway" of platelet aggregation. * **Option B (Phosphodiesterase inhibitors):** Drugs like **Dipyridamole and Cilostazol** work by inhibiting PDE, leading to increased intracellular cAMP, which inhibits aggregation and promotes vasodilation. * **Option D (Cyclooxygenase inhibitors):** This is the mechanism of **Aspirin**, which irreversibly inhibits COX-1, thereby preventing the synthesis of Thromboxane A2 (TXA2). **High-Yield Clinical Pearls for NEET-PG:** * **Prodrug Status:** Clopidogrel is a **prodrug** that requires activation by the hepatic cytochrome P450 enzyme, specifically **CYP2C19**. * **Drug Interaction:** Avoid concomitant use with **Omeprazole** (a PPI), as it inhibits CYP2C19, reducing the antiplatelet efficacy of Clopidogrel. * **Other P2Y12 Inhibitors:** Prasugrel (irreversible) and Ticagrelor (reversible). Ticagrelor is notable for not being a thienopyridine and not requiring metabolic activation. * **Clinical Use:** Primarily used in Dual Antiplatelet Therapy (DAPT) following Coronary Stent implantation and for secondary prevention of Stroke/MI.

Question 189: Which one of the following drugs is a parenteral direct thrombin inhibitor?

A. Enoxaparin
B. Apixaban
C. Dabigatran
D. Argatroban (Correct Answer)

Explanation: **Explanation:** The correct answer is **Argatroban**. **1. Why Argatroban is correct:** Direct Thrombin Inhibitors (DTIs) bind directly to thrombin (Factor IIa) and inhibit its enzymatic activity without requiring the cofactor antithrombin III. Argatroban is a synthetic L-arginine derivative that acts as a **parenteral** DTI. It is primarily used as an anticoagulant in patients with **Heparin-Induced Thrombocytopenia (HIT)** because it does not cross-react with heparin-induced antibodies. **2. Why the other options are incorrect:** * **Enoxaparin (Option A):** This is a Low Molecular Weight Heparin (LMWH). It acts **indirectly** by accelerating the activity of Antithrombin III, primarily inhibiting Factor Xa and, to a lesser extent, Factor IIa. * **Apixaban (Option B):** This is a Direct Factor Xa inhibitor (part of the DOAC class). It is administered **orally**, not parenterally. * **Dabigatran (Option C):** While Dabigatran is a Direct Thrombin Inhibitor, it is administered **orally** (it is the only oral DTI currently available). The question specifically asks for a parenteral agent. **3. NEET-PG High-Yield Pearls:** * **Parenteral DTIs:** Lepirudin, Desirudin, Bivalirudin (derived from leech saliva/hirudin), and Argatroban. * **Metabolism:** Argatroban is metabolized by the **liver** (safe in renal failure), whereas Bivalirudin and Lepirudin are cleared by the kidneys. * **Monitoring:** The effect of parenteral DTIs is monitored using **aPTT**. * **Reversal:** Idarucizumab is the specific reversal agent for Dabigatran, but there is no specific reversal agent for Argatroban.

Question 190: A 40-year-old male presented to the ER with bleeding diathesis and was diagnosed with Glanzmann thrombasthenia. This disorder is believed to be due to the absence of a particular platelet receptor protein. Which of the following drugs acts as an anti-platelet agent by inhibiting the same platelet receptor protein?

A. Ticlopidine
B. Tirofiban (Correct Answer)
C. Cilostazol
D. Dipyridamole

Explanation: **Explanation:** The core of this question lies in understanding the pathophysiology of **Glanzmann thrombasthenia** and matching it with the mechanism of action of anti-platelet drugs. **1. Why Tirofiban is Correct:** Glanzmann thrombasthenia is a rare autosomal recessive bleeding disorder characterized by a deficiency or dysfunction of the **Glycoprotein IIb/IIIa (GPIIb/IIIa)** receptor on the platelet surface. This receptor is essential for platelet aggregation as it binds to fibrinogen, forming "bridges" between platelets. **Tirofiban** (along with Abciximab and Eptifibatide) is a specific **GPIIb/IIIa receptor antagonist**. By inhibiting this receptor, it prevents the final common pathway of platelet aggregation, mimicking the defect seen in Glanzmann thrombasthenia. **2. Why the Other Options are Incorrect:** * **Ticlopidine:** This is a P2Y12 receptor antagonist (Thienopyridine). It prevents platelet activation by inhibiting the ADP pathway, not the GPIIb/IIIa receptor. * **Cilostazol:** This is a Phosphodiesterase-3 (PDE3) inhibitor. It increases cAMP levels in platelets and blood vessels, leading to vasodilation and inhibition of aggregation. It is primarily used in intermittent claudication. * **Dipyridamole:** This acts by inhibiting phosphodiesterase and adenosine uptake. It is often used in combination with Aspirin for stroke prevention. **Clinical Pearls for NEET-PG:** * **Bernard-Soulier Syndrome:** Characterized by a deficiency of **GPIb-IX-V** (the receptor for von Willebrand factor), leading to defective platelet **adhesion**. * **Final Common Pathway:** GPIIb/IIIa inhibitors are the most potent anti-platelet agents because they block the final step of aggregation regardless of the initial stimulus (ADP, Thromboxane A2, or Collagen). * **Abciximab:** A monoclonal antibody against GPIIb/IIIa; unlike Tirofiban, its binding is non-competitive and irreversible.

Practice by Chapter

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Oral Anticoagulants

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