Warfarin MCQs With Answer

Warfarin MCQs With Answer

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Warfarin MCQs With Answer are crafted for B. Pharm students to strengthen core knowledge of warfarin pharmacology, clinical use, monitoring, and patient safety. This concise, exam-focused set covers mechanism (VKORC1 inhibition), stereochemistry, CYP2C9 metabolism, dosing principles, INR targets, adverse effects (bleeding, skin necrosis, purple toe), reversal strategies (vitamin K, PCC), drug–food and drug–drug interactions, and pharmacogenetic implications. Questions emphasize practical decisions: initiation, bridging anticoagulation, lab interpretation, and management of over-anticoagulation. Answers are provided to help self-assessment and exam preparation. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Mechanism of action of warfarin is primarily inhibition of which enzyme?

  • Thrombin (factor IIa)
  • Vitamin K epoxide reductase (VKORC1)
  • Factor Xa
  • Gamma-glutamyl carboxylase

Correct Answer: Vitamin K epoxide reductase (VKORC1)

Q2. Which laboratory parameter is standardized and used to monitor warfarin anticoagulation?

  • Activated partial thromboplastin time (aPTT)
  • Bleeding time
  • International Normalized Ratio (INR)
  • Platelet count

Correct Answer: International Normalized Ratio (INR)

Q3. Which clotting test is prolonged earliest after initiating warfarin therapy?

  • Activated partial thromboplastin time (aPTT)
  • Thrombin time
  • Prothrombin time (reported as INR)
  • Bleeding time

Correct Answer: Prothrombin time (reported as INR)

Q4. Warfarin is administered clinically as which of the following?

  • Pure S-enantiomer only
  • Pure R-enantiomer only
  • Racemic mixture of R- and S-enantiomers
  • Prodrug converted to active metabolite

Correct Answer: Racemic mixture of R- and S-enantiomers

Q5. Which cytochrome P450 isoenzyme primarily metabolizes the more potent S-warfarin?

  • CYP3A4
  • CYP1A2
  • CYP2C9
  • CYP2D6

Correct Answer: CYP2C9

Q6. Which genetic polymorphisms most commonly affect warfarin dose requirements?

  • CYP3A4 and VKORC2 polymorphisms
  • CYP2C9 and VKORC1 polymorphisms
  • CYP2D6 and CYP1A2 polymorphisms
  • MTHFR and TPMT polymorphisms

Correct Answer: CYP2C9 and VKORC1 polymorphisms

Q7. Consumption of which food group is most likely to decrease warfarin anticoagulant effect?

  • Leafy green vegetables high in vitamin K
  • Citrus fruits high in vitamin C
  • High-protein meats
  • Dairy products high in calcium

Correct Answer: Leafy green vegetables high in vitamin K

Q8. Which class of antibiotics commonly increases warfarin effect by reducing gut vitamin K synthesis?

  • Aminoglycosides
  • Broad-spectrum antibiotics
  • Tetracyclines only
  • Antitubercular drugs only

Correct Answer: Broad-spectrum antibiotics

Q9. How does amiodarone typically interact with warfarin?

  • Decreases warfarin effect by inducing metabolism
  • No significant interaction
  • Increases warfarin effect by inhibiting CYP metabolism
  • Displaces warfarin from renal receptors

Correct Answer: Increases warfarin effect by inhibiting CYP metabolism

Q10. Rifampin alters warfarin activity by which mechanism?

  • Inhibits VKORC1
  • Induces hepatic enzymes, decreasing warfarin effect
  • Directly competes with warfarin for albumin binding
  • Blocks intestinal absorption of warfarin

Correct Answer: Induces hepatic enzymes, decreasing warfarin effect

Q11. Which statement is true regarding warfarin use in pregnancy?

  • Warfarin is safe throughout pregnancy
  • Warfarin is teratogenic and generally contraindicated in pregnancy
  • Warfarin causes no fetal effects in the first trimester
  • Warfarin is preferred over heparin for pregnant women

Correct Answer: Warfarin is teratogenic and generally contraindicated in pregnancy

Q12. For life-threatening bleeding on warfarin, the fastest recommended reversal strategy is:

  • Oral vitamin K alone
  • Temporary warfarin dose reduction
  • Prothrombin complex concentrate (PCC) with intravenous vitamin K
  • Fresh frozen plasma without vitamin K

Correct Answer: Prothrombin complex concentrate (PCC) with intravenous vitamin K

Q13. What is the approximate elimination half-life of warfarin in adults?

  • 2–6 hours
  • 12–18 hours
  • Approximately 36–42 hours (variable)
  • 7–10 days

Correct Answer: Approximately 36–42 hours (variable)

Q14. Why is the anticoagulant effect of warfarin delayed after a single dose?

  • Warfarin needs renal activation
  • Slow oral absorption only
  • Existing clotting factors must degrade and be replaced by undercarboxylated proteins
  • Immediate inhibition of platelets occurs instead of clotting factors

Correct Answer: Existing clotting factors must degrade and be replaced by undercarboxylated proteins

Q15. When initiating warfarin for acute venous thromboembolism, best practice regarding anticoagulation bridging is:

  • Start warfarin alone without heparin
  • Use LMWH or UFH overlap until INR therapeutic for ≥24 hours
  • Give a single high loading dose of warfarin only
  • Stop all anticoagulation during initiation

Correct Answer: Use LMWH or UFH overlap until INR therapeutic for ≥24 hours

Q16. Early warfarin-induced skin necrosis is primarily related to deficiency of which protein?

  • Protein C deficiency
  • Protein S overactivity
  • Antithrombin deficiency
  • Factor V Leiden mutation

Correct Answer: Protein C deficiency

Q17. Purple toe syndrome associated with warfarin is thought to result from:

  • Direct endothelial toxicity of warfarin
  • Cholesterol microembolization
  • Immune complex deposition in dermal vessels
  • Local infection of toe tissues

Correct Answer: Cholesterol microembolization

Q18. Warfarin’s plasma protein binding is approximately:

  • 10% bound
  • 50% bound
  • Approximately 99% bound to albumin
  • 100% unbound

Correct Answer: Approximately 99% bound to albumin

Q19. After achieving a stable warfarin dose and INR, routine monitoring interval is commonly:

  • Daily INR checks
  • Every 4 weeks (monthly)
  • Every 6 months only
  • Never recheck once stable

Correct Answer: Every 4 weeks (monthly)

Q20. Typical target INR range for a patient with a mechanical mitral valve is:

  • INR 1.0–1.5
  • INR 2.5–3.5
  • INR 4.5–5.5
  • INR has no relevance for valve patients

Correct Answer: INR 2.5–3.5

Q21. For most patients with non-valvular atrial fibrillation on warfarin, the recommended INR target is:

  • INR 1.0–1.5
  • INR 2.0–3.0
  • INR 3.5–4.5
  • INR 4.0–5.0

Correct Answer: INR 2.0–3.0

Q22. Nonsteroidal anti-inflammatory drugs (NSAIDs) and warfarin together primarily increase bleeding risk by:

  • Increasing INR significantly
  • Reducing warfarin absorption
  • Causing additive platelet dysfunction and mucosal damage without necessarily altering INR
  • Neutralizing warfarin effect

Correct Answer: Causing additive platelet dysfunction and mucosal damage without necessarily altering INR

Q23. Management of an asymptomatic patient with INR >10 and no bleeding typically includes:

  • Immediate PCC only
  • Stop warfarin and administer oral vitamin K
  • Continue warfarin and reassess in a week
  • Start aspirin to protect bleeding sites

Correct Answer: Stop warfarin and administer oral vitamin K

Q24. Which compound is the pharmacologic form of vitamin K used to reverse warfarin?

  • Phytonadione (vitamin K1)
  • Menadione (vitamin K3)
  • Ergocalciferol (vitamin D2)
  • Ascorbic acid (vitamin C)

Correct Answer: Phytonadione (vitamin K1)

Q25. Warfarin exerts its effect by preventing gamma-carboxylation of glutamic acid residues on which vitamin K-dependent clotting factor that has the shortest half-life?

  • Factor II
  • Factor VII
  • Factor X
  • Protein S

Correct Answer: Factor VII

Q26. Which antibiotic combination is known to potentiate warfarin effect by both inhibiting metabolism and displacing protein binding?

  • Amoxicillin-clavulanate
  • Sulfamethoxazole-trimethoprim (SMX-TMP)
  • Azithromycin only
  • Nitrofurantoin only

Correct Answer: Sulfamethoxazole-trimethoprim (SMX-TMP)

Q27. Which of the following lists includes proteins whose carboxylation is inhibited by warfarin?

  • Factors V, VIII, XIII
  • Factors II, VII, IX, X and proteins C and S
  • Fibrinogen and plasminogen only
  • Platelet factor 4 and von Willebrand factor

Correct Answer: Factors II, VII, IX, X and proteins C and S

Q28. Compared to younger adults, elderly patients typically require which adjustment when prescribing warfarin?

  • Higher initial and maintenance doses
  • No dose adjustment based on age
  • Lower initial and maintenance doses due to increased sensitivity
  • Substitute with aspirin instead of warfarin

Correct Answer: Lower initial and maintenance doses due to increased sensitivity

Q29. Pharmacogenetic testing for CYP2C9 and VKORC1 prior to warfarin initiation is:

  • Always mandatory for every patient
  • Useful to guide initial dosing but not universally required
  • Never useful clinically
  • Required only for pediatric patients

Correct Answer: Useful to guide initial dosing but not universally required

Q30. Which metric best reflects long-term quality of anticoagulation control in patients on warfarin?

  • Absolute INR value on a single visit
  • Time in therapeutic range (TTR)
  • Number of missed doses only
  • Serum warfarin concentration

Correct Answer: Time in therapeutic range (TTR)

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