Question:hard
Which of the following statements is TRUE about Warfarin?
Which of the following statements is TRUE about Warfarin?
Show Hint
Warfarin's anticoagulant effect is delayed and it is monitored by a specific coagulation test involving the extrinsic pathway.
Updated On: Jun 23, 2026
- It inhibits Vitamin K-dependent clotting factors by blocking Vitamin K epoxide reductase
- It acts immediately on administration and reaches full effect within 2 hours
- It is monitored by measuring aPTT
- It crosses the placenta and is safe in pregnancy
Show Solution
The Correct Option is A
Solution and Explanation
Warfarin pharmacology is one of the most frequently tested topics in NEET PG.
Mechanism:
Warfarin inhibits $\text{Vitamin K epoxide reductase (VKORC1)}$, preventing recycling of Vitamin K epoxide to active Vitamin K hydroquinone. This blocks $\gamma$-carboxylation of glutamate residues on Vitamin K-dependent factors: II, VII, IX, X, Protein C, Protein S.
Onset:
Delayed by 48-72 hours (existing factors must be cleared). First factor depleted = Factor VII (t1/2 = 4-6 h), causing early PT prolongation. Therapeutic full effect in 3-5 days.
Monitoring:
$\text{PT/INR}$ (Prothrombin Time) -- tests the extrinsic + common pathway (Factors VII, X, V, II, fibrinogen). Target INR for most indications = 2-3. aPTT monitors unfractionated heparin.
Key pharmacokinetic facts:
- Completely absorbed orally; highly protein-bound (99%); hepatic metabolism via CYP2C9
- Genetic variants: VKORC1 and CYP2C9 affect dose requirements
- Warfarin crosses the placenta (CONTRAINDICATED in pregnancy -- teratogenic)
Antidote: Vitamin K1 (phytomenadione) -- for non-urgent reversal; Fresh Frozen Plasma (FFP) or Prothrombin Complex Concentrate (PCC) for urgent reversal.
Drug interactions: Enzyme inducers (rifampicin, carbamazepine) decrease effect; enzyme inhibitors (azole antifungals, amiodarone, metronidazole) increase effect.
\[\boxed{\text{Inhibits Vitamin K epoxide reductase (VKORC1)}}\]
Mechanism:
Warfarin inhibits $\text{Vitamin K epoxide reductase (VKORC1)}$, preventing recycling of Vitamin K epoxide to active Vitamin K hydroquinone. This blocks $\gamma$-carboxylation of glutamate residues on Vitamin K-dependent factors: II, VII, IX, X, Protein C, Protein S.
Onset:
Delayed by 48-72 hours (existing factors must be cleared). First factor depleted = Factor VII (t1/2 = 4-6 h), causing early PT prolongation. Therapeutic full effect in 3-5 days.
Monitoring:
$\text{PT/INR}$ (Prothrombin Time) -- tests the extrinsic + common pathway (Factors VII, X, V, II, fibrinogen). Target INR for most indications = 2-3. aPTT monitors unfractionated heparin.
Key pharmacokinetic facts:
- Completely absorbed orally; highly protein-bound (99%); hepatic metabolism via CYP2C9
- Genetic variants: VKORC1 and CYP2C9 affect dose requirements
- Warfarin crosses the placenta (CONTRAINDICATED in pregnancy -- teratogenic)
Antidote: Vitamin K1 (phytomenadione) -- for non-urgent reversal; Fresh Frozen Plasma (FFP) or Prothrombin Complex Concentrate (PCC) for urgent reversal.
Drug interactions: Enzyme inducers (rifampicin, carbamazepine) decrease effect; enzyme inhibitors (azole antifungals, amiodarone, metronidazole) increase effect.
\[\boxed{\text{Inhibits Vitamin K epoxide reductase (VKORC1)}}\]
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