How it works
Warfarin inhibits this enzyme in the liver.
Vitamin K epoxide reductase
This lab value is used to monitor warfarin therapy.
INR (PT/INR)
Mechanical heart valves require this anticoagulant.
Warfarin
Antibiotics increase INR primarily by affecting this vitamin source.
Gut flora vitamin K production
Most common serious complication of warfarin.
Bleeding
Warfarin decreases synthesis of these clotting factors.
II, VII, IX, X (and Protein C and S)
Typical INR goal for atrial fibrillation, DVT, or PE.
2.0–3.0
Moderate-to-severe rheumatic mitral stenosis with AF requires this anticoagulant.
Warfarin
Amiodarone increases INR by inhibiting this warfarin metabolic pathway.
CYP450 metabolism
Painful skin necrosis occurring days after starting warfarin is due to deficiency of this protein.
Protein C
This clotting factor declines first after starting warfarin, making PT/INR rise early.
Factor VII
INR goal for most mechanical mitral valves.
2.5–3.5
This autoimmune thrombophilia is treated with warfarin rather than DOACs.
Antiphospholipid syndrome
Leafy green vegetables affect warfarin because they contain this nutrient.
Vitamin K
Purple toe syndrome occurs due to this pathophysiology.
Cholesterol microembolization
Reason patients become transiently hypercoagulable when starting warfarin.
Rapid depletion of Protein C before procoagulant factors decline
This clotting factor with the longest half-life determines full anticoagulant effect timing.
Factor II (prothrombin)
Name 2 renal indications to use Warfarin > DOAC
CrCl < 15 or dialysis
This common pain medication increases bleeding risk with warfarin.
NSAIDs
Warfarin is contraindicated in pregnancy because it causes this embryopathy.
Fetal warfarin syndrome (nasal hypoplasia, stippled epiphyses)
Warfarin is primarily metabolized by this hepatic enzyme system.
CYP450 (especially CYP2C9)
Time required for full warfarin effect after initiation.
About 5 days
This cardiac thrombus complication after MI is treated with warfarin.
Left ventricular thrombus
Name 3 antibiotics that significantly increase INR
TMP-SMX, metronidazole, fluoroquinolones, macrolides, tetracyclines
Patients with this inherited deficiency are at highest risk of warfarin skin necrosis.
Protein C deficiency