Warfarin Flashcards
(36 cards)
Why should baseline prothrombin measurements be taken before starting warfarin?
To assess coagulation status and identify any existing clotting disorders before initiating therapy.
What is the typical induction dose of warfarin for most patients?
10 mg daily for 2 days, adjusted based on individual factors.
In which populations is a lower starting dose (5 mg or less) of warfarin more appropriate?
Frail or elderly individuals, low body weight, liver disease, cardiac failure, or high bleeding risk.
What determines the subsequent dose of warfarin after initiation?
The international normalized ratio (INR) and other coagulation test results.
What is the usual maintenance dose range for warfarin?
3–9 mg daily.
When is concurrent heparin or low molecular weight heparin used with warfarin?
When an immediate anticoagulant effect is required, such as in DVT or PE.
What is the loading regimen of warfarin in atrial fibrillation?
1–2 mg daily with therapeutic INR typically achieved in 3–4 weeks.
How long should warfarin be continued in distal DVT?
At least 6 weeks.
How long is warfarin typically continued in proximal DVT or PE with a known risk factor?
At least 3 months.
When is long-term warfarin treatment recommended?
For recurrent DVT/PE, atrial fibrillation with high recurrence risk, or mechanical heart valves.
What are the main contraindications to warfarin?
Haemorrhagic stroke, active bleeding, severe liver disease, pregnancy, recent major surgery, and drug interactions with high bleeding risk.
What are common risk factors for bleeding while on warfarin?
GI bleeding history, peptic ulcers, recent stroke, uncontrolled hypertension, NSAID use, recent surgery.
What adverse effects should prompt immediate medical attention in a patient on warfarin?
Unexplained bleeding, bruising, blood in urine/stools, severe back pain, or painful skin rash.
What is warfarin-induced skin necrosis and who is at risk?
A rare, painful, localized thrombosis of skin vasculature; more common in protein C/S deficiency or HIT.
What is calciphylaxis and when might it occur with warfarin?
A rare, serious condition with skin necrosis and vascular calcification, seen especially in end-stage renal disease.
What dietary advice should be given to someone on warfarin?
Maintain consistent vitamin K intake; avoid cranberry juice and excessive green vegetables without adjusting the dose.
How should warfarin be managed before surgery?
Stop warfarin 3–5 days before; use heparin bridging if anticoagulation must be continued.
Is warfarin usually stopped before dental procedures?
No, not if the INR is under 4. INR should ideally be checked within 24–72 hours prior.
What drugs increase warfarin’s effect and may require INR monitoring?
Amiodarone, antibiotics (e.g., metronidazole), SSRIs, azoles, cranberry products, NSAIDs.
What drugs may reduce warfarin’s effect and require dose adjustment?
St John’s Wort, rifampicin, phenytoin, carbamazepine, phenobarbital, vitamin K supplements.
How frequently should INR be monitored when starting warfarin?
Daily or alternate days initially, then twice weekly, weekly, and less frequently once stable.
What INR level is generally targeted in warfarin therapy?
2.0–3.0, with a target of 2.5 for most indications.
What indicates poor anticoagulation control on warfarin?
Two INRs >5, one INR >8, two INRs <1.5, or TTR <65% in 6 months.
What changes can affect warfarin metabolism and dosing needs?
Thyroid status, acute illness, smoking cessation, weight changes, and genetic polymorphisms (CYP2C9, VKORC1).
