Question 1

How should I initiate warfarin therapy?

Accepted Answer

Warfarin should be started at 5 mg/day for most patients (2.5 mg/day if elderly, low body weight, heart failure, liver disease, or on interacting medications). Check INR on day 3–4 and dose-adjust using a validated initiation nomogram. A selective pharmacogenetic-based dosing approach (CYP2C9 and VKORC1 genotyping) may reduce time to therapeutic INR.

Question 2

What is the management of a critically high INR (>9) without bleeding?

Accepted Answer

Hold warfarin. Administer 2.5–5 mg oral vitamin K (oral is preferred — more predictable and less risk of anaphylaxis than IV). Recheck INR in 24 hours. If INR remains high, repeat vitamin K. Resume warfarin at a reduced dose when INR is therapeutic. Avoid subcutaneous vitamin K — absorption is erratic.

Question 3

How do I manage warfarin around surgery?

Accepted Answer

For most procedures, stop warfarin 5 days before surgery. For patients at high thromboembolic risk (mechanical valve, recent VTE <3 months), consider bridging with LMWH or unfractionated heparin. Resume warfarin 12–24 hours after surgery (evening of or next morning) if adequate haemostasis. Check INR on day 3 after resuming.