Warfarin is an oral anticoagulant prescribed to reduce the risk of blood clots. It contains warfarin sodium as its active component and belongs to the heart-and-blood-pressure therapeutic class. In Hong Kong, Warfarin is available by prescription only and is supplied as a pill in strengths of 1 mg, 2 mg, and 5 mg. The medication is regulated under the Pharmacy and Poisons Ordinance and must be dispensed by a licensed pharmacist.
Warfarin belongs to the vitamin K antagonist group. It blocks the enzyme vitamin K epoxide reductase complex 1 (VKORC1), which is essential for recycling vitamin K. Vitamin K is required for the hepatic synthesis of clotting factors II, VII, IX, and X, as well as proteins C and S. By inhibiting VKORC1, warfarin reduces the production of these clotting factors, thereby weakening the blood’s ability to form clots.
Warfarin is approved in Hong Kong for the following indications:
These uses are supported by international guidelines and local clinical practice standards.
These effects are usually mild and can be managed by dose adjustment under medical supervision.
Major Interactions (may increase bleeding risk)
Moderate Interactions (require INR monitoring)
Mechanism: Many interactions affect warfarin metabolism via cytochrome P450 enzymes (especially CYP2C9) or alter vitamin K status.
If specific interaction data for Warfarin is limited, patients should inform their healthcare provider of all medicines, supplements, and dietary habits.
This article provides educational information about Warfarin and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.
Changes in diet (especially intake of vitamin K-rich foods), new medications or supplements, illness, and variations in alcohol consumption can all affect INR levels. Consistent monitoring and communication with your healthcare provider help maintain stability.
Yes, you can travel with Warfarin, but you should carry a copy of your prescription and a letter from your doctor. Some countries may require documentation for controlled medicines; check Hong Kong’s outbound and inbound regulations before traveling.
Warfarin requires regular INR monitoring and has numerous drug-food interactions, while DOACs (e.g., apixaban, rivaroxaban) have fixed dosing and fewer interactions. However, Warfarin remains the preferred choice for patients with mechanical heart valves or severe kidney disease.
NSAIDs can increase bleeding risk and should generally be avoided unless specifically approved by your clinician. Acetaminophen is usually a safer alternative for mild pain.
Contact your healthcare provider for guidance. Do not double the next dose; your provider may advise a temporary dose adjustment based on your most recent INR.
You don’t need to avoid vitamin K foods entirely, but aim for a consistent intake. Sudden large increases in leafy greens, broccoli, or Brussels sprouts can reduce warfarin’s effectiveness.
Warfarin is metabolised in the liver, so severe hepatic impairment may increase bleeding risk. Dose adjustments and close INR monitoring are required, and alternative anticoagulants may be considered.
Routine kidney function tests are not required for warfarin alone, but if you have comorbid kidney disease or are taking other nephrotoxic drugs, periodic assessment is advisable.
Variants in the CYP2C9 and VKORC1 genes can affect warfarin metabolism and sensitivity. Genetic testing may help predict optimal initial dosing, but it is not mandatory and should be discussed with your provider.
Hair thinning or loss can occur as a side effect, usually mild and temporary. Upon dose reduction or discontinuation, hair growth typically returns to normal.
