Warfarin
What is Warfarin for?
Warfarin is an anticoagulant, also called a blood thinner. It works by blocking the clotting factors and hence slows down the process of blood clot formation.
It can be used to prevent embolisation (blockage of blood vessels) in rheumatic heart disease, atrial fibrillation (irregular heart rhythms), and after inserting a prosthetic heart valve, treat and prevent venous thrombosis (blood clot formed within a vein) and transient ischemic attacks (TIA / mini-stroke).
How to use it?
Warfarin can be taken by mouth as tablets. Your doctor will prescribe an initial starting dose based on your medical history, and this often ranges from 2-5mg daily. Warfarin doses are individualized, and will be adjusted based on your target prothrombin time (i.e. international normalized ratio [INR]).
Warfarin should be taken at the same time every day. Your doctor should tell you your target INR and for how long you should take Warfarin.
What are the side effects of Warfarin?
The most common side effect of Warfarin is bleeding. You must tell your doctor if you notice any signs of bleeding like unexplained bruises and nose or gum bleeds, as well as signs of internal bleeding like blood in your urine or stool.
Warfarin interacts with many medicines, including over-the-counter and prescription medicines. Always check with your doctor or pharmacist before using a new medicine while taking Warfarin.
Who should not take Warfarin?
People who
- are allergic to warfarin or any component of the preparation
- are prone to or have significant bleeding (e.g. with active gastrointestinal ulceration, cerebral aneurysm)
- have undergone or will undergo surgery of the eye or central nervous system
- are pregnant (except at the high risk of clot formation in blood vessels)
Pharmacist Tips:
- Keep a consistent intake of food with vitamin K, and avoid food with high vitamin K content such as spinach, since the effect of Warfarin is modified by vitamin K.
- Avoid activities that could easily lead to injury, and check for any signs of bleeding, such as bruising. Use a soft toothbrush and an electric razor.
- You may be prescribed an alternating dose to be taken on even and odd days.
- Make sure you take every dose, as you may risk a potentially fatal blood clot.
Common dosing schedule:
- Take Warfarin once at the same time every day. Pay attention to any dose changes made by your doctor.
This schedule is for reference only, adjustments may be made according to individual needs.
Some common medications Warfarin may interact with:
- Alcohol
- Amiodarone
- Antifungal agents, e.g. Econazole, Fluconazole
- Aspirin
- Cimetidine
- Coenzyme Q10
- Esomeprazole
- Paracetamol
- Many antibiotics, e.g. Amoxicillin, Ceftriaxone
- Statins, e.g. Simvastatin (except Atorvastatin)
Warfarin interacts with a large number of medications. Please notify your doctor or pharmacist if you are taking them, dosage adjustments might be needed.
Where to buy Warfarin in Hong Kong?
In Hong Kong, Warfarin is a prescription only medicine, and requires a prescription from a doctor to be purchased in a pharmacy. It can also be obtained from doctors. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.
For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at https://www.drugoffice.gov.hk
Need more information?
For detailed information about the use of Warfarin in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.
Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.
- 1mg / 3mg / 5mg (Tablets)