Issue date: September 2019
For review: September 2021
Ref: A-174/Medical specialties/Medicine/ZL/DVT v5
Studies began in the use of warfarin as a therapeutic anticoagulant in the early 1950’s and a famous early recipient of warfarin was the US president D Eisenhower who was prescribed the drug after having a heart attack in 1955.
Warfarin was initially sold as a pesticide against rats and mice and is still popular for this purpose today.
How does warfarin work?
Warfarin stops your blood from clotting within the blood vessels. It is also used to stop existing clots getting bigger (as in DVT) and to stop parts of clots breaking off and forming emboli (as in Pulmonary Embolism or PE). It is often common to refer to the delay in clotting as 'thinning' the blood.
Is the treatment safe?
Treatment with warfarin and Enoxaparin is safe as long as you follow the advice of your DVT clinic nurse and GP and/or the advice in your Anticoagulant Therapy Record Book.
You will need to have your blood tested at regular intervals at your GP surgery. Your International Normalised Ratio (INR) reading may vary, but will need to be kept within a certain range normally 2-3.
What does INR mean?
It stands for International Normalised Ratio (INR) and is a measure of how much longer it takes the blood to clot when oral (by mouth) anticoagulation is used. For example, if your INR is 2 the blood is taking approximately twice as long as normal to clot. The dose of warfarin needed to produce an INR which is effective (normally a result of between 2 and 3), the dose of warfarin required to maintain a stable dose of warfarin can be different for each person
How will my treatment be monitored?
Your treatment is monitored by regular blood testing. The INR is then measured and recorded in your Anticoagulant Therapy Record Book. Your warfarin dosage will be adjusted up or down depending on the result of your blood test: if the INR is too low, the warfarin dose is increased; if it is too high the dose is decreased.
For some people, it may be a very small dose, for others, it may be a larger dose. If you hear from your friends or neighbours that they are taking a lower dose than you, don’t let it upset you. Warfarin dosage is individualised to each particular patient.
In the first 6 weeks after your DVT has been diagnosed if your INR drops below 2 it is recommended that your GP restart Enoxaparin until your INR is above 2 again.
Are there any side effects?
The most common side effects of warfarin are bleeding and bruising. It can be in the form of prolonged bleeding from cuts, bleeding that does not stop by itself, nose bleeds, small or large bruises under the skin, bleeding gums when brushing the teeth.
More serious bleeding may present as red or dark brown urine, red or black stools, or coughing or vomiting bloodstained fluid or a nosebleed that won’t stop. Although these problems are - fortunately - rare, if they do occur they can be serious and you should see your GP urgently or go to your nearest Accident and Emergency department.
If you are involved in any kind of accident (for example, a car accident or falling down and hitting your head on the pavement) go to the nearest Accident and Emergency department. You will need to get checked for internal bleeding.
Other side effects
Hair loss: hair loss is an infrequent side effect of warfarin therapy and is reversible.
Rash: if you develop a rash after starting warfarin therapy notify your GP.
It is important to continue taking all medications prescribed by your consultant or GP. Some drugs affect how warfarin works. If your doctor prescribes any new medication, please ask him or her whether it interferes with warfarin.
Antibiotics in particular often cause problems with INR readings. If you are prescribed antibiotics you may need to attend for an INR earlier than usual for a blood test and this may need to be repeated a few days after stopping the course of antibiotics.
Avoid all aspirin-based drugs, including non-steroidal anti-inflammatory preparations such as ibuprofen unless prescribed by your doctor. Always seek advice from a pharmacist before purchasing any over the counter medicines, food or health supplements (this includes creams and ointments). Paracetamol and codeine can be taken safely with warfarin for pain although these can affect INR control if taken for prolonged periods.
You need to tell your doctor and pharmacist what herbal products you are taking, especially bromelains, coenzyme Q10, danshen, dong quai, fenugreek, horse chestnut, red clover, sweet clover and sweet woodruff, ginger, garlic, Ginkgo biloba, and St.John's wort.
Do not start taking any herbal products without talking to your doctor or pharmacist. This also includes some aromatherapy oils and muscle rubs such as “deep heat” which contain Methyl salicylate, which can increase the body’s sensitivity to warfarin.
Oral contraception (OCP)
While taking Warfarin and as long as the INR remains in the therapeutic range (2-3 usually), you are very well protected against a further DVT and a decisions regarding whether to stop these compounds does not need to be taken immediately.
In fact it is extremely sensible for ladies to continue taking the OCP whilst on Warfarin to prevent pregnancy, therefore protecting against the teratogenic (damage to the foetus in the womb) effects of Warfarin. However you should discuss future contraception to be used for when you have completed your Warfarin course. You must discontinue the OCP at least 4 weeks prior to stopping Warfarin. Progesterone only compounds (e.g. Mini-pill or Depot-Provera) are safe from a VTE (Venous Thrombo Embolism) viewpoint.
Hormone replacement therapy (HRT)
While taking Warfarin and as long as the INR remains in the therapeutic range, you are very well protected against a further DVT. A decision regarding whether to stop this medication does not need to be taken immediately however HRT will need to stop at least 4 weeks prior to stopping warfarin.
If bone protection is required then non-hormone compounds are available and should be discussed with your GP. For peri-menopausal symptoms, the situation may be difficult but alternatives to HRT are paramount.
Other hormone based treatments
Obviously, these treatments need to be continued and need to be discussed carefully with your Oncologist. The nurses in the DVT clinic will inform your oncology team about your DVT diagnosis, as there may be alternative treatments that can be prescribed for you which may carry less risk of a further DVT.
DO NOT stop taking this medication unless your oncologist or GP tells you to do so.
You should avoid drinking cranberry and grapefruit juice as they have been found to increase the effect of warfarin; also large amounts of ginger such as chocolate covered crystallised ginger chunks can increase the effect of warfarin and are best to be avoided. However a small amount of ginger in cakes and biscuits is safe.
Other than the above there are no dietary restrictions while you are on warfarin, as long as you eat a healthy well balanced diet and avoid strict diets or crash dieting. You should avoid dramatic changes in the amount and type of food you eat, particularly green vegetables and liver products.
Alcohol may increase your INR reading. However small quantities may be fine to drink. For example half a pint of beer, a glass of wine, or one measure of spirit. Binge drinking or sudden changes in consumption can be harmful. It is recommended you have 2 alcohol free days a week.
Tell your doctor if you are or plan to become pregnant. If you become pregnant or think you may be while taking warfarin, consult your doctor immediately.
It is advisable to have your INR checked before any overseas travel, so you can be sure of the correct dose whilst away from home. You may also need to have your INR checked while you are abroad, depending on the length of time you intend to be away.
Please ensure that you have valid medical insurance for your travel and that it covers you for warfarin treatment. Make sure that your insurer knows you are taking anticoagulation drugs.
Remember to pack sufficient quantities of your tablets for the length of your stay. It is advisable to take two packs one in your main luggage and one in your hand luggage. During your journey please keep as mobile as possible and keep well hydrated this advice applies for all types of travel: train, bus, plane and car. If you are driving please consider regular stops during your journey.
It is recommended once the initial period of swelling and pain has subsided and your warfarin treatment is stable to wear compression stockings.
This treatment has been shown to reduce the risk of a recurrent DVT, and can also reduce the risk of developing long-standing changes to your legs, called post-thrombotic syndrome. You should wear the stockings daily, for at least two years. If you do develop post-thrombotic syndrome, you may be advised to wear the stockings for more than two years.
The best type of stockings (or elastic compression hosiery as they are known) is grade 3 strength. This means that they are able to squeeze the legs, with a certain degree of force. This also means that they will feel very tight. This is normal. It will not be as comfortable as the socks, tights or stockings you are use to wearing, and they can take some getting used to.
Some people find that they cannot tolerate grade 3 stockings, and so grade 2 stockings (which create less of a squeezing force) can be used instead. You will need to see your GP, as Grade 3 compression requires a prescription from your GP.
Note: a compression stocking used following a DVT should be fitted professionally after an assessment and accurate measurement. Some people are not suitable for compression stockings owing to other conditions they may have. Do not just buy over-the-counter support stockings or flight socks that may be the wrong class or size and which may potentially cause more damage. Your stockings will also need replacing every 3-6 months.
If you are advised to wear a compression stocking, you should put it on each day whilst lying in bed before getting up. Wear it all day until you go to bed, or until you rest in the evening with the leg raised. Take the stocking off before going to bed.
The slight pressure from the stocking helps to prevent fluid seeping into the calf tissues from the outer veins, which carry the extra-diverted blood following a DVT. The stocking also reduces, and may prevent, calf swelling. This in turn reduces discomfort and the risk of skin ulcers forming.
Without treatment, up to 6 in 10 people who have a DVT may develop long-term symptoms in the calf. This is called post-thrombotic syndrome. Symptoms occur because the increased flow and pressure of the diverted blood into other veins can affect the tissues of the calf.
Symptoms can range from mild to severe and include: calf pain, discomfort, swelling, and rashes. An ulcer on the skin of the calf may develop in severe cases. 30% of people develop post thrombotic syndrome after DVT diagnosis, even if they are treated effectively.
Walking regularly / exercise
You should keep as active and mobile as possible, if you are able please walk regularly. Walking is thought to improve circulation in the affected leg and may help to reduce your risk of further DVT. Try to avoid standing still / in the same position for long periods of time.
If you are normally very active e.g. run, cycle or swim you can continue these activities as your symptoms begin to resolve however; you may find you need to restart at a lower intensity to begin with. Please keep well hydrated when exercising.
Contact sports are not recommended while taking anticoagulants due to the increased risk of injury and therefore internal bleeding with these sports.
Raising your leg whilst resting, ideally when you are resting, raise your leg. This reduces the pressure in the calf veins, and helps to prevent blood and fluid from pooling in the calves. “Raised” means that your foot is higher than your hip so gravity helps with blood flow returning from the calf.
The easiest way to raise your leg is to recline on a sofa with your leg up on a cushion. Sitting on the sofa or in a chair, with your feet on a footstool or pouffe is not keeping your feet up - the feet are well below your hips in this position. However; if you suffer from hip problems we do not expect you to be in pain trying to keep your leg raised in this position and if all you can manage is a little off the floor this is better than nothing.
Raise the foot of the bed a few inches if it is comfortable to sleep like this. This is so your foot and calf are slightly higher than your hip when you are asleep.
You may return to work, as you feel able, depending on your level of pain and swelling. If you are unable to return to work immediately you can self-certificate yourself for the first 7 days. After that you will require a sick certificate from your GP.
If you have an occupational health department you should inform them that you are taking an anticoagulant as this may restrict some of your duties e.g. fire service /military services.
If you are working in a potentially dangerous environment e.g. building site, we strongly recommend that you inform your manager / supervisor / work mate that you are taking an anticoagulant. If an accident occurred they would be able to inform emergency services that you are on anticoagulation if you were unable to do so yourself
Other healthcare / Alternative health professionals
You must inform your dentist that you are taking warfarin in most cases this will not affect your treatment but your dentist may require an up to date INR prior for more invasive treatment e.g. tooth extraction.
You should inform any practitioner who is treating you or seeing you in clinic that you are on warfarin. This includes physiotherapist, chiropractor, chiropodist, osteopath, herbalist, acupuncturist, aromatherapy, massage therapist, reflexology, if in doubt it is far better to tell them you are on warfarin as they may need to revise their treatment plan with you.
Other commonly asked questions
Why am I having injections of Heparin (Enoxaparin) as well as warfarin? Warfarin can take 5-7 days to reach a therapeutic level you therefore need a medication that is effective immediately to stop the clot getting any bigger.
This medication is called Enoxaparin (Clexane) it is also an anticoagulant that begins to work immediately and prevents the clot getting any bigger. It is given by injection into your abdomen. Once you level of warfarin is at a therapeutic level (INR level between 2.0 and 3.0); you will be told to stop the injections of Enoxaparin.
You will be taught how to give the injection to yourself. Your nurse will also teach a family member how to give you the injection if you wish. If you cannot give it to yourself you may need to attend hospital clinic for the injections to be given for you. If this is not an option then in limited circumstances a District nurse can be arranged to see you at home.
It is important to take these medications at the same time every day.
What do I do if I forget to take my warfarin?
If you remember your warfarin before midnight on the day you should have taken it then you can take it.
If you realise the next morning you had not taken your warfarin the day before do not take your warfarin in the morning take your normal dose at your normal time (usually between 6-8pm.)
Do not double the dose to compensate for the missed day. Make a note in your yellow anti coagulation record book that you missed a dose of warfarin. If you miss more than 2 consecutive days you should tell your GP immediately.
Should I take warfarin with food or on an empty stomach?
Warfarin should be taken on an empty stomach, either half hour before or one hour after a meal. Food impairs the absorption of the drug. It is okay to take it after a light snack, but don’t take it after a full meal.
Why do I have to take my warfarin in the evening?
It is recommended to take warfarin in the evening because on the day you have your regular INR test the blood results are not ready for the GP to review and decide on your dose of warfarin until late afternoon.
If your INR result is too high your GP will probably reduce your dose of warfarin unfortunately if you have already taken your warfarin dose adjustment will be delayed until the next day.
What happens if I need emergency surgery while I am on warfarin?
If you require emergency surgery your warfarin can be reversed very quickly. Which will return your clotting times to normal to decrease the risk of bleeding during surgery.
How should I store my warfarin?
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat, light and moisture (not in the bathroom). Return any medication that is out of date or no longer needed to your local pharmacy.
Why am I not having one of the new anticoagulants?
Several new oral anticoagulant drugs such as Dabigatran and Rivaroxaban are being introduced and are in the process of being licensed. They have the advantage of providing a stable level of anticoagulation on a regular dose which doesn’t require such constant monitoring and adjustment as warfarin. However it may be some time before these are widely available.
Can I have a tattoo while on warfarin?
It is normally recommended NOT to have a tattoo while taking warfarin because of the increased risk of bruising. Some people find the image can be “blurred”. You should inform the person who will be doing the tattoo, as the decision to proceed has to be made by yourself and your chosen tattoo artist.
Can I have a body piercing while on warfarin?
It is normally recommended NOT to have a body piercing while taking warfarin because of the increased risk of bruising and bleeding. This is particularly in areas with a very good blood supply such as the tongue; you should inform the person who will be doing the piercing as the decision to proceed has to be made by yourself and your chosen practitioner.
You should carry your yellow anticoagulation card with you at all times accidents can happen at any time and in any place and the emergency services will need to know if you are taking warfarin.