Blood that clots too readily can be life threatening. A blood clot in the vessels can cause a stroke. A clot in the leg (deep vein thrombosis or DVT) or lung (pulmonary embolism or PE) are equally dangerous. Approximately 350,000 Canadians may have an abnormal heart rhythm (atrial fibrillation). These people are three to six times more likely to have a stroke. The risk is higher because an abnormal rhythm allows blood to pool in the heart. When blood pools, it tends to form clots. These clots can be carried in the blood vessels to the brain, causing a stroke.
Fortunately, ‘blood thinners’ (anticoagulant medications) can help avoid these problems. They interrupt the process involved in forming blood clots. With an anticoagulant, blood clots are less likely to form unnecessarily, but can still form when needed. They also prevent blood from clotting as quickly.
For 20 years, the anticoagulant warfarin has effectively prevented stroke in people who have non-valvular atrial fibrillation. It has been used for more than 50 years to treat DVT. New alternatives to warfarin have recently been introduced. They include Pradaxa (dabigatran), Xarelto (rivaroxaban), and Eliquis (apixaban). Other medications, given by injection, also affect blood clotting.
When warfarin is prescribed, an appropriate dosage must be found. The response varies for each person and must be individualized according to lab results. Blood tests are necessary to determine the dose. Warfarin requires more detailed monitoring than the new oral anticoagulants. It takes about five days to reach maximum effect. Warfarin is also affected by foods that contain vitamin K (such as green leafy vegetables) and by certain medications. If a person receives too high of a dose of warfarin, vitamin K can be taken as an antidote.
The new medications seem very similar to each other. The mechanism to reduce blood clotting is more specific. There is no need for blood tests to monitor safety and effectiveness. Once a dose is taken, it begins to work within about two to four hours. These drugs have predictable pharmcokinetics (the way the drug moves through the body and is handled by the kidneys and liver) and pharmacodynamics (how the drug acts on the body). The choice of medication may be based on age, liver function, frequency of dosing (one dose per day versus two), and how the kidneys are working. Some medications require healthy kidneys that are able to eliminate waste.
Studies show that the new medications appear safer than warfarin and are simpler to use. They do not interact with any foods. Drug interactions are still possible, and are similar to those with warfarin. For instance, they may interact with other medications that reduce blood clots. The new medications are also much more expensive than warfarin.
The choice of anticoagulant can depend on several factors. The choice may be based on cost and convenience. Factors unique to the person, such as kidney and liver function, are also considered. With the new medications, no strategy can be used to identify whether a person has had too much of the medication. If there is too much, there is no antidote.
Your doctor may monitor your kidney function to check that the medication is at the best dose. The new anticoagulants work as well as warfarin. However, the chance of bleeding in the gastrointestinal or GI (digestive) system increases.
|Drug||Frequency||Adjustment of dose for kidney function||Blood test (INR)||Cost
|Pradaxa||Twice daily||Yes||No||About $120||No||No|
|Eliquis||Twice daily||No – not recommended if kidney function is less than 15 mL/min||No||About $120||No||No|
|Xarelto*||Once daily||Yes||No||About $110||No||No|
|Warfarin**||Once daily||No||Yes||About $20||Yes (vitamin K, prothrombin complex concentrate, fresh frozen plasma)||Foods containing vitamin K|
*Only Xarelto has been approved in Canada for treatment of DVT (dosage twice daily). Pradaxa and Elquis have not.
**The annual cost of warfarin monitoring is about $240, according to the Medical Advisory Secretariat (2009). Only the lab costs are captured in this cost amount. Indirect costs, such as the person’s time, time off work, and transportation costs, are not included.
Anyone who has had hip or knee surgery, an abnormal heart rhythm, or is at increased risk of stroke may benefit. People at risk may feel fine, and think that controlling their heart rate is only necessary if they have an abnormal heart rhythm. However, anticoagulants are also needed to reduce the risk of stroke. The new medications are approved to:
If using an anticoagulant, a doctor and health team may use two scoring tests to assess potential risk. The CHADS2 score assesses stroke risk, while HAS-BLED estimates the risk of bleeding too much. If the benefits outweigh the risks, an anticoagulant will be selected. A high CHADS2 score depends on several factors. Stroke risk increases if a person has diabetes, congestive heart failure, high blood pressure, structural heart disease, or a prior blood clot in an artery.
Currently, no specific antidote can neutralize the effect of these new medications. Skipping one or more doses will manage minor bleeding, such as a bleeding nose. The treatment for major bleeding is still evolving. In the hospital, treatment depends on each person’s situation. Sometimes expensive blood products are used to treat major bleeding.
Pradaxa causes stomach upset in over 10 per cent of people, and could trigger GI bleeding. Swallowing the capsules whole, and taking them with food or water, can reduce the risk. This medication must be stored in its original packaging to keep until its expiry date. Once the bottle is opened, it must be used within four months.
Xarelto should be taken with a meal so that it can be better absorbed. It may be crushed and taken with soft food like applesauce.
Eliquis can be taken with a meal, but this is not essential.
Taking the medication as directed is very important in preventing stroke. However, those using anticoagulant therapy often do not take the medication as they should, if at all. Having lab tests done often encourages people to follow directions. Blood tests allow doctors to check whether warfarin is being taken correctly. However, it is much more challenging to find out whether the newer medications are being taken correctly. Currently no blood test can show the medication’s level in the blood.
Warfarin stays in the body for up to five to seven days. The newer agents may leave the body within 24 to 36 hours.
Avoid Pradaxa if you have a stomach ulcer or non-ulcer dyspepsia (indigestion), or recent or recurrent stomach or intestine bleeding. If you have had recent bleeding in the GI tract, Eliquis may be a better choice. It has a lower incidence of GI bleeding than the others.
If cost is a concern, look into what might be covered through benefits, or discuss it with your health care provider.
Talking with your doctor will help you to understand the benefits and risks of these new medications. It is good to be aware of the available options. However, while a medication may be new, this does not always mean it is superior to an older product. The opposite can also be true. Cost, safety, convenience, and how well the medication works should all be considered when deciding which medication is best.