APS 101 takes you through the ins and outs of APS, providing facts and key information to help you better understand the disease.
APS 101 is written by Jacqueline Madison, MD, Assistant Professor in the Division of Rheumatology and member of the Jason Knight Lab. In this month’s edition, Dr. Madison discusses what medications are available to treat and prevent blood clots.
What types of blood thinners are used to treat and prevent blood clotting in APS?
In APS, there are two basic problems: inflammation and blood clots, also called thrombosis. Our group is trying to find the best ways to treat the inflammation (more on this in a future article). For now, let’s talk about how we can prevent blood clots.
Once someone with APS has had a clot, in almost all circumstances, they need to begin receiving “anticoagulation”. This is done through medications that function as “blood thinners”. There are a few options.
Heparin
In the short-term, if someone is hospitalized, they might receive heparin through an IV. Heparin is a natural product that binds to a protein called antithrombin. This activates antithrombin, which is then able to attach to, and interferes with, other proteins that stimulate blood clotting. Overall, this stops new clots from forming and allows the body to slowly, but surely, eliminate clots that are already present.
Low-molecular weight heparin
This is a medication that is made by modifying the heparin described above. As its name suggests, it is a smaller molecule and hence called “low-molecular weight heparin (LMWH)”. One common type is called enoxaparin (or brand name Lovenox). It works similarly to heparin, but the advantage is that it can be reliably administered as an injection just under the skin at home. Most patients can learn to do this themselves with no problem! LMWH can be considered as a treatment for many patients with APS. Some of the positives of LMWH are:
- Given at home (an injection once or twice per day)
- Blood tests can monitor how well it is working
- Reversing agents are available (in case a patient starts bleeding too much)
- Safe in pregnancy (does not cause birth defects)
Vitamin K antagonists
The most common anticoagulant medication used in APS is warfarin (also called brand name Coumadin). This medication is the “vitamin K antagonist” available in the United States. Other countries have ones that are slightly different. Vitamin K is needed to produce certain proteins in the body that promote blood clotting. Warfarin prevents the body from creating active vitamin K and hence these clotting proteins. This is an indirect mechanism, and it takes a few days for warfarin to take effect once it is started. Vitamin K antagonists are very well-studied in APS, and that is why they are usually our first choice. Some other positives of warfarin are:
- An oral medication in pill form
- Easy to monitor with a commonly available blood test (called international normalized ratio or INR)
- Reversible in case a patient starts bleeding too much
- Safe in people with kidney disease
Those who take warfarin of course know that there are also some frustrations including the need to keep natural vitamin K intake in their diet as stable as possible and the requirement for regular INR bloods tests. Also, when the medication is first being started, blood must be tested more frequently.
Direct oral anticoagulants
There is another category of anticoagulant medications called direct oral anticoagulants (DOACs). Each DOAC binds directly to a single protein important in forming clots (as compared with warfarin, which interferes with the production of several such proteins). Some examples of DOACs are rivaroxaban (Xarelto) and apixaban (Eliquis). We know that in some patients with APS, such as those with “triple-positive” antiphospholipid antibodies, these are typically not a good medication choice. It is not yet clear if there may be other circumstances in which their use is okay.
Antiplatelet medications
There is another type of treatment to prevent blood clots: antiplatelet medications. The most well-known example is aspirin. Antiplatelet medications work by preventing platelets (tiny cells in the blood that support blood clotting) from activating, clumping, and getting involved in clotting. In APS, there are typically three situations in which aspirin is recommended.
- Primary prevention: In some patients with antiphospholipid antibodies, but without a prior thrombotic event, aspirin may be recommended to prevent a clot before it happens. This is often a judgment call as there are few high-quality clinical trials telling us when we should do this.
- Obstetric APS: In patients with pregnancy complications related to APS, aspirin is often recommended in combination with LMWH to prevent these pregnancy complications.
- History of arterial blood clots: In some patients with clots that affect the arteries (examples are strokes and heart attacks), aspirin may be recommended in combination with an anticoagulant medication to prevent recurrent clots.
There are other types of antiplatelet medications, the most well-known being clopidogrel or Plavix, which is often given to patients who have had a heart attack. There are some specific cases where these other antiplatelet medications are used in APS, typically related to a patient’s other medical history.
Summary
Overall, there are a few options in terms of treating and preventing blood clots in APS, and each individual patient’s history needs to be considered in detail before choosing the best option. We, in rheumatology, work closely with our colleagues in hematology when making a recommendation for the best medications to treat our APS patients.
Contributed by Jacqueline Madison, MD
Join Our Email List
If you are interested in receiving updates on our patient care and research efforts, please join our APS Program email list.
