New medications prevent harmful blood clots

Among the fifteen million patients discharged from hospitals in the United States annually, an estimated 51 percent are at risk of developing blood clots, called “thromboses,” or of spread of these clots to vital organs, which we call “embolism.”

Prevention of blood clots is an important issue. We are particularly concerned about this problem in persons with underlying medical problems that predispose to poor circulation, such as swelling of the legs, diabetes, or chronically irregular heart beats.

Typically, we prescribe blood thinners in the wake of a catastrophic event involving a blood clot. Examples include a blood clot in the legs. This may occur out of the blue, as an “idiopathic” or unexplained phenomenon.

Other causes may include the use of birth control pills, prolonged immobility on a long airplane flight, or impaired circulation due to prior injuries to the legs. There are also less common conditions that predispose an individual to blood clot formation, including inherited deficiencies or mutations in blood coagulation proteins.

Hematologists are experts at sorting out these conditions, as internal medicine specialists with expertise in diagnosing and treating blood disorders. Systemic lupus erthematosus, an auto-immune disease within my own field of rheumatology, can cause the blood to be excessively prone to clotting. When you think of it, the blood is a marvelous body tissue, capable of clotting when we have an accident and get cut, but also capable of coursing unimpeded through our arteries and veins from day-to-day. It is no wonder that this marvelous balance is occasionally perturbed. In fact, it is amazing that our blood works as well as it does, most of the time.

The most feared complication of a lower extremity blood clot is the possibility of an embolus, or broken off clot, passing through the blood to the heart, brain or lungs. The latter condition, called a “pulmonary embolism,” is potentially life-threatening and often difficult to diagnose, causing the sudden onset of shortness of breath, chest pain, and even sudden death. Severe blood clots may necessitate life-long blood-thinning, or “anti-coagulation” therapy. Traditionally, this involved two medications, heparin and coumadin. Heparin has a rapid effect, and used to be given intravenously in hospitals.

About thirty years ago, researchers developed a more convenient type of heparin, called “low molecular weight,” which is injectable under the skin. As heparin thins the blood acutely, a longer acting medication taken orally, called coumadin, is typically prescribed. The problem with coumadin, however, is that patients on this medication require constant rechecking of blood tests, and constant adjustment of the medication. For example, dietary intake of high levels of vegetables can lower the effect of the medication, necessitating a higher dose. Conversely, some medications can alter metabolism of the drug, necessitating that coumadin doses be lowered. I once ran a clinic entirely devoted to adjusting coumadin levels on patients in a large institutional setting. That is how cumbersome coumadin therapy may be. New drugs, however, are on the horizon, if not already available.

Pradaxa (dabigatran etexilate) and Xarelto (rivaroxaban) are approved alternatives to coumadin. Last month, the Food and Drug Administration also announced approval of Eliquis (apixaban) as another anticlotting drug. Pharmaceutical manufacturers are jockeying to develop newer agents that offer greater ease of administration, with comparable efficacy to older agents.

Elderly patients with irregular heart rhythms, such as “atrial fibrillation,” represent a common therapeutic challenge. An irregular heart rhythm may lead to blood clot formation, with the potential for a secondary stroke developing. Staying active and well hydrated is a good idea for most patients. Contracting leg muscles, for example, improves circulation to and from the legs. For specific recommendations, see your physician.

Scott Anderson, M.D., Ph.D. (stamdphd@comcast.net) is Clinical Professor of Medicine, Division of Rheumatology, UC Davis. This column is informational, and does not constitute medical advice.