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Summaries for Patients |1 July 2003

How Long Should Blood Thinners Be Given to Patients Who Have Had a Pulmonary Embolism?

Article, Author, and Disclosure Information

What is the problem and what is known about it so far?

Blood clots sometimes form in leg veins and then break loose. When they travel to the lungs, they can cause serious or fatal consequences. The process of clot formation and breakaway is called thromboembolism, and blood clots that reach the lungs cause pulmonary embolism. Doctors can treat these problems with blood thinners. People who have had one pulmonary embolism are at increased risk for recurrent thromboembolism. The likelihood of recurrence depends on whether there is a transient problem that promotes clot formation (such as leg trauma) or no recognizable inciting event. Despite their effectiveness, blood thinners can also cause dangerous bleeding, so doctors prefer to treat patients with pulmonary embolism as briefly as possible. No one knows the safest treatment duration for a first pulmonary embolism, but doctors often give treatment for 3 months in patients with short-term risk factors and 6 months in those without known risk factors.

Why did the researchers do this particular study?

To find out if patients with a first pulmonary embolism benefited from extending blood-thinning therapy to 6 months (those with short-term risk factors) and to 1 year (those without known risk factors).

Who was studied?

326 patients who had completed 3 months of blood-thinning therapy for pulmonary embolism but had not experienced a recurrence or an episode of bleeding were included in the study. 145 of the patients had short-term risk factors for pulmonary embolism and 181 patients had no known risk factor.

How was the study done?

The researchers randomly assigned study participants to either stop blood thinners immediately or continue therapy (for an additional 3 months for those with short-term risk factors or 9 months for those with no known risk factors). They followed all participants to detect symptoms of recurrent pulmonary embolism and tested the suspected cases to confirm the diagnosis. They also recorded any episodes of major bleeding or other complications. Study participants returned for follow-up 3, 6, and 12 months after they entered the study and then every 6 months until the study was complete.

What did the researchers find?

33 patients had recurrent thromboembolic disease, but only one of these episodes occurred while the patient was still receiving blood thinners. Once blood thinners were stopped, patients who had received extended therapy were just as likely to develop thromboembolism as those who received shortened therapy. Complications were similar in both the groups.

What were the limitations of the study?

Since both patients and doctors knew the treatment group assignments, more tests may have been done to confirm recurrence in one group than the other.

What are the implications of the study?

Extended treatment with blood thinners does not seem to protect against recurrence once therapy has been discontinued. Patients at high risk for recurrence may best be treated by continuing blood thinners indefinitely.

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