"The study provides clear, consistent evidence that low-dose aspirin can help to prevent new venous blood clots and other cardiovascular events among people who are at risk because they have already suffered a blood clot," says the study's lead author, University of Sydney Professor, John Simes.
"The treatment effect of aspirin is less than can be achieved with warfarin or other new generation direct thrombin inhibitors, which can achieve more than an 80 per cent reduction in adverse circulatory and cardiopulmonary events.
"However, aspirin represents a useful treatment option for patients who are not candidates for anticoagulant drugs because of the expense or the increased risk of bleeding associated with anticoagulants."
Compared to placebo patients, those who took 100mg daily of aspirin had a one-third reduction in the risk of:
- thromboembolism, which is the obstruction of a blood vessel by a clot that has dislodged from another site in the circulation.
- deep vein thrombosis (DVT), which is the formation of a blood clot in a deep vein, predominantly in the legs.
- pulmonary embolism, which is a blood clot affecting the arteries that supply blood to the lungs.
- myocardial infarction (heart attack), stroke or cardiovascular death.
Most people who have had a blood clot in a leg vein (deep-vein thrombosis) or an embolism (where the clot blocks the blood flow) have anticoagulant drug treatment (such as warfarin) for at least 6 months, first to dissolve the clot and then to prevent it happening again.
However, long-term anticoagulant drugs are expensive and inconvenient, requiring frequent regular blood tests and adjustments to the dosage. Further, there is an elevated risk that the treatment could cause bleeding in some patients. For people who are not able to cope with this, the viable alternative of taking regular aspirin will be a great benefit.
"The study provides evidence that after a first venous thrombosis or embolism, daily aspirin reduces the risk of another event, without causing undue bleeding. This treatment is an alternative to long-term anticoagulation and will be especially useful for patients who do not want the inconvenience of close medical monitoring or the risk of bleeding," says Professor Simes.
"Aspirin will be ideal in the many countries where prolonged anticoagulant treatment is too expensive. A major benefit of this treatment is its cost-effectiveness. Aspirin is cheap, but it will save the treatment costs of the many recurrent clots that are prevented. This could mean a saving of millions of healthcare dollars worldwide."
Co-investigator Tim Brighton, a senior haematologist at Sydney's Prince of Wales Hospital, adds: "This important study demonstrates clearly that low-dose aspirin reduces the risks of further blood clot. This is especially important for patients who are not able to take long-term anticoagulant medications for whatever reason, such as personal preference, adverse effects of anticoagulant or cost."
The research collaboration combined the data from the Australia-led international ASPIRE study and the Italian WARFASA study. ASPIRE had 822 participants from Australia, New Zealand, Singapore, India and Argentina, followed up for an average of three years and WARFASA another 402 patients followed up for at least two years.