BMJ  2004;328 (10 April), doi:10.1136/bmj.328.7444.0-f

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Low dose aspirin safely reduced thrombosis in polycythaemia vera

Question Is low dose aspirin safe and effective for the prevention of thrombotic complications in patients with polycythaemia vera?

Synopsis Polycythaemia vera is associated with increased blood viscosity, which in turn leads to thrombotic complications. A previous study with high dose aspirin (900 mg/day) was unsuccessful because of a high risk of gastrointestinal bleeding. In this randomised controlled (double blinded) study, 518 patients with polycythaemia, no contraindication to aspirin, and no other indication for antithrombotic therapy were randomised (allocation concealed) to aspirin 100 mg/day or matching placebo. The average red cell count was 5.9 million cells per microlitre, and most patients had a normal platelet count (range 179 000 to 63 000 cells/mm³). The two primary end points were the combination of nonfatal myocardial infarction (MI), nonfatal stroke, or death from cardiovascular causes, and this combination plus pulmonary embolism (PE) and major venous thrombosis. The groups were balanced at the beginning of the study, analysis was by intention to treat, and patients were followed up for a mean of three years. The study was stopped earlier than intended because of difficulty recruiting patients and lack of funding. Patients were evaluated once a year, and end points were adjudicated by two or more evaluators blinded to the treatment assignment. There was a consistent but not always statistically significant benefit to treatment. The risk of the first (2% v 4.9%; P = 0.09) and second (3.2% v 7.9%; P = 0.03) composite end points was lower in the aspirin group. Thus, you would have to treat 21 patients to avoid one non-fatal myocardial infarction, non-fatal stroke, death from cardiovascular causes, pulmonary embolism, or major venous thrombosis. There were trends toward lower all cause mortality and for each of the individual clinical end points. The risk of major bleeding was similar, with three episodes in the aspirin group and two in the placebo group, but there was a trend toward more minor bleeding in the aspirin group (20 v 12 episodes; P = 0.1).

Bottom line Low dose aspirin (100 mg/day) is safe and reduces the risk of thrombotic complications in patients with polycythaemia vera who have a normal platelet count.

Level of evidence 1b (see www.infopoems.com/levels.html). Individual randomised controlled trials (with narrow confidence interval).

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Landolfi R, Marchioli R, Kutti, et al. Efficacy and safety of low-dose aspirin in polycythemia vera. N Engl J Med 2004;350: 114-24[Abstract/Free Full Text].

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^* Patient-Oriented Evidence that Matters. See editorial ( BMJ 2002;325: 983[Free Full Text])

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