Clopidogrel and Aspirin for the Treatment of Polycythemia Vera

Clopidogrel (Plavix) and aspirin are two antithrombotic agents (blood thinners) commonly
used in patients with previous thrombotic events (stroke or heart attack). Thrombosis is the
formation of a blood clot in a blood vessel. Patients with polycythemia vera are routinely
treated with aspirin which has been shown to be effective in reducing their thrombotic risk.
However, in polycythemia vera patients with previous thrombosis, a further benefit might be
obtained by using the combination of aspirin and clopidogrel which is routinely used in
patients with recent acute myocardial ischemia (reduced blood supply to the heart muscle).
The study will assess whether this combination therapy greatly increases the risk of
bleeding versus aspirin alone, if clopidogrel reduces biological factors that might lead to
a stroke or heart attack, and whether a high number of patients with polycythemia vera are
resistant to clopidogrel.

Approximately 200 subjects will be enrolled to the Myeloproliferative Disorders-Research
Consortium (MPD-RC) study in Europe and the United States with participation expected to
last for 7 months (6 months of receiving study medication plus a 30 day follow-up visit).