title: Antiplatelet drugs for polycythaemia vera and essential thrombocythaemia.
abstract: BACKGROUND
  Polycythaemia vera and essential thrombocythaemia are chronic Philadelphia-negative myeloproliferative disorders, which increase the risk of arterial and venous thrombosis as well as bleeding. In addition to the different therapeutic strategies available, aspirin is often used to prevent platelet aggregation.
  
  
  OBJECTIVE
  To quantify the benefit and harm of antiplatelet drugs for long-term primary and secondary prophylaxis of arterial and venous thrombotic events in patients with polycythaemia vera or essential thrombocythaemia.
  
  
  METHODS
  Our searched included the CENTRAL (The Cochrane Library, issue 1 2007), MEDLINE (1966 to 2007) and EMBASE (1980 to 2007) databases, online registers of ongoing trials and conference proceedings. The date of the last search was March 2007.
  
  
  METHODS
  All randomised controlled trials (RCTs) comparing long-term (>6 months) use of an antiplatelet drug versus placebo or no treatment in patients with polycythaemia vera or essential thrombocythaemia, diagnosed by established international criteria, with data for at least one of the selected outcomes, were included.
  
  
  METHODS
  Using a predefined extraction form, we collected and analysed the following data where appropriate: mortality from arterial and venous thrombotic events, mortality from bleeding episodes, fatal and non-fatal arterial thrombotic events, fatal and non-fatal venous thrombotic events, micro-circulation events, transient neurological and ocular manifestations, major and minor bleeding episodes, all-cause mortality and any adverse events. We based quantitative analysis of outcome data on an intention-to-treat principle. The overall treatment effect was estimated by the pooled odds ratio (OR) with 95% confidence interval (CI) using a fixed-effect model (Mantel-Haenszel).
  
  
  RESULTS
  Two RCTs that investigated 630 patients with an established diagnosis of polycythaemia vera, with no clear indication or contraindication to aspirin therapy, were included in this review. The use of aspirin, compared with placebo, was associated with a lower risk of fatal thrombotic events (although this benefit was not statistically significant (OR 0.20, 95% CI 0.03 to 1.14)) and did not increase the risk of major bleeding (OR 0.99, 95% CI 0.23 to 4.36). No studies have been published in patients with essential thrombocythaemia or studying other antiplatelet drugs.
  
  
  CONCLUSIONS
  The available evidence suggests that the use of aspirin is associated with a statistically non-significant reduction in the risk of fatal thrombotic events, without an increased risk of major bleeding, when compared with no treatment in patients polycythaemia vera who have no clear indication or contraindication to aspirin therapy.
authors.affiliation: University of Insubria, Department of Clinical Medicine, viale Borri, 57, Varese, Italy, 21100. alexsquizzo@libero.it
authors.forename: A
authors.initials: A
authors.lastname: Squizzato
authors.forename: E
authors.initials: E
authors.lastname: Romualdi
authors.forename: S
authors.initials: S
authors.lastname: Middeldorp
mesh_terms: D000925:Anticoagulants / Q000008:administration & dosage / Q000009:adverse effects; D001241:Aspirin / Q000008:administration & dosage* / Q000009:adverse effects; D006801:Humans; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage* / Q000009:adverse effects; D011087:Polycythemia Vera / Q000188:drug therapy*; D016032:Randomized Controlled Trials as Topic; D013920:Thrombocythemia, Essential / Q000188:drug therapy*; D013927:Thrombosis / Q000517:prevention & control*
chemical_list: D000925:Anticoagulants; D010975:Platelet Aggregation Inhibitors; D001241:Aspirin