The incidence of immune thrombocytopenia increases with older age. This population is at risk for arterial thrombosis. Due to an increased turn-over of platelets, low-dose aspirin once daily may be insufficient in this population to protect against arterial thrombosis. This study is aimed at assessing the pharmacodynamics of aspirin once daily on platelet function in these patients.

The incidence of immune thrombocytopenia increases with older age. About 20% of patients who develop immune thrombocytopenia are exposed to low-dose aspirin for arterial thrombosis prophylaxis. Moreover, immune thrombocytopenia patients have an increased risk for developing arterial thrombosis as compared with matched controls from the general population. Because ITP patients have an increased turn-over of platelets and aspirin is an irreversible inhibitor of cyclooxygenase-1, aspirin taken once daily may be insufficient to provide stable inhibition of platelet function. This has been demonstrated in myeloproliferative neoplasms with a higher platelet turn-over as well; aspirin is given twice daily to these patients. In immune thrombocytopenia, epidemiological findings sustain this assumption because aspirin is not associated to an increased risk of bleeding. The primary aim of this study is to assess the residual platelet function after 75 mg aspirin intake (H24). Secondary objectives are to assess the kinetics of platelet function after daily 75 mg aspirin intake and the relation with arterial thrombosis.

Inclusion Criteria:

• adult patients
• non-treated immune thrombocytopenia or immune thrombocytopenia with stable treatment (at least 1 month)
• treated with aspirin daily for a cardiovascular disease; stable platelet count < 100 x 109/L
• at least one month following an arterial thrombosis
• no other antiplatelet drug and anticoagulant
• female patient with childbearing potential must have acceptable method of birth control
• affiliated or benefiting from public health insurance

Exclusion Criteria:

• opposition to participate
• adults under guardianship or other legal protection
• deprived of their liberty by judicial or administrative decision
• pregnancy or breastfeeding