Aspirin noncompliance is the major cause of "aspirin resistance" in patients undergoing coronary stenting

Objectives We investigated the hypothesis that biological aspirin "resistance" may often be related to noncompliance in patients undergoing coronary stenting. Background Premature discontinuation of antiplatelet therapy has been identified as a major risk factor for stent thrombosis and prior aspirin withdrawal has been associated with poor prognosis after acute coronary syndrome. Methods We prospectively investigated the occurrence of aspirin noncompliance in 136 consecutive patients undergoing coronary stenting receiving aspirin 75 mg daily. We analyzed posttreatment maximal intensity of arachidonic acid-induced platelet aggregation (AA-Ag) during hospitalization after controlled intake of aspirin and 1 month after hospital discharge. After 1 month, all "non responders" received controlled aspirin 75 mg and assessment of response was repeated. Aspirin nonresponse was defined by AA-Ag >30%. Results During inhospital period, the range of AA-Ag varied from 0% to 34% with a mean value of 7.5% +/- 10%, and 4 patients (3%) were classified as nonresponders. One month after discharge, AA-Ag of the population was significantly higher than during the hospital phase (15.3 +/- 23 vs 7.5 +/- 10%, P = .0004), and 19 patients (14%) were identified as nonresponders. After controlled administration of aspirin, all but one of these nonresponders became responders and were identified as patients with noncompliance rather than biological resistance. Conclusion Aspirin resistance is rare in compliant patients using methods that directly indicate the degree of platelet cyclooxygenase inhibition. More than 10% of patients receiving aspirin for coronary stenting are noncompliant for aspirin therapy during the first month after stenting. These results suggest a need for improved education of these patients. (Am Heart J 2009; 157:889-93.)