Discrepancies in assessment of adherence to antiplatelet treatment after myocardial infarction.

The poor response to clopidogrel is multifactorial and includes, amongst others, low patient adherence to medication. The aim of this study was to assess the reported patient adherence to treatment with clopidogrel and confront it with adherence assessed by drug availability. We evaluated determinants of adherence and its impact on platelet aggregation and clinical outcome. The study population comprised 184 patients treated with primary percutaneous coronary intervention for acute myocardial infarction. Follow-up visits were scheduled at 3, 6 and 9 months after discharge. Patient adherence to clopidogrel was defined according to self-reported drug intake and verified based on data from the National Health Fund regarding the purchase of prescribed drugs. The patients were judged as adherent when the proportion of drug availability exceeded 80%. According to drug availability, 100 (54.3%) patients were adherent and 84 (45.7%) were nonadherent. The analysis identified the following factors as predictors of low adherence (<80%): adenosine diphosphate-induced platelet aggregation (ADP-PA) during hospitalization ≤45 U, male gender and occurrence of ST-elevation myocardial infarction [(STEMI) vs. non-STEMI (NSTEMI)], while three-vessel disease was predictive of high adherence to medication. Compared with drug availability-based assessment, self-reported drug intake was significantly different: 172 (94.5%) patients reported regular and 10 (5.5%) patients reported irregular intake of clopidogrel. Clinical follow-up suggested that the self-reported nonregular clopidogrel intake may discriminate patients with a high risk of cardiovascular events. We demonstrated a huge discrepancy between the two most widely used methods for the evaluation of adherence to clopidogrel in secondary prevention treatment in patients after STEMI and NSTEMI. ADP-PA during hospitalization ≤45 U, male gender and STEMI (vs. NSTEMI) were independent predictors of nonadherence while three-vessel disease was independently predictive of adherence to treatment with clopidogrel in the investigated population.