Background: Dual antiplatelet therapy with acetylsalicylic acid (ASA) and clopidogrel is the standard of care for secondary prevention. Premature discontinuation of clopidogrel is associated with an increased risk of myocardial infarction (MI) or death, and greater health care expenditure.
Aim: To develop an objective method for identification of patients with high risk of non-adherence to clopidogrel after MI.
Methods: A total of 189 patients were enrolled into a prospective, observational, single-centre study with a nine-month follow-up. Patients received a 600-mg loading dose and 75-mg maintenance dose of clopidogrel in combination with ASA doses of 300 mg and 75 mg, respectively. Adenosine diposphate-induced platelet aggregation (ADP-PA) was assessed during baseline hospitalisation and at three, six, and nine months after discharge. Adherence to medication with clopidogrel was defined as the proportion of drug availability based on data from the National Health Fund regarding prescribed drug purchases. Adherence was arbitrarily judged adequate when the proportion exceeded 80%.
Results: According to our hypothesis, ADP-PA in non-adherent patients should be higher at follow-up visits (at least once) as compared with measurement at hospitalisation. Based on the ROC curve analysis, the optimal cut-off point equal to 4 U was defined (p < 0.0001, 95% CI 0.562-0.654; sensitivity: 60.6%, specificity: 57.1%, positive predictive value: 63.3%, negative predictive value: 54.2%). The prevalence of true adherence to medication in groups of high and low probability of adherence defined according to developed criteria amounted 60 (50.8%) and 23 (32.4%) cases, respectively (p = 0.01).
Conclusions: The newly developed method of objective identification of patients with high risk of non-adherence to clopidogrel after MI is easily applicable and cheap, and, despite relatively low sensitivity and specificity, it efficiently differentiates patients with regard to clinical end-points during follow-up.
Keywords: ADP-induced platelet aggregation; adherence to medication; clopidogrel.