Compliance with antiplatelet therapy in patients with ischemic cerebrovascular disease. Assessment by platelet aggregation testing.

BACKGROUND AND PURPOSE Antiplatelet therapy is currently one of the methods for preventing transient ischemic attacks and cerebral thrombosis. Because antiplatelet agents are generally administered on a long-term basis, patient compliance is an important factor. The purpose of this study was to determine the compliance of patients during antiplatelet therapy by testing platelet aggregation. METHODS To establish the conditions for measuring platelet aggregation, the platelet aggregation test was performed in patients taking 81 mg/d aspirin or 200 mg/d ticlopidine at the following final concentrations of aggregation-inducing agents: 0.5, 1, 2, and 4 mumol/L ADP and 0.5 and 2 micrograms/mL collagen. The optimum measurement conditions for assessing patient compliance were determined. Under the conditions determined in the first study, platelet aggregation was assessed, and the effects of treatment were studied in 159 outpatients and 79 inpatients undergoing antiplatelet therapy. If the antiplatelet effect was insufficient, compliance was checked by interview. RESULTS The agents used and the final concentrations found to be optimum for assessing platelet aggregation were 2 micrograms/mL collagen for patients taking aspirin 81 mg/day and 2 mumol/L ADP for patients taking ticlopidine 200 mg/d. In 17 (10%) of the 159 outpatients, platelet aggregation was not adequately reduced because of noncompliance with their antiplatelet therapy. CONCLUSIONS This study indicated that monitoring of compliance is important for outpatients on antiplatelet therapy. It is best if platelet aggregation can be checked, but when this is impossible it is necessary to assess compliance periodically and provide patient guidance.