[Is antiplatelet therapy always effective?]

Acetylsalicylic acid (ASA) and clopidogrel (KLP) therapy is associated with the high degree of variability in response to the drug and some patients are drug-resistant. The aim of our study was to evaluate the individual response to antiplatelet therapy in patients at high risk of cardiovascular events treated with ASA (n = 131), KLP (n = 51) or ASA + KLP (n = 34).

Investigations were performed in them by light transmission aggregometry and in selected patients by VASP fosforylation.

Good response to ASA treatment with arachidonic acid-induced platelet aggregation inhibition < 20% reached 75.0% of patients, partial response with 20-40% inhibition 12.9% of patients and poor response with > 40 % inhibition 12.1 % of patients. Good response to KLP treatment with 20 µmol/l ADP-induced platelet aggregation inhibition < 60% reached 66.1% of patients, partial response with 60-70% inhibition 13.9% of patients and poor response > 70% in 20% of patients. In patients treated by KLP + ADP induced platelet aggregation correlated with VASP fosforylation. We found, that 50% of KLP-treated and 44.4% of ASA-treated patients obtained the adequate response to therapy by compliance improvement. In 80% of patients, which did not respond to KLP therapy in daily dose of 75 mg, the adequate response after the increase to daily dose of 150 mg was observed. The increase of ASA daily dose above 100 mg did not improve in our patients their response to therapy. However, in those patients without a good response to low-dose ASA (< 100 mg daily) the increase to daily dose of 100 mg effectively influenced the aggregatory response.

Laboratory monitoring of individual response allows the optimalization of the antiplatelet therapy. The patients who could profit from other type of antiplatelet therapy, such as prasugrel and ticagrelor, can be selected by this method.