Effects of acetylsalicylic acid in stroke patients. Evidence of nonresponders in a subpopulation of treated patients.

Platelet reactivity (PR) was tested two and 12 hours after acetylsalicylic acid (ASA) intake in 82 stroke patients, aged 59 +/- 14 years (33 female and 49 male). 10% of these patients showed a pathologically enhanced PR at least two hours after intake of 500 mg ASA (= primary ASA-nonresponder (PNR)). Only 10 hours later, a further 26% of these ASA treated patients exhibited a pathological platelet reactivity (greater than 1.25) (= secondary ASA-nonresponder (SNR)). Single ASA dosages of 500 mg or 200 mg were of identical effectiveness. Additional administration of metoclopramide in combination with 100 mg ASA was more effective as compared to a single dosage of 1000 mg ASA. Those who were SNR at onset of ASA therapy remained SNR as well 28 days later. The change from a normal, ASA corrected PR, to pathological PR values before a period of 12 hours ended seemed a sudden and irreversible event that could only be corrected by the next ASA application.