ABNORMALLY HIGH PLATELET ACTIVITY AFTER DISCONTINUATION OF ACETYLSALICYLIC-ACID TREATMENT

Production of 12-L-hydroxy-5,8,10-heptadecatrienoic acid (12-HHT) from platelets and bleeding times were studied in 32 males during acetylsa licylic acid (ASA) treatment and 1 and 2 weeks after withdrawal. All p atients (age 42-77 years) had ASA treatment because of angina pectoris . The metabolite 12-HHT is formed in the same amount as the proaggrega tory and vasoactive metabolite thromboxane A(2). Initially the daily A SA dose was 75 mg (n = 15), 160 mg (n = 12) or 250-300 mg (n = 5). in all patients, median 12-HHT level increased from 40 to 240 g/ 750 x 10 (6) platelets (P < 0.001) 1 week after withdrawal of ASA, and four pat ients had abnormally high values. Median bleeding time decreased from 312 to 268 s (P = 0.003) in the 75 mg group and from 315 to 235 s in t he 160 mg group (P = O.01). Two weeks after withdrawal of ASA, median 12-HHT was 390 g/750 x 10(6) platelets and eight patients (25%) had ab normally high values. One patient still had a prolonged bleeding time. Wide interindividual variations were observed in all groups. Our resu lts indicate that rapid withdrawal of ASA, may cause abnormally high 1 2-HHT levels reflecting increase of thromboxane A(2) with possible haz ardous effects in patients with cardiovascular disease.