Summary
Low-dose acetylsalicylic acid (ASA) has been shown to be beneficial in patients with
acute myocardial infarction and unstable angina pectoris. Oral administration of ASA
is difficult in the acute phase of these syndromes. In this study we evaluated the
effect of 25 mg, 50 mg or 100 mg of ASA given as an intravenous bolus injection on
platelet function and fibrinolysis in healthy males and related this to plasma concentrations
of ASA. No adverse effects were found. A complete inhibition of serum thromboxane
B2 synthesis was demonstrated 5 min after injection of 100 mg ASA intravenously. ASA
disappeared from the circulation within 60 min after bolus injection and at this time
thromboxane B2 synthesis was inhibited dose-dependently by 71%, 90% and 100% for doses of 25 mg,
50 mg and 100 mg, respectively. Inhibition of thromboxane B2 synthesis after 100 mg of intravenous ASA was still 96.5% at 24 h and 93.4% at 48
h after the injection. The bleeding time measured at 30 min after ASA administration
was significantly prolonged on the average by 70 s, 144 s and 211 s after 25 mg, 50
mg and 100 mg of ASA, respectively. Minor, but significant changes were found in tissue
plasminogen activator antigen and in plasminogen activator inhibitor within the first
hour after injection of low dose ASA, but similar changes were found after injection
of saline. No change in tissue plasminogen activator activity was found. We conclude,
that intravenous administration of low dose ASA is safe and easy, and that almost
immediate, complete blockage of serum thromboxane B2 synthesis can be obtained after a single intravenous bolus injection of 100 mg.
