Magnitude and time course of impaired primary haemostasis after stopping chronic low and medium dose aspirin in healthy volunteers.

Aspirin ingestion within the previous 7-10 days is often considered a relative contraindication to performing invasive procedures. However, aspirin is an important component of many patients' treatment and withholding therapy for this time may be dangerous. To measure both the magnitude of the impairment in primary haemostasis induced by aspirin and how much recovery of platelet function occurs within 48 h of stopping aspirin, we studied serial changes in bleeding time (BT) in a randomized, double-blind, placebo-controlled study. Fifty-two healthy volunteers had BT performed before and at 2, 9, 24 and 48 h after a 7-day course of either aspirin 75 mg, 300 mg or placebo. The main outcome recorded was BT at each time. Nearly 25% of subjects had extended BT to more than 10 min, but no BT were greater than 10 min, 48 h after stopping aspirin. There was a small but statistically significant (P < 0.01) difference between the 48-h and baseline BT in both aspirin groups (49 and 64 s in the 75 mg and 300 mg groups, respectively). There was no difference in the magnitude or time course of effect between low and medium dose aspirin (P = 0.392 and P = 0.797, respectively). We conclude that despite considerable inter-individual variability in the magnitude of aspirin effect on primary haemostasis, the time course of effect was consistent. In healthy volunteers, the defect in primary haemostasis had largely disappeared 48 h after the last dose.