Population variability in the effect of aspirin on platelet function. Implications for clinical trials and therapy.

Little or nothing is known about how the inhibitory effect of aspirin on platelets distributes in the general population. We describe a simple whole-blood assay for the extent of aspirin-induced inhibition of platelet aggregation and its application to 31 aspirin-treated subjects. Platelet inhibition to two or more 325-mg aspirin tablets was measured using a newly developed method in 31 healthy, young adults. These subjects showed a wide range of variation in their response to aspirin, which in subsequent studies was found to be stable over time. The effect persisted even when the steps of gut absorption and liver metabolism were bypassed. We conclude that the response of platelets to aspirin varies to the extent that a significant proportion of the population may be nonresponsive and that this variability may be intrinsic to platelets and/or their blood environment.