The clinical relevance of response variability to antiplatelet therapy.

Interindividual variability in the pharmacological response to antiplatelet drugs has been reported in some studies. Suboptimal response to aspirin, as determined by specific tests (serum thromboxane B(2)), appears to be rare and in most cases is caused by poor compliance. In contrast, studies using specific tests to measure the pharmacological effect of clopidogrel showed a wide variability of responses, with a significant number of subjects (approximately one-third) who were very poor responders. Interindividual differences in the extent of metabolism of clopidogrel to its active metabolite is the most plausible mechanism for the observed interindividual variability in platelet inhibition. Tailored treatment based on laboratory monitoring of platelet function has been proposed as a solution to poor responsiveness to clopidogrel. However, we still need to identify the ideal laboratory test and to answer basic questions on its clinical utility and cost-effectiveness before monitoring clopidogrel therapy can be recommended in clinical practice.