Response variability to clopidogrel: is tailored treatment, based on laboratory testing, the right solution?

Clopidogrel is an antithrombotic prodrug, whose active metabolite inhibits platelet function by irreversibly binding to the platelet receptor for adenosine diphosphate, P2Y(12). Wide inter-individual variability of response to clopidogrel has been reported in several studies: a significant proportion of treated patients (about one-third) exhibit a suboptimal inhibition of platelet function. Genetic and environmental factors that influence the absorption and/or the extent of metabolism of clopidogrel to its active metabolite account for the observed variability of response. Tailored treatment based on the results of laboratory tests of platelet function has been proposed as a solution to this problem, which has important clinical implications. Although it is often considered a desirable evolution of modern medicine, tailored treatment based on laboratory tests is actually an old remedy (of yet unproven efficacy, in the case of antiplatelet therapy) for the problem of response variability to antithrombotic drugs with unpredictable bioavailability. When possible, the use of alternative drugs with more uniform and predictable bioavailability, and with favourable profiles in terms of risk/benefit and cost-benefit ratios should be preferred. Moreover, tailored treatment with laboratory tests must be validated in randomized clinical trials before its implementation can be recommended. We still need to identify and standardize the laboratory test for this purpose, as well as answer basic questions on its clinical utility and cost-effectiveness, before tailoring clopidogrel therapy based on laboratory tests can be recommended in clinical practise.