Antiplatelet ‘resistance’ and ‘non‐responders’: what do these terms really mean?

Abstract

The term 'resistance' should be restricted to very specialized physiologic circumstances, if not abandoned altogether. The term 'non-responder' needs to be placed in the context of the question: 'Non-responder to what?' Even if we would somehow magically know what an optimal response to antiplatelet therapy was, it will still be challenging to demonstrate an 'inadequate' response to antiplatelet therapy. At present there are two alternatives--give more drug or give additional drugs. Both strategies may work in further inhibiting platelet function, but both strategies can also be associated with an increased risk of bleeding. The trick, for the future, much as with our antihypertensive and lipid-lowering armamentaria, will be to know in whom to do what with which drug, and why. Single isolated measurements are not useful--if you don't know where you started, how we would know that antiplatelet drug is producing an 'adequate' clinical effect? There is no evidence of any sort of absolute 'threshold' that must be exceeded for treatment to be effective, and in the absence of this, if we are to evaluate the effect of a given drug, we have to have baseline values (off drug), therapeutic values (on drug), and some sort of assessment of both resting (unstimulated) and agonist-provoked (stimulated) platelet function. Moreover, given all of the different things that platelets do, the ideal assessment of platelet function and drug responsiveness will need to incorporate more than one agonist and some sort of assessment of both platelet activation and platelet aggregation. No one man (or test) tells us everything; it is the totality of the information that gives us the most complete picture. And, ultimately, we need to more firmly establish how the variability in platelet function and drug-associated changes in that function correlates with long-term, hard-endpoint clinical events.