Background: A reduced or nonresponse of some patients to P2Y12 inhibitors, especially clopidogrel,
has often been described with low or nonresponder rates ranging between 4% and 57%.
At German Heart Centers, clopidogrel in combination with acetylsalicylic acid is used
as a dual antiplatelet therapy as standard and in accordance with guidelines after
acute coronary syndrome and cardiac surgery bypass. An initial loading dose, however,
is often waived due to potential bleeding complications. We thus investigated these
patients regarding clopidogrel reactivity and influence of the missing loading dose.
Methods: 214 patients with acute coronary syndrome and CABG were included. Medication with
75 mg clopidogrel was commenced on the 6th postoperative day on average. A loading
dose of 300 or 600 mg was not administered. After the second single dose we tested
for clopidogrel reactivity using light transmission aggregometry utilizing VerifyNow.
We looked for the percentage of platelet inhibition, respondence rate and influence
of the missing saturation dose.
Results: 195 patients (91%) were found to be responders (percentage platelet inhibition above
50%). 19 patients (9%) were in the low responder range with a percentage inhibition
under 50%. In this group we found seven patients with postoperative thrombocytosis
over 500.000 platelets.
Conclusion: Our study shows the efficacy of a therapy without loading dose. A reduced or nonresponse
of some patients can be recognized by testing in advance. For these patients it is
necessary to change medication swiftly. It can be speculated that exceptionally high
platelet counts may be a reason for a reduced response and not only a coincidence.
This, however, needs to be investigated in a further study.
