Abstract 2863: Prevalence of Clopidogrel Resistance in Healthy Volunteers
Background: Previous studies have demonstrated that some pts with ACS do not adequately respond to clopidogrel. Some have attributed this “resistance” to increased baseline platelet reactivity in ACS pts. Whether similar variability in response to clopidogrel is evident in clinically stable pts had not been previously evaluated.
Method: We studied 50 healthy volunteers (20 M, age = 51.8 ± 6.1). We measured % platelet aggregation using platelet rich plasma (PRP) with 5 and 20 μM ADP at baseline, 2 and 24 hrs following clopidogrel (300 mg) plus ASA (325 mg). Subjects were classified into 4 groups according to their response at 2 and 24-hour post clopidogrel dose: Group I: <10% inhibition; Group II: 10% to 29% inhibition; Group III: 30% to 50% inhibition; and Group IV: >50% inhibition.
Results: The mean inhibition in response to 5 μM ADP at 2 and 24 hrs were 33.3 ± 21.9% and 39.2 ± 14.6%, respectively. The mean inhibition in response to 20 μM ADP at 2 and 24 hrs were 19.5 ± 15.6% and 27.6 ± 13.6%, respectively. The number of subjects classified in each group is summarized in table⇓ below.
Conclusion: Platelet inhibition increased at 24 hrs vs. 2 hrs. A substantial portion of a normal population exhibits “resistance” suggesting that baseline platelet activation is not an important determinant of this phenomenon.