Summary
The inhibitory platelet effect of clopidogrel is insufficient in approximately 5 to
30% of patients. These low responders (LR) face a significantly higher risk of cardiovascular
complications. The therapeutic management of LR is still undefined. In the present
study, we evaluate a novel therapeutic algorithm to reduce the incidence of clopidogrel
resistance. One hundred sixty-one patients on 100 mg ofAspirin co-medication underwent
elective coronary stenting and were given an initial dosage of 600 mg clopidogrel,
followed by 75 mg clopidogrel daily. 48 h later, the platelet responsiveness was tested
with ADP (5–20 μM) stimulation by impedance aggregometry (Chronolog 590). A significant
rise in impedance (> 5 Ω after 6 minutes, aggregation index > 65%) was defined as
LR. In this subgroup, platelets were stimulated with the selective P2Y12-ADP receptor antagonist 2-MeS AMP. One hundred twenty-three patients were clopidogrel-responders
(76.4%) and 38 patients were LR (23.6%). A defect of the ADP-receptor P2Y12 was found in three out of 38 LR (7.9%). Inhibition of platelet aggregation indicating
clopidogrel-responsiveness was achieved with either a clopidogrel high-dose regimen
(22/38, 57.9%); a repeat loading dose, doubling the maintenance dose) or with an alternative
therapy with ticlopidine (8/38 (21.1%); 250 mg twice daily).Thus the incidence of
LR was reduced from 23.6% to 5.0%. Our aggregometer–guided therapeutic algorithm reduced
the relative percentage of clopidogrel LR by 78.9%.This approach could prove to be
helpful in achieving a further decrease in the incidence of clopidogrel resistance.
Keywords
Aggregation - clopidogrel - low-responder - resistance - ticlopidine