Dual antiplatelet drug resistance is a risk factor for cardiovascular events after percutaneous coronary intervention.
BACKGROUND
Nonresponsiveness to clopidogrel and acetylsalicylic acid (ASA), a frequent result of platelet aggregometry studies, has unclear clinical and prognostic significance.


METHODS
We performed impedance aggregometry in 182 patients 12-24 h after percutaneous coronary intervention (PCI) and a 600-mg loading dose of clopidogrel, adding 5 micromol/L ADP and 1 mg/L collagen to diluted whole blood to determine platelet inhibition by clopidogrel and ASA, respectively. Samples from nonresponders were incubated in vitro with methyl-S-adenosine monophosphate or ASA to distinguish between pharmacodynamic and pharmacokinetic types of resistance. We assessed a combined primary endpoint of myocardial infarction, target vessel revascularization, late stent thrombosis, or cardiac death.


RESULTS
Nineteen patients (10.4%) were dual nonresponders (nonresponsive to both ASA and clopidogrel), and 163 patients (89.6%) were designated responders. The latter group also included 15 and 14 single nonresponders (responsive to either clopidogrel or ASA, respectively), who exhibited endpoint frequencies comparable to those of full responders (n = 134). Pharmacokinetic resistance was most prevalent. Primary endpoints occurred more frequently in dual nonresponders (n = 6, 31.6%) than in responders (n = 20, 12.3%) (relative risk 2.57; 95% CI 1.18-5.61; log-rank P = 0.03). Multivariate analysis confirmed dual nonresponsiveness (hazard ratio 2.9; 95% CI 1.17-7.2; P = 0.02) as an independent risk factor.


CONCLUSIONS
Dual nonresponders carry a high cardiovascular risk after PCI and should obtain intensified antiplatelet therapy and follow-up.
Department of Medicine III, University of Heidelberg, Germany. boris.ivandic@med.uni-heidelberg.de
Boris T
BT
Ivandic
Mareike
M
Sausemuth
Hesham
H
Ibrahim
Evangelos
E
Giannitsis
Meinrad
M
Gawaz
Hugo A
HA
Katus
D000368:Aged; D001241:Aspirin / Q000627:therapeutic use*; D002318:Cardiovascular Diseases / Q000209:etiology*; D000077144:Clopidogrel; D015331:Cohort Studies; D004351:Drug Resistance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010975:Platelet Aggregation Inhibitors / Q000627:therapeutic use*; D012307:Risk Factors; D013988:Ticlopidine / Q000031:analogs & derivatives* / Q000627:therapeutic use
D010975:Platelet Aggregation Inhibitors; D000077144:Clopidogrel; D013988:Ticlopidine; D001241:Aspirin