Determination of Clopidogrel Resistance by Whole Blood Platelet Aggregometry and Inhibitors of the P2Y12 Receptor

Abstract

Background: Inhibition of platelet aggregation by clopidogrel may be insufficient in up to 30% of users. These nonresponders carry an increased risk of cardiovascular events. We reported here a simple assay to study clopidogrel responsiveness. Methods: Electrical impedance aggregometry was performed in diluted whole blood in the presence of 5 and 20 mol/L ADP. Some samples were incubated with 0.1 mmol/L methyl-S-adenosine monophosphate (Me-SAMP), a P2Y 12 receptor blocker, to maximize inhibition of aggregation before aggregometry. To validate the assay, we analyzed 6-min impedance in 21 healthy probands and 244 patients with coronary artery disease (CAD). Results: At 5 mol/L ADP, the imprecision of the assay was 11%. Mean (SD) impedance of the healthy cohort was 12.2 (2.2) ⍀. The mean ؊ 3 SD was used to define the cutoff for clopidogrel responsiveness: responders and nonresponders exhibited a 6-min impedance <5 ⍀ and >5 ⍀, respectively. Samples from nonresponders were incubated with MeSAMP and analyzed again to distinguish pharmacokinetic and pharmacodynamic types of resistance. Sixteen percent of CAD patients were classified as nonresponders (38 and 2 cases of pharmacokinetic and pharmacodynamic resistance, respectively). Female sex was strongly associated with clopidogrel resistance (P ‫؍‬ 0.0002, Fisher exact test). A higher clopidogrel loading dose (P ‫؍‬ 0.0353, MannWhitney U-test) was given to responders (median, 450

Relationship between thromboelastography and long-term ischemic events as gauged by the response to clopidogrel in patients undergoing elective percutaneous coronary intervention

“…Interestingly, the current results based on a Cox model indicated that female patients had a much higher risk of experiencing ischemic events than did male patients, and a previous study yielded a similar finding. Several studies have indicated that HPR is more prevalent in females than males because of a stronger platelet aggregation reaction to platelet agonist stimulation (13)(14)(15). This might be caused by a high of clotting at the baseline, the effects of female hormone, or a diminished reaction to clopidogrel in female patients.…”

Determination of Aspirin Responsiveness by Use of Whole Blood Platelet Aggregometry

“…The increase in impedance (⍀) is associated with the amount of platelet aggregates deposited on the electrodes after the addition of a platelet agonist (12 ). Details of the aggregometry method have been reported (13 ). We started aggregation by addition of collagen or arachidonic acid (AA), final concentrations 1 mg/L and 0.5 mmol/L, respectively.…”

Dual Antiplatelet Drug Resistance Is a Risk Factor for Cardiovascular Events after Percutaneous Coronary Intervention

“…Such studies are difficult to perform because standardized assays for aggregometry are lacking (6 ). Recently, we validated assays using impedance aggregometry to study the aggregation responses to ASA and clopidogrel (7,8 ). We enhanced the specificity of these assays by in vitro incubation of blood samples with ASA or methyl-S-adenosine monophos-phate (Me-S-AMP), a selective ADP-(P2Y 12 )-receptor blocker.…”

“…This information is helpful for patient management because platelet inhibition can be improved by increased doses of clopidogrel and/or ASA in patients with a pharmacokinetic resistance. In comparison, pharmacodynamic resistance is less frequent (with a prevalence of approximately 2%) but requires switching to an alternative antiplatelet drug (7,8 ).…”