More on: adenosine diphosphate-inducible platelet reactivity shows a pronounced age dependency in the initial phase of antiplatelet therapy with clopidogrel

Relationship between clopidogrel-related polymorphisms and variable platelet reactivity at 1 year: A cohort study from Han Chinese

Background:

This study was designed to investigate the effect of clopidogrel-related gene polymorphisms on platelet reactivity and clinical outcome in Chinese Han patients.

Materials and Methods:

Three hundred and thirty-six percutaneous coronary intervention - treated patients were recruited and followed for 1 year. Blood samples were collected from all patients for DNA genotyping. The platelet reactivity unit was measured by the VerifyNow technique. The CYP2C19*2, CYP2C19*3, CYP2C19*17, ATP-binding cassette subfamily B member 1, ITGB3, CYP2C9*3, CYP2B6*9, and P2Y12 alleles were assessed.

Results:

The clinical endpoints were related to previous heart disease history (11.90% vs. 28.57%, P = 0.017), stroke (12.24% vs. 16.67%, P = 0.039), and diabetes (27.55% vs. 52.38%, P = 0.047). High on-treatment platelet reactivity (HTPR) was frequent in advanced age (P = 0.019), male gender (P = 0.016), hypertension (P = 0.033), and chronic renal failure (P = 0.040). There were more endpoints in the CYP2C19*2 and P2Y12 mutant carriers (76.19% vs. 43.20%, P < 0.001; 50.00% vs. 35.71%, P = 0.001, respectively), whereas fewer in the CYP2C19*17 mutant carriers (11.90% vs. 56.46%, P = 0.001). CYP2C19*2 and P2Y12 polymorphism manifested HTPR (194.25 ± 45.91 vs. 151.38 ± 58.14, P < 0.001; 180.33 ± 67.25 vs. 161.89 ± 56.49, P = 0.008, respectively), whereas CYP2C19*17 mutant improved platelet reactivity (97.17 ± 45.38 vs. 169.08 ± 57.15, P = 0.003). However, there were no further cardiovascular deaths in endpoint patients.

Conclusion:

In Han Chinese people of mainland China, clopidogrel-related gene polymorphisms are related to variable platelet reactivity after clopidogrel maintenance dosing, which influences major adverse cardiovascular events, without an effect on cardiac death.

Pharmacogenetics in Oral Antithrombotic Therapy

Certain antithrombotic drugs exhibit high patient-to-patient variability that significantly impacts the safety and efficacy of therapy. Pharmacogenetics offers the possibility of tailoring drug treatment to patients based on individual genotypes, and this type of testing has been recommended for 2 oral antithrombotic agents, warfarin and clopidogrel, to influence use and guide dosing. Limited studies have identified polymorphisms that affect the metabolism and activity of newer oral antithrombotic drugs, without clear evidence of the clinical relevance of such polymorphisms. This article provides an overview of the current status of pharmacogenetics in oral antithrombotic therapy.

Advanced age and high-residual platelet reactivity in patients receiving dual antiplatelet therapy with clopidogrel or ticagrelor

ESSENTIALS: Dual antiplatelet therapy (DAPT) in elderly patients requires balancing bleedings and thrombosis. Impact of age on high residual on-treatment platelet reactivity (HRPR) on DAPT was studied. A reduced effectiveness of adenosine diphosphate antagonists was observed over 70 years of age. The occurrence of HRPR was increased among elderly patients with both clopidogrel and ticagrelor.

BACKGROUND

The aim of the present study was to evaluate the impact of age on platelet function and the occurrence of high residual on-treatment platelet reactivity (HRPR) in patients treated with dual antiplatelet therapy (DAPT) using acetylsalicilic acid (ASA) and clopidogrel or ticagrelor.

METHODS

Patients treated with DAPT (ASA and clopidogrel or ticagrelor) were scheduled for platelet function assessment at 30-90 days post-discharge. By whole blood impedance aggregometry, HRPR was considered for ASPI test values > 862 AU*min (for ASA) and adenosine diphosphate (ADP) test values > 417 AU*min (for ADP antagonists). Elderly patients were defined as those aged ≥ 70 years.

RESULTS

Among 494 patients on DAPT, 224 (45.3%) were ≥ 70 years old. ADP-mediated platelet aggregation increased with decades of age (279.3 ± 148.6 vs. 319.6 ± 171.1 vs. 347.3 ± 190.1 vs. 345.7 ± 169.2), whereas no difference was observed for ASA response. A reduced effectiveness of ADP antagonists was observed among elderly patients; in fact, among the 117 patients displaying HRPR (23.7%), a higher prevalence was observed among patients over 70 years old (30.4% vs. 18.1%; adjusted odds ratio (OR) [95% confidence interval (CI)] = 2.19 [1.29-3.71]). Similar results were obtained among the 266 clopidogrel-treated patients (38.5% vs. 27.9%; adjusted OR [95% CI] = 2.91 [1.46-5.8]) and in the 228 patients receiving ticagrelor (19.1% vs. 8.1%; adjusted OR [95% CI] = 2.55 [1.02-8.59]).

CONCLUSION

In patients receiving dual antiplatelet therapy, advanced age is independently associated with a reduced effectiveness of ADP antagonists and a higher rate of HRPR with both clopidogrel and ticagrelor.

Hematocrit alters VerifyNow P2Y12 assay results independently of intrinsic platelet reactivity and clopidogrel responsiveness

BACKGROUND

The VerifyNow P2Y12 assay assesses the adequacy of clopidogrel therapy by measuring ADP-induced platelet activation in whole blood. Low hematocrit is associated with high clopidogrel on-treatment platelet reactivity (HTPR) defined by this assay.

OBJECTIVES

To characterize the effect of hematocrit on VerifyNow values and determine if it is due to hematocrit-dependent changes in intrinsic platelet reactivity or an in vitro assay phenomenon.

PATIENTS/METHODS

Adenosine diphosphate-induced platelet activation was measured using the VerifyNow P2Y12 assay, whole blood impedance and light transmission platelet aggregometry (LTA) before and after clopidogrel loading in 113 patients undergoing elective cardiac catheterization. Iso-TRAP-induced platelet activation was additionally measured using the VerifyNow device. Multivariate modeling employing clinical and laboratory variables was used to investigate the association between hematocrit and VerifyNow values.

RESULTS

VerifyNow P2Y12 reaction units (PRU) and iso-TRAP Base units before and after clopidogrel loading, but not their relative change, exhibited strong negative correlation with hematocrit (P ≤ 0.0005 for both). While hematocrit remained a strong predictor of post-clopidogrel PRU (P = 0.001) in multivariate modeling, it was independent of post-clopidogrel ADP-induced platelet reactivity as measured by LTA (P = 0.001). Correcting for the effects of hematocrit resulted in a 15-39% reduction in the prevalence of HTPR defined by thresholds of 208-236 PRU.

CONCLUSIONS

The effect of hematocrit on VerifyNow PRU values is an in vitro phenomenon that is independent of intrinsic change in ADP-induced platelet reactivity and clopidogrel responsiveness. Correcting for hematocrit when using this assay may more accurately identify patients with HTPR that may benefit from alternative antiplatelet therapy.

Relation of aspirin response to age in patients with stable coronary artery disease

Recent studies have suggested that clopidogrel response may vary significantly with age. Limited data are available exploring the age dependency of ex vivo aspirin response in young and old patients with stable coronary artery disease. Patients with stable coronary artery disease (n = 583) who had been treated with aspirin 75 to 325 mg/day for ≥1 week were recruited from a general cardiology practice. The study cohort was divided into 2 groups: patients aged <75 years (n = 438) and patients aged ≥75 years (n = 145). Aspirin response was determined using the VerifyNow Aspirin Test, and resistance was defined as ≥500 or 550 aspirin reaction units (ARU). The independent predictive value of age on VerifyNow score (as a continuous function) was determined using multivariate linear regression, adjusted for gender, body mass index, and diabetes mellitus. Younger and older patients had similar baseline clinical profiles, including relative doses of aspirin therapy. The mean VerifyNow Aspirin Test score was significantly higher in patients aged ≥75 years: 450 ± 54 versus 434 ± 53 ARU (p = 0.0007). After accounting for the primary covariates, age remained a predictor of VerifyNow score (p = 0.007). Aspirin resistance on the basis of the 500-ARU cutoff was higher in older patients (19% vs 11%, p = 0.009), but there was no difference when the 550-ARU cutoff was used (7% vs 5%, p = 0.40). In conclusion, aspirin response differs significantly by age in patients with stable CAD.

Acute coronary syndromes: considerations for improved acceptance and implementation of management guidelines

The management of acute coronary syndrome in Europe is covered by various European Society of Cardiology guidelines, which although valuable, are complex and may not always provide clear guidance in everyday clinical practice. Consequently, implementation of the guideline recommendations is frequently suboptimal. To complicate matters further, a wealth of new data from large trials examining novel anti-thrombotic agents will become or are already available, necessitating guideline updates. This article summarizes the gaps between current guideline-recommended treatment of acute coronary syndrome and daily practice as dictated by the evidence base, including recent trials. Reasons for the suboptimal implementation of the current European Society of Cardiology guidelines and possible solutions to making these more practice oriented are presented.

Are P2Y12 reaction unit (PRU) and % inhibition index equivalent for the expression of P2Y12 inhibition by the VerifyNow assay? Role of haematocrit and haemoglobin levels

The results of the whole blood VerifyNow P2Y12 assay can be expressed as platelet reaction units (PRU) or % inhibition index (%inh), but an optimal cut-off for the assessment of high on-treatment platelet reactivity (HPR) predictive of clinical events has been validated only for PRU. The aim of the study was to study the influence of haematological variables, such as platelet and leukocyte counts or haematocrit / haemoglobin, within the limits indicated by the manufacturer for assay validity, on the results of the test. We performed a comparison of PRU and %inh in a series 186 samples obtained from a clinical trial on patients under dual antiplatelet therapy. The results show that PRU significantly decreases with increasing haematocrit / haemoglobin, whereas %inh does not, due to a parallel change in PRU and iso-TRAP baseline value. PRU and % inhibition index are not equivalent for the definition of HPR, because of their different sensitivities to haematocrit / haemoglobin.