Suboptimal response to clopidogrel and the effect of prasugrel in acute coronary syndromes

Prasugrel in the treatment of acute coronary syndrome

Dual antiplatelet therapy is the mainstay therapy in patients with acute coronary syndrome. The combination of aspirin and a P2Y12 inhibitor in patients who receive a coronary stent reduces the rate of stent thrombosis and the rates of major adverse cardiovascular events. The newer P2Y12 inhibitors (prasugrel and ticagrelor) have better efficacy than clopidogrel. Prasugrel provides greater inhibition of platelet aggregation and has a rapid onset of action. Current acute coronary syndrome guidelines recommend the use of both newer P2Y12 inhibitors. However, emerging data have shown that prasugrel is more efficient than ticagrelor in reducing the incidence of nonfatal myocardial infarction, stroke or cardiovascular death, without increased risk of major bleeding.

Impact of reduced-dose prasugrel vs. standard-dose clopidogrel on in-hospital outcomes of percutaneous coronary intervention in 62 737 patients with acute coronary syndromes: a nationwide registry study in Japan

Aims 

In Japan, reduced-dose prasugrel (loading/maintenance dose, 20/3.75 mg) has been approved for use in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI), because of the higher bleeding risk among East Asians. However, its safety in the real-world population has not been investigated. We aimed to evaluate the effectiveness and safety of reduced-dose prasugrel vs. standard-dose clopidogrel in ACS patients undergoing PCI.

Methods and results 

Acute coronary syndrome patients who underwent PCI in 2016, who were treated with either reduced-dose prasugrel or standard-dose clopidogrel in addition to aspirin, were identified from the nationwide Japanese PCI registry. The primary outcome was in-hospital mortality following PCI. Secondary outcomes included stent thrombosis and bleeding complication after PCI. Among 62 737 ACS patients who underwent PCI at any of 986 participating centres across Japan (clopidogrel 31.9%; prasugrel 68.1%), we identified 12 016 propensity score-matched pairs (24 032 patients; age 69.4 ± 12.2 years; female 24.9%; ST-elevation myocardial infarction 42.3%). Compared with standard-dose clopidogrel, reduced-dose prasugrel was associated with increased risk of bleeding [odds ratio (OR) 1.65, 95% confidence interval (CI) 1.10–2.51; P = 0.016], but both had similar rates of mortality (OR 1.11, 95% CI 0.89–1.38; P = 0.371) and stent thrombosis (OR 1.29, 95% CI 0.73–2.30; P = 0.387) as well as similar falsification endpoints of cardiac tamponade and emergent operation.

Conclusion 

In Japanese ACS patients undergoing PCI, the risk of bleeding is higher when using reduced-dose prasugrel than when using standard-dose clopidogrel, but there is no significant difference in in-hospital mortality and incidence of stent thrombosis between the two antiplatelet regimens.

Comparison of factors affecting platelet reactivity in various platelet function tests

Previous studies have reported that various factors affect ADP-induced platelet reactivity during clopidogrel therapy. The aim of this study was to determine whether clinical and laboratory variables for platelet reactivity during dual antiplatelet therapy (DAPT) are dependent on the assay used. We enrolled 904 patients receiving DAPT following coronary intervention. Platelet reactivity was measured using three methods: the VerifyNow P2Y12 assay, multiple electrode aggregometry (MEA) ADP assay, and the light transmittance aggregometry (LTA) ADP assay at 24-48 h following coronary intervention. The VerifyNow results demonstrated a significant inverse correlation with hematocrit value (r = -0.268, p < 0.0001); however, MEA results had no such correlation with hematocrit (r = 0.044, p = 0.188). There was a positive correlation between the MEA results and platelet count (r = 0.255, p < 0.0001). LTA was weakly influenced by hematocrit (r = -0.064, p = 0.057) and platelet count (r = 0.069, p = 0.040). Gender (odds ratio 1.53, 95% CI 1.10-2.14, p = 0.013) and hematocrit (odds ratio 0.91,95% CI 0.88-0.94, p < 0.0001) were the independent variables for HPR by VerifyNow. Smoking (odds ratio 0.38, 95% CI 0.16-0.94, p = 0.036) and platelet count (odds ratio 1.01, 95% CI 1.00-1.01, p < 0.0001) were independent factors for HPR when using the MEA assay, whereas platelet count (odds ratio 1.00, 95% CI 1.00-1.01, p = 0.006) was identified as the only independent variable for HPR when using LTA. The incidence of HPR and the influencing variables involved are dependent on the platelet function test used.

CYP2C19 and CYP2D6 genotypes in Pacific peoples

The study of pharmacogenetic variants in populations which reside in Oceania has been focused mainly on CYP2C19 and CYP2D6. Statements about the high prevalence of CYP2C19 no function genotype in 'Pacific Islanders' can be found in the literature. This review article summarizes the published information about these pharmacogenes in this geographical region and highlights the differences observed between Melanesian and Polynesian populations. It is not appropriate to combine the prevalence data of pharmacogenetic variants, particularly CYP2C19, across this region. Indeed, apocryphal assumptions about CYP2C19 no function alleles and possible effect on the therapeutic activity of clopidogrel are unhelpful and reiterate the importance of assessing the individual patient rather than relying on inappropriate ethnicity-based assumptions for drug dosing decisions.

Prevalence and significance of CYP2C19*2 and CYP2C19*17 alleles in a New Zealand acute coronary syndrome population

BACKGROUND

High on-treatment platelet reactivity has been associated with poor outcomes following acute coronary syndromes (ACS). Both the loss of function CYP2C19*2 allele and the gain of function CYP2C19*17 allele along with a range of clinical characteristics have been associated with variation in the response to clopidogrel.

AIM

The study aims to examine the frequency of CYP2C19 variants and understand the factors associated with on-treatment platelet reactivity in a New Zealand ACS population.

METHODS

We prospectively enrolled 312 ACS patients. We collected clinical characteristics and measured on-treatment platelet reactivity using two validated point-of-care assays, VerifyNow and Multiplate. DNA was extracted and CYP2C19*2 and *17 alleles were identified using real-time polymerase chain reaction.

RESULTS

CYP2C19*2 or CYP2C19*17 alleles were observed in 101 (32%) and 106 (34%) of patients, respectively, with significant differences in distribution by ethnicity. In Maori and Pacific Island patients, 47% (confidence interval (CI) 31-63%) had CYP2C19*2 and 11% (CI 4-19%) CYP2C19*17 compared with 26% (CI 19-32%) and 41% (CI 32-49%) in white people. Carriage of CYP2C19*2 alleles was associated with higher levels of platelet reactivity measured by either assay, but we observed no relationship between platelet reactivity and CYP2C19*17. In multivariate analysis diabetes, clopidogrel dose and CYP2C19*2 status were all significant independent predictors of platelet reactivity.

CONCLUSIONS

Both CYP2C19*2 and *17 were common in a New Zealand ACS population, with CYP2C19*2 observed in almost half the Maori and Pacific Island patients. CYP2C19*2, diabetes and clopidogrel dose were independent contributors to on-treatment platelet reactivity.

The future of pharmacogenetics in the treatment of heart failure

Heart failure is a common disease with high levels of morbidity and mortality. Current treatment comprises β-blockers, ACE inhibitors, aldosterone antagonists and diuretics. Variation in clinical response seen in patients begs the question of whether there is a pharmacogenetic component yet to be identified. To date, the genes most studied involve the β-1, β-2, α-2 adrenergic receptors and the renin-angiotensin-aldosterone pathway, mainly focusing on SNPs. However results have been inconsistent. Genome-wide association studies and next-generation sequencing are seen as alternative approaches to discovering genetic variations influencing drug response. Hopefully future research will lay the foundations for genotype-led drug management in these patients with the ultimate aim of improving their clinical outcome.

Challenges and solutions in medically managed ACS in the Asia-Pacific region: expert recommendations from the Asia-Pacific ACS Medical Management Working Group

Acute coronary syndromes (ACS) remain a leading cause of mortality and morbidity in the Asia-Pacific (APAC) region. International guidelines advocate invasive procedures in all but low-risk ACS patients; however, a high proportion of ACS patients in the APAC region receive solely medical management due to a combination of unique geographical, socioeconomic, and population-specific barriers. The APAC ACS Medical Management Working Group recently convened to discuss the ACS medical management landscape in the APAC region. Local and international ACS guidelines and the global and APAC clinical evidence-base for medical management of ACS were reviewed. Challenges in the provision of optimal care for these patients were identified and broadly categorized into issues related to (1) accessibility/systems of care, (2) risk stratification, (3) education, (4) optimization of pharmacotherapy, and (5) cost/affordability. While ACS guidelines clearly represent a valuable standard of care, the group concluded that these challenges can be best met by establishing cardiac networks and individual hospital models/clinical pathways taking into account local risk factors (including socioeconomic status), affordability and availability of pharmacotherapies/invasive facilities, and the nature of local healthcare systems. Potential solutions central to the optimization of ACS medical management in the APAC region are outlined with specific recommendations.