Implications of Inter-Individual Differences in Clopidogrel Metabolism, with Focus on Pharmacogenetics

Pharmacogenomics Informs Cardiovascular Pharmacotherapy

Precision medicine exemplifies the emergence of personalized treatment options which may benefit specific patient populations based upon their genetic makeup. Application of pharmacogenomics requires an understanding of how genetic variations impact pharmacokinetic and pharmacodynamic properties. This particular approach in pharmacotherapy is helpful because it can assist in and improve clinical decisions. Application of pharmacogenomics to cardiovascular pharmacotherapy provides for the ability of the medical provider to gain critical knowledge on a patient's response to various treatment options and risk of side effects.

Pharmacogenomic phase transition from personalized medicine to patient-centric customized delivery

Personalized medicine has been a booming area in clinical research for the past decade, in which the detailed information about the patient genotype and clinical conditions were collected and considered to optimize the therapy to prevent adverse reactions. However, the utility of commercially available personalized medicine has not yet been maximized due to the lack of a structured protocol for implementation. In this narrative review, we explain the role of pharmacogenetics in personalized medicine, next-generation personalized medicine, i.e., patient-centric personalized medicine, in which the patient's comfort is considered along with pharmacogenomics to be a primary factor. We extensively discuss the classifications, strategies, tools, and drug delivery systems that can support the implementation of patient-centric personalized medicine from an industrial perspective.

P450 Pharmacogenetics in Indigenous North American Populations

Indigenous North American populations, including American Indian and Alaska Native peoples in the United States, the First Nations, Métis and Inuit peoples in Canada and Amerindians in Mexico, are historically under-represented in biomedical research, including genomic research on drug disposition and response. Without adequate representation in pharmacogenetic studies establishing genotype-phenotype relationships, Indigenous populations may not benefit fully from new innovations in precision medicine testing to tailor and improve the safety and efficacy of drug treatment, resulting in health care disparities. The purpose of this review is to summarize and evaluate what is currently known about cytochrome P450 genetic variation in Indigenous populations in North America and to highlight the importance of including these groups in future pharmacogenetic studies for implementation of personalized drug therapy.

Pharmacogenomics of oral antiplatelet drugs

Pharmacogenomics has been implicated in the response variability of antiplatelet drugs in coronary artery disease (CAD), particularly for aspirin and clopidogrel. A large number of studies and several meta-analyses have been published on this topic, but until recently, there have been no clear conclusions and no definite guidelines on the clinical use of pharmacogenetic testing before prescribing antiplatelet drugs for CAD. In this review, the available evidence is summarized. The most consistent results are on clopidogrel, where CYP2C19 loss-of-function alleles are associated with stent thrombosis events. We recommend to genotype for CYP2C19 loss-of-function alleles in patients with CAD who are to undergo percutaneous coronary intervention and stenting, and to adjust the antiplatelet treatment based on the genotyping results.

Pharmacogenetic landscape of clopidogrel in north Indians suggest distinct interpopulation differences in allele frequencies

AIM

Clopidogrel, a widely used antiplatelet drug, exhibits high interindividual variability; more than 80% of which could be explained by genetic polymorphisms. We built an allele frequency map of variants affecting clopidogrel response in north Indians.

MATERIALS & METHODS

We mined a cross-sectional population-scale genome-wide dataset of 2128 Indo-Europeans residing in north India for presence of variants associated with pharmacogenetics of clopidogrel.

RESULTS

Our analysis reveals significant differences in population-scale allele frequencies between Indians and the global population. Indians had a higher allele frequency for variants in the CYP2C9*2, CYP2C9*3 and P2RY1 genes whereas lower frequency for the ABCB1, CYP1A2, CYP2C19*2C, CYP3A5 and PON1 genes compared with the global population. Furthermore, from our study we proposed a model to explain the higher prevalence of clopidogrel metabolizers in north Indians.

CONCLUSION

This is the largest population-scale genetic epidemiology study that provides a high-resolution map of variants associated with clopidogrel response that could be potentially valuable to clinicians to rationally plan appropriate dosage for therapy in resource poor conditions based on population level allele frequencies.

Comparison of effects of two different formulations of clopidogrel bisulfate tablets on platelet aggregation and bleeding time in healthy Korean volunteers: A single-dose, randomized, open-label, 1-week, two-period, phase IV crossover study

BACKGROUND

Clopidogel bisulfate, an oral antiplatelet agent that works by inhibiting adenosine diphosphate-induced platelet aggregation, is used in the treatment of coronary artery disease, peripheral vascular disease, and cerebrovascular disease. The newly developed generic version of Clopidogrel bisulfate has a mechanism of action comparable to the reference formulation.

OBJECTIVE

The aim of this study was to assess and compare the pharmacodynamic effects and safety profile of these 2 formulations of Clopidogrel bisulfate in healthy volunteers.

METHODS

This was a single-dose, randomized, openlabel, 1-week, 2-period, Phase IV crossover study conducted from July 2008 to February 2009. Healthy volunteers were randomly assigned to receive a 1-week course of the test formulation followed by a 1-week course of the reference formulation (each, 300 mg on day 1, then 75 mg for 6 days), or the reverse sequence, separated by a 2-week washout period. Inhibition of platelet aggregation and the effect on bleeding time were used to evaluate pharmacodynamic effects. Variables included the mean maximal activity (E(max)) of the percent inhibition of platelet aggregation and bleeding time. Blood was sampled at screening, on the morning before each first drug administration (days 1 and 21), the day after the completion of each 7-day treatment course (days 8 and 28), and 7 days after completion of each 7-day treatment course (days 14 and 34). The bioequivalence of the 2 pharmaceutical formulations was tested. The safety profiles included assessment of vital signs, laboratory test results, and the incidence of adverse events and adverse drug reactions.

RESULTS

Two of the original 32 healthy Korean volunteers were excluded because of screening failure or withdrawal of consent. Therefore, 30 volunteers (16 males; mean [SD] age, 28.6 [8.0] years; age range, 19-51 years; mean weight, 62.4 [9.5] kg; weight range, 45-78 kg) were recruited into the study. E(max) and bleeding time did not differ significantly between the 2 groups. The mean change in E(max) was 44.1% (22.5%) and 44.3% (24.2%) and the mean change in bleeding time was 4.8 (3.7) and 4.6 (3.8) minutes after 7 days' administration of the test formulation and the reference formulation, respectively. The geometric mean ratio (90% CI) was 99.5 (82.9-116.2) and was within the bioequivalence acceptance range of 80% to 120%. Vital signs and platelet and neutrophil counts were within normal limits. None of the volunteers experienced any adverse events or adverse drug reactions.

CONCLUSION

In this study of healthy volunteers, there were no significant differences between the 2 tablet formulations of Clopidogrel bisulfate in pharmacodynamic effects or safety profile.

Association between CYP2C19*2 variant and clinical outcome in Clopidogrel treated patients from Republic of Macedonia

Clopidogrel is the thienopyridine of choice for prevention of ischemic events and stent thrombosis in patients with atherotrombotic disease. Recent studies suggest that certain genetic variants involving CYP450 system are responsible for wide interindividual variability in treatment response profiles among clopidogrel treated individuals. The aim of this study was to define the prevalence of most common CYP2C19*2: 681G>A (rs4244285) allelic variant in Macedonian population and determine the risk association with major cardiovascular adverse events in clopidogrel treated patients with atherotrombotic cardiovascular disease. CYP2C19 *2 genotype was assessed in 198 subjects from R.Macedonia. The association between the reduced function CYP2C19 *2 A allele and clinical outcome was evaluated in 67 clopidogrel treated patients within a follow up period of at least 6 months (from 6 to 60 months) after initializing clopidogrel therapy. The population frequency of polymorphic A allele responsible for impaired clopidogrel metabolism in Macedonian population was 0.18. CYP2C19*2 variant was significantly associated with increased rate of adverse cardiovascular events in the allelic (OR= 3.188; 95% CI= 1.437-7.058), dominant (OR=3.477; 95% CI= 1.256-9.630) and co-dominant model ( OR=6.750, 95% CI: 1.186-38.410) of statistical analysis (adjusted OR= 2.619; Ptrend=0.0088). The influence of CYP2C19*2 was most strongly correlated with worse event free survival in patients carrying AA genotype (log rank P = 0.0024) and patients carrying at least one CYP2C19*2 reduced function allele (log rank P=0.0058). CYP2C19*2 genetic variant in the population from Republic of Macedonia has similar distribution as determined in other European populations. Carriage of reduced function CYP2C19 *2 allele is associated with worse event free survival in clopidogrel treated patients with atherotrombotic disorders.