CYP2C19 Genotype and Stroke Risk Score: Implications for Clopidogrel Therapy and Recurrent Events

1. INTRODUCTION

Stroke is the second leading cause of death and disability worldwide [1]. Ischemic and hemorrhagic stroke subtypes differ in etiology, risk factors, treatment, and outcomes [2]. The Trial of ORG 10172 in Acute Stroke Treatment (TOAST) classification categorizes ischemic stroke subtypes based on underlying mechanisms [3]. Despite similarities in acute management, secondary prevention strategies for each subtype vary [4, 5]. Antiplatelet therapy, in conjunction with lifestyle modification and vascular risk factor control (e.g., blood pressure, low-density lipoprotein cholesterol), is commonly prescribed for secondary stroke prevention. Aspirin is frequently utilized as an antiplatelet agent due to its affordability and accessibility [6]. However, for aspirin-intolerant patients, clopidogrel is an evidence-based alternative for secondary stroke prevention [7-9].

Clopidogrel, a prodrug, requires hepatic cytochrome P450 (CYP450), primarily CYP2C19, for its conversion into its active metabolite [10]. The two most frequent loss-of-function polymorphisms are CYP2C19*2 and CYP2C19*3 [11, 12]. The prevalence of these polymorphisms varies by race, reaching 65% in East Asian populations [13]. In Thai populations, however, prevalence estimates have ranged from 5% to 55% [14-17]. Although substantial evidence has demonstrated the impact of CYP2C19 polymorphisms on cardiovascular events after percutaneous coronary intervention [18-20] or ischemic stroke [21-23], the evidence remains insufficient to recommend routine pretreatment genotyping for CYP2C19 polymorphisms. This study aimed to determine the prevalence of CYP2C19 polymorphisms in a Thai population and assess their impact on recurrent ischemic stroke and myocardial infarction risk.

2. METHODS

3. RESULTS

A total of 126 patients were recruited based on the inclusion criteria. The mean age was 70.45 ± 12.48 years, with a male predominance (n=94, 74.6%). The majority of participants were of Thai nationality (n=78, 61.9%), followed by Asian (n=38, 30.1%) and Western (n=10, 8%) ethnicities. The baseline characteristics, detailed in Table 1, revealed a significant difference between CYP2C19 carriers and noncarriers only in the history of type 2 diabetes mellitus (p=0.003).

The overall distribution of CYP2C19 phenotypes was as follows: 39 normal metabolizers (31%), 61 intermediate metabolizers (48.4%), 16 poor metabolizers (12.7%), and 10 ultrarapid metabolizers (7.9%). Within the Thai subpopulation, these distributions were 30 (38.5%), 38 (48.7%), 9 (11.5%), and 1 (1.3%), respectively. Tables 2 and 3 provide further details on the phenotype frequencies. The reasons for checking CYP2C19 phenotype in our patients were as follows: 1. Before prescribing clopidogrel in 65 patients (51.6%), 2. Had recurrent cardiovascular events when taking clopidogrel in 28 patients (22.2%), 3. Clopidogrel was prescribed by a previous physician but CYP2C19 phenotype was never checked in 33 patients (26.2%). None of the patients taking clopidogrel were on medications known to affect its metabolism (e.g., omeprazole, esomeprazole, fluconazole, fluoxetine, rifampicin, or phenytoin). Additionally, none were using medications that could cause cardiovascular events, such as nonsteroidal anti-inflammatory drugs (NSAIDs), antipsychotics, or triptans.

As of December 2023, 64 patients (50.8%) were alive, 11 (8.7%) had died, and 51 (40.5%) were lost to follow-up. Of the 11 deceased patients, 2 died from recurrent ischemic stroke, with both exhibiting the intermediate metabolizer CYP2C19 phenotype.

Clopidogrel was prescribed for secondary prevention in 109 patients (86.5%) due to previous ischemic stroke (n=28, 22.2%) or coronary artery disease (n=81, 64.3%), while 17 patients (13.5%) received clopidogrel for acute treatment. The dosage of clopidogrel for acute treatment was a 300 mg loading dose, followed by 75 mg once daily. For secondary prevention, the dosage was 75 mg once daily. Among clopidogrel users, recurrent stroke occurred in 12 patients (9.5%), and recurrent myocardial infarction was experienced by 16 patients (12.7%), all exhibiting intermediate or poor CYP2C19 metabolism phenotypes. Among the 12 patients with recurrent stroke, 5 were prescribed clopidogrel following myocardial infarction, and 7 were prescribed it following ischemic stroke. Among the 16 patients with recurrent myocardial infarction, 14 had been prescribed clopidogrel after myocardial infarction, and 2 after ischemic stroke. For all patients who had recurrent ischemic stroke, their etiology is small vessel disease. The duration between the first dose of clopidogrel and the onset of a cardiovascular event was available to calculate in 41 patients. The median time from starting clopidogrel to either recurrent stroke or myocardial infarction was 817 days (range 324–1871). For recurrent stroke alone, the median time was 1284 days (range 476–1871), while for recurrent myocardial infarction alone, the median time was 533 days (range 236–2275). A statistically significant difference was observed between carriers and noncarriers for recurrent stroke (p=0.028) and myocardial infarction (p=0.004), as detailed in Table 1. Notably, carriers demonstrated a significantly increased risk of recurrent myocardial infarction (odds ratio [OR] 29.89, 95% confidence interval [CI] 2.29–390.73, p=0.01) but not of recurrent stroke (OR 4.54, 95% CI 0.50–41.53, p=0.18). In a subgroup analysis of patients who were not lost to follow-up, 75 patients (59.5%) remained. Recurrent stroke occurred in 7 patients (9.3%), including 6 carriers (4 alive, 2 deceased) and 1 noncarrier (alive). Recurrent myocardial infarction occurred in 12 carriers (16%), all of whom were alive. A statistically significant difference was observed between carriers and noncarriers for recurrent myocardial infarction (p=0.006) but not recurrent ischemic stroke (p=0.413).

Following CYP2C19 genotyping, 52 patients (41.3%) with intermediate or poor metabolizer phenotypes were switched from clopidogrel to alternative antiplatelet therapies before any recurrent cardiovascular events. However, 13 patients (10.3%) continued clopidogrel despite their CYP2C19 status (12 intermediate, 1 poor). Of these, 6 were lost to follow-up, while the remaining 7 were monitored for a median of 396 days (range 308–1046) without experiencing further cardiovascular events by the end of December 2023.

Using the ESRS, 105 patients (83.3%) were classified as at high risk for recurrent stroke (ESRS ≥3). Stratifying patients based on both carrier status and the ESRS into 4 groups revealed that recurrent stroke and myocardial infarction were significantly elevated only in carriers in the high-risk subgroup (p=0.048 and p=0.006, respectively). Within the high-risk subgroup, carriers maintained a significantly increased risk of recurrent myocardial infarction (OR 29.14, 95% CI 2.01–422.0, p=0.013) but not of recurrent stroke (OR 4.18, 95% CI 0.43–41.16, p=0.22). Table 4 displays information categorized into 4 groups (low-risk, high-risk, carrier, and noncarrier).

Subgroup analysis focusing on intermediate metabolizers revealed a persistent, significant increase in recurrent stroke and myocardial infarction compared to noncarriers (p=0.04 and p=0.021, respectively). This significance was predominantly driven by patients with a high risk for recurrent stroke (ESRS ≥3).

4. DISCUSSION

Recent years have seen substantial advancements in acute stroke management aimed at reducing the global stroke burden. Despite the expanded time frame for reperfusion therapies such as intravenous recombinant tissue plasminogen activator and mechanical thrombectomy, a significant proportion of stroke patients remain ineligible and require antiplatelet therapy [4]. While aspirin alone was historically the mainstay for acute ischemic stroke [26, 27], the therapeutic landscape has evolved with emerging evidence supporting alternative antiplatelet agents. Although data on the use of clopidogrel for acute stroke treatment is limited, the medication is considered a first-line agent for secondary prevention [28]. Dual antiplatelet therapy, which combines aspirin with either clopidogrel or ticagrelor, has demonstrated superiority over aspirin alone in reducing recurrent stroke and mortality in patients with minor acute ischemic stroke or high-risk transient ischemic attack [29].

In secondary stroke prevention, along with controlling vascular risk factors, various antiplatelet options are available. These options include single or dual therapies, each with specific indications for different patient subgroups [7-9, 30-33].

Given its role as a cornerstone of secondary stroke prevention, the efficacy of clopidogrel is paramount. In addition to drug interactions with proton pump inhibitors or CYP2C19 inhibitors, genetic polymorphisms in the CYP2C19 gene are a significant contributor to antiplatelet resistance and subsequent recurrent stroke [34]. This polymorphism categorizes individuals into ultrarapid, normal, intermediate, and poor metabolizers. Patients classified as intermediate or poor metabolizers exhibit significantly lower levels of the active clopidogrel metabolite, resulting in reduced platelet inhibition [35].

In our study, the prevalence of CYP2C19 carriers was 61.1% overall and 60.2% in the Thai population, consistent with previous literature [16]. Although recurrent ischemic stroke was significantly more frequent in carriers than in noncarriers (14.3% vs. 2.0%, p=0.028), the OR did not reach statistical significance (OR 4.54, 95% CI 0.50–41.53, p=0.18) due to the limited sample size. The prevalence of CYP2C19*17 alleles in our study was very high (15.8%) compared to previous studies, which found only 0.5-4% in Asian populations [11]. This result may be influenced by selection bias, as our study included only patients with available CYP2C19 test results, rather than all patients taking clopidogrel. This could have led to an overestimation of the prevalence.

The high loss-to-follow-up rate (40%) was addressed by utilizing the ESRS to identify high-risk patients (ESRS ≥3) instead of assuming that they all have recurrent events. In this subgroup, carriers exhibited a greater rate of recurrent stroke than noncarriers did (p=0.048), although the odds ratio remained statistically nonsignificant (OR 4.18, 95% CI 0.43–41.16, p=0.22).

Conversely, the incidence of recurrent myocardial infarction was significantly greater in carriers than in noncarriers, with a statistically significant OR observed both with and without ESRS subgrouping. Even after subgrouping to only patients who were not lost to follow-up, the remaining 75 patients (59.5%), there is still a statistically significant difference between carrier and noncarriers in recurrent myocardial infarction. However, the OR could not be calculated due to mismatched observed and expected event rates (the Hosmer-Lemeshow test indicated that the model did not fit the data, p < 0.05).

Aside from the limited sample size, the lack of statistical significance in recurrent ischemic stroke may be attributed to the silent or mild nature of 8%–30% of strokes, resulting in underdiagnosis [36]. Conversely, myocardial infarction typically presents with more overt symptoms, with chest pain occurring in 80%–90% of cases, facilitating detection [37].

Recent studies corroborate our findings of a higher rate of recurrent cardiovascular events in intermediate or poor metabolizers than in noncarriers [38-41]. However, our results diverge from previous research when stratified by the ESRS. A prior study revealed no benefit of ticagrelor over clopidogrel in reducing recurrent stroke among high-risk carriers (ESRS ≥3) but a significant reduction in low-risk patients (ESRS <3) [42]. In our study, we found that clopidogrel failed to secondary prevention of cardiovascular events among high-risk carriers (ESRS ≥3). The discrepancy in the findings may be attributable to the limitations of the prior study. Notably, that research constituted a post hoc analysis of the CHANCE-2 trial and exclusively included Chinese individuals who are known for having a higher incidence of intracranial stenosis. These factors warrant consideration when interpreting the contrasting findings regarding the interaction between CYP2C19 status, the ESRS, and the treatment effect.

The majority of research examining the relationship between CYP2C19 genotype and clopidogrel response has focused on myocardial infarction patients undergoing percutaneous coronary intervention. No randomized controlled trials have demonstrated that routine genetic testing improves clinical outcomes. This lack of definitive evidence extends to ischemic stroke patients, with limited studies and no randomized trials investigating this relationship [43]. Due to the uncertain role of genetic testing, current guidelines for preventing recurrent cardiovascular events do not recommend routine CYP2C19 pharmacogenetic screening prior to clopidogrel initiation [5, 44].

5. STUDY LIMITATIONS

Our study has several limitations. First, the sample size was small compared to that of previous studies [15, 16]. This limited sample size may be due to the lack of recommendations for CYP2C19 testing prior to clopidogrel initiation and the retrospective design precluding genetic testing during recruitment. Second, the high loss-to-follow-up rate (40%) was likely influenced by two factors. These factors included patients seeking care at other hospitals under Thailand’s Universal Coverage Scheme (a government health insurance program) after emergency management at our hospital and the inclusion of foreign patients (38%). Third, 50% of patients who were prescribed clopidogrel underwent CYP2C19 evaluation within the same episode. If the results (typically available within 3 days) identified loss-of-function alleles, the antiplatelet therapy was promptly changed (41.3% of patients), which potentially reduced the incidence of recurrent ischemic stroke and myocardial infarction. Finally, our study included only patients with available CYP2C19 genotype data, and due to the retrospective nature of the study, this may have introduced selection bias that affected the outcomes and also imbalance in genetic polymorphism distribution.

Despite these limitations, our study has notable strengths. Few studies have investigated the association between CYP2C19 polymorphisms and recurrent ischemic stroke risk in clopidogrel users. Moreover, we demonstrated a heightened risk of recurrent ischemic stroke in carriers with a high ESRS value (≥3). This novel finding suggests that CYP2C19 screening may be warranted in this high-risk subgroup, a concept not previously explored in the literature.

CONCLUSION

The prevalence of carriers of CYP2C19 loss-of-function alleles exceeds 50% in the population and substantially impacts clinical outcomes when clopidogrel is used. Carriers exhibit a markedly greater incidence of recurrent ischemic stroke and myocardial infarction, particularly among high-risk patients identified by the ESRS. Therefore, screening for the CYP2C19 phenotype should be considered before prescribing clopidogrel to patients with a high ESRS. There are high loss-to-follow-up rates in our patients with many limitations from study design, making interpretation of our findings need to be cautious. Given our study’s small sample size and retrospective design, larger prospective cohort studies are necessary to further evaluate the impact of CYP2C19 loss-of-function alleles on clinical outcomes.

REFERENCES