Lipophilic statins do not affect the antiplatelet potency of clopidogrel

This letter to the editor discusses the results of the recently published study by Smith et al. which demonstrated that lipophilic statins metabolized through the cytochrome P-450 isoform 3A4 (CYP3A4) do not influence the antiplatelet effectiveness of clopidogrel in patients undergoing elective percutaneous coronary intervention. These results as well as those of other recent studies suggest that there is no adverse interaction between clopidogrel and CYP3A4-metabolized statins, during the maintenance phase of therapy (i.e., 2 or more days after the drug co-administration) either at the platelet or at the clinical level.     

Lipophilic statins interfere with the inhibitory effects of clopidogrel on platelet function--a flow cytometry study.

AIMS: Clopidogrel is a pro-drug which is converted to an active, unstable drug by cytochrome P450 (CYP). The active drug irreversibly blocks one specific platelet adenosine 5'-diphosphate (ADP) receptor (P2Y12). It has been recently suggested that the most abundant human CYP isoform, 3A4, activates clopidogrel. Since certain lipophilic statins (i.e. simvastatin, atorvastatin, lovastatin) are a substrate of CYP3A4, we were interested in potential drug interactions between clopidogrel and statins. METHODS: In patients with coronary artery disease (n=47) in whom clopidogrel treatment was initiated for balloon angioplasty and stent implantation, blood samples were taken at 0, 5 and 48 h after oral administration of clopidogrel (loading dose 300 mg, followed by 75 mg daily). ADP-stimulated (1, 10, 100 micromol/l) expression of P-selectin (CD62P) on platelets was measured by flow cytometry, and used as a marker for the antiplatelet effect of clopidogrel. RESULTS: Pre-treatment with statins (atorvastatin, simvastatin) reduced significantly (10 micromol/l ADP stimulation) the inhibitory effects of clopidogrel during the loading phase (relative reduction after 5 h 29.3%) and, to a lesser extent during the maintenance phase (relative reduction after 48 h 16.6%). In addition we found a considerable individual heterogeneity in the response and three patients (6%) were identified in whom clopidogrel exerted almost no effect. CONCLUSION:Certain statins which are substrates of the CYP3A4 isoform competitively inhibit the metabolic activation of clopidogrel. As a result the relative clopidogrel induced platelet inhibition (P-selectin-expression) is diminished--but still there is a relative clopidogrel effect of more than 80% in the maintenance phase. It may be reasonable to test the therapeutic efficacy of clopidogrel in those patients who require long-term treatment.     

Lack of evidence of a clopidogrel-statin interaction in the CHARISMA trial.

OBJECTIVES: The purpose of this study was to evaluate the potential impact of clopidogrel and statin interaction in a randomized, placebo-controlled trial with long-term follow-up. BACKGROUND: There are conflicting data regarding whether statins predominantly metabolized by CYP3A4 reduce the metabolism of clopidogrel to its active metabolite and diminish its clinical efficacy. METHODS: The CHARISMA trial was a randomized trial comparing long-term 75 mg/day clopidogrel versus placebo in patients with cardiovascular disease or multiple risk factors on aspirin. The primary end point was a composite of myocardial infarction, stroke, or cardiovascular death at median follow-up of 28 months. We performed a secondary analysis evaluating the interaction of clopidogrel versus placebo with statin administration, categorizing baseline statin use to those predominantly CYP3A4 metabolized (atorvastatin, lovastatin, simvastatin; CYP3A4-MET) or others (pravastatin, fluvastatin; non-CYP3A4-MET). RESULTS: Of 15,603 patients enrolled, 10,078 received a statin at baseline (8,245 CYP3A4-MET, 1,748 non-CYP3A4-MET) and 5,496 did not. For the overall population, the primary end point was 6.8% with clopidogrel and 7.3% with placebo (hazard ratio [HR] 0.93; p = 0.22). This was similar among patients on CYP3A4-MET (5.9% clopidogrel, 6.6% placebo, HR 0.89; p = 0.18) or non-CYP3A4-MET statin (5.7% clopidogrel, 7.2% placebo, HR 0.78; p = 0.19). There was no interaction between statin types and randomized treatment (p = 0.69). Patients on atorvastatin (n = 4,127) (5.7% clopidogrel, 7.1% placebo, HR 0.80; p = 0.06) or pravastatin (n = 1,440) (5.1% clopidogrel, 7.0% placebo, HR 0.72; p = 0.13) had similar event rates. CONCLUSIONS: Despite theoretic concerns and ex vivo testing suggesting a potential negative interaction with concomitant clopidogrel and CYP3A4-MET statin administration, there was no evidence of an interaction clinically in a large placebo-controlled trial with long-term follow-up.     

Thienopyridine-Associated Drug-Drug Interactions: Pharmacologic Mechanisms and Clinical Relevance

The thienopyridines inhibit platelet activation and aggregation by directly inhibiting the platelet P2Y12 adenosine diphosphate receptor. The available thienopyridines are prodrugs and must be converted into active forms by the cytochrome P450 (CYP) enzyme system. An important portion of the variability in platelet response to clopidogrel is explained by the variability in plasma concentrations of the clopidogrel active metabolite. Several reports have thus progressively raised concerns about potential drug interactions as a result of inhibition or induction of CYP450 enzymes. Pharmacokinetics and pharmacodynamics studies have notably shown that concomitant use of clopidogrel and some proton pump inhibitors reduces the antiplatelet effect of clopidogrel. Several other drugs (metabolized through CYP3A4 such as statins or antifungals) similarly impact the pharmacologic response to clopidogrel. Conversely, agents that induce CYP activity increase clopidogrel responsiveness. However, the data supporting the clinical relevance of such pharmacological drug interactions have been controversial. This review will provide an overview of the mechanisms underlying thienopyridine-associated drug-drug interactions, and highlight the most recent developments in the field and propose guidance for the practitioner.     

Influence of statin treatment on platelet inhibition by clopidogrel – a randomized comparison of rosuvastatin,atorvastatin and simvastatin co‐treatment

Objectives. Possible interactions between clopidogrel and atorvastatin, simvastatin or rosuvastatin (a ‘non‐CYP3A4’ metabolized statin) were investigated in a randomized prospective study using sensitive and specific ex vivo platelet function tests. Methods. Patients with coronary artery disease participating in a double‐blind study comparing lipid‐lowering effects of atorvastatin (20–80 mg OD; n = 22) and rosuvastatin (10–40 mg OD; n = 24) were studied before and after 2 weeks treatment with clopidogrel 75 mg OD after completed statin dose titration. In addition, 23 patients were randomized to open‐label simvastatin 40 mg OD. Results. Clopidogrel inhibited 10 μmol L^?1 ADP‐induced platelet aggregation by 40 ± 27%, 57 ± 28% and 51 ± 29%, respectively, in patients on rosuvastatin, atorvastatin and simvastatin treatment. The other platelet tests yielded similar results. No dose‐dependent effects of rosuvastatin or atorvastatin co‐treatment on clopidogrel efficacy were observed. Conclusions. Treatment with CYP3A4 metabolized statins, atorvastatin or simvastatin, did not attenuate the platelet inhibitory effect of clopidogrel maintenance treatment compared with the non‐CYP3A4 metabolized, rosuvastatin.     

Pharmacological interactions of statins

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are effective in reducing the risk of coronary events, and are generally very well tolerated. However, simvastatin, lovastatin, cerivastatin and atorvastatin are biotransformed in the liver primarily by cytochrome P450 (CYP) 3A4, and clinical experience has shown that the risk of adverse effect, such as myopathy, increases with concomitant use of statins with drugs that substantially inhibit CYP 3A4 at therapeutic doses. Indeed, pharmacokinetic interactions (e.g. increased bioavailability), myositis, and rhabdomyolysis have been reported following concurrent use of atorvastatin, cerivastatin, simvastatin or lovastatin and cyclosporine A, mibefradil or nefazodone. In contrast, fluvastatin (mainly metabolized by CYP 2C9) and pravastatin (eliminated by other metabolic routes) are less subject to this interaction. Nevertheless, an increase in pravastatin bioavailability has been reported in the presence of cyclosporine A, possibly because of an interaction at the level of biliary excretion. In summary, some statins may have lower adverse drug interaction potential than others, which is an important determinant of safety during long-term therapy.     

Multiple antiplatelet effects of clopidogrel are not modulated by statin type in patients undergoing percutaneous coronary intervention

We investigated whether statin type or dose influenced the inhibition of platelet function induced by clopidogrel in a prospective, open, parallel group study in patients undergoing elective percutaneous coronary intervention. Patients were taking CYP3A4 metabolised atorvastatin (n = 20) or simvastatin (n = 21), non-CYP3A4 metabolised pravastatin (n = 11) or fluvastatin (n = 2), or no statin therapy (n = 5). ADP and TRAP-induced platelet aggregation were measured using optical aggregometry, whole-blood single-platelet counting, and the Ultegra and Plateletworks point-of-care systems. Platelet pro-coagulant activity (annexin V binding and microparticle formation), P-selectin expression and platelet-leukocyte conjugate formation were assessed by flow cytometry. Platelet responses were measured at baseline, 4 h post clopidogrel 300 mg, and after 10 and 28 days with clopidogrel 75 mg daily. Clopidogrel significantly inhibited both ADP and TRAP-induced platelet responses over time, with steady state inhibition achieved by day 10. This was demonstrated by all techniques used. There was no significant effect of statin type or dose on platelet responses by any method at any time-point. In conclusion, statins do not influence the inhibitory effects of clopidogrel on multiple platelet responses, including aggregation, P-selectin expression, platelet-leucocyte conjugate formation and pro-coagulant responses, in patients undergoing elective PCI.     

Antiplatelet drug interactions

Both laboratory studies in healthy volunteers and clinical studies have suggested adverse interactions between antiplatelet drugs and other commonly used medications. Interactions described include those between aspirin and ibuprofen, aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs), and the thienopyridine, clopidogrel, and drugs inhibiting CYP2C19, notably the proton pump inhibitors (PPI) omeprazole and esomeprazole. Other interactions between thienopyridines and CYP3A4/5 have also been reported for statins and calcium channel blockers. The ibuprofen/aspirin interaction is thought to be caused by ibuprofen blocking the access of aspirin to platelet cyclo-oxygenase. The thienopyridine interactions are caused by inhibition of microsomal enzymes that metabolize these pro-drugs to their active metabolites. We review the evidence for these interactions, assess their clinical importance and suggest strategies of how to deal with them in clinical practice. We conclude that ibuprofen is likely to interact with aspirin and reduce its anti-platelet action particularly in those patients who take ibuprofen chronically. This interaction is of greater relevance to those patients at high cardiovascular risk. A sensible strategy is to advise users of aspirin to avoid chronic ibuprofen or to ingest aspirin at least 2 h prior to ibuprofen. Clearly the use of NSAIDs that do not interact in this way is preferred. For the clopidogrel CYP2C19 and CYP3A4/5 interactions, there is good evidence that these interactions occur. However, there is less good evidence to support the clinical importance of these interactions. Again, a reasonable strategy is to avoid the chronic use of drugs that inhibit CYP2C19, notably PPIs, in subjects taking clopidogrel and use high dose H2 antagonists instead. Finally, anti-platelet agents probably interact with other drugs that affect platelet function such as selective serotonin reuptake inhibitors, and clinicians should probably judge patients taking such combination therapies as at high risk for bleeding.     

两种他汀类药物对不同细胞色素P450酶2C19基因型患者氯吡格雷抗血小板作用的影响

目的观察2种他汀类药物对不同细胞色素P450酶(CYP)2C19基因型的急性冠状动脉综合征(ACS)患者氯吡格雷抗血小板作用的影响。方法选取接受CYP2C19基因型检测的老年ACS患者200例,根据服用他汀类药物及CYP2C19基因型分为6组:阿托伐他汀+快代谢组(A组)40例,瑞舒伐他汀+快代谢组(B组)40例;阿托伐他汀+中代谢组(C组)46例,瑞舒伐他汀+中代谢组(D组)46例;阿托伐他汀+慢代谢组(E组)14例,瑞舒伐他汀+慢代谢组(F组)14例。在使用氯吡格雷前(基线)、联合服用他汀类药物前(治疗前)及服用他汀类药物7 d(治疗后),测定二磷酸腺苷诱导的血小板聚集率;随访6个月,观察主要不良心血管事件(MACE)的发生率。结果与基线比较,治疗前和治疗后A组、B组、C组、D组、E组和F组血小板聚集率明显降低(P<0.05),且治疗后较治疗前更低[(3.9±0.2)%vs(5.2±0.3)%;(3.8±0.2)%vs(5.3±0.3)%;(4.9±0.4)%vs(5.3±0.3)%;(5.0±0.3)%vs(5.1±0.4)%;(5.0±0.4)%vs(5.2±0.3)%;(4.9±0.5)%vs(5.1±0.4)%,P<0.05];治疗后在相同基因代谢类型中,A组与B组、C组与D组、E组与F组血小板聚集率比较,无统计学差异(P>0.05);治疗后在不同基因代谢类型中,A组血小板聚集率明显低于C组和E组(P<0.05),B组血小板聚集率明显低于D组和F组,差异有统计学意义(P<0.05);C组与E组,D组与F组血小板聚集率比较,差异无统计学意义(P>0.05)。6组MACE发生率比较,差异无统计学意义(P>0.05)。结论2种他汀类药物对于同一代谢基因型组氯吡格雷抗血小板活性没有影响,对于不同代谢基因型患者氯吡格雷抗血小板活性有影响,氯吡格雷抗血小板活性受到CYP2C19基因多态性的影响。     

Accelerated platelet inhibition by switching from atorvastatin to a non-CYP3A4-metabolized statin in patients with high platelet reactivity (ACCEL-STATIN) study

Aims CYP3A4-metabolized statins can influence the pharmacodynamic effect of clopidogrel. We sought to assess the impact of switching to a non-CYP3A4-metabolized statin on platelet function among patients receiving clopidogrel and atorvastatin with high on-treatment platelet reactivity (HPR). Methods and results Percutaneous coronary intervention (PCI)-treated patients (n= 50) with HPR [20 μM adenosine diphosphate (ADP)-induced maximal platelet aggregation (MPA) >50%] were enrolled during chronic administration of atorvastatin (10 mg/day) and clopidogrel (75 mg/day) (≥6 months). They were randomly assigned to a 15-day therapy with either rosuvastatin 10 mg/day (n= 25) or pravastatin 20 mg/day (n= 25). Platelet function was assessed before and after switching by conventional aggregometry and the VerifyNow P2Y12 assay. Genotyping was performed for CYP2C19*2/*3, CYP3A5*3, and ABCB1 C3435T alleles. The primary endpoint was the absolute change in 20 μM ADP-induced MPA. After switching, MPAs after stimuli with 20 and 5 μM ADP were decreased by 6.6% (95% confidence interval: 3.2-10.1%; P < 0.001), and 6.3% (95% confidence interval: 2.5-10.2%; P = 0.002), respectively. Fifty-two P2Y12 reaction units fell (95% confidence interval: 35-70; P < 0.001) and the prevalence of HPR decreased (24%; P < 0.001). Pharmacodynamic effects were similar after rosuvastatin and pravastatin therapy. In addition to smoking status, the combination of calcium channel blocker usage and ABCB1 C3435T genotype significantly affected the change of 20 μM ADP-induced MPA. Conclusions Among PCI-treated patients with HPR during co-administration of clopidogrel and atorvastatin, switching to a non-CYP3A4-metabolized statin can significantly decrease platelet reactivity and the prevalence of HPR. This switching effect appears similar irrespective of the type of non-CYP3A4-metabolized statin.     

Does differing metabolism by cytochrome P450 have clinical importance?

The cytochrome P450 (CYP) is a group of enzymes that oxidatively modify drugs to a more water-soluble form for renal excretion. Nearly 50% of all clinically used medications and endogenous steroids are metabolized by the CYP enzyme 3A4, which explains why many of the important potential drug interactions involved this enzyme. Despite an excellent safety record, CYP 3A4 statins (lovastatin, simvastatin, atorvastatin) taken concomitantly with a potent CYP 3A4 inhibitor may increase the risk for adverse events (myopathy, rhabdomyolysis). This article describes the clinical significance of CYP metabolism as the pathways relate to the use of statins, including brief discussions on statins, fibrates, cyclosporine, and calcium channel blockers. In light of these potential interactions, continued vigilance by physicians is necessary to ensure the safe use of statins.     

Frequency of CYP3A4, CYP3A5, CYP2C9 , and CYP2C19 variant alleles in patients receiving clopidogrel that experience repeat acute coronary syndrome

The presence of cytochrome P450 (CYP) variant alleles may reduce the activation of the prodrug clopidogrel to its active state. This research evaluated the frequency of variant alleles in the genes coding for CYP3A4, CYP3A5, CYP2C9, and CYP2C19 enzymes in patients on clopidogrel therapy and experiencing repeat acute coronary syndrome (ACS) compared to a control group with a matching ethnic composition. Real-time polymerase chain reaction was used for allelic discrimination. Complete data were obtained for 92 patients enrolled over a 3-month period. There were no significant differences in the presence of the examined CYP3A4, CYP3A5, CYP2C9, or CYP2C19 variant alleles between the two groups. The present data indicate that patients currently receiving clopidogrel therapy who present with repeat ACS do not have higher frequency of the examined variant alleles compared to a control group.     

Common sequence variations in the P2Y12 and CYP3A5 genes do not explain the variability in the inhibitory effects of clopidogrel therapy

The efficacy of the platelet P2Y12 receptor antagonist clopidogrel, which undergoes cytochrome-mediated metabolism to its active form, shows marked inter-individual variability. We investigated whether polymorphic variations in the P2Y12 gene, which have been linked to platelet aggregation phenotypes, or the cytochrome P450 3A5 gene 6986G > A polymorphism, which largely determines CYP3A5 expression, influence the response to clopidogrel therapy. Fifty-four patients listed for elective percutaneous coronary intervention were studied using ADP-induced optical aggregometry, whole-blood single platelet counting (WBSPC) aggregometry, and flow-cytometric analysis of platelet P-selectin expression and platelet-monocyte conjugate formation. Platelet reactivity was measured at baseline, 4 h post clopidogrel 300 mg, and 10 and 28 days following clopidogrel 75 mg daily. A further 55 patients were studied using ADP-induced WBSPC at baseline and 4 h post clopidogrel 600 mg. Patients were genotyped for P2Y12 haplotype and the CYP3A5 6986G > A single nucleotide polymorphism. Neither genotype was found to significantly influence the inhibition of platelet responses by either clopidogrel regimen. In conclusion, common sequence variations within the P2Y12 and CYP3A5 genes do not contribute any major effect to the inter-patient variability in clopidogrel efficacy.     

Cytochrome P450 2C19 loss-of-function polymorphism is a major determinant of clopidogrel responsiveness in healthy subjects

The capacity of clopidogrel to inhibit ADP-induced platelet aggregation shows wide intersubject variability. To determine whether frequent functional variants of genes coding for candidate cytochrome P450 (CYP) isoenzymes involved in clopidogrel metabolic activation (CYP2C19*2, CYP2B6*5, CYP1A2*1F, and CYP3A5*3 variants) influence the platelet responsiveness to clopidogrel, we conducted a prospective pharmacogenetic study in 28 healthy white male volunteers treated for 7 days with clopidogrel 75 mg/d. We observed that pharmacodynamic response to clopidogrel was significantly associated with the CYP2C19 genotype. Twenty of the subjects were wild-type CYP2C19 (*1/*1) homozygotes, while the other 8 subjects were heterozygous for the loss-of-function polymorphism CYP2C19*2 (*1/*2). Baseline platelet activity was not influenced by the CYP2C19 genotype. In contrast, platelet aggregation in the presence of 10 muM ADP decreased gradually during treatment with clopidogrel 75 mg once daily in *1/*1 subjects, reaching 48.9% +/- 14.9% on day 7 (P < .001 vs baseline), whereas it did not change in *1/*2 subjects (71.8% +/- 14.6% on day 7, P = .22 vs baseline, and P < .003 vs *1/*1 subjects). Similar results were found with VASP phosphorylation. The CYP2C19*2 loss-of-function allele is associated with a marked decrease in platelet responsiveness to clopidogrel in young healthy male volunteers and may therefore be an important genetic contributor to clopidogrel resistance in the clinical setting.     

Pitavastatin - pharmacological profile from early phase studies

Pitavastatin has been designed as a synthetic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor with a novel cyclopropyl moiety that results in several differences compared to other statins. These include effective inhibition of cholesterol synthesis and increased lipoprotein lipase expression at lower doses than other statins, and significant high-density lipoprotein-cholesterol and apolipoprotein A1-elevating activity that persists with time. The safety, tolerability and pharmacokinetics of pitavastatin and its major metabolite, pitavastatin lactone, have been investigated in a variety of patient groups with similar results, which suggests dosage adjustments are not required for gender, age or race. In healthy subjects, pitavastatin is well tolerated at the approved doses with no serious adverse events. The bioavailability of pitavastatin is, at 60%, higher than that of any other statin and the majority of the bioavailable fraction of an oral dose is excreted unchanged in the bile. The entero-hepatic circulation of unchanged drug contributes to the prolonged duration of action and allows once-daily, any-time dosing. Pitavastatin is only slightly metabolised by cytochrome P450 (CYP) 2C9 and not at all by CYP3A4. Neither pitavastatin nor its lactone form, have inhibitory effects on CYP, and CYP3A4 inhibitors have no effect on pitavastatin concentrations. Moreover, P-glycoprotein-mediated transport does not play a major role in the drug's disposition and pitavastatin does not inhibit P-glycoprotein activity. Pitavastatin is transported into the liver by several hepatic transporters but OATP1B1 inhibitors have relatively little effect on plasma concentrations compared with other statins. In general, interactions, except with multi-transporter inhibitors like ciclosporin, are not clinically significant. Consequently, pitavastatin has minimal drug-food and drug-drug interactions making it a treatment option in the large group of dyslipidaemic people that require multidrug therapy.     

Common sequence variations in the P2Y12 and CYP3A5 genes do not explain the variability in the inhibitory effects of clopidogrel therapy

The efficacy of the platelet P2Y₁₂ receptor antagonist clopidogrel, which undergoes cytochrome-mediated metabolism to its active form, shows marked inter-individual variability. We investigated whether polymorphic variations in the P2Y₁₂ gene, which have been linked to platelet aggregation phenotypes, or the cytochrome P450 3A5 gene 6986G?>?A polymorphism, which largely determines CYP3A5 expression, influence the response to clopidogrel therapy. Fifty-four patients listed for elective percutaneous coronary intervention were studied using ADP-induced optical aggregometry, whole-blood single platelet counting (WBSPC) aggregometry, and flow-cytometric analysis of platelet P-selectin expression and platelet-monocyte conjugate formation. Platelet reactivity was measured at baseline, 4?h post clopidogrel 300?mg, and 10 and 28 days following clopidogrel 75?mg daily. A further 55 patients were studied using ADP-induced WBSPC at baseline and 4?h post clopidogrel 600?mg. Patients were genotyped for P2Y₁₂ haplotype and the CYP3A5 6986G?>?A single nucleotide polymorphism. Neither genotype was found to significantly influence the inhibition of platelet responses by either clopidogrel regimen. In conclusion, common sequence variations within the P2Y₁₂ and CYP3A5 genes do not contribute any major effect to the inter-patient variability in clopidogrel efficacy.     

Effect of cytochrome p450 polymorphisms on platelet reactivity after treatment with clopidogrel in acute coronary syndrome

Genetic polymorphisms of cytochrome P450 (CYP) isoforms may promote variability in platelet response to clopidogrel. This study was conducted to analyze, in 603 patients with non-ST elevation acute coronary syndromes, the effect of CYP3A4, CYP3A5, and CYP2C19 gene polymorphisms on clopidogrel response and post-treatment platelet reactivity assessed by adenosine diphosphate (ADP)-induced platelet aggregation, vasodilator-stimulated phosphoprotein phosphorylation index, and ADP-induced P-selectin expression. The CYP2C19*2 polymorphism was significantly associated with ADP-induced platelet aggregation, vasodilator-stimulated phosphoprotein phosphorylation index, and ADP-induced P-selectin expression in recessive (p <0.01, p <0.007, and p <0.06, respectively) and codominant (p <0.08, p <0.0001, and p <0.009, respectively) models, but the CYP3A4*1B and CYP3A5*3 polymorphisms were not. The CYP2C19*2 allele carriers exhibited the highest platelet index levels in multivariate analysis (p = 0.03). After covariate adjustment, the CYP2C19*2 allele was more frequent in clopidogrel nonresponders, defined by persistent high post-treatment platelet reactivity (ADP-induced platelet aggregation >70%; p = 0.03). In conclusion, the present data suggest that the CYPC19*2 allele influences post-treatment platelet reactivity and clopidogrel response in patients with non-ST elevation acute coronary syndromes.     

Genetic determinants of on-clopidogrel high platelet reactivity

Clopidogrel has been used (alone or in association with aspirin) to prevent vascular complications in atherothrombotic patients, to prevent stent thrombosis (ST) in patients undergoing percutaneous coronary intervention (PCI) and as a long-term prevention of cardiovascular and cerebrovascular events. Unfortunately, it is important to note that there are a number of patients who, during clopidogrel therapy, show and maintain a high platelet reactivity (PR), similar to that observed before the start of antiplatelet therapy. Clopidogrel pro-drug is absorbed in the intestine and this process is influenced by P-glycoprotein-1 (P-GP). Its conversion into 2-oxo clopidogrel is regulated by cytochromes (CYP) called CYP2C19, CYP2B6 and CYP1A2. Whereas, the final transformation into the active metabolite is regulated by CYP called CYP2C19, CYP2C9, CYP2B6, CYP3A4, CYP3A5 and, as recently emerged, by the glycoprotein paraoxonase-1 (PON1). The genes encoding these enzymes are characterized by several polymorphisms. Some of these are able to modify the activity of proteins, reducing the concentration of active metabolite and the values of on-clopidogrel PR. Only one gene polymorphism (CYP2C19*17) increases the clopidogrel metabolization and so the clopidogrel-induced platelet inhibition. Several studies have clearly associated these gene polymorphisms to both ischemic and bleeding complications in patients receiving dual antiplatelet therapy. The aim of this review is to describe the principal gene polymorphisms influencing on-clopidogrel PR and their relationship with long-term clinical outcome.     

Clopidogrel Resistance: case reports of CYP2C19 gene variants in suspected coronary stent thrombosis

Clopidogrel is a widely used anti-platelet agent for the prevention of arterial thrombosis. Clopidogrel is administered as a pro-drug and metabolised to its active metabolite by the hepatic cytochrome P450 2C19 (CYP2C19) enzyme. The active metabolite is responsible for the anti-platelet activity of clopidogrel. Recent studies demonstrate that single nucleotide polymorphisms, (SNP's), in the gene for CYP2C19 result in significantly reduced production of the active metabolite of clopidogrel. Additional studies demonstrate that patients with SNP's in the CYP2C19 gene, including CYP2C19*2,*3,*4, and *5, have reduced production of the active metabolite of clopidogrel, reduced inhibition of platelet aggregation and increased incidence of coronary, cerebrovascular, and coronary stent thrombosis. We have been interested in determining the CYP2C19 genotype in cases of coronary stent thrombosis whilst on clopidogrel treatment and provide two case reports of coronary stent thrombosis whilst taking clopidogrel with subsequent CYP2C19 genotyping. As patients at risk of atherothrombosis in general, and stent thrombosis in particular, may be receiving or considered for anti-platelet therapy including clopidogrel, genotyping for CYP2C19 SNP's may be of benefit in the selection of appropriate anti-platelet therapy.