The Metabolism of Clopidogrel: CYP2C19 Is a Minor Pathway.

The major metabolic pathway of clopidogrel is conversion to carboxylic acid by an esterase (CES1), forming clopidogrelic acid (SR26334) that is inactive. There is agreement on the structure of the active metabolite; however, there are differing views about the mechanism of its formation. Sanofi studied the conversion of clopidogrel to the active metabolite using human liver microsomes. It was concluded that 2-oxo-clopidogrel was formed via CYP3A oxidation. From a subsequent in vitro study by Sankyo of the metabolism of clopidogrel using recombinant DNA CYPs, it was concluded that CYP2C19 was the major oxidative pathway. Such CYPs can give false-negative results particularly with drugs such as clopidogrel that have high first-pass metabolism in the enterocyte. CYP3A is present in the enterocyte but not CYP2C19. However, the view that clopidogrel is a CYP2C19 substrate was reinforced by a finding that omeprazole, a CYP2C19 inhibitor, reduced the ability of clopidogrel to inhibit platelet aggregation. The drug-drug interaction study of clopidogrel with omeprazole had the effect of reducing the area under the curve (AUC) of the clopidogrel active metabolite by 45%. However, a drug interaction study with a CYP3A inhibitor, grapefruit juice, caused a 6-fold reduction in the AUC of the active metabolite. Clopidogrel is therefore now considered to be primarily a CYP3A4/5 substrate. CYP2C19 has a minor role whose effect can be detected using a sensitive methodology such as platelet aggregometry.

Clopidogrel, CYP2C19, and a Black Box.

It has been presumed that CYP2C19 has a major role in the metabolism of clopidogrel. This presumption has been based on in vitro drug metabolism studies using microsomes from baculovirus infected insect cells (BD-Supersomes™). If clopidogrel were primarily a CYP2C19 substrate, a drug/drug interaction with CYP2C19 inhibitors, such as proton pump inhibitors (PPIs), for example, omeprazole and lansoprazole would be anticipated. Several ex vivo studies, using ADP stimulated platelet aggregation, suggested that there was such an interaction. The data from these studies served as a basis for FDA to provide a "Black Box" warning for the clopidogrel label in March of 2010. However, a prospective clinical study, COGENT, and several large meta-analyses have failed to demonstrate a negative effect on major adverse cardiovascular events (MACE), with concomitant administration of clopidogrel and PPIs. The in vitro work using "Supersomes" was revisited. In vitro metabolism using hepatosomes, which resemble the native cytochrome P-450 enzyme expression, has confirmed the earlier work that clopidogrel is primarily a CYP3A substrate. This result correlates better with clinical findings. The absence of an increase in MACE by concomitant administration of PPIs, which are CYP2C19 inhibitors, to a regimen including clopidogrel, is therefore not surprising. A hypothesis is offered to explain why subjects, who carry two reduced function alleles of CYP2C19, may have more reactive platelets.

Impact of CYP2C19 variant genotypes on clinical efficacy of antiplatelet treatment with clopidogrel: systematic review and meta-analysis.

OBJECTIVE: To evaluate the accumulated information from genetic association studies investigating the impact of variants of the cytochrome P450 (CYP) 2C19 genotype on the clinical efficacy of clopidogrel. DESIGN: Systematic review and meta-analysis with a structured search algorithm and prespecified eligibility criteria for retrieval of relevant studies; dominant genetic model assumptions and quantitative methods for calculating summary effect estimates from study level odds ratios; systematic assessment of bias within and between studies; and grading of the cumulative evidence by consensus criteria. DATA SOURCES: Medline, Embase, the Cochrane Library, online databases, contents pages and bibliographies of general medical, cardiovascular, pharmacological, and genetic journals. Eligibility criteria for selecting studies Original full length reports assessing the cumulative incidence of major adverse cardiovascular events or stent thrombosis over a follow-up period of at least a month in association with carrier status for the loss of function or gain of function CYP2C19 allele in adult patients with coronary artery disease and a clinical presentation of acute coronary syndrome or stable angina pectoris who were taking clopidogrel. RESULTS: 15 studies met the inclusion criteria. The random effects summary odds ratio for stent thrombosis in carriers of at least one CYP2C19 loss of function allele versus non-carriers combining nine studies was 1.77 (95% confidence interval 1.31 to 2.40; P < 0.001). This nominally significant odds ratio was subject to considerable bias across the studies (small study effect bias and replication diversity). The adjustment for these quality modifiers tended to abolish the association. The corresponding random effects summary odds ratio of major adverse cardiovascular events for 12 studies combined was 1.11 (0.89 to 1.39; P = 0.36). The random effects summary odds ratio of stent thrombosis in carriers versus non-carriers of at least one CYP2C19*17 gain of function allele for three studies combined was 0.99 (0.60 to 1.62; P = 0.96), and the corresponding odds ratio of major adverse cardiovascular events in five studies was 0.93 (0.75 to 1.14; P = 0.48). The overall quality of epidemiological evidence was graded as low, which excludes reliable clinical assessments. CONCLUSIONS: Accumulated information from genetic association studies does not indicate a substantial or consistent influence of CYP2C19 gene polymorphisms on the clinical efficacy of clopidogrel. The current evidence does not support the use of individualised antiplatelet regimens guided by CYP2C19 genotype.

Clopidogrel resistance: pharmacokinetic or pharmacogenetic?

Clopidogrel is important for the management of acute coronary syndromes and, along with aspirin, is recommended in the American College of Cardiology/American Heart Association guideline. It is also used along with aspirin, during the placement of coronary artery stents. Clopidogrel resistance was recognized in such procedures, as several patients did not have the anticipated platelet aggregation response to an ex vivo adenosine diphosphate challenge. From the EXCELSIOR study, which investigated the phenomenon, it was appreciated that it was present prior to treatment with clopidogrel and was therefore an intrinsic property of the patient's platelets. From other studies, it was appreciated that the patients who had clopidogrel resistance had a defective allele *2/ in the CYP2C19 gene. Furthermore, there was a dose response evident in that the homozygotes CYP2C19*2/*2 had platelets that responded even less well to clopidogrel than the heterozygotes CYP2C19*2 that responded less well than the wild-type homozygote. The involvement of the phenomenon with CYP2C19 led some to believe that it was a pharmacokinetic issue. However, the major oxidative metabolic pathway for clopidogrel by which the reactive intermediate is formed is CYP3A4. It is suggested that there is a linkage between a polymorphism of the platelet receptor P2Y12 and the polymorphism of CYP2C19.

Vasodilator effects of the endothelin ET receptor selective antagonist BMS-193884 in healthy men.

AIMS: A number of endothelin receptor antagonists (ERAs) are currently in clinical development as potential therapies in states characterized by vasoconstriction, such as systemic hypertension. We investigated the haemodynamic effects of locally and systemically active doses of BMS-193884, an endothelin A (ET(A)) receptor selective ERA, and its influence on vasoconstriction to endothelin-1 (ET-1) in healthy men. METHODS: In three separate randomized, placebo-controlled studies, the forearm blood flow (FBF) response to intra-arterial (i.a.) infusion of ET-1 (5 pmol min(-1)) was assessed during i.a. co-infusion of BMS-193884 (5 and 50 nmol min(-1)), and at 12 and at 24 h after oral administration of BMS-193884 (50, 100 and 200 mg at 12 h; and 200 mg at 24 h). Data were examined by repeated-measures analysis of variance (anova) with treatment and subject as factors. RESULTS: ET-1 caused significant forearm vasoconstriction, attenuated after oral dosing with BMS-193884 (200 mg) at 12 (P < 0.01) and 24 h (P < 0.0001). BMS-193884 (50 nmol min(-1), i.a.) caused local vasodilatation (25 +/- 11%) when infused alone (P = 0.02) and abolished forearm vasoconstriction to ET-1 (P < 0.0001 vs. ET-1 alone). Orally, BMS-193884 (200 mg) caused a reduction in total systemic vascular resistance at 12 (-14 +/- 9%, P = 0.03) and 24 h (-12 +/- 7%, P < 0.0001). There was no rise in plasma ET-1 levels. CONCLUSION: BMS-193884 causes local and systemic vasodilatation and attenuation of local vasoconstriction to ET-1. The absence of a rise in plasma endothelin levels suggests BMS-193884 is selective for the ET(A) receptor. This form of pharmacodynamic modelling may be useful in the development of ERAs in cardiovascular disease.

Additive benefits of pravastatin and aspirin to decrease risks of cardiovascular disease: randomized and observational comparisons of secondary prevention trials and their meta-analyses.

BACKGROUND: In randomized trials of secondary prevention, pravastatin sodium and aspirin reduce risks of cardiovascular disease. Pravastatin has a predominantly delayed antiatherogenic effect, and aspirin has an immediate antiplatelet effect, raising the possibility of additive clinical benefits. METHODS: In 5 randomized trials of secondary prevention with pravastatin (40 mg/d), comprising 73 900 patient-years of observation, aspirin use was also prescribed in varying frequencies, and data were available on a large number of confounding variables. We tested whether pravastatin and aspirin have additive benefits in the 2 large trials (Long-term Intervention With Pravastatin in Ischaemic Disease trial and the Cholesterol and Recurrent Events trial) that were designed to test clinical benefits. We also performed meta-analyses of these 2 trials and 3 smaller angiographic trials that collected clinical end points. In all analyses, multivariate models were used to adjust for a large number of cardiovascular disease risk factors. RESULTS: Individual trials and all meta-analyses demonstrated similar additive benefits of pravastatin and aspirin on cardiovascular disease. In meta-analysis, the relative risk reductions for fatal or nonfatal myocardial infarction were 31% for pravastatin plus aspirin vs aspirin alone and 26% for pravastatin plus aspirin vs pravastatin alone. For ischemic stroke, the corresponding relative risk reductions were 29% and 31%. For the composite end point of coronary heart disease death, nonfatal myocardial infarction, coronary artery bypass graft, percutaneous transluminal coronary angioplasty, or ischemic stroke, the relative risk reductions were 24% and 13%. All relative risk reductions were statistically significant. CONCLUSION: More widespread and appropriate combined use of statins and aspirin in secondary prevention of cardiovascular disease will avoid large numbers of premature deaths.