Variability in Individual Responsiveness to Clopidogrel: Clinical Implications, Management, and Future Perspectives

Resistance to clopidogrel: a review of the evidence.

Aspirin and the thienopyridines ticlopidine and clopidogrel are antiplatelet agents that display good antithrombotic activity. In the past few years, the concept of aspirin resistance has been largely emphasized in the medical literature, although its definition is still uncertain. I suggest that “aspirin-resistant” should be considered as a description for those individuals in whom aspirin fails to inhibit thromboxane A 2 production, irrespective of the results of unspecific tests of platelet function, such as the bleeding time, platelet aggregation, or the PFA-100 system. Less well known than aspirin resistance, but certainly better characterized, is the issue of “clopidogrel resistance,” which is probably mostly caused by inefficient metabolism of the prodrug clopidogrel to its active metabolite. At present, aspirin and clopidogrel resistance should not be looked for in the clinical setting, because there is no definite demonstration of an association with clinical events conditioning cost-effective changes in patient management.

Aspirin and clopidogrel: Efficacy, safety, and the issue of drug resistance

The biotransformation of prasugrel to R-138727 (2-[1-2-cyclopropyl-1-(2-fluorophenyl)-2-oxoethyl]-4-mercapto-3-piperidinylidene]acetic acid) involves rapid deesterification to R-95913 (2-[2-oxo-6,7-dihydrothieno[3,2-c]pyridin-5(4H)-yl]-1-cyclopropyl-2-(2-fluorophenyl)ethanone) followed by cytochrome P450 (P450)-mediated formation of R-138727, the metabolite responsible for platelet aggregation. For identification of the P450s responsible for the formation of the active metabolite, the current studies were conducted with R-95913 as the substrate. Incubations required supplementation with reduced glutathione. Hyperbolic kinetics (K(m) 21-30 microM), consistent with a single enzyme predominating, were observed after incubations with human liver microsomes. Correlation analyses revealed a strong relationship between R-138727 formation and CYP3A-mediated midazolam 1'-hydroxylation (r(2) = 0.98; p CYP2B6>CYP2C19 approximately CYP2C9>CYP2D6. A monoclonal antibody to CYP2B6 and the CYP3A inhibitor ketoconazole substantially inhibited R-138727 formation, whereas inhibitors of CYP2C9 (sulfaphenazole) and CYP2C19 (omeprazole) did not. Scaling of in vitro intrinsic clearance values from expressed enzymes to the whole liver using a relative abundance approach indicated that either CYP3A4 alone or CYP3A4 and CYP2B6 are the major contributors to R-138727 formation. R-95913 and R-138727 were also examined for their ability to inhibit metabolism mediated by five P450s. R-138727 did not inhibit the P450s tested. In vitro, R-95913 inhibited CYP2C9, CYP2C19, CYP2D6, and CYP3A, with K(i) values ranging from 7.2 microM to 82 microM, but did not inhibit CYP1A2. These K(i) values exceed circulating concentrations in humans by 3.8- to 43-fold. Therefore, neither R-95913 nor R-138727 is expected to substantially inhibit the P450-mediated metabolism of coadministered drugs.

https://dmd.aspetjournals.org/content/dmd/early/2006/01/13/dmd.105.007989.full.pdf

Interactions of two major metabolites of prasugrel, a thienopyridine antiplatelet agent, with the cytochromes p450

Background
Published pharmaceutical industry–sponsored trials are more likely than non-industry-sponsored trials to report results and conclusions that favor drug over placebo. Little is known about potential biases in drug–drug comparisons. This study examined associations between research funding source, study design characteristics aimed at reducing bias, and other factors that potentially influence results and conclusions in randomized controlled trials (RCTs) of statin–drug comparisons.

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Factors associated with findings of published trials of drug-drug comparisons: why some statins appear more efficacious than others.

Background— The antiplatelet effect of clopidogrel may be attenuated by short-term coadministration of lipophilic statins. We investigated whether the coadministration of atorvastatin for 5 weeks in patients with acute coronary syndromes (ACS) could affect the antiplatelet potency of clopidogrel. Methods and Results— Forty-five hypercholesterolemic patients with the first episode of an ACS were included in the study. Patients were randomized to receive daily either 10 mg of atorvastatin (n=21) or 40 mg of pravastatin (n=24). Thirty patients who underwent percutaneous coronary intervention (PCI) received a loading dose of 375 mg of clopidogrel, followed by 75 mg/d for at least 3 months. In the remaining 15 patients who refused to undergo PCI, clopidogrel therapy was not administered. Eight normolipidemic patients with the first episode of an ACS were also included and received only clopidogrel. The serum levels of soluble CD40L and the adenosine 5′-diphosphate– or thrombin receptor activating peptide-14–in...

Atorvastatin Does Not Affect the Antiplatelet Potency of Clopidogrel When It Is Administered Concomitantly for 5 Weeks in Patients With Acute Coronary Syndromes

The platelet integrin receptor alphaIIbbeta3 plays a critical role in thrombosis and haemostasis by mediating interactions between platelets and several ligands, primarily fibrinogen. We have previously shown that the synthetic peptide YMESRADRKLAEVGRVYLFL corresponding to residues 313-332 of alphaIIb, is a potent inhibitor of platelet aggregation and fibrinogen binding to alphaIIbbeta3, interacting with fibrinogen rather than the receptor. Furthermore, we have demonstrated that the biological activities of the above peptide are due to the sequence YMESRADR, which corresponds to residues 313-320. By using new synthetic peptide analogues we investigated the structural characteristics responsible for the biological activity of YMESRADR as well the possible influence of the adjacent amino acids on the peptide's biological potency. According to our results, the synthetic octapeptide YMESRADR, is a potent inhibitor of platelet aggregation and P-selectin expression. Furthermore, YMESRADR inhibits fibrinogen binding but it does not significantly influence the binding of PAC-1 to ADP-activated platelets. The inhibitory potency of YMESRADR was gradually diminished by deleting the YMES sequence from the amino terminus and prolonging the carboxyl terminus of this peptide with the KLAE sequence. Extension of YMESRADR towards the amino terminus with the GAPL sequence (GAPLYMESRADR) does not modify the biological activity of YMESRADR. Furthermore, extension of GAPLYMESRADR at its carboxy terminus with the KLAE sequence (GAPLYMESRADRKLAE) significantly diminished its biological potency. Substitution of E315 with D significantly enhances antiaggregatory potency and completely abolishes the inhibitory effect on P-selectin expression. Importantly, the D315-containing peptides inhibit to a similar extent both fibrinogen and PAC-1 binding to activated alphaIIbbeta3 in contrast to the E315-containing peptide which only inhibits fibrinogen binding. In conclusion, the present study suggests that the YMESRADR sequence 313-320 of alphaIIb, is an important functional region of the insert connecting the beta2 and beta3 antiparallel beta-strands of the W5 blade of the alphaIIb subunit. Structural changes significantly modify the biological properties of this region.

Investigation of the role of adjacent amino acids to the 313-320 sequence of the alphaIIb subunit on platelet activation and fibrinogen binding to alphaIIbbeta3.

The αIIbβ3 receptor, which is the most abundant receptor on the surface of platelets, can interact with a variety of adhesive proteins including fibrinogen, fibronectin and the von Willebrand factor. Fibrinogen binding on αIIbβ3 is an event essential for platelet aggregation and thrombus formation. Mapping of the fibrinogen-binding domains on αIIb subunit suggested the sequence 313–332 as a possible binding site. This region was restricted to sequence αIIb 313–320 (Y313MESRADR320) using synthetic octapeptides overlapping by six residues. The YMESRADR octapeptide inhibits ADP-stimulated human platelets aggregation and binds to immobilized fibrinogen. In this study, we used the Ala scanning methodology within the sequence 313–320 aiming to evaluate the contribution of each amino acid in inhibiting platelet aggregation. It was found that the substitution of Y313, M314, E315 or S316 by A does not affect the activity of the parent octapeptide. The–RADR-motif seems to be the most essential for the biological activity of the αIIb 313–320 site. The conformational analysis of the YAESRADR, YMESAADR and YMESRAAR analogs by using NMR spectroscopy and distance geometry calculations revealed significant differences in their conformational states in DMSO-d6. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.

Foteini I. Rodis

Papers

Atorvastatin Does Not Affect the Antiplatelet Potency of Clopidogrel When It Is Administered Concomitantly for 5 Weeks in Patients With Acute Coronary Syndromes

Investigation of the role of adjacent amino acids to the 313-320 sequence of the alphaIIb subunit on platelet activation and fibrinogen binding to alphaIIbbeta3.

Structure–activity relationships of αIIb 313–320 derived peptide inhibitors of human platelet aggregation