7. Comparison of pro-drugs and active drugs and clinical consequences Drug type Metabolizer Phenotype Effect on drug metabolism Potential consequence Prodrug Needs metabolism to work (clopidogrel) Poor to intermediate Slow Poor drug efficacy, patient at risk of therapeutic failure due ↓ levels of active drug. Accumulation of prodrug, patient at increased risk of drug-induced side effects. Ultrarapid Fast Good drug efficacy, rapid effect. Possible accumulation of active drug -> potential of adverse effects. Active drug Metabolized to inactive drug (omeprazole) Poor to intermediate Slow Accumulation of active drug, patient is at increased risk of drug-induced side effects. Patient requires lower dosage . Ultrarapid Fast Poor drug efficacy, patient is at risk of therapeutic failure. Patient likely will require higher dosage.
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9. P2X 1 P2Y 12 ATP Shape change Angiolillo DJ et al JACC 2007 P2Y 1 G q Initiation of Platelet Aggregation IP3 PKC GP IIb/IIIa receptor activation G 12 DAG + Shape change Granule secretion Stabilization of Platelet Aggregation β γ GP IIb/IIIa receptor activation Rap1b PKB/Akt α i AC cAMP VASP VASP-P cAMP PI3K Clopidogrel 85% inactive metabolites (Esterases in blood) Gastro-intestinal absorption ADP Ca 2+ flux Ca 2+ mobilization PLC β MLCK-P “ Rho” Hepatic CYP Biotransformation GP IIb/IIIa receptor activation PGE 1 PIP2 G i 15% active metabolite HOOC * HS N O Cl OCH 3 N S O Cl O CH 3 C AC G s
10. T.E. Klein , J.T. Chang, M.K. Cho, K.L. Easton, R. Fergerson, M. Hewett, Z. Lin, Y. Liu, S. Liu, D.E. Oliver, D.L. Rubin, F. Shafa, J.M. Stuart and R.B. Altman , " Integrating Genotype and Phenotype Information: An Overview of the PharmGKB Project " ( 220k PDF ), The Pharmacogenomics Journal (2001) 1, 167-170 .
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13. Clopidogrel Response Variability 20% do not have adequate response GP IIb/IIIa receptor expression Hepatic Metabolism Cytochrome P450 pathway Poor compliance Inadequate administration Variable absorption Genetic polymorphisms CYP2C19PMs, CYP2C9*3, ABCB1 Drug-drug interactions Genetic polymorphisms P2Y12 receptor Alternate pathways of platelet activation Genetic polymorphisms O’Donoghue M, Wiviott SD. Circulation. 2006;114:e600-e606 Simon T et al.NEJM. 2009;363-75 Feher G et al. Clin Genetics. 2009; 75:1-18. Intestinal Absorption P2Y 12 Receptor (irreversible inhibition) Active Metabolite
14. Mechanisms of Clopidogrel Response Variability Inhibition of Platelet Aggregation (Wide Response Variability) 1 Clopidogrel Bisulfate Intestinal Absorption Inactive Carboxylic Acid Metabolite CYP3A4 CYP3A5 CYP2C19 CYP2C9 Active Thiol Metabolite P2Y 12 Receptor Limited absorption capacity with ceiling effect at 600mg loading dose 7 Hepatic P450 Cytochromes CYP3A4 inducers: rifampin CYP3A4 inhibitors: erythromycin 2C19 Genetic polymorphisms 2C19 inhibitors Multistep Conversion 15% Esterases 85% 1. Gurbel PA et al. Thromb Res . 2007;120:311-21. 2. Taubert et al. Clin Pharmacol . 2006;80:486-501. 3. von Beckerth et al. Eur Heart J. 2007;28:1814-9. P-glycoprotein (MDR1 3435T genotype) 2 ? Smoking (induction) CYP1A2 CYP2B6, 2C19 2C9*3 Genetic polymorphisms
15. Why do we need PPI’s with clopidogrel? Deepak LB, et al. Circulation 2008; 118:1894-1909
16. K i ( μ M) values of PPI’s for CYP2C19 enzyme Li X, Andersson TB, Ahlstrom M, Weidolf L. Comparison of inhibitory effects of the proton pump-inhibiting drugs omeprazole, esomeprazole, lansoprazole, pantoprazole, and rabeprazole on human cytochrome p450 activities. Drug Metab Dispos. 2004 August 1;32(8):821-7. Brand Generic Ki (μM) Model Inhibitor HLM a rCYP2C19 b Ticlopidine HLM 0.31±0.05 rCYP2C19 0.68±0.04 Prilosec omeprazole 6.2±0.8 2.4±0.05 Aciphex rabeprazole 21.3±2.8 (2.4±0.1) c 18.8±1.3 (2.8± 0.1) d Nexium esomeprazole 8.6±1.0 7.9±0.5 Prevacid lansoprazole 0.45±0.07 0.74±0.09 Protonix pantoprazole 69.4±9.2 15.3±1.1 a,b marker reaction used was S-Mephenytoin 4-Hydroxylation c,d rabeprazole thioether; HLM=human liver microsomes
17. Risk of All-Cause Mortality and Recurrent ACS in Patients Taking Clopidogrel and PPI Ho PM, Maddox TM, Wang L, et al. JAMA. 2009;301(9):937-944. 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0 0 90 180 270 360 450 540 630 720 810 900 990 1080 Days Since Discharge Proportion of Deaths or Recurrent ACS Neither clopidogrel nor PPI PPI without clopidogrel Clopidogrel + PPI Clopidogrel without PPI
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Editor's Notes
This CYP2C isozyme, the least expressed, was the first to be discovered due to its marked genetic polymorphism, resulting in ( S )-mephenytoin-poor (PM) and extensive metabolizer (EM) phenotypes. Although not initially of any particular clinical interest, the CYP2C19 isozyme was later found to show a marked preference for proton-pump inhibitors (PPI) like omeprazole and pantoprazole, and numerous additional important drugs have been identified as major CYP2C19 substrates in recent years. CYP2C19 plays a prominent role in the metabolism of several first- and second-generation antidepressants, cyclophosphamide, proguanil, voriconazole, propranolol.
One of the most common, with an allelic frequency of 15% to 30%, is designated CYP2C19*2. This polymorphism causes a splicing defect and a complete loss in enzyme activity, presenting phenotypically as a poor metabolizer. The CYP2C19*17 variant is associated with ultrarapid metabolizers and seems relatively common in Swedes (18 percent), Ethiopians (18 percent), and Chinese (4 percent).
The PM phenotype results from two null alleles, leading to the absence of functional CYP2C19 protein, whereas extensive metabolizers carry at least one functional allele. Poor metabolizers have markedly reduced or absent enzyme activity. Intermediate metabolizers have reduced enzyme activity. Ultrarapid metabolizers have high enzyme activity. The investigators found that the presence of the *17 polymorphism was indeed associated with a higher level of platelet inhibition, as measured with multipleelectrode platelet aggregometry, in a gene-dose– dependent manner (ie, homozygotes had greater platelet inhibition than heterozygotes, who had greater inhibition than wild types).
The remaining 15% of the absorbed clopidogrel is rapidly and extensively metabolized by the liver and the plasma concentration of the parent compound is below the detection limit beyond 2 h post dosing. . Purinergic receptors and mechanism of action of clopidogrel. Clopidogrel is a pro-drug of which approximately 85% is hydrolyzed by esterases in the blood to inactive metabolites and only 15% is metabolized by the cytochrome P450 (CYP) system in the liver into an active metabolite. The active metabolite irreversibly inhibits the adenosine diphosphate (ADP) P2Y12 receptor. The P2X1 receptor, which uses adenosine triphosphate (ATP) as an agonist, is involved in platelet shape change through extracellular calcium influx and helps to amplify platelet responses mediated by other agonists. Activation of the P2Y1 receptor leads to alteration in shape and initiates a weak and transient phase of platelet aggregation. The binding of ADP to the Gi-coupledP2Y12 receptor liberates the Gi protein subunits ai and bg, resulting in stabilization of platelet aggregation. The ai subunit inhibits adenylyl cyclase (AC) and, thus, reduces cyclic adenosine monophosphate (cAMP) levels, which diminishes cAMP-mediated phosphorylation of vasodilator-stimulated phosphoprotein (VASP-P). The status of VASP-P modulates glycoprotein (GP) IIb/IIIa receptor activation. The subunit bg activates the phosphatidylinositol 3-kinase (PI3K), which leads to GP IIb/IIIa receptor activation through activation of a serine-threonine protein kinase B (PKB/Akt) and of Rap1b GTP binding proteins. Prostaglandin E1 (PGE1) activates AC, which increases cAMP levels and status of VASP-P. Solid arrows indicate activation; dotted arrows indicate inhibition. Acts by binding to ADP receptors on platelets, preventing platelet aggregation and thrombosis • Great variability in response to clopidogrel – 4 - 20% of individuals are resistant
Given that only an estimated 2% of ingested clopidogrel ends up bound to platelets, it is easy to appreciate that small changes in its metabolism may substantially affect platelet p2y12 inhibition. Hepatic metabolism is essential to the generation of the active metabolite of clopidogrel, specifically, 2 sequential oxidative steps through the cytochrome P450 (CYP) system.2 This superfamily of proteins, which encompasses 57 genes and 18 families, is involved in 80% of oxidative drug metabolism, as well as the metabolism of many other exogenous and endogenous chemicals, including arachidonic acid and eicosanoids, steroids, lipids, bile acids, and vitamins.3 We now know that a variety of P450 enzymes contribute to clopidogrel metabolism. The first metabolic step, which leads to 2-oxo-clopidogrel, is catalyzed by 3 enzymes (CYP1A2, CYP2B6, and CYP2C19), whereas the second step, which culminates in the active metabolite, involves 4 enzymes (CYP2B6, CYP2C9, CYP2C19, and CYP3A4). Estimates of the contribution ratio ( f m P450) of CYP1A2, CYP2B6, and CYP2C19 to 2-oxo-clopidogrel formation were 35.8, 19.4, and 44.9%, respectively, suggesting that the contribution of CYP2C19 to this oxidation process was higher compared with the other two P450s. Estimates of the f m P450 of CYP2B6, CYP2C9, CYP2C19, and CYP3A4 for the active metabolite formation were 32.9, 6.76, 20.6, and 39.8%, respectively, suggesting that the contribution of CYP3A4 to the active metabolite formation was greater compared with the other three P450s.
With the CYP2C19 enzyme involved in both steps, contributing to an estimated 45% of 2-oxo-clopidogrel generated and 21% of its conversion to active metabolite, it is understandable why so much recent research has focused on the potential impact of drugs and genetic polymorphisms that influence the activity of this enzyme.
The delayed onset of action of clopidogrel is one of its limitations, thus, it needs a loading dose to shorten it when rapid inhibition is required, such as in the context of ACS or PCI. 600mg loading dose is widely used given the positive result evidence. There are about 5%-40% low responders or resistant patients identefied. Variability factors in brief: genetic, cellular, and clinical factors. Genetic factors: 1. Gene ABCB1 codes for MDR1 Pgp involved in clopidogrel absorption. Patient with variant alleles may have reduced active metabolite generation after administration of a loading dose of clopidogrel. Conflicting evidence. 2. CYP isoenzymes involved in metabolism of clopidogrel: CYP3A4, 3A5, 2C9 and 2C19 polymorphisms. Clopidogrel-induced antiplatelet effects may be affected by several cellular factors. For example, an accelerated platelet turnover has been suggested to diminish clopidogrel responsiveness. Upregulation of P2Y1 and P2Y12 receptors to be implicated in clopidogrel variability in response.
Lower Ki = greater inhibition. Different PPIs available are metabolized by CYP isoforms mainly CYP2C19 and Cyp3A4. Omeprazole is primarily metabolized by CYP2C19 as well as inhibit CYP2C19.
In this retrospective cohort study by Ho and colleagues, concomitant use of clopidogrel and a proton pump inhibitor (PPI) after hospital discharge for ACS was associated with an increased risk of adverse outcomes than use of clopidogrel without a PPI, suggesting that use of PPI may be associated with attenuation of benefits of clopidogrel after ACS. Of 8205 patients with ACS taking clopidogrel after hospital discharge, 63.9% (n=5244) were prescribed PPI at discharge, during follow-up, or both and 36.1% (n=2961) were not prescribed PPI. Median follow-up after hospital discharge was 521 days (interquartile range, 305-779 days). Death or rehospitalization for ACS occurred in 20.8% (n=615) of patients prescribed clopidogrel without PPI and 29.8% (n=1561) of patients prescribed clopidogrel plus PPI. In multivariable analysis, use of clopidogrel plus PPI at any point in time was associated with an increased risk of death or rehospitalization for ACS compared with use of clopidogrel without PPI (adjusted odds ratio, 1.25; 95% CI, 1.11-1.41). In multivariable analyses with medication use as a time-varying covariate, periods of use of clopidogrel without PPI were associated with a significantly lower risk of adverse events compared with periods without the use of either clopidogrel or PPI ( P <.001). However, this association appeared to be attenuated when comparing periods of use of clopidogrel plus PPI use with periods without use of either clopidogrel or PPI (shown in figure on slide). Ho PM, Maddox TM, Wang L, et al. Risk of adverse outcomes associated with concomitant use of clopidogrel and proton pump inhibitors following acute coronary syndrome. JAMA. 2009;301(9):937-944.
In conclusion, the findings of this meta-analysis suggest that there is conflicting and inconsistent evidence on the impact of the clopidogrel PPI interaction on cardiovascular outcomes, and certainly no evidence of any effect on overall mortality. Clinicians should carefully weigh up the real dangers of an increase in gastrointestinal haemorrhage events [13] before routinely avoiding the use of PPIs in patients taking clopidogrel. List all the clopidogrel interactions found in the program, cyp3a4 inducers and cyp2c19 inducers
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