Special Section: Clopidogrel Commentary
Clopidogrel, CYP2C19 and Proton Pump Inhibitors: What We Know and What it Means
The Journal of Clinical Pharmacology 54(8) 884–888 © 2014, The American College of Clinical Pharmacology DOI: 10.1002/jcph.337
Sudharshan Hariharan, PhD1, Mary Ross Southworth, PharmD2, and Rajanikanth Madabushi, PhD1
Keywords clinical pharmacology (CPH), drug interactions, pharmacokinetics and drug metabolism, cardiovascular (CAR), pharmacogenomics
The bioactivation pathway of clopidogrel is complex. CYP2C19 has been identified as a key determinant in the formation of the active metabolite of clopidogrel. However, the clinical relevance of reduced CYP2C19 function has been a point of contention in the scientific community. This has led to debate on instructions for use of clopidogrel in situations where patients are concomitantly administered drugs that inhibit CYP2C19, such as proton pump inhibitors.1,2 This commentary aims to put into perspective the available evidence and rationalizes the instructions for use with proton pump inhibitors.
Metabolic Pathway of Clopidogrel The approval of Plavix1 (clopidogrel) in 1997 represented a significant therapeutic option for reducing atherothrombotic events in patients documented by recent stroke, myocardial infarction or established peripheral arterial disease.3 This resulted in rapid and widespread use, even though some of the pharmacologic characteristics of clopidogrel were not fully understood. Of importance, the bioactivation pathway of clopidogrel was not delineated at the time of drug approval. However, it was known that an unidentified moiety, presumably mediated via hepatic cytochrome P450 (CYP450) enzyme system, was responsible for its antiplatelet activity by binding irreversibly to the adenosine diphosphate P2Y12 receptor of the human platelet.4–6 The active moiety was eventually discovered, but quantification was challenging because it is highly unstable.7 Lack of a bioanalytical assay to quantify the active moiety greatly hindered progress toward a better understanding of the bioactivation of clopidogrel. With use, many literature reports surfaced about the variability in therapeutic response to clopidogrel treatment, resulting in a need to understand better the sources of such variability.8–11 This led to the evaluation of the impact of polymorphic variants of
suspected CYP450 isozymes on the antiplatelet activity of clopidogrel. Early publications showed that the presence of loss-of-function (LOF) alleles of CYP2C19 enzyme markedly decreased the antiplatelet effect of clopidogrel, suggesting a role for CYP2C19 in the bioactivation pathway.12–16 These findings prompted the Food and Drug Administration (FDA) to require the manufacturer of Plavix1 to perform a series of clinical pharmacology studies which were designed to (i) examine the role of CYP450 isozymes in the bioactivation of clopidogrel, (ii) to evaluate the impact of LOF alleles of CYP2C19 on the pharmacokinetics (PK) and pharmacodynamics (PD) of clopidogrel, and (iii) to assess the drug interaction potential with proton pump inhibitors (particularly omeprazole) that are known CYP2C19 inhibitors.17 The in vitro study using individual recombinant human CYP (rhCYP) isoforms showed the bioactivation of clopidogrel involved multiple enzymes.3 The two-step process begins with the formation of 2-oxo-clopidogrel followed by the generation of the active thiol metabolite. It is important to mention that the thiol metabolite exists in a mixture of diastereomers (H1–H4), and only the H4 isomer, which now can be quantified, is reported to be responsible for the antiplatelet activity of clopidogrel.18 The metabolic pathway leading to the formation of the 1
Office of Clinical Pharmacology, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD, USA 2 Division of Cardiovascular and Renal Products, Office of New Drugs, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD, USA Submitted for publication 31 May 2014; accepted 2 June 2014. Corresponding author: Rajanikanth Madabushi, Ph.D., 10903 New Hampshire Avenue, White Oak Bldg. 51, Rm. 2173, Silver Spring, MD 20993, USA Email: [email protected]
Hariharan et al
active metabolite of clopidogrel was shown to be mediated by CYP1A2, 2B6, 2C19, and 3A4/5.3 Although in vitro studies identified CYP2C19 amongst other CYP isozymes in the metabolic pathway, results from in vivo PK and PD studies suggested a significant role for CYP2C19, consistent with the early reported clinical studies. In subjects with two LOF alleles of CYP2C19, the mean exposure to active metabolite was 58%–71% lower compared to subjects with no LOF alleles of CYP2C19, following 300 mg loading and 75 mg maintenance doses, respectively.19 Reductions in antiplatelet effect were also observed using multiple PD (inhibition of platelet aggregation) assays. Similar findings have also been reported following co-administration of clopidogrel with omeprazole, a CYP2C19 inhibitor.20 These results clearly show a critical role for CYP2C19 in the formation of the active metabolite of clopidogrel. The substantial decrease in the exposure to active metabolite in subjects with two LOF alleles of CYP2C19 is surprising, considering that CYP3A4, a high capacity enzyme system, also contributes to the metabolic pathway of clopidogrel. One possible hypothesis is the widely cited work by Kazui et al, that CYP2C19, but not CYP3A4, is the key metabolic enzyme in one of the conversion steps.21 Their experiments identified CYP1A2, 2B6, and 2C19 in the first step (formation of 2-oxo-clopidogrel) and CYP2B6, 2C9, 2C19, and 3A4 in the second step (formation of active metabolite). This hypothesis can explain the findings reported for CYP2C19 genetic variant as well as the modest decrease in exposure to the active metabolite upon co-administration with ketoconazole, a strong CYP3A inhibitor.22 This is also consistent with the findings reported following intraduodenal administration of 2-oxo-clopidogrel, the intermediate, and clopidogrel, the parent, in rats.23 When 2oxo-clopidogrel is administered, the active metabolite was detected in the portal vein, suggesting a potential for CYP3A in this step. However, oral administration of clopidogrel did not result in any detectable levels of either 2-oxo-clopidogrel or the active metabolite in the portal vein, thus providing support to the role of non-CYP3Amediated hepatic metabolism in the first conversion step. Nevertheless, the applicability of these findings to humans remains to be seen. With emerging information, the understanding of clopidogrel’s bioactivation becomes more complex. It was recently reported that grapefruit juice (GFJ) produced a substantial reduction in the exposure to the active metabolite of clopidogrel, a surprising finding given that the effects of GFJ are usually attributed to inhibition of gut wall CYP3A.24 However, it has also been reported that the active components of GFJ inhibit a variety of CYP450 isoforms in vitro, including CYP2C19 and 1A2.25 Because GFJ studies carry a lot of variability in terms of strength of the juice, the concentrations of the
885 active moieties, volume and frequency of administration, no conclusion can be drawn until such results are consistently reproduced. It has also been reported that the formation of clopidogrel’s active metabolite is a hydrolysis step mediated by paraoxonase-1 (PON-1) instead of via CYP-dependent pathways.26 However, other researchers have not been able to reproduce this so far.27–31 From a chemistry perspective, the work from Dansette et al suggest that PON-1 mediates the formation of the endoisomer of thiol metabolite of clopidogrel (inactive), where the double bond migrates from an exocyclic to an endocyclic position in the piperidine ring.32
Use with Proton Pump Inhibitors Of all the complexities associated with the metabolism of clopidogrel, the role of CYP2C19 stands out as the most consistent and well characterized finding. As evidence from in vivo studies indicated a critical role for CYP2C19 in the bioactivation pathway, there was a clear need to evaluate potential drug interactions between clopidogrel and CYP2C19 modulators. Proton pump inhibitors are commonly co-prescribed with clopidogrel to minimize antiplatelet treatment-related gastrointestinal bleeding. Some of these proton pump inhibitors, eg, omeprazole, also happen to be inhibitors of CYP2C19, so these drugs were an obvious choice to evaluate for drug interaction potential. Dose adjustments or recommendations for intrinsic and extrinsic factors are typically provided based on the results from dedicated PK and/or PD studies with an understanding of the exposure–response relationship. Similarly for clopidogrel, the PK and PD drug interaction study performed by manufacturers of Plavix1 formed the primary basis for providing recommendations in the label. Concomitant administration of clopidogrel with a high dose of omeprazole (80 mg) resulted in a decrease to the exposure of the active metabolite by 40% compared to clopidogrel administered alone.20 Another study was conducted where administration of clopidogrel and omeprazole was separated by 12 hours, because the inhibition of CYP2C19 by omeprazole was thought to be competitive. However, the results from the dose-staggered drug interaction study showed a similar decrease in the exposure to the active metabolite as that seen with concomitant administration.20 These studies not only established a significant interaction between omeprazole and clopidogrel, but also suggested that the interaction is mechanistic and staggering the dose would not alleviate the interaction. Clopidogrel exerts its pharmacological effect by inhibiting platelet aggregation; hence it is reasonable to expect that a reduction in platelet inhibition due to decrease in exposure to the active metabolite would affect the clinical efficacy of clopidogrel. Although the exact relationship between active metabolite concentration or
The Journal of Clinical Pharmacology / Vol 54 No 8 (2014)
886 the extent of platelet inhibition and reduction in risk of cardiovascular events has not been established, the potential clinical consequence of the decrease in antiplatelet effects might be inferred by looking at other drugs that act by a similar mechanism. Specifically, drugs that achieve higher platelet inhibition compared to clopidogrel, eg, prasugrel, have demonstrated greater cardiovascular risk reduction.33,34 It should also be noted that in Acute Coronary Syndrome (ACS) patients who were on a background of aspirin, clopidogrel demonstrated a 20% cardiovascular risk reduction compared to placebo.35 This can be interpreted as a crude measure of the nature of antiplatelet-cardiovascular outcome relationship for irreversible P2Y12 inhibitors. Therefore, it is reasonable to associate potential loss of clinical effectiveness in instances that result in significant decrease in exposure to active metabolite and antiplatelet activity. Co-administration of omeprazole and esomeprazole clearly resulted in a significant reduction in the exposure to the active metabolite, thus warranting recommendations to avoid use of these medications with clopidogrel.3,20,36 The recommendation to avoid concomitant use with clopidogrel does not apply to all members of the ‘proton pump inhibitor’ class, because the impact of this interaction is relatively less severe with other studied proton pump inhibitors—pantoprazole, lansoprazole, or dexlansoprazole.20,37 A significant interaction for omeprazole or esomeprazole could likely be due to mechanistic differences in the nature of CYP2C19 inhibition compared to other proton pump inhibitors. In contrast to agents that are reversible in nature, the S-omeprazole isomer of the racemic omeprazole mixture is known to be a mechanism based inhibitor of CYP2C19.38,39 Inhibitors of this type, deactivate the enzyme in an irreversible fashion which further explains why separation in the time of administration of clopidogrel and omeprazole made no difference on the extent of inhibition. Despite the PK and PD evidence, the clinical consequence of this drug interaction is extensively debated, raising questions on the recommendation for use of clopidogrel with omeprazole or esomeprazole in the Plavix1 package insert.1,2 Criticism is largely related to the lack of clear evidence of this interaction from cardiovascular outcome studies that are not prospectively designed to evaluate this interaction. Large observational studies and post-hoc analyses have not consistently demonstrated an association with omeprazole and poor cardiovascular outcomes when given with clopidogrel. However, these analyses are inherently confounded and subject to bias and should be interpreted with caution. By and large the scientific community considers the lack of a signal of a significant interaction from a retrospective analysis as evidence of no effect creating a situation where it might seem that there is a disconnect between instructions for use and existing data or evidence.
Even COGENTa, the only prospective randomized trial designed to determine the clinical impact of using clopidogrel with omeprazole, was primarily aimed to evaluate the effect on gastrointestinal outcomes.40 Though effect on cardiovascular outcomes was a prespecified safety endpoint, no a priori sample size calculation was performed based on this endpoint. The results from COGENT are well known and extensively debated. Some consider the results of COGENT reassuring because it did not demonstrate an interaction with concomitant administration of clopidogrel and omeprazole. However, it is important to view the results from COGENT with a perspective on its design, primarily the size of the study, and results from another study of clopidogrel, CUREb. CURE enrolled 12,562 ACS patients to yield a 20% reduction in cardiovascular risk comprised of a composite of death, myocardial infarction, and stroke for clopidogrel compared to placebo.35 To evaluate clopidogrel’s interaction with omeprazole, which would be expected to be a fraction of clopidogrel’s effect size, a trial with a sample size bigger than that enrolled in CURE may be required. Therefore, COGENT with 3,873 patients was significantly underpowered to rule out an adverse effect for omeprazole in terms of cardiovascular outcomes. In addition, there exist differences in the patient population and the components of the cardiovascular endpoint between the trials which further limit the interpretation of the results from COGENT.41 Evidence from PK and PD studies showing a decrease in active metabolite exposure and platelet inhibition supports a recommendation to avoid concomitant use of clopidogrel and omeprazole or esomeprazole. The lack of clinical evidence from a prospectively designed study ruling out an interaction is not reassuring. However, it is interesting to note that scientific literature on clopidogrel has been continuously evolving even years past its approval. FDA recognizes that a residual uncertainty may exist and will continue to assess emerging data that may play a role in further optimizing the instructions for use of Plavix1. Acknowledgments The authors thank Dr. Shiew Mei Huang, Dr. Mehul Mehta and Dr. Norman Stockbridge for their critical insight and help with preparation of this commentary.
References 1. Depta JP, Bhatt DL. Omeprazole and clopidogrel: should clinicians be worried? Cleve Clin J Med. 2010;77(2):113–116. 2. Tantry US, Kereiakes DJ, Gurbel PA. Clopidogrel and proton pump inhibitors: influence of pharmacological interactions on clinical
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outcomes and mechanistic explanations. JACC Cardiovasc Interv. 2011;4(4):365–380. U.S. Food and Drug Adminsitration. Prescribing information: Plavix1. 2013. Available at: http://www.accessdata.fda.gov/ drugsatfda_docs/label/2013/020839s058lbl.pdf. Accessed May 30, 2014. Mills DC, Puri R, Hu CJ, et al. Clopidogrel inhibits the binding of ADP analogues to the receptor mediating inhibition of platelet adenylate cyclase. Arterioscler Thromb. 1992;12(4):430–436. Savi P, Combalbert J, Gaich C. The antiaggregating activity of clopidogrel is due to a metabolic activation by the hepatic cytochrome P450-1A. Thromb Haemost. 1994;72(2):313–317. Savi P, Herbert JM, Pflieger AM. Importance of hepatic metabolism in the antiaggregating activity of the thienopyridine clopidogrel. Biochem Pharmacol. 1992;44(3):527–532. Savi P, Pereillo JM, Uzabiaga MF. Identification and biological activity of the active metabolite of clopidogrel. Thromb Haemost. 2000;84(5):891–896. Gurbel PA, Bliden KP, Hiatt BL, O’Connor CM. Clopidogrel for coronary stenting: response variability, drug resistance, and the effect of pretreatment platelet reactivity. Circulation. 2003; 107(23):2908–2913. Gurbel PA, Lau WC, Bliden KP, Tantry US. Clopidogrel resistance: implications for coronary stenting. Curr Pharm Des. 2006; 12(10):1261–1269. Serebruany VL, Steinhubl SR, Berger PB, Malinin AI, Bhatt DL, Topol EJ. Variability in platelet responsiveness to clopidogrel among 544 individuals. J Am Coll Cardiol. 2005;45(2):246–251. Siller-Matula J, Schror K, Wojta J, Huber K. Thienopyridines in cardiovascular disease: focus on clopidogrel resistance. Throm Haemost. 2007;97(3):385–393. Fontana P, Hulot JS, De Moerloose P, Gaussem P. Influence of CYP2C19 and CYP3A4 gene polymorphisms on clopidogrel responsiveness in healthy subjects. J Throm Haemost. 2007; 5(10):2153–2155. Frere C, Cuisset T, Morange PE, et al. Effect of cytochrome p450 polymorphisms on platelet reactivity after treatment with clopidogrel in acute coronary syndrome. Am J Cardiol. 2008; 101(8):1088–1093. Hulot JS, Bura A, Villard E, et al. Cytochrome P450 2C19 loss-offunction polymorphism is a major determinant of clopidogrel responsiveness in healthy subjects. Blood. 2006;108(7):2244–2247. Mega JL, Close SL, Wiviott SD, et al. Cytochrome p-450 polymorphisms and response to clopidogrel. N Engl J Med. 2009;360(4):354–362. Simon T, Verstuyft C, Mary-Krause M, et al. Genetic determinants of response to clopidogrel and cardiovascular events. N Engl J Med. 2009;360(4):363–375. U.S. Food and Drug Adminsitration. Early communication about an ongoing safety review of clopidogrel bisulfate (marketed as Plavix1). 2009. Available at: http://www.fda.gov/Drugs/ DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/DrugSafetyInformationforHeathcareProfessionals/ ucm079520.htm Accessed May 30, 2104. Tuffal G, Roy S, Lavisse M, et al. An improved method for specific and quantitative determination of the clopidogrel active metabolite isomers in human plasma. Throm Haemost. 2011;105 (4):696–705. Simon T, Bhatt DL, Bergougnan L, et al. Genetic polymorphisms and the impact of a higher clopidogrel dose regimen on active metabolite exposure and antiplatelet response in healthy subjects. Clin Pharmacol Ther. 2011;90(2):287–295. Angiolillo DJ, Gibson CM, Cheng S, et al. Differential effects of omeprazole and pantoprazole on the pharmacodynamics and pharmacokinetics of clopidogrel in healthy subjects: randomized,
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placebo-controlled, crossover comparison studies. Clin Pharmacol Ther. 2011;89(1):65–74. Kazui M, Nishiya Y, Ishizuka T, et al. Identification of the human cytochrome P450 enzymes involved in the two oxidative steps in the bioactivation of clopidogrel to its pharmacologically active metabolite. Drug Metab Dispos. 2010;38(1):92–99. Farid NA, Payne CD, Small DS, et al. Cytochrome P450 3A inhibition by ketoconazole affects prasugrel and clopidogrel pharmacokinetics and pharmacodynamics differently. Clin Pharmacol Ther. 2007;81(5):735–741. Qiu Z, Li N, Song L, et al. Contributions of intestine and plasma to the presystemic bioconversion of vicagrel, an acetate of clopidogrel. Pharm Res. 2014;31(1):238–251. Holmberg MT, Tornio A, Neuvonen M, Neuvonen PJ, Backman JT, Niemi M. Grapefruit juice inhibits the metabolic activation of clopidogrel. Clin Pharmacol Ther. 2014;95(3):307–313. Tassaneeyakul W, Guo LQ, Fukuda K, Ohta T, Yamazoe Y. Inhibition selectivity of grapefruit juice components on human cytochromes P450. Arch Biochem Biophys. 2000;378(2):356–363. Bouman HJ, Schomig E, van Werkum JW, et al. Paraoxonase-1 is a major determinant of clopidogrel efficacy. Nat Med. 2011; 17(1):110–116. Ancrenaz V, Desmeules J, James R, et al. The paraoxonase-1 pathway is not a major bioactivation pathway of clopidogrel in vitro. Br J Pharmacol. 2012;166(8):2362–2370. Kreutz RP, Nystrom P, Kreutz Y, et al. Influence of paraoxonase-1 Q192R and cytochrome P450 2C19 polymorphisms on clopidogrel response. Clin Pharmacol. 2012;4:13–20. Reny JL, Combescure C, Daali Y, Fontana P, Group PONM-A. Influence of the paraoxonase-1 Q192R genetic variant on clopidogrel responsiveness and recurrent cardiovascular events: a systematic review and meta-analysis. J Thromb Haemost. 2012; 10(7):1242–1251. Rideg O, Komocsi A, Magyarlaki T. Impact of genetic variants on post-clopidogrel platelet reactivity in patients after elective percutaneous coronary intervention. Pharmacogenomics. 2011; 12(9):1269–1280. Tang XF, Wang J, Zhang JH, et al. Effect of the CYP2C19 2 and 3 genotypes, ABCB1 C3435T and PON1 Q192R alleles on the pharmacodynamics and adverse clinical events of clopidogrel in Chinese people after percutaneous coronary intervention. Eur J Clin Pharmacol. 2013;69(5):1103–1112. Dansette PM, Rosi J, Bertho G, Mansuy D. Cytochromes P450 catalyze both steps of the major pathway of clopidogrel bioactivation, whereas paraoxonase catalyzes the formation of a minor thiol metabolite isomer. Chem Res Toxicol. 2012;25(2):348– 356. U.S. Food and Drug Adminsitration. Prescribing information: Effient1. 2013. Available at: http://www.accessdata.fda.gov/ drugsatfda_docs/label/2013/022307s010lbl.pdf. Accessed May 30, 2014. Payne CD, Li YG, Small DS, et al. Increased active metabolite formation explains the greater platelet inhibition with prasugrel compared to high-dose clopidogrel. J Cardiovasc Pharmacol. 2007;50(5):555–562. Yusuf S, Zhao F, Mehta SR, et al. Effects of clopidogrel in addition to aspirin in patients with acute coronary syndromes without ST-segment elevation. N Engl J Med. 2001;345(7):494–502. Andersson T, Nagy P, Niazi M, et al. Effect of esomeprazole with/ without acetylsalicylic Acid, omeprazole and lansoprazole on pharmacokinetics and pharmacodynamics of clopidogrel in healthy volunteers. Am J Cardiovasc Drugs. 2014;14(3):217–227. Frelinger, III AL, Lee RD, Mulford DJ, et al. A randomized, 2-period, crossover design study to assess the effects of dexlansoprazole, lansoprazole, esomeprazole, and omeprazole on
888 the steady-state pharmacokinetics and pharmacodynamics of clopidogrel in healthy volunteers. J Am Coll Cardiol. 2012; 59(14):1304–1311. 38. Boulenc X, Djebli N, Shi J, et al. Effects of omeprazole and genetic polymorphism of CYP2C19 on the clopidogrel active metabolite. Drug Metab Dispos. 2012;40(1):187–197. 39. Ogilvie BW, Yerino P, Kazmi F, et al. The proton pump inhibitor, omeprazole, but not lansoprazole or pantoprazole, is a
The Journal of Clinical Pharmacology / Vol 54 No 8 (2014) metabolism-dependent inhibitor of CYP2C19: implications for coadministration with clopidogrel. Drug Metab Dispos. 2011; 39(11):2020–2033. 40. Bhatt DL, Cryer BL, Contant CF, et al. Clopidogrel with or without omeprazole in coronary artery disease. N Engl J Med. 2010; 363(20):1909–1917. 41. Southworth MR, Temple R. Interaction of clopidogrel and omeprazole. N Engl J Med. 2010;363(20):1977.
Clopidogrel, CYP2C19 and Proton Pump Inhibitors: What We Know and What it Means
The Journal of Clinical Pharmacology 54(8) 884–888 © 2014, The American College of Clinical Pharmacology DOI: 10.1002/jcph.337
Sudharshan Hariharan, PhD1, Mary Ross Southworth, PharmD2, and Rajanikanth Madabushi, PhD1
Keywords clinical pharmacology (CPH), drug interactions, pharmacokinetics and drug metabolism, cardiovascular (CAR), pharmacogenomics
The bioactivation pathway of clopidogrel is complex. CYP2C19 has been identified as a key determinant in the formation of the active metabolite of clopidogrel. However, the clinical relevance of reduced CYP2C19 function has been a point of contention in the scientific community. This has led to debate on instructions for use of clopidogrel in situations where patients are concomitantly administered drugs that inhibit CYP2C19, such as proton pump inhibitors.1,2 This commentary aims to put into perspective the available evidence and rationalizes the instructions for use with proton pump inhibitors.
Metabolic Pathway of Clopidogrel The approval of Plavix1 (clopidogrel) in 1997 represented a significant therapeutic option for reducing atherothrombotic events in patients documented by recent stroke, myocardial infarction or established peripheral arterial disease.3 This resulted in rapid and widespread use, even though some of the pharmacologic characteristics of clopidogrel were not fully understood. Of importance, the bioactivation pathway of clopidogrel was not delineated at the time of drug approval. However, it was known that an unidentified moiety, presumably mediated via hepatic cytochrome P450 (CYP450) enzyme system, was responsible for its antiplatelet activity by binding irreversibly to the adenosine diphosphate P2Y12 receptor of the human platelet.4–6 The active moiety was eventually discovered, but quantification was challenging because it is highly unstable.7 Lack of a bioanalytical assay to quantify the active moiety greatly hindered progress toward a better understanding of the bioactivation of clopidogrel. With use, many literature reports surfaced about the variability in therapeutic response to clopidogrel treatment, resulting in a need to understand better the sources of such variability.8–11 This led to the evaluation of the impact of polymorphic variants of
suspected CYP450 isozymes on the antiplatelet activity of clopidogrel. Early publications showed that the presence of loss-of-function (LOF) alleles of CYP2C19 enzyme markedly decreased the antiplatelet effect of clopidogrel, suggesting a role for CYP2C19 in the bioactivation pathway.12–16 These findings prompted the Food and Drug Administration (FDA) to require the manufacturer of Plavix1 to perform a series of clinical pharmacology studies which were designed to (i) examine the role of CYP450 isozymes in the bioactivation of clopidogrel, (ii) to evaluate the impact of LOF alleles of CYP2C19 on the pharmacokinetics (PK) and pharmacodynamics (PD) of clopidogrel, and (iii) to assess the drug interaction potential with proton pump inhibitors (particularly omeprazole) that are known CYP2C19 inhibitors.17 The in vitro study using individual recombinant human CYP (rhCYP) isoforms showed the bioactivation of clopidogrel involved multiple enzymes.3 The two-step process begins with the formation of 2-oxo-clopidogrel followed by the generation of the active thiol metabolite. It is important to mention that the thiol metabolite exists in a mixture of diastereomers (H1–H4), and only the H4 isomer, which now can be quantified, is reported to be responsible for the antiplatelet activity of clopidogrel.18 The metabolic pathway leading to the formation of the 1
Office of Clinical Pharmacology, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD, USA 2 Division of Cardiovascular and Renal Products, Office of New Drugs, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD, USA Submitted for publication 31 May 2014; accepted 2 June 2014. Corresponding author: Rajanikanth Madabushi, Ph.D., 10903 New Hampshire Avenue, White Oak Bldg. 51, Rm. 2173, Silver Spring, MD 20993, USA Email: [email protected]
Hariharan et al
active metabolite of clopidogrel was shown to be mediated by CYP1A2, 2B6, 2C19, and 3A4/5.3 Although in vitro studies identified CYP2C19 amongst other CYP isozymes in the metabolic pathway, results from in vivo PK and PD studies suggested a significant role for CYP2C19, consistent with the early reported clinical studies. In subjects with two LOF alleles of CYP2C19, the mean exposure to active metabolite was 58%–71% lower compared to subjects with no LOF alleles of CYP2C19, following 300 mg loading and 75 mg maintenance doses, respectively.19 Reductions in antiplatelet effect were also observed using multiple PD (inhibition of platelet aggregation) assays. Similar findings have also been reported following co-administration of clopidogrel with omeprazole, a CYP2C19 inhibitor.20 These results clearly show a critical role for CYP2C19 in the formation of the active metabolite of clopidogrel. The substantial decrease in the exposure to active metabolite in subjects with two LOF alleles of CYP2C19 is surprising, considering that CYP3A4, a high capacity enzyme system, also contributes to the metabolic pathway of clopidogrel. One possible hypothesis is the widely cited work by Kazui et al, that CYP2C19, but not CYP3A4, is the key metabolic enzyme in one of the conversion steps.21 Their experiments identified CYP1A2, 2B6, and 2C19 in the first step (formation of 2-oxo-clopidogrel) and CYP2B6, 2C9, 2C19, and 3A4 in the second step (formation of active metabolite). This hypothesis can explain the findings reported for CYP2C19 genetic variant as well as the modest decrease in exposure to the active metabolite upon co-administration with ketoconazole, a strong CYP3A inhibitor.22 This is also consistent with the findings reported following intraduodenal administration of 2-oxo-clopidogrel, the intermediate, and clopidogrel, the parent, in rats.23 When 2oxo-clopidogrel is administered, the active metabolite was detected in the portal vein, suggesting a potential for CYP3A in this step. However, oral administration of clopidogrel did not result in any detectable levels of either 2-oxo-clopidogrel or the active metabolite in the portal vein, thus providing support to the role of non-CYP3Amediated hepatic metabolism in the first conversion step. Nevertheless, the applicability of these findings to humans remains to be seen. With emerging information, the understanding of clopidogrel’s bioactivation becomes more complex. It was recently reported that grapefruit juice (GFJ) produced a substantial reduction in the exposure to the active metabolite of clopidogrel, a surprising finding given that the effects of GFJ are usually attributed to inhibition of gut wall CYP3A.24 However, it has also been reported that the active components of GFJ inhibit a variety of CYP450 isoforms in vitro, including CYP2C19 and 1A2.25 Because GFJ studies carry a lot of variability in terms of strength of the juice, the concentrations of the
885 active moieties, volume and frequency of administration, no conclusion can be drawn until such results are consistently reproduced. It has also been reported that the formation of clopidogrel’s active metabolite is a hydrolysis step mediated by paraoxonase-1 (PON-1) instead of via CYP-dependent pathways.26 However, other researchers have not been able to reproduce this so far.27–31 From a chemistry perspective, the work from Dansette et al suggest that PON-1 mediates the formation of the endoisomer of thiol metabolite of clopidogrel (inactive), where the double bond migrates from an exocyclic to an endocyclic position in the piperidine ring.32
Use with Proton Pump Inhibitors Of all the complexities associated with the metabolism of clopidogrel, the role of CYP2C19 stands out as the most consistent and well characterized finding. As evidence from in vivo studies indicated a critical role for CYP2C19 in the bioactivation pathway, there was a clear need to evaluate potential drug interactions between clopidogrel and CYP2C19 modulators. Proton pump inhibitors are commonly co-prescribed with clopidogrel to minimize antiplatelet treatment-related gastrointestinal bleeding. Some of these proton pump inhibitors, eg, omeprazole, also happen to be inhibitors of CYP2C19, so these drugs were an obvious choice to evaluate for drug interaction potential. Dose adjustments or recommendations for intrinsic and extrinsic factors are typically provided based on the results from dedicated PK and/or PD studies with an understanding of the exposure–response relationship. Similarly for clopidogrel, the PK and PD drug interaction study performed by manufacturers of Plavix1 formed the primary basis for providing recommendations in the label. Concomitant administration of clopidogrel with a high dose of omeprazole (80 mg) resulted in a decrease to the exposure of the active metabolite by 40% compared to clopidogrel administered alone.20 Another study was conducted where administration of clopidogrel and omeprazole was separated by 12 hours, because the inhibition of CYP2C19 by omeprazole was thought to be competitive. However, the results from the dose-staggered drug interaction study showed a similar decrease in the exposure to the active metabolite as that seen with concomitant administration.20 These studies not only established a significant interaction between omeprazole and clopidogrel, but also suggested that the interaction is mechanistic and staggering the dose would not alleviate the interaction. Clopidogrel exerts its pharmacological effect by inhibiting platelet aggregation; hence it is reasonable to expect that a reduction in platelet inhibition due to decrease in exposure to the active metabolite would affect the clinical efficacy of clopidogrel. Although the exact relationship between active metabolite concentration or
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886 the extent of platelet inhibition and reduction in risk of cardiovascular events has not been established, the potential clinical consequence of the decrease in antiplatelet effects might be inferred by looking at other drugs that act by a similar mechanism. Specifically, drugs that achieve higher platelet inhibition compared to clopidogrel, eg, prasugrel, have demonstrated greater cardiovascular risk reduction.33,34 It should also be noted that in Acute Coronary Syndrome (ACS) patients who were on a background of aspirin, clopidogrel demonstrated a 20% cardiovascular risk reduction compared to placebo.35 This can be interpreted as a crude measure of the nature of antiplatelet-cardiovascular outcome relationship for irreversible P2Y12 inhibitors. Therefore, it is reasonable to associate potential loss of clinical effectiveness in instances that result in significant decrease in exposure to active metabolite and antiplatelet activity. Co-administration of omeprazole and esomeprazole clearly resulted in a significant reduction in the exposure to the active metabolite, thus warranting recommendations to avoid use of these medications with clopidogrel.3,20,36 The recommendation to avoid concomitant use with clopidogrel does not apply to all members of the ‘proton pump inhibitor’ class, because the impact of this interaction is relatively less severe with other studied proton pump inhibitors—pantoprazole, lansoprazole, or dexlansoprazole.20,37 A significant interaction for omeprazole or esomeprazole could likely be due to mechanistic differences in the nature of CYP2C19 inhibition compared to other proton pump inhibitors. In contrast to agents that are reversible in nature, the S-omeprazole isomer of the racemic omeprazole mixture is known to be a mechanism based inhibitor of CYP2C19.38,39 Inhibitors of this type, deactivate the enzyme in an irreversible fashion which further explains why separation in the time of administration of clopidogrel and omeprazole made no difference on the extent of inhibition. Despite the PK and PD evidence, the clinical consequence of this drug interaction is extensively debated, raising questions on the recommendation for use of clopidogrel with omeprazole or esomeprazole in the Plavix1 package insert.1,2 Criticism is largely related to the lack of clear evidence of this interaction from cardiovascular outcome studies that are not prospectively designed to evaluate this interaction. Large observational studies and post-hoc analyses have not consistently demonstrated an association with omeprazole and poor cardiovascular outcomes when given with clopidogrel. However, these analyses are inherently confounded and subject to bias and should be interpreted with caution. By and large the scientific community considers the lack of a signal of a significant interaction from a retrospective analysis as evidence of no effect creating a situation where it might seem that there is a disconnect between instructions for use and existing data or evidence.
Even COGENTa, the only prospective randomized trial designed to determine the clinical impact of using clopidogrel with omeprazole, was primarily aimed to evaluate the effect on gastrointestinal outcomes.40 Though effect on cardiovascular outcomes was a prespecified safety endpoint, no a priori sample size calculation was performed based on this endpoint. The results from COGENT are well known and extensively debated. Some consider the results of COGENT reassuring because it did not demonstrate an interaction with concomitant administration of clopidogrel and omeprazole. However, it is important to view the results from COGENT with a perspective on its design, primarily the size of the study, and results from another study of clopidogrel, CUREb. CURE enrolled 12,562 ACS patients to yield a 20% reduction in cardiovascular risk comprised of a composite of death, myocardial infarction, and stroke for clopidogrel compared to placebo.35 To evaluate clopidogrel’s interaction with omeprazole, which would be expected to be a fraction of clopidogrel’s effect size, a trial with a sample size bigger than that enrolled in CURE may be required. Therefore, COGENT with 3,873 patients was significantly underpowered to rule out an adverse effect for omeprazole in terms of cardiovascular outcomes. In addition, there exist differences in the patient population and the components of the cardiovascular endpoint between the trials which further limit the interpretation of the results from COGENT.41 Evidence from PK and PD studies showing a decrease in active metabolite exposure and platelet inhibition supports a recommendation to avoid concomitant use of clopidogrel and omeprazole or esomeprazole. The lack of clinical evidence from a prospectively designed study ruling out an interaction is not reassuring. However, it is interesting to note that scientific literature on clopidogrel has been continuously evolving even years past its approval. FDA recognizes that a residual uncertainty may exist and will continue to assess emerging data that may play a role in further optimizing the instructions for use of Plavix1. Acknowledgments The authors thank Dr. Shiew Mei Huang, Dr. Mehul Mehta and Dr. Norman Stockbridge for their critical insight and help with preparation of this commentary.
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