University of Suleimani Collage of pharmacy Subject: Clopidogril as prodrug Prepared by : Hardi Sdiq
Clopidogrel IntroductionClopidogrel, 2-(2-chlorophenyl)-2-(2, 4, 5, 6, 7, 7a hexahydrothieno [3, 2c]pyridine-5yl-acetic acid methylester, is a thienopyridine prodrug usedclinically to inhibit ADP-induced platelet aggregation .The drug, usually inform of hydrogen sulfate, was launched on the market following a successfulclinical evaluation and demonstration of superior efficacy versus aspirin inpreventing thrombotic events in high risk patients . In 1997, it was approved by the United States Food and Drug Administration(FDA) for the reduction of myocardial infarction, stroke, and vascular death inpatients with recent stroke recent myocardial infarction, or establishedperipheral arterial disease. Clopidogrel is a prescription with proven efficacyand a well-established safety profile in a broad range of patients, and it shouldbe noted that this drug, as a prodrug, shows no appreciable activity in vitro andit requires hepatic biotransformation catalyzed by cytochrome P450 isozymes todisplay its antiaggregation property . As well known, prodrug has lots of advantages. For example, it can bedesigned to overcome pharmaceutical, pharmacokinetic, or pharmacodynamicbarriers such as insufficient chemical stability, poor solubility, unacceptabletaste or odor, irritation or pain, insufficient oral absorption, inadequate blood-brain barrier permeability, marked presystemic metabolism, and toxicity.However, it is worth recalling that many successful prodrugs in current use arein fact accidental prodrugs .
As for clopidogrel, its variability in individual responsiveness becomes anemerging clinical problem, currently drawing a hot global attention. Despiteuse of clopidogrel, a considerable number of patients continue to havecardiovascular events and notably, there is a growing degree of evidence thatrecurrence of ischemic complications may be attributed to poor response toclopidogrel . Quite recently, on basis of four large trials, which reported thatcytochrome P450 2C19 (CYP2C19) were important risk factors predictingapparent failure of clopidogrel efficacy, clopidogrel has been regarded as adrug with high-risk pharmacokinetics, defined as a risk of serious drug toxicitywhen drug concentrations depend on variable activity of a single metabolicpathway. In this paper, the panorama advancement in pharmacologicalresearch on clopidogrel was reviewed in aspects of its anti-platelet mechanism,pharmacokinetic studies, drug resistance mainly focusing on drug-druginteractions and genetic polymorphisms At last we emphasized the importanceof detecting the patients’ platelet aggregation during use of clopidogrel, aimingto provide reference for reasonable drug applications in clinic . Antiplatelet mechanismClopidogrel has an absolute S configuration at carbon 7. and the correspondingR enantiomer is totally devoid of anti-platelet aggregation, thus indicating thenecessity of the configuration of this asymmetric carbon for the biologicalactivity . It is an orally administered prescription and requires biotransformationin vivo by hepatic cytochrome P450 isoenzymes to an active metabolite (Act-Met) containing a free thiol group. The highly unstable active metabolitepresumably forms a disulphide bridge between a reactive thiol group and acysteine residue of the P2Y12 platelet receptor. The P2Y12 receptors play animportant role in the activation of platelets, and coactivation of this receptor isessential for ADP-induced activation of platelet fibrinogen receptor. Activationof the P2Y12 receptor leads to a complex series of intracellular signaling eventsthat result in activation of the glycoprotein (GP) platelet aggregation, andstabilization of the platelet aggregate. The P2Y12 receptor has 2 free cysteinesIIb/IIIa receptor, granule release, amplification of in its extracellular domains(Cys17 and Cys270), both of which are targets of thiol reagents. Ding et alspeculated on that the active metabolite of clopidogrel formed disulfide bridgeswith both Cys17 and Cys270 in the P2Y12 receptor, and thereby inactivated thereceptor. But Savi et al . disagreed with that hypothesis. They furtherdeciphered the mechanism of action of clopidogrel and of its active metaboliteon P2Y12 receptors . They pointed out the involvement of cysteine 97 withinthe first extracellular loop of P2Y12 in the mechanism of action of Act-Met anddemonstrated that P2Y12 receptors preferentially associated as functional
oligomeric complexes within microdomains at the cell surface, and the activemetabolite of clopidogrel coupled through a disulfide bridge to the P2Y12receptor, presumably to the cysteine residue in the first extracellular loop andthis resulted in oligomers dissociating into dimeric receptors that are partitionedout of lipid rafts, thereby losing the ability to bind their endogenous ligands.Another study showed that clopidogrel inhibited ADP-induced plateletaggregation and also inhibited collagen-, and thrombin- induced aggregation,however the inhibitory effect on collagen- and thrombin-induced aggregationcould be overcome by increased concentrations of these agonists, suggestingthat clopidogrel indirectly inhibits the effect of these agonists via the attenuationof ADP-mediated amplification of the platelet response.
Pharmacokinetic studiesClopidogrel requires oxidation by cytochrome P450 enzymes (CYPs) togenerate a metabolite that is an active inhibitor of ADP induced plateletaggregation. However, only a small proportion of administered clopidogrel ismetabolized by P450. The majority of clopidogrel is hydrolyzed by esterases toan inactive carboxylic acid derivative that accounts for 85% of the clopidogrelrelated compounds circulating in plasma . The active metabolite of clopidogrelis formed via two sequential CYP-dependent steps , involving CYP1A2,CYP2B6, CYP2C9, CYP2C19, and CYP3A4.Pharmacokinetic applications require highly selective assays with high samplethroughput capacity. So initially, the easier strategy employed for thedetermination of clopidogrel was to merely measure the inactive moiety becauseit was found in abundance following in vivo dosing either in clinical samples orin preclinical species. The measurement of the inactive carboxylic acidmetabolite served the purpose of documenting the pharmacokinetic profile ofclopidogrel in an indirect manner. It has been well known that the actual plasmaconcentrations of parent drug and/or active metabolite(s) are of major interest inpharmacokinetic studies. However, the plasma concentrations of the parent drugclopidogrel are very low (pg·mL-1 levels) due to its extensive metabolismfollowing oral administration in humans, and although pharmacodynamicactivity is produced by the active moiety in vivo, it was elusive forquantification in any of the body fluids owing to its labile nature until recently,therefore the bioanalysis of the parent clopidogrel itself and its active metabolite(AM) pose immense challenges. Thanks to the advancement in the LC-MS/MStechnology and availability of plethora of options for optimization and enhanceddetection, the way has been well paved for the better understanding of thepharmacokinetics of clopidogrel as well as its AM. Nowadays, a number ofanalytical methods have been published that have the ability to measure theparent drug, clopidogrel, and while some of them have the ability to evenmeasure the active moiety, a thiol compound, at extremely low concentrations .Nirogi et al developed and validated a simple, sensitive and rapid high-performance liquid chromatography/positive electrospray ionization tandemmass spectrometry method for the assay of clopidogrel in human plasma. TheLLOQ of this method was determined as much low as 5 pg·mL-1. Takahashia etal used the alkylating reagent2-bromo-3’-methoxyacetophenone(MP) tostabilize clopidogrel-AM in blood and then extracted the samples by solid-phasewith a C2 disk plate. The calibration curve ranged from 0.5 to 250 ng·mL-1with good linearity. In the intra- and inter-assay reproducibility tests, theaccuracy and precision were within 12% relative error and 6% coefficient ofvariation, respectively. The derivatized MP-AM was stable in human plasma for4 months at -80 . The validated method was also successfully used to analyzeclinical samples and determine the pharmacokinetics of clopidogrel AM.
What should I avoid while taking PlavixWhile you are taking Plavix, do not take aspirin or other NSAIDs (non-steroidalanti-inflammatory drugs) without your doctors advice. NSAIDs includeibuprofen (Advil, Motrin), naproxen (Aleve, Naprosyn, Naprelan, Treximet),celecoxib (Celebrex), diclofenac (Cataflam, Voltaren), indomethacin (Indocin),meloxicam (Mobic), and othersAvoid activities that may increase your risk of bleeding or injury. Use extra careto prevent bleeding while shaving or brushing your teethAvoid drinking alcohol. It may increase your risk of bleeding in your stomachor intestines. ConclusionAtherothrombosis is important and affects different parts of our circulation, notonly coronary circulation but also cerebral and peripheral circulation, andplatelets play an important role in thrombus formation in response to vascularinjury. Therefore, use of anti platelet agents has been thought of as thecornerstone of treatment for patients with thrombosis diseases. Clopidogrel, asecond-generation thienopyridine, inhibits platelet aggregation by blocking theadenosine diphosphate (ADP)-dependent activation of platelets mediated by theADP P2Y12 receptor on platelets. Although the clinical benefits conferred by clopidogrel have been welldemonstrated, there are still a number of clinical limitations including delayedplatelet inhibition, variability in response, drug resistance, and a prolonged timeto recovery of platelet function. Now we can sense that the concerns about thisdrug have been transferred from its efficacy to these limitations, whichstimulate interests in studying the reasons and resolvents of its disadvantages aswell as in developing new agents with more potent and consistent inhibition ofplatelet function. . So far, the mechanisms underlying interindividual variabilityin response to clopidogrel have not been fully elucidated but are probablymultifactorial, and even patients with a high body mass index (BMI) exhibited asuboptimal platelet response , thus managing an inadequate response toantiplatelet therapy still represents a major challenge. Clopidogrel is a prodrug
with high-risk pharmacokinetics, on the other hand, clopidogrelnonresponsiveness is prevalent , so we agree with such standpoint .thatclinically useful risk stratification requires an easily performed and reproduciblemeasure of platelet aggregation, and standardized definitions of response thatcorrelate with clinical outcomes and point-of-care assays of platelet functionmay ultimately improve the ability of clinicians to modify therapy on the basisof response . Referrences1-clopidogrel. Circulation 1999; 100:1667-1672. 2. Feliste R, Delebasse´e D,Simon M F, Chap H, Derfreyn G, Valle´e E, Douste-Blazy L and Maffrand J P.Broad-spectrum antiplatelet activity of PCR5332 and PCR4099 involves thesuppression of the effects of released ADP. Thromb Res 1987; 48:403-415.2-. CAPRIE Steering Committee. A randomised, blinded, trial of SR25990Cversus aspirin in patients at risk of ischaemic events (CAPRIE). Lancet 1996;348:1329-1339.3-. Ettmayer P, Amidon G L, Clement B and Testa B. Lessons Learned fromMarketed and Investigational Prodrugs. J Med Chem 2004; 47(10):2393-2404.4. Angiolillo D J, Fernandez-Ortiz A, Bernardo E, Alfonso F, Macaya C, BassT A. and Costa M A. Variability in Individual Responsiveness to ClopidogrelClinical Implications, Management, and Future Perspectives. JACC 2007;49(14):1505-15165. Roden D M and Stein C M. Clopidogrel and the Conceptof High-Risk Pharmacokinetics. Circulation 2009; 119:2127-21306. Stockl, KM; et al. (2010). "Risk of Rehospitalization for Patients UsingClopidogrel With a Proton Pump Inhibitor". Arch Intern Med (AmericanMedical Association) 170 (8): 704–710. doi:10.1001/archinternmed.2010.34.ISSN 1538-3679. PMID 20421557