Clopidogrel

src: c8.alamy.com

Clopidogrel, sold as the brandname Plavix among others, is an antiplatelet medication that is used to reduce the risk of heart disease and stroke in those at high risk. It is also used together with aspirin in heart attacks and following the placement of a coronary artery stent (dual antiplatelet therapy). It is taken by mouth. Onset of effects is about 2 hours and lasts for 5 days.

Common side effects include headache, nausea, easy bruising, itching, and heartburn. More severe side effects include bleeding and thrombotic thrombocytopenic purpura. While there is no evidence of harm from use during pregnancy, such use has not been well studied. Clopidogrel is in the thienopyridine-class of antiplatelets. It works by irreversibly inhibiting a receptor called P2Y₁₂ on platelets.

Clopidogrel was first written about in 1982 and was approved for medical use in 1998. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale cost in the developing world is about 0.77 to 31.59 USD per month. In the United States a month of treatment costs less than 25 USD.

Video Clopidogrel

Medical use

Clopidogrel is used to prevent heart attack and stroke in people who are at high risk of these events, including those with a history of myocardial infarction and other forms of acute coronary syndrome, stroke, and those with peripheral artery disease.

Treatment with clopidogrel or a related drug is recommended by the American Heart Association and the American College of Cardiology for people who:

Present for treatment with a myocardial infarction with ST-elevation including

A loading dose given in advance of percutaneous coronary intervention (PCI), followed by a full year of treatment for those receiving a vascular stent
A loading dose given in advance of fibrinolytic therapy, continued for at least 14 days

Present for treatment of a non-ST elevation myocardial infarction or unstable angina

Including a loading dose and maintenance therapy in those receiving PCI and unable to tolerate aspirin therapy
Maintenance therapy for up to 12 months in those at medium to high risk for which a noninvasive treatment strategy is chosen

In those with stable ischemic heart disease, treatment with clopidogrel is described as a "reasonable" option for monotherapy in those who cannot tolerate aspirin, as is treatment with clopidogrel in combination with aspirin in certain high risk patients.

It is also used, along with acetylsalicylic acid (ASA, aspirin), for the prevention of thrombosis after placement of a coronary stent or as an alternative antiplatelet drug for people intolerant to aspirin.

Clopidogrel's benefit is primarily in those who smoke cigarettes (25% benefit), with only slight (8%) benefit in those who do not smoke cigarettes.

Consensus-based therapeutic guidelines also recommend the use of clopidogrel rather than ASA for antiplatelet therapy in people with a history of gastric ulceration, as inhibition of the synthesis of prostaglandins by ASA can exacerbate this condition. In people with healed ASA-induced ulcers, however, those receiving ASA plus the proton pump inhibitor esomeprazole had a lower incidence of recurrent ulcer bleeding than those receiving clopidogrel. However, prophylaxis with proton pump inhibitors along with clopidogrel following acute coronary syndrome may increase adverse cardiac outcomes, possibly due to inhibition of CYP2C19, which is required for the conversion of clopidogrel to its active form. The European Medicines Agency has issued a public statement on a possible interaction between clopidogrel and proton pump inhibitors. However, several cardiologists have voiced concern that the studies on which these warnings are based have many limitations and that it is not certain whether an interaction between clopidogrel and proton pump inhibitors is real.

Maps Clopidogrel

Adverse effects

Serious adverse drug reactions associated with clopidogrel therapy include:

Thrombotic thrombocytopenic purpura (incidence: four per million patients treated)
Hemorrhage - the annual incidence of hemorrhage may be increased by the coadministration of aspirin.

In the CURE trial, people with acute coronary syndrome without ST elevation were treated with aspirin plus clopidogrel or placebo and followed for up to one year. The following rates of major bleed were seen:

Any major bleeding: clopidogrel 3.7%, placebo 2.7%
Life-threatening bleeding: clopidogrel 2.2%, placebo 1.8%
Hemorrhagic stroke: clopidogrel 0.1%, placebo 0.1%

The CAPRIE trial compared clopidogrel monotherapy to aspirin monotherapy for 1.6 years in people who had recently experienced a stroke or heart attack. In this trial the following rates of bleeding were observed.

Gastrointestinal hemorrhage: clopidogrel 2.0%, aspirin 2.7%
Intracranial bleeding: clopidogrel 0.4%, aspirin 0.5%

In CAPRIE, itching was the only adverse effect seen more frequently with clopidogrel than aspirin. In CURE, there was no difference in the rate of non-bleeding adverse events.

Rashes and itching were uncommon in studies (between 0.1 and 1% of people); serious hypersensitivity reactions are rare.

Structure and Stereochemistry of the Active Metabolite of ...

src: dmd.aspetjournals.org

Interactions

Clopidogrel generally has a low potential to interact with other pharmaceutical drugs. Combination with other drugs that affect blood clotting, such as aspirin, heparins and thrombolytics, showed no relevant interactions. Naproxen did increase the likelihood of occult gastrointestinal bleeding, as might be the case with other nonsteroidal anti-inflammatory drugs. As clopidogrel inhibits the liver enzyme CYP2C9 in cellular models, it has been theorized that it might increase blood plasma levels of drugs that are metabolized by this enzyme, such as phenytoin and tolbutamide. Clinical studies showed that this mechanism is irrelevant for practical purposes.

In November 2009, the FDA announced that clopidogrel should be used with caution in people using the proton pump inhibitors omeprazole or esomeprazole, but pantoprazole appears to be safe. The newer antiplatelet agent prasugrel has minimal interaction with (es)omeprazole, hence might be a better antiplatelet agent (if no other contraindications are present) in people who are on these proton pump inhibitors.

Clopidogrel Hydrochloride 75mg tablets Stock Photo: 28292303 - Alamy

src: c8.alamy.com

Pharmacology

Mechanism of action

Clopidogrel is a prodrug, which is activated in two steps, first by CYP2C19, CYP1A2 and CYP2B6, then by CYP2C19, CYP2C9, CYP2B6 and CYP3A. The active metabolite then specifically and irreversibly inhibits the P2Y₁₂ subtype of ADP receptor, which is important in activation of platelets and eventual cross-linking by the protein fibrin. Platelet inhibition can be demonstrated two hours after a single dose of oral clopidogrel, but the onset of action is slow, so a loading dose of either 600 or 300 mg is administered when a rapid effect is needed.

Pharmacokinetics and metabolism

After repeated oral doses of 75 mg of clopidogrel (base), plasma concentrations of the parent compound, which has no platelet-inhibiting effect, are very low and, in general, are below the quantification limit (0.258 µg/l) beyond two hours after dosing.

Clopidogrel is activated in the liver by cytochrome P450 enzymes, including CYP2C19. Due to opening of the thiophene ring, the chemical structure of the active metabolite has three sites that are stereochemically relevant, making a total of eight possible isomers. These are: a stereocentre at C4 (attached to the --SH thiol group), a double bond at C3--C16, and the original stereocentre at C7. Only one of the eight structures is an active antiplatelet drug. This has the following configuration: Z configuration at the C3--C16 double bond, the original S configuration at C7, and, although the stereocentre at C4 cannot be directly determined, as the thiol group is too reactive, work with the active metabolite of the related drug prasugrel suggests the R-configuration of the C4 group is critical for P2Y₁₂ and platelet-inhibitory activity.

The active metabolite has an elimination half-life of about 0.5 to 1.0 h, and acts by forming a disulfide bridge with the platelet ADP receptor. Patients with a variant allele of CYP2C19 are 1.5 to 3.5 times more likely to die or have complications than patients with the high-functioning allele.

Following an oral dose of ¹⁴C-labeled clopidogrel in humans, about 50% was excreted in the urine and 46% in the feces in the five days after dosing.

Effect of food: Administration of clopidogrel bisulfate with meals did not significantly modify the bioavailability of clopidogrel as assessed by the pharmacokinetics of the main circulating metabolite.
Absorption and distribution: Clopidogrel is rapidly absorbed after oral administration of repeated doses of 75-milligram clopidogrel (base), with peak plasma levels (about 3 mg/l) of the main circulating metabolite occurring around one hour after dosing. The pharmacokinetics of the main circulating metabolite are linear (plasma concentrations increased in proportion to dose) in the dose range of 50 to 150 mg of clopidogrel. Absorption is at least 50% based on urinary excretion of clopidogrel-related metabolites.

Clopidogrel and the main circulating metabolite bind reversibly in vitro to human plasma proteins (98% and 94%, respectively). The binding is not saturable in vitro up to a concentration of 110 ?g/ml.

Metabolism and elimination: In vitro and in vivo, clopidogrel undergoes rapid hydrolysis into its carboxylic acid derivative. In plasma and urine, the glucuronide of the carboxylic acid derivative is also observed.

In March 2010, the U.S. FDA added a boxed warning to Plavix alerting that the drug can be less effective in people unable to metabolize the drug to convert it to its active form.

Pharmacogenetics

CYP2C19 is an important drug-metabolizing enzyme that catalyzes the biotransformation of many clinically useful drugs, including antidepressants, barbiturates, proton pump inhibitors, and antimalarial and antitumor drugs. Clopidogrel is one of the drugs metabolized by this enzyme.

Several recent landmark studies have proven the importance of 2C19 genotyping in treatment using clopidogrel. In March 2010, the FDA put a black box warning on Plavix to make patients and healthcare providers aware that CYP2C19-poor metabolizers, representing up to 14% of patients, are at high risk of treatment failure and that testing is available. Patients with variants in cytochrome P-450 2C19 (CYP2C19) have lower levels of the active metabolite of clopidogrel, less inhibition of platelets, and a 3.58-times greater risk for major adverse cardiovascular events such as death, heart attack, and stroke; the risk was greatest in CYP2C19 poor metabolizers.

src: drugsdetails.com

Marketing and litigation

Plavix is marketed worldwide in nearly 110 countries, with sales of US$6.6 billion in 2009. It had been the second-top-selling drug in the world for a few years as of 2007 and was still growing by over 20% in 2007. U.S. sales were US$3.8 billion in 2008.

Before the expiry of its patent, clopidogrel was the second best-selling drug in the world. In 2010, it grossed over US$9 billion in global sales.

In 2006, generic clopidogrel was briefly marketed by Apotex, a Canadian generic pharmaceutical company before a court order halted further production until resolution of a patent infringement case brought by Bristol-Myers Squibb. The court ruled that Bristol-Myers Squibb's patent was valid and provided protection until November 2011. The FDA extended the patent protection of clopidogrel by six months, giving exclusivity that would expire on May 17, 2012. The FDA approved generic versions of Plavix on May 17, 2012.

Generic clopidogrel is marketed by many companies worldwide under many brand names, including combination drugs with acetylsalicylic acid (aspirin).

Mechanism of Action for Clopidogrel - YouTube

src: i.ytimg.com

Research

Use in cats

Clopidogrel has also been shown to be effective at decreasing platelet aggregation in cats, so its use in prevention of feline aortic thromboembolism has been advocated.