P2Y12 INHIBITORS

• ACRONYMS AND DEFINITIONS

• ACC - American College of Cardiology
• ACS - Acute coronary syndrome (myocardial infarction or unstable angina)
• A fib - Atrial fibrillation
• AHA - American Heart Association
• ASA - Acetylsalicylic acid (aspirin)
• CABG - Coronary artery bypass graft
• CAD - Coronary artery disease
• CVD - Cardiovascular disease (heart attack and stroke)
• DAPT - Dual antiplatelet therapy (aspirin + P2Y12 inhibitor)
• HIT - Heparin induced thrombocytopenia
• MI - Myocardial infarction
• NSTEMI - Non-ST-Elevation Myocardial Infarction
• PAD - Peripheral artery disease
• PPI - Proton pump inhibitor (ex. Prilosec®, Protonix®, Nexium®, Prevacid®, etc.)
• PCI - Percutaneous coronary intervention. Heart cath and associated procedures - stents, angioplasty, etc.
• RCT - Randomized controlled trial
• STEMI - ST-elevation myocardial infarction
• TIA - Transient ischemic attack

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• DRUGS IN CLASS

• Thienopyridines
• Clopidogrel (Plavix®)
• Prasugrel (Effient®)
• Ticlopidine (Ticlid®)


• Other
• Ticagrelor (Brilinta®)

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• MECHANISM OF ACTION

• Activated platelets release adenosine diphosphate (ADP), a chemical that activates other platelets by stimulating surface P2Y12 receptors. As platelet recruitment grows, a clot begins to form. P2Y12 inhibitors block ADP-stimulated platelet activation, hindering clot formation. Clopidogrel, prasugrel, and ticlopidine irreversibly inhibit receptors, while ticagrelor is a reversible inhibitor.
• After starting P2Y12 inhibitors, full antiplatelet effects are seen at the following intervals: (1) within 2 hours for ticagrelor, (2) after 3 days for prasugrel, (3) at 4 - 5 days with maintenance doses (75 mg) of clopidogrel or within 2 to 6 hours if a loading dose is given. [12,13,15,34]
• Illustration of platelet activation

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• FDA-APPROVED INDICATIONS

• Clopidogrel (Plavix®)
• Acute Coronary Syndrome (ACS)
• Plavix is indicated to reduce the rate of myocardial infarction and stroke (MI) in patients with non-ST-segment elevation ACS [unstable angina (UA)/non-ST-elevation myocardial infarction (NSTEMI)], including patients who are to be managed medically and those who are to be managed with coronary revascularization. Plavix should be administered in conjunction with aspirin.
• Plavix is indicated to reduce the rate of myocardial infarction and stroke in patients with acute ST-elevation myocardial infarction (STEMI) who are to be managed medically. Plavix should be administered in conjunction with aspirin.
• Recent MI, Recent Stroke, or Established Peripheral Arterial Disease - In patients with established peripheral arterial disease or with a history of recent myocardial infarction (MI) or recent stroke, Plavix is indicated to reduce the rate of MI and stroke.


• Prasugrel (Effient®)
• Acute Coronary Syndrome (ACS) - to reduce the rate of thrombotic cardiovascular events (including stent thrombosis) in patients with ACS who are to be managed with percutaneous coronary intervention


• Ticagrelor (Brilinta®)
• Acute coronary syndrome or a history of myocardial infarction - ticagrelor is indicated to reduce the risk of cardiovascular death, myocardial infarction, and stroke in patients with acute coronary syndrome or a history of MI. For at least the first 12 months following ACS, it is superior to clopidogrel.
• Coronary artery disease but no prior stroke or myocardial infarction - ticagrelor is indicated to reduce the risk of a first MI or stroke in patients with coronary artery disease at high risk for such events. While use is not limited to this setting, the efficacy of ticagrelor was established in a population with type 2 diabetes mellitus. See THEMIS trial for more.
• Acute ischemic stroke or transient ischemic attack (TIA) - ticagrelor is indicated to reduce the risk of stroke in patients with acute ischemic stroke (NIH Stroke Scale score ≤ 5) or high-risk transient ischemic attack (TIA). See THALES trial for more.


• Ticlopidine (Ticlid®)
• Stroke and TIA - to reduce the risk of thrombotic stroke (fatal or nonfatal) in patients who have experienced stroke precursors, and in patients who have had a completed thrombotic stroke
• Acute coronary syndrome - as adjunctive therapy with aspirin to reduce the incidence of subacute stent thrombosis in patients undergoing successful coronary stent implantation

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• ACUTE CORONARY SYNDROME (ACS)

• Patients with ACS are treated with dual antiplatelet therapy (DAPT) consisting of aspirin and a P2Y12 inhibitor. Links to DAPT guidelines and studies are provided below.
• DAPT recommendations - guidelines from the AHA on DAPT therapy
• DAPT therapy studies - studies directly comparing clopidogrel, ticagrelor, and prasugrel
• DAPT duration studies - studies comparing different lengths of DAPT

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• SECONDARY PREVENTION OF CVD

• See antiplatelet therapy for the secondary prevention of CVD

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• SECONDARY PREVENTION OF STROKE

• See antiplatelet therapy for the secondary prevention of stroke and TIA

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• ATRIAL FIBRILLATION

• See antiplatelet therapy in atrial fibrillation

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• PERIPHERAL ARTERY DISEASE (PAD)

• Overview
• Antiplatelet therapy is recommended in patients with peripheral artery disease because they are at increased risk of heart disease and stroke. The study below compared ticagrelor to clopidogrel in patients with symptomatic PAD.

• STUDY
  EUCLID trial - Clopidogrel vs Ticagrelor in Patients with Symptomatic PAD, NEJM (2017) [PubMed abstract]
• Design: Randomized, controlled trial (N=13,885, length= median 30 months) in patients with symptomatic PAD
• Treatment: Ticagrelor 90 mg twice daily vs Clopidogrel 75 mg once daily. Aspirin was not allowed.
• Primary outcome: First occurrence of any event in the composite of cardiovascular death, myocardial infarction, or ischemic stroke (defined as any stroke not shown to be primarily hemorrhagic)
• Results:
• Primary outcome: Ticagrelor - 10.8%, Clopidogrel 10.6% (p=0.65)
• Major bleeding: Ticagrelor - 1.6%, Clopidogrel 1.6% (p=0.49)
• Findings: In patients with symptomatic peripheral artery disease, ticagrelor was not shown to be superior to clopidogrel for the reduction of cardiovascular events. Major bleeding occurred at similar rates among the patients in the two trial groups.

• 2016 AHA PAD recommendations
• Antiplatelet therapy with aspirin alone (range 75–325 mg per day) or clopidogrel alone (75 mg per day) is recommended to reduce MI, stroke, and vascular death in patients with symptomatic PAD
• In asymptomatic patients with PAD (ABI ≤ 0.90), antiplatelet therapy is reasonable to reduce the risk of MI, stroke, or vascular death
• In asymptomatic patients with borderline ABI (0.91 – 0.99), the usefulness of antiplatelet therapy to reduce the risk of MI, stroke, or vascular death is uncertain
• The effectiveness of dual-antiplatelet therapy (aspirin and clopidogrel) to reduce the risk of cardiovascular ischemic events in patients with symptomatic PAD is not well established
• Dual-antiplatelet therapy (aspirin and clopidogrel) may be reasonable to reduce the risk of limb-related events in patients with symptomatic PAD after lower extremity revascularization [33]

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• SIDE EFFECTS

• Bleeding
• P2Y12 inhibitors exert their therapeutic effect by inhibiting arterial clot formation, which also increases the risk of unwanted bleeding. Bleeding risk varies among individuals and depends on a variety of factors, including indication, age, comorbid conditions, and concomitant medications. See individual trials under relevant indications for estimations of risk. Recommendations for treating significant active bleeding are available here - reversing P2Y12 inhibitors.

• Thrombotic thrombocytopenic purpura (TTP)
• Thrombotic thrombocytopenic purpura, a rare but serious condition marked by low platelets and hemolytic anemia, has been reported in patients receiving P2Y12 inhibitors, sometimes within 2 weeks of therapy initiation. Ticlopidine carries a higher risk than other P2Y12 inhibitors, particularly during the first three months of therapy, and the manufacturer recommends monitoring blood counts every 2 weeks during this time. Symptoms of TTP include gastrointestinal complaints, bleeding, purpura, hematuria, and neurologic abnormalities. If TTP is suspected, P2Y12 inhibitors should be stopped, and treatment should be started immediately.

• Hypersensitivity reactions
• Hypersensitivity reactions, including rash and angioedema, have been reported in patients receiving P2Y12 inhibitors. Cross-reactivity between the thienopyridines (clopidogrel, prasugrel, ticlopidine) has also been observed. P2Y12 inhibitors are contraindicated in patients with known hypersensitivity.

• Ticagrelor (Brilinta®)
• Dyspnea (shortness of breath)
• In trials, 14 - 20% of ticagrelor-treated patients developed dyspnea compared to 6 - 8% of placebo-treated patients. Ticagrelor-induced dyspnea is usually mild-to-moderate and often resolves with continued treatment. In a substudy of the PLATO trial, pulmonary function testing at one month and six months of therapy did not show adverse lung effects in 199 randomly selected patients. Ticagrelor-induced dyspnea does not require treatment, and the drug may be continued unless symptoms become intolerable.

• Central sleep apnea
• Central sleep apnea, including Cheyne-Stokes respirations, has been reported in the postmarketing setting in patients receiving ticagrelor. After discontinuation, symptoms have been shown to recur when ticagrelor restarted. Use caution in susceptible patients and consider alternatives if symptoms persist.

• Ventricular pause
• Ventricular pause, a condition where there is an abnormally long interval between ventricular contractions, has been observed in ticagrelor-treated patients. The pauses are typically asymptomatic, diminish after 30 days, and appear to be related to an undefined action at the sinoatrial node. In a study that compared ticagrelor to clopidogrel, ventricular pauses were seen in 6% of ticagrelor-treated patients and 3.5% of clopidogrel-treated patients during the first month of therapy; after 1 month, rates were 2.2% and 1.6%, respectively. Ticagrelor should be used with caution in patients with bradyarrhythmias. [16,17]

• Uric acid increase
• Ticagrelor can raise uric acid levels. In the PLATO trial, average uric acid levels increased by 0.6 mg/dl in ticagrelor-treated patients compared to 0.2 mg/dl in clopidogrel-treated patients. There was no difference in the incidence of gout between groups. [15]

• Serum creatinine increase
• In the PLATO study, 7.4% of patients receiving ticagrelor had an increase of greater than 50% in their serum creatinine level compared to 5.9% of patients receiving clopidogrel. The increases typically decreased with continued therapy and were reversible upon discontinuation. Adverse renal outcomes did not differ between groups. [15]

• Ticlopidine (Ticlid®)
• Neutropenia
• Ticlopidine can cause neutropenia that peaks around 4 to 6 weeks after initiation. In stroke trials, neutrophil counts less than 1200 cells/μl were observed in 2.4% of patients, and counts less than 450 cells/μl were seen in 0.8%. After discontinuation, counts typically rise above 1200 cells/μl in 1 to 3 weeks. Monitor blood counts every 2 weeks during the first 3 months of therapy, and continue monitoring in patients with reduced or abnormal counts. Patients who develop signs of infection should be checked for neutropenia.

• Aplastic anemia
• Aplastic anemia has been reported in the postmarketing setting in patients receiving ticlopidine. Most cases occurred around 4 to 8 weeks of therapy, and the estimated incidence may be as high as one in every 4000 to 8000 patients. Monitor blood counts every 2 weeks during the first 3 months of therapy, and continue monitoring in patients with reduced or abnormal counts. Patients who develop signs of infection should be checked for neutropenia.

• Thrombocytopenia
• Rare cases of thrombocytopenia unrelated to TTP have been reported in patients receiving ticlopidine

• Cholesterol elevations
• Ticlopidine increases total cholesterol and triglyceride levels by 8% to 10%

• Gastrointestinal side effects
• In trials, ticlopidine-treated patients had a higher incidence of gastrointestinal side effects than placebo-treated patients: diarrhea (12.5% vs 4.5%), nausea (7% vs 1.7%), and dyspepsia (7% vs 0.9%)

• Rash
• In trials, 5.1% of ticlopidine-treated patients reported a rash compared to 0.6% of placebo-treated patients

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• CONTRAINDICATIONS

• Clopidogrel (Plavix®)
• Active bleeding
• Known hypersensitivity


• Prasugrel (Effient®)
• Active bleeding
• Prior TIA or stroke (see precautions)
• Known hypersensitivity


• Ticagrelor (Brilinta®)
• History of intracranial hemorrhage
• Active bleeding
• Known hypersensitivity


• Ticlopidine (Ticlid®)
• Presence of a hemostatic disorder or active pathological bleeding (such as bleeding peptic ulcer or intracranial bleeding)
• Presence of hematopoietic disorders such as neutropenia and thrombocytopenia or a past history of either TTP or aplastic anemia
• Known hypersensitivity
• Severe liver disease

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• PRECAUTIONS

• Kidney disease
• Clopidogrel (Plavix®)
• There is limited data on the use of clopidogrel in patients with moderate-to-severe kidney disease. In studies, patients with CrCl < 60 ml/min showed low (25%) inhibition of ADP-induced platelet aggregation after repeated dosing of clopidogrel 75 mg.
• Prasugrel (Effient®)
• No dose adjustment is necessary in patients with kidney disease
• Ticagrelor (Brilinta®)
• No dose adjustment is necessary in patients with kidney disease
• Ticlopidine (Ticlid®)
• CrCl ≥ 60 ml/min: no dose adjustment necessary
• CrCl < 60 ml/min: has not been studied extensively. Exposure is increased. Use caution and consider dose reductions.

• Liver disease
• Clopidogrel (Plavix®)
• No dosage adjustment is necessary in patients with liver disease
• Prasugrel (Effient®)
• Child-Pugh A/B: no dosage adjustment necessary
• Child-Pugh C: has not been studied
• Ticagrelor (Brilinta®)
• Child-Pugh A: no dosage adjustment necessary
• Child-Pugh B: has not been studied extensively. Use caution.
• Child-Pugh C: DO NOT USE. Has not been studied.
• Ticlopidine (Ticlid®)
• Child-Pugh A/B: exposure is increased. Use caution.
• Child-Pugh C: DO NOT USE. Has not been studied.

• History of stroke or TIA (prasugrel)
• Prasugrel is contraindicated in patients with a prior history of stroke or TIA. In the TRITON TIMI 38 trial, patients with a history of stroke or TIA had a higher rate of stroke on prasugrel when compared to clopidogrel (6.5% vs 1.2%)

• Geriatric (prasugrel)
• Prasugrel is not recommended in patients ≥ 75 years old. In the TRITON TIMI 38 trial, patients ≥ 75 had a higher risk of fatal bleeding events compared to those taking clopidogrel (1% vs 0.1%)

• Low body weight (prasugrel)
• Prasugrel exposure is increased in patients weighing less than 60 kg (132 pounds), and in the TRITON TIMI 38 trial, this subpopulation had a higher risk of bleeding
• Consider lowering the maintenance dose to 5 mg daily in patients weighing less than 60 kg, with the understanding that this dose has not been prospectively studied

• Bradyarrhythmias (ticagrelor)
• Ventricular pauses, a side effect of ticagrelor, can exacerbate bradyarrhythmias, including sick sinus syndrome, second- or third-degree AV block, and bradycardia-related syncope. Use caution in susceptible patients. (see ventricular pauses)

• HIT lab interference (ticagrelor)
• Ticagrelor can inhibit donor platelets in the heparin-induced platelet aggregation (HIPA) assay used to diagnose heparin-induced thrombocytopenia (HIT), leading to false-negative results. Ticagrelor does not affect Anti-PF4 antibody testing, which is also used to diagnose HIT.

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• STOPPING BEFORE PROCEDURES

• Professional recommendations
• See periprocedural antithrombotic recommendations


• Manufacturer recommendations for stopping P2Y12 inhibitors before surgery or procedures that have a high risk of bleeding:
• Clopidogrel (Plavix®) - stop for at least 5 days
• Prasugrel (Effient®) - stop for at least 7 days
• Ticagrelor (Brilinta®) - stop for at least 5 days

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• REVERSING P2Y12 INHIBITORS

• Clopidogrel and prasugrel
• Clopidogrel and prasugrel irreversibly bind platelets, inactivating them for life. Theoretically, platelet transfusion can be used to restore platelet activity in bleeding patients, but this practice has not proven effective in small trials. Moreover, a randomized trial published in 2016 that compared platelet transfusion to standard care in 190 patients with intracerebral hemorrhage receiving antiplatelet therapy (mostly aspirin) found that transfusions led to worse outcomes. [PMID 27178479]
• The ACC 2020 bleeding management guidelines for antithrombotics state that the routine use of platelet transfusions to stop bleeding in patients on antiplatelet therapy is not supported, although it may be considered in certain situations. [35]


• Ticagrelor
• Ticagrelor reversibly binds platelets, which means it can unbind native platelets and bind transfused ones. The ticagrelor prescribing information states that platelet transfusions did not reverse the antiplatelet effect of ticagrelor in healthy volunteers and is unlikely to be of clinical benefit in patients with bleeding.
• A monoclonal antibody fragment called bentracimab has been developed that binds ticagrelor and inactivates it. In a phase 1 study of healthy volunteers published in 2019, it immediately and completely reversed the effects of ticagrelor. [PMID 30883047]. It has not yet received FDA-approval.

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• PLATELET FUNCTION MONITORING

• The effects of antiplatelet therapy can vary between individuals. Assays are available that measure platelet reactivity (e.g. VerifyNow®) in treated patients, and theoretically, results can be used to adjust therapy and improve outcomes. Two large studies summarized below evaluated the effects of platelet function monitoring in patients receiving coronary stents.


• The ARCTIC study compared platelet function monitoring to no monitoring in patients (n=2440) treated with aspirin + clopidogrel or prasugrel after coronary stenting. Platelet function monitoring was performed during the first month of therapy, and patients with high reactivity received additional doses of medication. The study found no benefit of monitoring for a composite outcome of death, myocardial infarction, stent thrombosis, stroke, or urgent revascularization at one year. [PMID 23121439]
• The ANTARCTIC study compared platelet function monitoring to no monitoring in patients (n=877) 75 years and older treated with aspirin + prasugrel after coronary stenting for ACS. Platelet function monitoring was performed during the first month of therapy, and patients with high reactivity had their prasugrel dose increased, while patients with low reactivity were switched to clopidogrel. The study found no benefit of platelet function monitoring for a composite outcome of cardiovascular death, myocardial infarction, stroke, stent thrombosis, urgent revascularization, and bleeding at one year. [PMID 27581531]


• SUMMARY: There is no evidence that platelet function monitoring improves outcomes in patients receiving DAPT for coronary stents

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• DRUG INTERACTIONS

• NOTE: Drug interactions presented here are NOT all-inclusive. Other interactions may exist. The interactions presented here are meant to encompass commonly prescribed medications and/or interactions that are well-documented. Always consult your physician or pharmacist before taking medications concurrently. CLICK HERE for more information on drug interactions.


• All P2Y12 Inhibitors
• Drugs that slow gastric emptying (e.g. opiates, GLP-1 analogs) - drugs that slow gastric emptying may delay the absorption of P2Y12 inhibitors. Consider parenteral antiplatelet agents in acute coronary syndrome.
• Drugs that increase the risk of bleeding - drugs that inhibit coagulation may increase the risk of bleeding when taken with P2Y12 inhibitors
• Drugs that may increase the risk of bleeding include:
• Anagrelide (Agrylin®)
• Aspirin
• Direct thrombin inhibitors (dabigatran)
• Factor Xa inhibitors (e.g. rivaroxaban, apixaban)
• Fish oil (e.g. Vascepa®)
• NSAIDs (e.g. ibuprofen, naproxen)
• SSRIs and SNRIs (e.g. fluoxetine, venlafaxine)
• Vorapaxar (Zontivity®)
• Warfarin (Coumadin®)


• Clopidogrel (Plavix®)
• Bupropion (Wellbutrin®) - clopidogrel inhibits CYP2B6 which can lead to elevated bupropion levels. When taken together, doses of bupropion may need to be decreased.
• CYP2C19 inhibitors - see clopidogrel and CYP2C19 below
• CYP2C19 inducers - inducers of CYP2C19 may increase exposure to the active metabolite of clopidogrel and increase the risk of bleeding. Clopidogrel should not be given with CYP2C19 strong inducers (e.g. rifampin) and caution should be used when combining with other inducers.
• CYP2C8 substrates - the acyl-β-glucuronide metabolite of clopidogrel is a CYP2C8 strong inhibitor. Clopidogrel may increase exposure to CYP2C8 substrates.
• Omeprazole (Prilosec®) and esomeprazole (Nexium®) - DO NOT COMBINE with clopidogrel. See clopidogrel and PPIs below
• Repaglinide (Prandin®) - repaglinide is a sensitive CYP2C8 substrate. Clopidogrel increases repaglinide exposure by 4 - 5 fold. Repaglinide should not be given with clopidogrel. If concomitant use cannot be avoided, initiate repaglinide at a dose of 0.5 mg before each meal and titrate based on blood sugars. Do not exceed 4 mg/day. When clopidogrel is added to repaglinide, repaglinide doses should be reduced to no more than 4 mg/day.


• Ticagrelor (Brilinta®)
• Aspirin - in the management of patients with ACS, the use of ticagrelor with maintenance doses of aspirin > 100 mg/day decreased the effectiveness of ticagrelor. Aspirin maintenance doses should be 75 - 100 mg/day when taken with ticagrelor.
• CYP3A strong inhibitors and inducers - ticagrelor should not be taken with strong CYP3A4 inhibitors or inducers
• Digoxin - ticagrelor may increase digoxin levels. Monitor levels when starting concurrent therapy.
• Lovastatin (Mevacor®) - ticagrelor may cause higher blood levels of lovastatin. The manufacturer recommends the lovastatin dose not exceed 40 mg when taken with Ticagrelor
• Simvastatin (Zocor®) - ticagrelor may cause higher blood levels of simvastatin. The manufacturer recommends the simvastatin dose not exceed 40 mg when taken with Ticagrelor


• Ticlopidine (Ticlid®)
• Bupropion (Wellbutrin®) - ticlopidine inhibits CYP2B6 which can lead to elevated bupropion levels. When taken together, doses of bupropion may need to be decreased.
• Phenytoin (Dilantin®) - ticlopidine may raise phenytoin levels. Monitor levels when starting concurrent therapy.

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• CLOPIDOGREL AND PPIs

• Overview
• Clopidogrel (Plavix®) is a prodrug that must be metabolized before it becomes active. The enzyme that converts clopidogrel to its active metabolite is CYP2C19. If another drug inhibits CYP2C19 or a person has weak CYP2C19 enzymes (see CYP2C19 poor metabolizers below), clopidogrel may not be metabolized extensively, and its effectiveness may be reduced.
• Proton pump inhibitors (PPIs) are a class of widely used medications, and two PPIs, omeprazole (Prilosec®) and esomeprazole (Nexium®), inhibit CYP2C19. Theoretically, these drugs could reduce the antiplatelet activity of clopidogrel.
• The COGENT trial detailed below looked at the effect of taking omeprazole (Prilosec®) with clopidogrel on clinical outcomes. Omeprazole is a moderate CYP2C19 inhibitor.

• Professional recommendations
• The clopidogrel PI states that clopidogrel should not be taken with omeprazole or esomeprazole. It goes on to say that dexlansoprazole (Dexilant®), lansoprazole (Prevacid®), and pantoprazole (Protonix®) have less of an effect on clopidogrel's antiplatelet activity than omeprazole or esomeprazole.

• Summary
• The clopidogrel PI recommends against concomitant omeprazole or esomeprazole. The COGENT trial detailed above did not find that omeprazole affected clopidogrel's efficacy; however, the trial was stopped early due to funding loss.
• Since several other cheap PPIs are now available (see proton pump inhibitors), patients should generally avoid omeprazole and esomeprazole when taking clopidogrel

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• CLOPIDOGREL AND POOR CYP2C19 METABOLIZERS

• Overview
• Clopidogrel is a prodrug that must be metabolized by CYP2C19 to become active. The genes that code for the CYP2C19 enzyme (CYP2C19 alleles) can vary between individuals and races (see below). Some alleles decrease the activity of the enzyme (loss-of-function alleles), while others increase its activity (gain-of-function alleles). Theoretically, clopidogrel may not be as effective in patients with loss-of-function alleles.
• Two randomized controlled trials have looked at the effects of CYP2C19 metabolizer status on antiplatelet therapy. The TAILOR-PCI study evaluated patients undergoing PCI, and the CHANCE-2 study enrolled patients with recent stroke or TIA. Those studies are reviewed below, along with two post-hoc analyses of clopidogrel trials that compared outcomes between subjects based on their CYP2C19 metabolizer status.

• Race and CYP2C19 metabolizer status
• The most common CYP2C19 loss-of-function alleles are the *2 and *3 variants. One loss-of-function allele leads to a 47% reduction in CYP2C19 activity, and two loss-of-function alleles lead to a 65% reduction. People with one loss-of-function allele are considered "intermediate metabolizers," and people with two loss-of-function alleles are considered "poor metabolizers." Also of note, the *17 allele increases the activity of CYP2C19, and carriers are considered ultra-rapid metabolizers.
• The prevalence of CYP2C19 alleles among different races is given below
• Prevalence of at least one loss-of-function allele by ethnicity:
• Asians: 51 - 55%
• African-Americans: 33 - 40%
• Caucasians: 24 - 30%
• Mexican-Americans: 18% [22]
• Prevalence of two loss-of-function alleles by ethnicity (poor metabolizers):
• Chinese: 14%
• African-Americans: 4%
• Caucasians: 2% [12]

• STUDY
  TAILOR-PCI study - Genotype-guided Therapy vs Clopidogrel in Patients Undergoing PCI, JAMA (2020) [PubMed abstract]
• Design: Randomized, open-label trial (N=5302 | length = 12 months) in patients with ACS or stable CAD who were undergoing PCI
• Treatment: Genotype-guided (patients with CYP2C19*2 or *3 loss of function alleles received ticagrelor; otherwise, they received clopidogrel) vs Clopidorel. All patients received daily aspirin (81 mg).
• Primary outcome: Composite of cardiovascular death, myocardial infarction, stroke, stent thrombosis, and severe recurrent ischemia at 12 months
• Results:
• Primary outcome: Genotype-guided - 4%, Clopidogrel - 5.9% (p=0.06)
• Stent thrombosis: Genotype-guided - 0.2%, Clopidogrel - 0.9% (p=0.05)
• 29% of patients in the genotype-guided group received ticagrelor
• Findings: Among CYP2C19 loss of function carriers with ACS and stable CAD undergoing PCI, genotype-guided selection of an oral P2Y12 inhibitor, compared with conventional clopidogrel therapy without point-of-care genotyping, resulted in no statistically significant difference in a composite endpoint of cardiovascular death, myocardial infarction, stroke, stent thrombosis, and severe recurrent ischemia based on the prespecified analysis plan and the treatment effect that the study was powered to detect at 12 months.

• STUDY
  CHANCE-2 study - Ticagrelor vs Clopidogrel in CYP2C19 Loss-of-Function Carriers with Stroke or TIA, NEJM (2021) [PubMed abstract]
• Design: Randomized, placebo-controlled trial (N=6412 | length = 90 days) in patients with minor stroke or TIA and CYP2C19 loss-of-function alleles
• Treatment: Ticagrelor 180 mg on day 1 followed by 90 mg twice daily vs Clopidogrel 300 mg on day 1 followed by 75 mg once daily. All patients also received aspirin at a loading dose of 75 - 300 mg, followed by 75 mg daily for 21 days.
• Primary outcome: New ischemic or hemorrhagic stroke at 90 days
• Results:
• Baseline allele status: One loss-of-function allele - 78%, Two loss-of-function alleles - 22%
• Primary outcome: Ticagrelor - 6%, Clopidogrel - 7.6% (p=0.008)
• Severe or moderate bleeding: Ticagrelor - 0.3%, Clopidogrel - 0.3% (p=0.66)
• Findings: Among Chinese patients with minor ischemic stroke or TIA who were carriers of CYP2C19 loss-of-function alleles, the risk of stroke at 90 days was modestly lower with ticagrelor than with clopidogrel. The risk of severe or moderate bleeding did not differ between the two treatment groups, but ticagrelor was associated with more total bleeding events than clopidogrel.

• STUDY
  TRITON TIMI 38 - Post-hoc Analysis of CYP2C19 Metabolizer Status, NEJM (2009) [PubMed abstract]
• Design: Post-hoc analysis of a subgroup of patients (N=1477) in the TRITON TIMI 38 trial (N=13,608 | length - 5 months) where patients with acute coronary syndrome who were to undergo PCI were randomized to clopidogrel or prasugrel
• Comparison: Outcomes in carriers of ≥ one CYP2C19 loss-of-function allele(s) vs noncarriers among 1477 patients treated with clopidogrel
• Primary outcomes: Composite of death from cardiovascular causes, heart attack, or stroke
• Results:
• Primary outcome: Carriers - 12.1%, Noncarriers - 8% (p=0.01)
• Findings: Among persons treated with clopidogrel, carriers of a reduced-function CYP2C19 allele had significantly lower levels of the active metabolite of clopidogrel, diminished platelet inhibition, and a higher rate of major adverse cardiovascular events, including stent thrombosis, than did noncarriers.

• STUDY
  CHANCE Trial - Post-hoc Analysis of CYP2C19 Metabolizer Status, JAMA (2016) [PubMed abstract]
• Design: Post-hoc analysis in a subgroup of patients (N=2933) in the CHANCE trial (N=5170 | length - 90 days) where patients with a TIA or minor stroke were randomized to aspirin + clopidogrel or aspirin for 90 days
• Comparison: Outcomes in carriers of CYP2C19 loss-of-function alleles vs noncarriers among 2933 patients treated with clopidogrel
• Primary outcome: Recurrent stroke within 90 days
• Results:
• Primary outcome in carriers: Aspirin - 10.8%, Aspirin + clopidogrel - 9.4% (p=0.64)
• Primary outcome in noncarriers: Aspirin - 12.4%, Aspirin + clopidogrel - 6.7% (p<0.01)
• A significant interaction (p=0.02) was found between carrier status and the primary outcome
• Findings: Among patients with minor ischemic stroke or transient ischemic attack, the use of clopidogrel plus aspirin compared with aspirin alone reduced the risk of a new stroke only in the subgroup of patients who were not carriers of the CYP2C19 loss-of-function alleles. These findings support a role of CYP2C19 genotype in the efficacy of this treatment.

• FDA recommendations
• The FDA placed a "boxed warning" on clopidogrel stating that the effectiveness of clopidogrel is diminished in poor metabolizers. It states that "tests are available to identify patients who are CYP2C19 poor metabolizers" and one should "consider use of another platelet P2Y12 inhibitor in patients identified as CYP2C19 poor metabolizers."

• Summary
• The studies above show that the efficacy of clopidogrel is reduced in patients with CYP2C19 loss-of-function alleles. The most convincing trial is the CHANCE-2 study that only enrolled patients with reduced CYP2C19 function and randomized them to ticagrelor or clopidogrel. Ticagrelor was found to be superior; although, the effect was modest with an absolute risk reduction of 1.6% for recurrent stroke.
• In contrast to these studies, a study published in 2021 that compared DAPT therapy with ticagrelor or clopidogrel in South Koreans, a population with a high prevalence of loss-of-function alleles, found that clopidogrel was superior to ticagrelor for a composite outcome of CV death, MI, stroke, and bleeding (see TALOS-AMI study).
• Clopidogrel appears to be slightly less effective in carriers of CYP2C19 loss-of-function alleles. Doctors may choose to avoid clopidogrel in high-risk populations, but there are some costs; ticagrelor has no generic and is much more expensive, while prasugrel has a generic but is only approved for ACS managed with PCI. If prolonged P2Y12 inhibitor therapy is required, genotype-guided therapy may be cost-effective.

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• LONG TERM SAFETY

• Clopidogrel was approved for use in the U.S. in 1997. Prasugrel was approved in 2009 and ticagrelor in 2011.
• Clopidogrel has been widely prescribed and has a proven safety record. Prasugrel and ticagrelor have less data, but they have been studied in a number of large trials and appear to be safe when used appropriately.

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• DOSING

• P2Y12 inhibitor dosing chart

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• BIBLIOGRAPHY

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