ST elevation myocardial infarction thienopyridine therapy
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Antiplatelet therapy is a mainstay of pharmacotherapy in STEMI. In the International Study of Infarct Survival 2 (ISIS 2), aspirin reduced mortality in STEMI as much as streptokinase (by approximately 42%) when compared to the administration of neither agent. [1]
Thienopyridines inhibit ADP mediated platelet activation and have been found to further improve outcomes of STEMI patients treated with a fibrinolytic agent for STEMI. There are at present two agents available in this class, Ticlopidine and clopidogrel. Prasugrel is currently an investigational drug in this class. As an adjunct to fibrinolytic therapy, clopidogrel has been associated with improved patency in the CLARITY trial (300 mg loading dose and 75 mg/day maintenance dose), and a reduction in mortality in the COMMIT trial (75 mg/day loading and maintenance dose). Among STEMI patients treated with a fibrinolytic agent, co-administration of clopidogrel at a loading dose of 300 mg and a maintenance dose of 75 mg/day should be viewed as the standard of care.
In contrast to fibrinolytic therapy, the optimal timing and dose of clopidogrel among primary angioplasty patients has not been established in randomized trials.
Efficacy and safety of Clopidogrel among patients treated with a fibrinolytic agent
Angiographic efficacy of Clopidogrel as adjunctive therapy to fibrinolysis in STEMI patients
The angiographic effectiveness of clopidogrel as adjunctive therapy to fibrinolytic administration was evaluated in the Clopidogrel as Adjunctive Reperfusion Therapy (CLARITY)-TIMI 28 trial. [2] [3] [4] This study randomized 3,491 STEMI patients to treatement with either placebo or a 300 mg loading dose of clopidogrel followed by a maintenance dose of 75 mg/day. The trial demonstrated a 35% relative risk reduction in the incidence of an occluded artery on angiography, death, or MI associated with clopidogrel administration. [2]
Safety of Clopidogrel in CLARITY
Clopidogrel administration was not associated with an increase in TIMI major bleeding or intracranial hemorrhage (ICH). Indeed, the incidence of all causes of stroke was reduced by 46% (P = 0.052).
Generalizability of results from CLARITY
There was no heterogeneity in the treatment benefit (that is a consistent benefit was observed) irrespective of:
- Type of fibrinolytic (2/3rds of patients were treated with a fibrin-specific agent such as tPA, rPA, nPA, or TNK) or
- Tyep of antithrombin administered (45.8% received UFH, 29.6% received enoxaparin, 24.5% received both or none).
It is important to note that the following patient groups were excluded from participation in CLARITY, and the results of CLARITY are not applicable to these subgroups: patients over 75 years of age, those with creatinine > 2.5 mg/dL, patients with cardiogenic shock, or patients who had previously undergone coronary artery bypass grafting (CABG). It should also be noted that the rate of PCI or CABG was high at 63%. This may be due to the fact protocol-mandated angiography was performed in countries with a high rate of adjunctive PCI such as Europe and the United States.
Reduction in mortality associated with clopidogrel administration in conjunction with fibrinolytic agents: Results of COMMIT
The COMMIT (ClOpidogrel and Metoprolol in Myocardial Infarction Trial) collaborative group evaluated the safety and efficacy of clopidogrel as an adjunct to fibrinolytic therapy in 45,852 patients at 1250 Chinese hospitals who presented in the first 24 hours of STEMI (93% had ST segment elevation or left bundle branch block, the rest had ST segment depression). [5] As adjunctive therapy to 162 mg of aspirin daily, patients were randomized to clopidogrel 75 mg daily without a 300 mg loading dose which continued until discharge or up to 4 weeks in hospital (mean 15 days in survivors)(n=22,961) or placebo (n=22,891). Clopidogrel administration was associated with a 9% relative reduction (95% CI 3-14) in the co-primary endpoint of death, reinfarction, or stroke (2121 [9.2%] clopidogrel vs 2310 [10.1%] placebo; p=0.002). This would translate into to nine fewer deaths, re MIs or strokes per 1000 patients treated for two weeks. Likewise, there was a 7% relative risk reduction (95% CI 1-13) in all cause death (1726 [7.5%] vs 1845 [8.1%]; p=0.03). The benefits were consistent across a broad range of subgroups, antithrombins and fibrinolytic agents.
With respect to safety, there was no excess of fatal stroke or intracranial hemmorhage associated with clopidogrel administration, either in patients of all ages (134 [0.58%] vs 125 [0.55%]; p=0.59), or among patients who were over 70 years of age.
Dosing of clopidogrel in STEMI
Fibrinolytic therapy patients
Data from the non-ST elevation MI population does demonstrate that a 600 mg oral dose achieves sustained inhibition more rapidly than a 300 mg dose. A 600 mg dose does not, however, achieve a higher level of inhibition. The FDA package insert loading dose is 300 mg, but in clinical practice both 300 and 600 mg doses are used. A loading dose of 600 mg of clopidogrel has not been studied in conjunction with fibrinolytic therapy and cannot be recommended.
Primary PCI patients
The optimal loading dose in patients with STEMI undergoing primary PCI has not been rigorously evaluated in randomized trials. The ARMYDA 2 trial evaluated the efficacy of 300 mg vs 600 mg of clopidogrel before elective PCI, and the benefits observed in this trial (a reduction in the risk of death, MI or target vessel revascularization from 12% to 4%, p=0.041) may not be applicable to the STEMI population. [6] In the HORIZONS AMI trial, a loading dose of 600 vs 300 mg of clopidogrel was associated with a lower rate of death (3.1% vs 1.9%, p=0.03) as well as reinfarction (2.4% vs 1.3%, p=0.02) and a trend toward lower rates of stroke (1.0% vs 0.4%, p=0.058). There was no difference in pre-PCI flow between the two strategies. 30 day stent thrombosis was lower among patients treated with a 600 mg loading dose of clopidogre (1.7% vs 3.5%, p=0.03). An important confounder was the fact that 7.5% of patients treated with a 600 mg loading dose received a GP IIbIIIa inhibitor in the emergency room compared to only 3.2% of those treated with a 300 mg loading dose (p<0.0001). There were also large and significant imbalances in Killip class, femoral access, closure device use, and peak ACT between the two loading doses (all p<0.0001). In a multivariate model, a 600 mg loading dose of Clopidogrel was indpendently associated with a lower rate of 30 day major adverse cardiac events (MACE) when compared to the lower 300 mg loading dose (OR 0.72, p=0.036). A 600 mg loading dose was not a multivariate preditor of the specific endpoint of death/MI or bleeding. Given the non randomized nature of this analysis, and the potential confounders, these findings should be interpreted with caution and no firm recommendations can be made regarding the optimal loading dose of clopidogrel before primary PCI from this analysis.
Side effects of thienopyridines
Ticlopidine administration has been associated with neutropenia and thrombotic thrombocytopenia (TTP). It is as a result of these potential side effects that clopidogrel is often prescribed instead. Clopidogrel may also be preferred because of the lack of need for laboratory monitoring, and once-daily dosing. It should be noted, however, that approximately one third to one quarter of patients may be resistant to clopidogrel, which is a pro-drug. For those patients who develop stent thrombosis while on clopidogrel, ticlopidine may be an optimal substitution because it is not a pro-drug and is not metabolized by the same pathway as clopidogrel.
ACC/AHA Guidelines (DO NOT EDIT) [7]
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Class I1. Clopidogrel 75 mg per day orally should be added to aspirin in patients with STEMI regardless of whether they undergo reperfusion with fibrinolytic therapy or do not receive reperfusion therapy. (Level of Evidence: A) Treatment with clopidogrel should continue for at least 14 days. (Level of Evidence: B) 2. In patients taking clopidogrel in whom CABG is planned, the drug should be withheld for at least 5 days and preferably for 7 days unless the urgency for revascularization outweighs the risks of excess bleeding. (Level of Evidence: B) Class IIa1. In patients less than 75 years of age who receive fibrinolytic therapy or who do not receive reperfusion therapy, it is reasonable to administer an oral loading dose of clopidogrel 300 mg. (Level of Evidence: C) (No data are available to guide decision making regarding an oral loading dose in patients 75 years of age or older.) 2. Long-term maintenance therapy (e.g., 1 year) with clopidogrel (75 mg per day orally) is reasonable in STEMI patients regardless of whether they undergo reperfusion with fibrinolytic therapy or do not receive reperfusion therapy. (Level of Evidence: C) |
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Sources
- The 2004 ACC/AHA Guidelines for the Management of Patients With ST-Elevation Myocardial Infarction [8]
- The 2007 Focused Update of the ACC/AHA 2004 Guidelines for the Management of Patients with ST-Elevation Myocardial Infarction [7]
References
- ↑ "Randomized trial of intravenous streptokinase, oral aspirin, both, or neither among 17,187 cases of suspected acute myocardial infarction: ISIS-2.ISIS-2 (Second International Study of Infarct Survival) Collaborative Group". J. Am. Coll. Cardiol. 12 (6 Suppl A): 3A–13A. 1988. PMID 2903874. Unknown parameter
|month=ignored (help) - ↑ 2.0 2.1 Sabatine MS, Cannon CP, Gibson CM; et al. (2005). "Addition of clopidogrel to aspirin and fibrinolytic therapy for myocardial infarction with ST-segment elevation". N. Engl. J. Med. 352 (12): 1179–89. doi:10.1056/NEJMoa050522. PMID 15758000. Unknown parameter
|month=ignored (help) - ↑ Sabatine MS, Morrow DA, Montalescot G; et al. (2005). "Angiographic and clinical outcomes in patients receiving low-molecular-weight heparin versus unfractionated heparin in ST-elevation myocardial infarction treated with fibrinolytics in the CLARITY-TIMI 28 Trial". Circulation. 112 (25): 3846–54. doi:10.1161/CIRCULATIONAHA.105.595397. PMID 16291601. Unknown parameter
|month=ignored (help) - ↑ Gibson CM, Murphy SA, Pride YB; et al. (2008). "Effects of pretreatment with clopidogrel on nonemergent percutaneous coronary intervention after fibrinolytic administration for ST-segment elevation myocardial infarction: a Clopidogrel as Adjunctive Reperfusion Therapy-Thrombolysis in Myocardial Infarction (CLARITY-TIMI) 28 study". Am. Heart J. 155 (1): 133–9. doi:10.1016/j.ahj.2007.08.034. PMID 18082504. Unknown parameter
|month=ignored (help) - ↑ Chen ZM, Jiang LX, Chen YP; et al. (2005). "Addition of clopidogrel to aspirin in 45,852 patients with acute myocardial infarction: randomised placebo-controlled trial". Lancet. 366 (9497): 1607–21. doi:10.1016/S0140-6736(05)67660-X. PMID 16271642. Unknown parameter
|month=ignored (help) - ↑ Patti G, Chello M, Candura D; et al. (2006). "Randomized trial of atorvastatin for reduction of postoperative atrial fibrillation in patients undergoing cardiac surgery: results of the ARMYDA-3 (Atorvastatin for Reduction of MYocardial Dysrhythmia After cardiac surgery) study". Circulation. 114 (14): 1455–61. doi:10.1161/CIRCULATIONAHA.106.621763. PMID 17000910. Unknown parameter
|month=ignored (help) - ↑ 7.0 7.1 Antman EM, Hand M, Armstrong PW; et al. (2008). "2007 Focused Update of the ACC/AHA 2004 Guidelines for the Management of Patients With ST-Elevation Myocardial Infarction: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines: developed in collaboration With the Canadian Cardiovascular Society endorsed by the American Academy of Family Physicians: 2007 Writing Group to Review New Evidence and Update the ACC/AHA 2004 Guidelines for the Management of Patients With ST-Elevation Myocardial Infarction, Writing on Behalf of the 2004 Writing Committee". Circulation. 117 (2): 296–329. doi:10.1161/CIRCULATIONAHA.107.188209. PMID 18071078. Unknown parameter
|month=ignored (help) - ↑ Antman EM, Anbe DT, Armstrong PW, Bates ER, Green LA, Hand M, Hochman JS, Krumholz HM, Kushner FG, Lamas GA, Mullany CJ, Ornato JP, Pearle DL, Sloan MA, Smith SC, Alpert JS, Anderson JL, Faxon DP, Fuster V, Gibbons RJ, Gregoratos G, Halperin JL, Hiratzka LF, Hunt SA, Jacobs AK (2004). "ACC/AHA guidelines for the management of patients with ST-elevation myocardial infarction: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Revise the 1999 Guidelines for the Management of Patients with Acute Myocardial Infarction)". Circulation. 110 (9): e82–292. PMID 15339869. Unknown parameter
|month=ignored (help)