Antiplatelet therapy in acute coronary syndromes

Prasugrel versus clopidogrel antiplatelet therapy after acute coronary syndrome: matching treatments with patients

Antithrombotic therapy is imperative in the management of patients presenting with an acute coronary syndrome (ACS). The combination of antiplatelet therapy in conjunction with antithrombotic therapy has become the standard of care in improving the morbidity and mortality of patients with an ACS and in reducing ischemic complications of percutaneous coronary intervention. Patients with an ACS are at increased risk for a recurrent event, both in-hospital and for several months afterward. Secondary prevention to reduce these events is accomplished through the establishment of appropriate medical therapy. Dual antiplatelet therapy with aspirin and adenosine 5'-diphosphate P2Y(12) receptor blockers such as ticlopidine or clopidogrel are integral components of this regimen; however, both of these thienopyridines have a relatively slow onset of action and variable bioavailability. Prasugrel, a third-generation thienopyridine approved by the US FDA in 2009, has a more rapid onset of platelet inhibition than clopidogrel and ticlopidine because of increased efficiency of prodrug-to-active metabolite conversion. The result is higher and less variable concentration of the active metabolite within 60 minutes following oral dosing. Phase II and III trials assessing the safety and efficacy of prasugrel have been completed, including JUMBO-TIMI 26, PRINCIPLE-TIMI 44, and TRITON-TIMI 38. These trials demonstrated greater inhibition of platelet aggregation and lower rates of the composite endpoint of death, non-fatal myocardial infarction, and stroke compared with clopidogrel. However, major bleeding occurred more frequently with prasugrel treatment than with clopidogrel. This review highlights the current state of evidence-based antiplatelet therapy and provides guidance on appropriate use of prasugrel in cardiovascular medicine.

Ticagrelor: a novel oral antiplatelet agent

OBJECTIVE

To review the pharmacology, clinical efficacy, and tolerability of ticagrelor and to discuss implications for use in the elderly.

DATA SOURCE

A literature search was conducted in MEDLINE from 1966 to July 2010 using the MESH terms and key words AZD6140, ticagrelor, P2Y12 receptor antagonist. The search was limited to studies in English language with human subjects.

STUDY SELECTION AND DATA EXTRACTION

Randomized controlled clinical trials were reviewed. References that were deemed relevant to pharmacodynamic/pharmacokinetic studies of P2Y₁₂ antagonists and their historical background were also included.

DATA SYNTHESIS

Ticagrelor is the first reversible oral P2Y₁₂ antagonist currently undergoing Food and Drug Administration review for approval. The advantages of ticagrelor over clopidogrel are a more rapid onset of action, offset, and reversibility at the platelet P2Y₁₂ receptor site. In the Study of Platelet Inhibition and Patient Outcomes trial, ticagrelor reduced the incidence of death as a result of cardiovascular causes, with no increase in major bleeding or bleeding related to coronary artery bypass graft (CABG) compared with clopidogrel. Subgroup analyses suggested that elderly patients may benefit more from ticagrelor than from clopidogrel. However, the increase in non-CABG-related bleeding and unique adverse events may limit ticagrelor's use in the elderly.

CONCLUSION

The use of ticagrelor in the elderly should be determined on a case-by-case basis. More studies need to be conducted prior to establishing a role in therapy for the elderly.

Platelet responsiveness to yohimbine hydrochloride and MRS2179 in the context of the interaction between collagen and epinephrine in acute coronary syndrome

Acute coronary syndrome (ACS) covers a spectrum of clinical conditions ranging from unstable angina, Non-ST segment elevation myocardial infarction (NSTEMI), or ST segment elevation myocardial infarction (STEMI). This study encompasses patients with acute coronary syndrome, who were receiving the dual antiplatelet therapy of aspirin and clopidogrel. The focus of the study was to gain insight into the role of selective P2Y1 antagonism using MRS2179 in such cases as well as its effects, if any, on collagen-epinephrine interaction. All the cases showed greater potency of inhibition of the interaction when yohimbine hydrochloride (YH), a blocker of alpha2A-adrenoreceptor, was used compared to MRS2179, a P2Y1 antagonist, although there was variability in responsiveness to the antiplatelet drugs. These findings indicate that alpha2A-adrenoreceptors of platelets in this group play a major role in precipitating the interactive effect of collagen and epinephrine. The dose-response effect as studied by platelet aggregometry showed that the required molar concentration to block the interactive effect in the case of YH was less than that of MRS2179. Hence, it is postulated that although there may be an impairment of collagen-induced aggregation by MRS2179, the interactive effect of collagen-epinephrine may not be impaired by MRS2179 as efficaciously as YH.