A phase 1 study of prasugrel in patients with sickle cell disease: pharmacokinetics and effects on ex vivo platelet reactivity.

AIMS: Prasugrel is a novel thienopyridine P2Y12 adenosine diphosphate (ADP) receptor antagonist that inhibits ADP-mediated platelet activation and aggregation. Accordingly, it may be useful in reducing platelet-related ischaemia in sickle cell disease (SCD). Exposure to prasugrel's active metabolite (Pras-AM) and its antiplatelet activity in SCD have not been investigated. METHODS: Thirteen adult patients with SCD and an equal number of matched healthy control subjects were studied before and after 12 days of 5.0 or 7.5 mg day(-1) prasugrel treatment. Platelet reactivity was assessed by light transmission aggregometry (LTA), impedance aggregometry (MEA), VerifyNow® P2Y12, vasodilator-stimulated phosphoprotein (VASP) phosphorylation and Plateletworks. Exposure to Pras-AM was also assessed. RESULTS: At baseline, patients with SCD showed increased platelet reactivity vs. healthy control subjects with VerifyNow (408 vs. 323 P2Y12 reaction units (PRU), respectively, P = 0.003) and MEA (106 vs. 77 area under the aggregation curve (AU.min), P = 0.002); lower platelet reactivity index with VASP flow cytometry (59 vs. 79% platelet reactivity index (PRI), P = 0.018); and no significant differences with LTA, VASP enzyme-linked immunosorbent assay or Plateletworks. Relative to baseline, prasugrel significantly reduced platelet reactivity by all assays in both populations (all P < 0.05). Prasugrel was well tolerated, with no bleeding-related events in patients with SCD. The mean concentration-time profiles of Pras-AM were comparable between healthy subjects and patients with SCD following a single 10 mg prasugrel dose and following the 12th dose of 7.5 or 5 mg prasugrel. CONCLUSIONS: Results demonstrate that in response to prasugrel, patients with SCD and healthy subjects have similar degrees of platelet inhibition and exposure to Pras-AM, and provide a basis for further study of prasugrel in patients with SCD.

Bleeding complications with the P2Y12 receptor antagonists clopidogrel and ticagrelor in the PLATelet inhibition and patient Outcomes (PLATO) trial.

AIMS More intense platelet-directed therapy for acute coronary syndrome (ACS) may increase bleeding risk. The aim of the current analysis was to determine the rate, clinical impact, and predictors of major and fatal bleeding complications in the PLATO study. METHODS AND RESULTS PLATO was a randomized, double-blind, active control international, phase 3 clinical trial in patients with acute ST elevation and non-ST-segment elevation ACS. A total of 18 624 patients were randomized to either ticagrelor, a non-thienopyridine, reversibly binding platelet P2Y(12) receptor antagonist, or clopidogrel in addition to aspirin. Patients randomized to ticagrelor and clopidogrel had similar rates of PLATO major bleeding (11.6 vs. 11.2%; P = 0.43), TIMI major bleeding (7.9 vs. 7.7%, P = 0.56) and GUSTO severe bleeding (2.9 vs. 3.1%, P = 0.22). Procedure-related bleeding rates were also similar. Non-CABG major bleeding (4.5 vs. 3.8%, P = 0.02) and non-procedure-related major bleeding (3.1 vs. 2.3%, P = 0.05) were more common in ticagrelor-treated patients, primarily after 30 days on treatment. Fatal bleeding and transfusion rates did not differ between groups. There were no significant interactions for major bleeding or combined minor plus major bleeding between treatment groups and age ≥75 years, weight <60 kg, region, chronic kidney disease, creatinine clearance <60 mL/min, aspirin dose >325 mg on the day of randomization, pre-randomization clopidogrel administration, or clopidogrel loading dose. CONCLUSION Ticagrelor compared with clopidogrel was associated with similar total major bleeding but increased non-CABG and non-procedure-related major bleeding, primarily after 30 days on study drug treatment. Fatal bleeding was low and did not differ between groups.

Ticagrelor: a novel reversible oral antiplatelet agent.

The complex mechanism of platelet activation creates an optimal target for pharmacological treatment in patients with acute coronary syndromes. Current antiplatelet medications that are used in addition to aspirin include the thienopyridines, clopidogrel and prasugrel, but there are several limitations to the use of these medications. Clopidogrel and prasugrel irreversibly bind to the P2Y12 receptor, creating a prolonged antiplatelet effect which can be undesirable when surgery is needed. Clopidogrel requires hepatic activation and produces variable platelet inhibition based on genetic polymorphisms. Prasugrel has more consistent platelet inhibition than clopidogrel but carries with it an increased risk of serious bleeds. Ticagrelor is a drug in a new chemical class that reversibly binds the P2Y12 receptor and noncompetitively blocks adenosine diphosphate-induced platelet activation. It was specifically designed to address the limitations of the available antiplatelet agents while maintaining comparable or better antiplatelet effects. It does not require metabolic activation and demonstrates greater platelet inhibition, a faster offset of action and comparable bleeding risk compared to clopidogrel. The pivotal PLATO (The Study of Platelet Inhibition and Patient Outcomes) trial in patients with an acute coronary syndrome demonstrated improved cardiovascular outcomes, including a reduction in myocardial infarctions and vascular events using ticagrelor as compared to clopidogrel with comparable rates of major bleeds. A puzzling finding from that trial was the lack of benefit with ticagrelor in patients enrolled from the United States, which has led to ticagrelor not being approved at this time in this country. The main adverse events with ticagrelor are bleeding and dyspnea, the latter of which is of unclear etiology and of unknown long-term clinical concern. In summary, ticagrelor is an exciting new oral antiplatelet drug that seems to be more efficacious than clopidogrel, with comparable safety. Whether issues of geographic disparities in response and the unusual side effect of dyspnea ultimately prove problematic has yet to be determined. Nonetheless, ticagrelor is a drug that has the potential to change the standard of care of patients with acute coronary syndromes.

Oral antiplatelet agents in ACS: from pharmacology to clinical differences.

Antiplatelet agents play an essential role in the treatment of acute coronary syndrome (ACS). Numerous clinical trials have established the value of antiplatelet therapies for ACS. Aspirin (ASA), thienopyridines and GP IIb/IIIa antagonists comprise the major classes of antiplatelet therapies demonstrated to be of benefit in the treatment of ACS. Thienopyridines are a class of drugs that function via inhibition of the adenosine diphosphate (ADP) P2Y12 platelet receptors. Currently, clopidogrel, a second generation thienopyridine, is the main drug of choice and the combination of aspirin and clopidogrel is administered orally for the treatment of ACS. Recently, a third generation of thienopyridines has been introduced represented by prasugrel that has demonstrated promising results in ACS patients treated with percutaneous coronary intervention (PCI). A number of nonthienopyridine oral antiplatelet drugs are under development, and one of them, ticagrelor has already been tested in a major phase III clinical trial, PLATO, with the inclusion of a broad spectrum of patients with ACS. The present review aims to discuss the present knowledge about the safety and efficacy of oral antiplatelet treatment of patients with ACS.