Dose-dependent inhibition of human platelet aggregation by prasugrel and its interaction with aspirin in healthy subjects

An Aspirin-Free Versus Dual Antiplatelet Strategy for Coronary Stenting: STOPDAPT-3 Randomized Trial

BACKGROUND

Bleeding rates on dual antiplatelet therapy (DAPT) within 1 month after percutaneous coronary intervention (PCI) remain high in clinical practice, particularly in patients with acute coronary syndrome or high bleeding risk. Aspirin-free strategy might result in lower bleeding early after PCI without increasing cardiovascular events, but its efficacy and safety have not yet been proven in randomized trials.

METHODS

We randomly assigned 6002 patients with acute coronary syndrome or high bleeding risk just before PCI either to prasugrel (3.75 mg/day) monotherapy or to DAPT with aspirin (81-100 mg/day) and prasugrel (3.75 mg/day) after loading of 20 mg of prasugrel in both groups. The coprimary end points were major bleeding (Bleeding Academic Research Consortium 3 or 5) for superiority and cardiovascular events (a composite of cardiovascular death, myocardial infarction, definite stent thrombosis, or ischemic stroke) for noninferiority with a relative 50% margin.

RESULTS

The full analysis set population consisted of 5966 patients (no-aspirin group, 2984 patients; DAPT group, 2982 patients; age, 71.6±11.7 years; men, 76.6%; acute coronary syndrome, 75.0%). Within 7 days before randomization, aspirin alone, aspirin with P2Y12 inhibitor, oral anticoagulants, and intravenous heparin infusion were given in 21.3%, 6.4%, 8.9%, and 24.5%, respectively. Adherence to the protocol-specified antiplatelet therapy was 88% in both groups at 1 month. At 1 month, the no-aspirin group was not superior to the DAPT group for the coprimary bleeding end point (4.47% and 4.71%; hazard ratio, 0.95 [95% CI, 0.75-1.20]; Psuperiority=0.66). The no-aspirin group was noninferior to the DAPT group for the coprimary cardiovascular end point (4.12% and 3.69%; hazard ratio, 1.12 [95% CI, 0.87-1.45]; Pnoninferiority=0.01). There was no difference in net adverse clinical outcomes and each component of coprimary cardiovascular end point. There was an excess of any unplanned coronary revascularization (1.05% and 0.57%; hazard ratio, 1.83 [95%CI, 1.01-3.30]) and subacute definite or probable stent thrombosis (0.58% and 0.17%; hazard ratio, 3.40 [95% CI, 1.26-9.23]) in the no-aspirin group compared with the DAPT group.

CONCLUSIONS

The aspirin-free strategy using low-dose prasugrel compared with the DAPT strategy failed to attest superiority for major bleeding within 1 month after PCI but was noninferior for cardiovascular events within 1 month after PCI. However, the aspirin-free strategy was associated with a signal suggesting an excess of coronary events.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04609111.

Pharmacokinetics and Pharmacodynamics of Approved and Investigational P2Y12 Receptor Antagonists

Coronary artery disease remains the major cause of mortality worldwide. Antiplatelet drugs such as acetylsalicylic acid and P2Y12 receptor antagonists are cornerstone treatments for the prevention of thrombotic events in patients with coronary artery disease. Clopidogrel has long been the gold standard but has major pharmacological limitations such as a slow onset and long duration of effect, as well as weak platelet inhibition with high inter-individual pharmacokinetic and pharmacodynamic variability. There has been a strong need to develop potent P2Y12 receptor antagonists with more favorable pharmacological properties. Prasugrel and ticagrelor are more potent and have a faster onset of action; however, they have shown an increased bleeding risk compared with clopidogrel. Cangrelor is highly potent and has a very rapid onset and offset of effect; however, its indication is limited to P2Y12 antagonist-naïve patients undergoing percutaneous coronary intervention. Two novel P2Y12 receptor antagonists are currently in clinical development, namely vicagrel and selatogrel. Vicagrel is an analog of clopidogrel with enhanced and more efficient formation of its active metabolite. Selatogrel is characterized by a rapid onset of action following subcutaneous administration and developed for early treatment of a suspected acute myocardial infarction. This review article describes the clinical pharmacology profile of marketed P2Y12 receptor antagonists and those under development focusing on pharmacokinetic, pharmacodynamic, and drug-drug interaction liability.

The Rationale for and Clinical Pharmacology of Prasugrel 5 mg

Prasugrel is a third-generation thienopyridine platelet P2Y₁₂ adenosine diphosphate (ADP) receptor antagonist administered with aspirin for the treatment of patients with acute coronary syndrome (ACS) with planned percutaneous coronary intervention. Prasugrel is administered periprocedurally at an oral loading dose of 60 mg followed by daily maintenance doses (MDs) of 10 mg for most patients and 5 mg for patients weighing <60 kg or aged ≥75 years. Data from a prasugrel phase III study, TRITON-TIMI 38, suggested that a lower MD might be more suitable for patients weighing <60 kg or aged ≥75 years; subsequent pharmacokinetic and pharmacodynamic studies have indicated that prasugrel 5 mg reduced platelet reactivity in these populations to an extent similar to that of prasugrel 10 mg in heavier or younger patients. Clinical experience with prasugrel 5 mg is limited, and additional studies are needed to verify the clinical efficacy and safety of this dose in these challenging populations.

Prasugrel hydrochloride for the treatment of acute coronary syndrome patients

INTRODUCTION

Dual antiplatelet therapy (DAPT) with aspirin combined with either a thienopyridine (clopidogrel or prasugrel) or acyclopentyl-triazolo-pyrimidine (ticagrelor) plays a vital role in the management of acute coronary syndrome (ACS) especially in those undergoing percutaneous coronary intervention (PCI) but even those being managed medically. Observational studies and some formal studies have shown patients on the standard dual antiplatelet regimen (clopidogrel and aspirin) continue to have further ischemic events and can suffer stent thrombosis. It has been demonstrated that clopidogrel is associated with a delayed onset of action with a considerable inter-individual variation to treatment thus making it difficult to achieve an optimal level of platelet inhibition. Areas covered: This article will review the current evidence that is available regarding the effectiveness and safety of prasugrel in ACS patients undergoing percutaneous coronary intervention (PCI). Expert commentary: Prasugrel is an oral third-generation inhibitor of platelet activation and aggregation. Laboratory studies and early phase clinical trials show prasugrel has a faster onset of action, is more potent and has reduced inter-patient response variability compared to clopidogrel. The published studies so far demonstrated that prasugrel when compared to clopidogrel also shows a higher degree of effectiveness in the prevention of platelet-initiated thrombotic events in patients with ACS undergoing PCI, however these benefits are offset somewhat by an increased bleeding risk.

Platelet Aggregation Inhibitory Effects and Pharmacokinetics of Prasugrel Used in Combination With Aspirin in Healthy Japanese Subjects

We evaluated the pharmacokinetics and pharmacodynamics of prasugrel used in combination with aspirin in healthy Japanese subjects. All subjects received aspirin 100 mg/day. Subsequently, in the single‐administration study, 23 subjects also received prasugrel 20 or 30 mg, and in the multiple‐administration study, 20 subjects received a loading dose of prasugrel 20 or 30 mg on day 1, followed by a maintenance dose of prasugrel 5 or 7.5 mg/day, respectively, on days 2–5. In both studies, the plasma concentration of the active metabolite of prasugrel, R‐138727, reached a maximum 0.5 hours after administration and rapidly decreased within 4 hours. In the single‐administration study, the inhibitory effect on adenosine diphosphate–induced platelet aggregation was significantly higher in the prasugrel 20‐ and 30‐mg groups than in the placebo group at all times (1–144 hours) after administration. In the multiple‐administration study, a similar antiplatelet effect was found after both the loading dose and the maintenance dose and was maintained for 3–6 days after the last administration. There were study drug‐related adverse events; however, all were mild, and none was clinically significant.

Pharmacokinetics and pharmacodynamics of prasugrel in healthy Japanese subjects

This randomized double-blind and placebo-controlled study assessed the pharmacodynamics and pharmacokinetics of prasugrel in healthy adult Japanese male subjects after single (n = 50) and multiple (n = 40) oral administration. With a single administration of prasugrel (2-30 mg), the plasma concentration of the active metabolite increased rapidly, reached a maximum at 30 min after administration, and then decreased rapidly within 4 h. The 5 mg and higher doses prevented ADP-induced platelet aggregation in a dose-dependent manner. Further analyses showed that 30 mg prasugrel exhibited the peak inhibition, and 20 mg prasugrel showed a nearly equivalent effect. With multiple doses (2.5-10 mg), the pharmacokinetic parameters on Day 1 and Day 7 were similar, and no accumulation attributable to multiple dosing was observed. The inhibitory effect on ADP-induced platelet aggregation increased with doses from 2.5 to 7.5 mg, and reached the peak level at 7.5 mg. Regarding safety, all of the drug-related adverse events observed were mild, and there were no clinically significant bleeding-related adverse events. This study indicates that a single oral administration of prasugrel at a dose of up to 30 mg and a maintenance dose of up to 10 mg are tolerated in Japanese healthy subjects.

Prasugrel in children with sickle cell disease: pharmacokinetic and pharmacodynamic data from an open-label, adaptive-design, dose-ranging study

INTRODUCTION

This phase 2 study was designed to characterize the relationship among prasugrel dose, prasugrel's active metabolite (Pras-AM), and platelet inhibition while evaluating safety in children with sickle cell disease. It was open-label, multicenter, adaptive design, dose ranging, and conducted in 2 parts. Part A: Patients received escalating single doses leading to corresponding increases in Pras-AM exposure and VerifyNow®P2Y12 (VN) platelet inhibition and decreases in VNP2Y12 reaction units and vasodilator-stimulated phosphoprotein platelet reactivity index. Part B: Patients were assigned daily doses (0.06, 0.08, and 0.12 mg/kg) based on VN pharmacodynamic measurements at the start of 2 dosing periods, each 14±4 days. Platelet inhibition was significantly higher at 0.12 mg/kg (56.3%±7.4%; least squares mean±SE) compared with 0.06 mg/kg (33.8%±7.4%) or 0.08 mg/kg (37.9%±5.6%). Patients receiving 0.12 mg/kg achieved ≥30% platelet inhibition; only 1 patient receiving 0.06 mg/kg exceeded 60% platelet inhibition. High interpatient variability in response to prasugrel and the small range of exposures precluded rigorous characterization of the relationship among dose, Pras-AM, and platelet inhibition.

SAFETY

No hemorrhagic events occurred in Part A; 3 occurred in Part B, all mild and self-limited.

CONCLUSIONS

Most children with sickle cell disease may achieve clinically relevant platelet inhibition with titration of daily-dose prasugrel.

Plasma viscosity, functional fibrinogen, and platelet reactivity in vascular surgery patients

BACKGROUND

Platelet reactivity changes with shear stress, which in turn depends on whole blood and plasma viscosity (PV). Platelets interact with fibrinogen during thrombus formation, and fibrinogen is a determinant of PV. The respective role of PV and fibrinogen on platelet function is still unclear.

METHODS

30 patients undergoing vascular surgery were admitted to this study. In each patient we measured PV using a cone-on-plate viscosimeter, functional fibrinogen using thromboelastometry, and platelet reactivity to thrombin receptor activating peptide (TRAP) stimulation using multi-electrode aggregometry. Routine coagulation parameter were measured.

RESULTS

At the univariate analysis, platelet reactivity was positively associated with mean platelet volume (R2 = 0.15, P = 0.033) and PV (R2 = 0.35, P = 0.0006), and negatively associated with serum bilirubin (R2 = 0.20, P = 0.013) and international normalized ratio (INR) (R2 = 0.19, P = 0.017). At the multivariable analysis, only PV (P = 0.001) and INR (P = 0.019) remained independent predictors of platelet reactivity.

CONCLUSION

PV is directly and independently associated with platelet reactivity, whereas functional fibrinogen is not. Aspirin treatment is inadequate to correct thrombin-induced platelet aggregation. In presence of hyperviscosity, patients at high cardiovascular risk, may benefit from more aggressive anti-platelet treatments.

Human platelet protease-activated receptor-1 responsiveness to thrombin related to P2Y12 inhibition

Dual antiplatelet therapy with aspirin and adenosine diphosphate (ADP) receptor inhibitors significantly improves the outcome of patients with stable coronary heart disease. However, abundant thrombin generation, which is not influenced by this dual antiplatelet therapy, is a major reason for recurrent thromboembolic disease in these patients. We, therefore, assessed in a hypothesis generating study in patients with stable coronary artery disease specifically the relation of responsiveness of the platelet thrombin receptor protease-activated receptor (PAR)-1 to the magnitude of the inhibition of the ADP receptor. PAR-1 regulation was studied prospectively in 86 consecutive patients with stable coronary artery disease treated with aspirin and clopidogrel (67 patients) or prasugrel (19 patients) and correlated the data to ADP inducible platelet reactivity by impedance aggregometry. PAR-1 expression did not differ between patients on aspirin and clopidogrel vs patients on aspirin and prasugrel (P > 0.5). PAR-1 levels were correlated to P-selectin expression (P < 0.0001). The higher the PAR-1 expression the more profound was the in vitro thrombin-inducible platelet activation. However, neither ex vivo PAR-1 expression nor in vitro thrombin-inducible PAR-1 were correlated to ADP-inducible platelet aggregation (P > 0.5). Thus, like in a real life scenario, patients with stable ischemic heart disease on dual antiplatelet therapy may express high levels of PAR-1, which are associated with profound thrombin-inducible platelet activation. This responsiveness cannot be predicted by the magnitude of ADP responsiveness.

A double-blind, randomized, multicenter phase 2 study of prasugrel versus placebo in adult patients with sickle cell disease

Background

Platelet activation has been implicated in the pathogenesis of sickle cell disease (SCD) suggesting antiplatelet agents may be therapeutic. To evaluate the safety of prasugrel, a thienopyridine antiplatelet agent, in adult patients with SCD, we conducted a double-blind, randomized, placebo-controlled study.

Methods

The primary endpoint, safety, was measured by hemorrhagic events requiring medical intervention. Patients were randomized to prasugrel 5 mg daily (n = 41) or placebo (n = 21) for 30 days. Platelet function by VerifyNow® P2Y12 and vasodilator-stimulated phosphoprotein assays at days 10 and 30 were significantly inhibited in prasugrel- compared with placebo-treated SCD patients.

Results

There were no hemorrhagic events requiring medical intervention in either study arm. Mean pain rate (percentage of days with pain) and intensity in the prasugrel arm were decreased compared with placebo. However, these decreases did not reach statistical significance. Platelet surface P-selectin and plasma soluble P-selectin, biomarkers of in vivo platelet activation, were significantly reduced in SCD patients receiving prasugrel compared with placebo. In sum, prasugrel was well tolerated and not associated with serious hemorrhagic events.

Conclusions

Despite the small size and short duration of this study, there was a decrease in platelet activation biomarkers and a trend toward decreased pain.

Residual platelet activation through protease-activated receptors (PAR)-1 and -4 in patients on P2Y12 inhibitors

BACKGROUND

Dual antiplatelet therapy with aspirin and thienopyridines has improved outcomes of patients after coronary stent implantation. However, current knowledge suggests that thrombin generation is not affected by inhibition of the P2Y12 receptor, and therefore, platelet activation may still occur.

METHODS

The response to agonists specific for protease-activated receptors (PAR)-1 and -4 was tested by multiple electrode impedance aggregometry in 82 patients on stable doses of clopidogrel or prasugrel, and in 55 healthy controls.

RESULTS

Based on the consensus cut-off value for adenosine diphosphate (ADP) responsiveness, only one out of 19 patients on prasugrel, but 22 out of 63 patients on clopidogrel had high on-treatment residual platelet reactivity in response to exogenous ADP (p=0.01). Among the patients with adequate ADP P2Y12 receptor inhibition (n=59), we still observed 32 patients (54.2%) with normal response to the PAR-1 activator SFLLRN (26 patients on clopidogrel, 81.2%; 6 patients on prasugrel, 18.8%), and 37 patients (63.8%) with a normal response to the PAR-4 activator AYPGKF (29 patients on clopidogrel, 78.4%; 8 patients on prasugrel, 21.6%). The degree of PAR-agonists inducible platelet activation was directly correlated with the activation induced by ADP (r>0.5 and p<0.001 for both agonists). Moreover, SFLLRN and AYPGKF inducible platelet reactivities were strongly correlated (r=0.75, p<0.001).

CONCLUSION

PAR responsiveness is preserved in the majority of patients with adequate clopidogrel-mediated inhibition of the platelet P2Y12 receptor, and still in about 20% of those with adequate inhibition by prasugrel.

Importance of potent P2Y(12) receptor blockade in acute myocardial infarction: focus on prasugrel

INTRODUCTION

Prasugrel therapy is recommended in patients with acute coronary syndromes (ACS) undergoing percutaneous coronary intervention (PCI).

AREAS COVERED

This article reviews the efficacy and safety profile of prasugrel, cost considerations, and its role in clinical practice based on published data. The authors searched PubMed and Ovid databases for English language clinical trial articles involving the use of prasugrel in human subjects and patients, published through June 2012. The keyword "prasugrel" was used. The review focuses on clinical trials, but other articles including Food and Drug Administration documents are also reviewed.

EXPERT OPINION

Prasugrel has a more rapid and greater pharmacodynamic (PD) effect than clopidogrel. No significant drug - drug interactions have been reported. In a large-scale randomized clinical trial, prasugrel was associated with better protection against ischemic event occurrence compared to clopidogrel, but more bleeding in ACS patients undergoing PCI. Adverse outcomes outweighed the benefit of prasugrel in certain subgroups, including patients over the age of 75, those weighing less than 60 kg, and patients with a prior history of stroke or transient ischemic attack. In subsequent PD studies, prasugrel therapy showed suboptimal platelet inhibition in selected patients. In addition, "hyper-responsiveness" to prasugrel may increase the risk of serious bleeding in high-risk patients. More detailed studies are warranted to explore antiplatelet regimens tailored to optimally limit ischemic and bleeding event occurrences. A Phase-III TRILOGY trial (NCT00699998) will indicate the clinical efficacy and safety of prasugrel in patients with non-ST-segment elevation ACS, who are medically managed without coronary revascularization.

Genotypic and phenotypic assessment of platelet function and response to P2Y12 antagonists

The P2Y12-ADP receptor antagonists are the cornerstone of oral antiplatelet therapy in the secondary prevention of coronary artery disease, especially after acute coronary syndrome or percutaneous coronary intervention. Currently, the therapeutic agents available to block the receptor include clopidogrel and prasugrel; ticagrelor is not available everywhere. Clopidogrel was the gold standard, but recently it has been challenged by prasugrel and ticagrelor. One pitfall of clopidogrel is that in some patients it cannot induce optimal platelet reactivity inhibition in connection with several factors, including some genetic polymorphisms of enzymes participating in its bioabsorption or metabolism. This variability of response can be evaluated by platelet reactivity monitoring. This comprehensive review provides the available data regarding the genotypic and phenotypic interaction with the response to P2Y12-ADP receptor antagonists and discusses the concept of personalized antiplatelet therapy based on a genotypic or phenotypic profile.

A comparison of prasugrel at the time of percutaneous coronary intervention or as pretreatment at the time of diagnosis in patients with non-ST-segment elevation myocardial infarction: design and rationale for the ACCOAST study

BACKGROUND

The precise risk/benefit of thienopyridine pretreatment and the optimal dosage and timing of a thienopyridine loading dose (LD) for patients presenting with non-ST-segment elevation (NSTE) acute coronary syndromes are still being debated. Prasugrel, a novel thienopyridine, is an appropriate drug to address this issue as it provides predictably high and rapid inhibition of platelet aggregation.

STUDY DESIGN

ACCOAST is a phase 3, multicenter, parallel-group, double-blind, and event-driven study designed to compare 2 prasugrel LD schedules in patients with NSTE myocardial infarction who are scheduled for coronary angiography/percutaneous coronary intervention (PCI). Approximately 4,100 patients will be randomly assigned to an initial LD of 30 mg of prasugrel after the diagnosis followed by coronary angiography with an additional dose of 30 mg of prasugrel given at the time of PCI (pretreatment) or an LD of 60 mg of prasugrel given to patients undergoing PCI at the time of the procedure (non-pretreatment). All patients undergoing PCI will receive 5 or 10 mg of prasugrel daily. The primary objective is to test the hypothesis that prasugrel pretreatment is superior to prasugrel non-pretreatment as measured by a reduction in the composite end point of cardiovascular death, myocardial infarction, stroke, urgent revascularization, or glycoprotein IIb/IIIa inhibitor bailout through 7 days from randomization. Key safety end points include TIMI (Thrombolysis In Myocardial Infarction) major and minor bleeding risks.

CONCLUSIONS

The ACCOAST study will provide important evidence with regard to the benefits and risks of prasugrel pretreatment compared with administration of prasugrel at the time of PCI in patients with NSTE myocardial infarction.

TRITON and beyond: new insights into the profile of prasugrel

Prasugrel, a third-generation thienopyridine antiplatelet agent, demonstrated superior efficacy to clopidogrel but with an increased risk of bleeding in the phase III pivotal registration Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition with Prasugrel-Thrombolysis in Myocardial Infarction (TRITON-TIMI 38). This article reviews and discusses select components of a large literature of prasugrel data that has emerged since the TRITON-TIMI 38 (TRITON) study primary disclosure.

Effect of intrinsic and extrinsic factors on the clinical pharmacokinetics and pharmacodynamics of prasugrel

Thienopyridines are inactive prodrugs that are converted in vivo to active metabolites, which irreversibly bind to and inactivate platelet P2Y(12) receptors, and inhibit platelet activation and aggregation. Prasugrel is a third-generation thienopyridine, recently approved for prevention of thrombotic cardiovascular complications in patients with an acute coronary syndrome undergoing percutaneous coronary intervention. Prasugrel is converted to its active metabolite (Pras-AM; compound R-138727) in two sequential steps: (i) rapid and complete hydrolysis by intestinal human carboxylesterase-2 to form a thiolactone intermediate; and (ii) oxidation of the thiolactone by cytochrome P450 (CYP) enzymes in the gut and/or the liver. CYP3A and CYP2B6 are the primary CYPs contributing to Pras-AM formation, with smaller contributions from CYP2C9 and CYP2C19. Prasugrel is rapidly absorbed and metabolized, with Pras-AM plasma concentrations peaking at about 0.5 hours after oral administration; this helps to account for the rapid onset of inhibition of platelet aggregation (IPA) achieved by prasugrel. In the clinical pharmacology programme for prasugrel, bodyweight had the greatest effect of all covariates that were tested. In the phase III TRITON-TIMI 38 trial, the mean exposure to Pras-AM was 42% greater in patients weighing < 60 kg than in patients with the study population median bodyweight of 85 kg. In a pharmacodynamic meta-analysis of data from healthy subjects a decrease of 1 kg in bodyweight was associated with an increase in IPA of approximately 0.26 percentage points (p < 0.0001). Pras-AM exposure was greater in subjects aged ≥ 75 years, but exposure differences were not as large as those for bodyweight. Pras-AM exposure was greater in Asians than in Caucasians, but this appeared to result from a disproportionately greater exposure difference in Asian subjects with low bodyweight. Sex and allelic variation in CYPs 1A2, 2B6, 2C19, 2C9, 3A4 and 3A5 appeared to have no clinically relevant effect on Pras-AM exposure or IPA. Consistent with the lack of association between genetic status and these pharmacokinetic and pharmacodynamic results in healthy subjects, no significant association was detected between these allelic variants and the composite primary endpoint (cardiovascular death, non-fatal myocardial infarction or non-fatal stroke) in the TRITON-TIMI 38 trial. Studies in renally impaired subjects and subjects with mild or moderate hepatic impairment have indicated that dose adjustment is not required in these patient populations. Prasugrel has few clinically significant drug-drug interactions. Potent CYP3A inhibitors, gastric acid suppressants and food have been shown to reduce the rate of formation of Pras-AM but not its overall exposure. This pharmacokinetic effect reduced the rate of onset of IPA after a loading dose but did not affect the peak IPA after a loading dose or the IPA during maintenance dosing. Potent induction of CYP3A, as well as smoking--which induces CYP1A2--did not affect Pras-AM exposure or IPA. Prior treatment with clopidogrel did not influence tolerability to prasugrel and did not appear to alter IPA during prasugrel treatment. Prasugrel did not affect the activities of CYP2C9, CYP2C19 or P-glycoprotein, but it weakly inhibited CYP2B6. The inhibition of CYP2B6 is potentially clinically significant only for drugs that have a narrow therapeutic window and have CYP2B6 as the primary elimination pathway. No interaction was detected between prasugrel and heparin. Although prasugrel did not alter warfarin pharmacokinetics, prasugrel and warfarin should not be used together, because of an increased bleeding risk associated with their concomitant use.

Preventing serious sequelae after an acute coronary syndrome: the consequences of thrombosis versus bleeding with antiplatelet therapy

Acute coronary syndrome (ACS) is associated with a persistent prothrombotic state, placing patients at high risk of subsequent ischemic events. Guidelines recommend the use of dual antiplatelet therapy with aspirin + a thienopyridine (clopidogrel) for at least a year after ACS in most patients, except those who undergo coronary artery bypass grafting. Clinical studies demonstrate that this strategy significantly reduces the risk of ischemic events at the expense of a small increase in the risk of bleeding. Physicians must balance the risk of bleeding against the benefit of ischemia prevention, bearing in mind that ischemic events are generally more common than major bleeding and often associated with more catastrophic consequences or ongoing morbidity. The relationship between bleeding and mortality is complicated by the fact that many risk factors for bleeding are also those for mortality and that bleeding may lead to discontinuation of antiplatelet therapy, thereby increasing the risk for an ischemic event. Data suggest that physicians tend to overestimate the risk of bleeding and underestimate the risk of ischemia. Careful patient selection and thorough patient education are the keys to managing antiplatelet therapy after ACS, especially as newer more potent antiplatelet agents, such as prasugrel, become available.

What is the risk of intensifying platelet inhibition beyond clopidogrel? A systematic review and a critical appraisal of the role of prasugrel

Thienopyridines are a class of drug targeting the platelet adenosine diphosphate 2 receptor. They have been shown to significantly reduce platelet activity exerting an important role in those clinical settings in which such an effect is beneficial. Ticlopidine was first to be introduced several years ago but it was quickly replaced by clopidogrel as it had a better risk/benefit profile. Recently, prasugrel has been developed and tested in several ex vivo studies and clinical trials showing able to provide a more powerful antiplatelet effect at the expense of a higher risk of bleeding complications. Great debate rose around its recent approval in the US as well as in Europe. This review aims at exploring the development and available clinical data of this third-generation thienopyridine while discussing its practical implementation in routine practice.

Prasugrel

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Inhibition of platelet aggregation with prasugrel and clopidogrel: an integrated analysis in 846 subjects

This integrated analysis compared speed of onset, level of platelet inhibition, and response variability to prasugrel and clopidogrel in healthy subjects and in patients with stable coronary artery disease with data pooled from 24 clinical pharmacology studies. Data from subjects (N = 846) were categorized into the following treatment groups: prasugrel 60 mg loading dose (LD)/10 mg maintenance dose (MD), clopidogrel 300 mg LD/75 mg MD, or clopidogrel 600 mg LD/75 mg MDs. Maximum platelet aggregation (MPA) and inhibition of platelet aggregation (IPA) to 5 and 20 muM ADP were assessed by turbidimetric aggregometry. A linear mixed-effect model compared the MPA and IPA between treatments over time points evaluated in the integrated database, and covariates affecting platelet inhibition were identified. Prasugrel 60 mg LD resulted in faster onset, greater magnitude, and more consistent levels of inhibition of platelet function compared to either clopidogrel 300 mg or 600 mg LDs. Greater and more consistent levels of platelet inhibition were observed with the prasugrel 10 mg MD compared to the clopidogrel 75 mg MD. This integrated analysis confirms the findings of earlier individual studies, that prasugrel achieves faster onset of greater extent and more consistent platelet inhibition compared to the approved and higher loading doses of clopidogrel. Gender, race, body weight, and age were identified as statistically significant covariates impacting platelet inhibition.

Prasugrel for the treatment of patients with acute coronary syndrome

Prasugrel (CS-747, LY640315) is a novel member of the thienopyridine class of oral anti-platelet agents (also including ticlopidine and clopidogrel). Like other thienopyridines, prasugrel is a prodrug that is inactive in vitro. Prasugrel’s conversion to its active metabolite is more rapid and efficient than that of other thienopyridines, with a less strict dependence on specific cytochrome P-450 enzymes. Prasugrel’s active metabolite (R-138727) binds specifically and irreversibly to the platelet P2Y12 purinergic receptor, thus inhibiting ADP-mediated platelet activation and aggregation. Preclinical data and early clinical data in healthy subjects showed greater platelet inhibition and consistency with prasugrel as opposed to clopidogrel. Clinical studies in patients with cardiovascular disease confirmed the greater efficacy of prasugrel compared with clopidogrel. Collectively, these phase 1/1b studies and a phase 2 study (JUMBO-TIMI 26) aided in dose selection for the phase 3 trial (TRITON-TIMI 38) in patients with acute coronary syndrome undergoing percutaneous coronary intervention. This trial once again confirmed the greater anti-platelet effect of prasugrel, but also highlighted a higher risk of bleeding, even fatal. Another phase 2 trial (PRINCIPLE-TIMI 44) compared prasugrel and high-dose clopidogrel in patients undergoing cardiac catheterization for planned PCI.

Efficacy and safety of prasugrel compared with clopidogrel in patients with acute coronary syndromes: results of TRITON-TIMI 38 trials

Current guidelines recommend dual antiplatelet therapy using aspirin and clopidogrel for non-ST elevation acute coronary syndromes (ACS). Despite the established benefits of this approach, many patients continue to have recurrent atherothrombotic events. Moreover, it is often difficult to achieve an adequate inhibition of platelet aggregation with clopidogrel in clinical practice. Prasugrel is an orally administered P2Y12 receptor antagonist that is more potent, more rapid in onset and more consistent in its inhibition of platelet aggregation than currently approved doses of clopidogrel. The trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition with Prasugrel - Thrombolysis in Myocardial Infarction 38 (TRITON-TIMI 38) randomized 13,608 moderate-to-high-risk patients with ACS (with or without ST-segment elevation) undergoing percutaneus coronary intervention to compare prasugrel with clopidogrel for a median of follow-up time of 14.5 months. The TRITON-TIMI 38 trial demonstrated a significant reduction in ischemic events in patients randomized to prasugrel compared with those treated with clopidogrel. This beneficial effect, however, was associated with a significant increase in major bleeding.

P2Y12 Inhibitors in Cardiovascular Disease: Focus on Prasugrel

OBJECTIVE

To review the literature describing the pharmacology, pharmacokinetic properties, efficacy, and adverse effects of prasugrel, a new thienopyridine.

DATA SOURCES

A literature search was conducted (1966–November 2008) of the MEDLINE, Current Contents, EMBASE, and International Pharmaceutical Abstract databases using the key words prasugrel, CS-747, LY640315, and P2Y12. Bibliographies of identified literature were also reviewed for additional references.

STUDY SELECTION AND DATA EXTRACTION

All reports published in English that evaluated prasugrel (or its chemical synonyms) were reviewed. Abstracts without subsequently published reports were excluded.

DATA SYNTHESIS

Given the high rate of recurrent coronary events despite current antiplatelet therapies, agents with potentially greater efficacy are under investigation. Prasugrel is a novel thienopyridine prodrug that is rapidly metabolized to its active platelet-inhibitory metabolite (R-138727) and exerts antiplatelet activity through antagonism of P2Y12 receptors. Prasugrel is very similar in structure and mechanism of action to clopidogrel, as they both possess a methoxycarbonyl group that provides increased pharmacologic activity and an improved hematologic safety profile when compared with ticlopidine. In addition, when compared with clopidogrel, prasugrel demonstrates greater potency and less interpatient variability in the inhibition of platelet aggregation, less in vitro hyporesponsiveness, and, in patients with acute coronary syndromes, a reduced rate of ischemic events. However, this reduction in ischemic events was accompanied by an increased risk of major and fatal bleeding.

CONCLUSIONS

Prasugrel appears to be a promising antiplatelet agent, with emerging clinical data in direct comparison with clopidogrel supporting its role in reducing recurrent ischemic events. Further studies are needed to evaluate the safety and efficacy of prasugrel across various patient populations and clinical scenarios.

THIS ARTICLE IS APPROVED FOR CONTINUING EDUCATION CREDIT ACPE UNIVERSAL PROGRAM NUMBER

407-000-09-001-H01-P

Prasugrel: a new antiplatelet drug for the prevention and treatment of cardiovascular disease

Prasugrel, trade name Effient, is an investigational new antiplatelet drug currently under review for clinical use by the Food and Drug Administration. It is a thienopyridine analog with a structure similar to that of clopidogrel and ticlopidine. Thienopyridine derivatives inhibit platelet aggregation induced by adenosine diphosphate by irreversibly inhibiting the binding of adenosine diphosphate to the purinergic P2Y12 receptor on the platelet surface. Prasugrel has been shown to be a potent antiplatelet agent with a faster, more consistent, and greater inhibition of platelet aggregation compared with clopidogrel. It is debatable, however, how effectively these pharmacologic benefits will translate to clinical benefits. The results of the large TRITON-TIMI 38 trial, which compared prasugrel and clopidogrel in patients with acute coronary syndrome who were scheduled to receive coronary stents, demonstrated a significant reduction in ischemic events, including stent thrombosis, with prasugrel, but with an increased risk of major bleeding. The exact role of prasugrel in the management of ischemic heart disease is still being defined, but the risk:benefit ratio will likely play a major role in directing the best place for therapy with this new agent.

Interaction of the active metabolite of prasugrel, R-138727, with cysteine 97 and cysteine 175 of the human P2Y12 receptor

BACKGROUND

The P2Y(12) receptor plays a crucial role in platelet aggregation and is the target of platelet aggregation inhibitors, including the thienopyridine compound prasugrel.

OBJECTIVE

The present study analyzed the effects of R-138727 (2-[1-[2-cyclopropyl-1-(2-fluorophenyl)-2-oxoethyl]-4-mercapto-3-piperidinylidene]acetic acid), the active metabolite of prasugrel, on recombinant wild-type and mutant human P2Y(12) receptors in order to identify the molecular site of action of R-138727.

METHODS

The function of wild-type and mutant P2Y(12) receptors stably expressed in Chinese hamster ovary cells was assessed by measuring the 2-methylthio-ADP-mediated inhibition of forskolin-stimulated cellular cAMP production.

RESULTS

In cells expressing wild-type receptors, R-138727 potently inhibited receptor function with a half-maximal concentration below 1 microm. The mode of action was irreversible. The same effect of R-138727 was observed in cells expressing Cys17Ala/Cys270Ala constructs. In contrast, in cells expressing either a Cys97Ala construct or a Cys175Ala construct, R-138727 failed to inhibit the response to the agonist. When cells expressing wild-type receptors were pretreated with the P2 receptor antagonists ATP or suramin, no effect of R-138727 was observed. Similar experiments with N-acetylcysteine 10 microm showed no interference of N-acetylcysteine with R-138727.

CONCLUSIONS

The experiments demonstrate a potent and irreversible action of R-138727 at the recombinant human P2Y(12) receptor. The data suggest that R-138727 interacts with cysteine 97 (upper portion of the predicted third transmembrane region) and cysteine 175 (second extracellular loop) of the receptor, which are likely to form a disulfide bridge in native receptors. Moreover, the data also suggest that this site of action of R-138727 is close to the ligand-binding site of the receptor.

Increased active metabolite formation explains the greater platelet inhibition with prasugrel compared to high-dose clopidogrel

Prasugrel pharmacodynamics and pharmacokinetics after a 60-mg loading dose (LD) and daily 10-mg maintenance doses (MD) were compared in a 3-way crossover study to clopidogrel 600-mg/75-mg and 300-mg/75-mg LD/MD in 41 healthy, aspirin-free subjects. Each LD was followed by 7 days of daily MD and a 14-day washout period. Inhibition of platelet aggregation (IPA) was assessed by turbidometric aggregometry (20 and 5 microM ADP). Prasugrel 60-mg achieved higher mean IPA (54%) 30 minutes post-LD than clopidogrel 300-mg (3%) or 600-mg (6%) (P < 0.001) and greater IPA by 1 hour (82%) and 2 hours (91%) than the 6-hour IPA for clopidogrel 300-mg (51%) or 600-mg (69%) (P < 0.01). During MD, IPA for prasugrel 10-mg (78%) exceeded that of clopidogrel (300-mg/75-mg, 56%; 600-mg/75-mg, 52%; P < 0.001). Active metabolite area under the concentration-time curve (AUC0-tlast) after prasugrel 60-mg (594 ng.hr/mL) was 2.2 times that after clopidogrel 600-mg. Prasugrel active metabolite AUC0-tlast was consistent with dose-proportionality from 10-mg to 60-mg, while clopidogrel active metabolite AUC0-tlast exhibited saturable absorption and/or metabolism. In conclusion, greater exposure to prasugrel's active metabolite results in faster onset, higher levels, and less variability of platelet inhibition compared with high-dose clopidogrel in healthy subjects.

Greater inhibition of platelet aggregation and reduced response variability with prasugrel versus clopidogrel: an integrated analysis

Multiple studies report response variability to a 300-mg clopidogrel loading dose (LD). Pooled platelet aggregometry data compared responses (change in maximal platelet aggregation [DeltaMPA] or inhibition of platelet aggregation [IPA]) to clopidogrel 300-mg (n = 131) or prasugrel 60-mg (n = 109) LDs. Poor responder rates were determined using empiric criteria (IPA < 10% and DeltaMPA < 10% for 20 microM and 5 microM adenosine diphosphate [ADP]) and Bayesian model-based criteria (IPA < 20% and DeltaMPA < 15% for 20 microM ADP; IPA < 25% and DeltaMPA < 20% for 5 microM ADP). Prasugrel achieved greater DeltaMPA and IPA from 2 to 24 hours post-LD (P < .001). For 20 microM ADP, poor responder rates for clopidogrel ranged from 17% to 43%; no prasugrel poor responders were observed. Regardless of the criterion, prasugrel 60 mg achieved greater IPA and fewer poor responders than the clopidogrel 300-mg LD.

The influence of P2Y12 receptor deficiency on the platelet inhibitory activities of prasugrel in a mouse model: evidence for specific inhibition of P2Y12 receptors by prasugrel

Prasugrel is a novel orally active thienopyridine with faster, higher and more reliable inhibition of platelet aggregation than clopidogrel reflecting its metabolism in vivo to an active metabolite with selective P2Y(12) antagonistic activity. Several lines of evidence support the contention that prasugrel provides selective P2Y(12) receptor antagonistic activity. To date, however, direct evidence of P2Y(12) specific action by prasugrel in vivo is limited. In the present study, effects of prasugrel on ex vivo platelet aggregation were examined in wild type (WT) and P2Y(12)(-/-) mice. In WT mice, prasugrel showed platelet inhibition that was 8.2 times more potent than clopidogrel. In P2Y(12)(-/-) mice, ADP induced platelet aggregation was minimal, and its extent was similar to that in prasugrel-treated WT mice. In addition, no further inhibition of platelet aggregation was observed after administration of prasugrel to P2Y(12)(-/-) mice. Furthermore, prasugrel-treated WT mice showed similar aggregation patterns using collagen- and murine PAR-4 agonist peptide to those of P2Y(12)(-/-) mice treated with vehicle or prasugrel. Overall, these results clearly provide additional in vivo evidence that prasugrel has selective P2Y(12) antagonistic activity.