Pharmacodynamic assessment of platelet inhibition by prasugrel vs. clopidogrel in the TRITON-TIMI 38 trial

Clinical implications of drug-drug interactions with P2Y12 receptor inhibitors

Polypharmacy in patients undergoing coronary artery stenting or in those presenting with an acute coronary syndrome is common. Nevertheless, the risk of drug-drug interactions in patients treated simultaneously with P2Y12 receptor inhibitors is less well considered in routine clinical practice. Whereas the irreversible P2Y12 receptor inhibitors clopidogrel and prasugrel are prodrugs requiring cytochrome P450 (CYP) enzymes for metabolic activation, such activation is not necessary for the direct-acting reversible P2Y12 receptor inhibitor ticagrelor. Several drugs frequently used in cardiology have been shown to interact with the metabolism of P2Y12 receptor inhibitors in pharmacodynamic studies. Whereas several drug-drug interactions have been described for clopidogrel and ticagrelor, prasugrel seems to have a low potential for drug-drug interactions. The clinical implications of these interactions have raised concern. In general, concomitant administration of P2Y12 receptor antagonists and strong inhibitors or inducers of CYP3A/CYP2C19 should be performed with caution in patients treated with clopidogrel/ticagrelor. Under most circumstances, clinicians have the option of prescribing alternative drugs with less risk of drug-drug interactions when used concomitantly with P2Y12 receptor inhibitors.

Comparison of the degree of platelet aggregation inhibition with prasugrel versus clopidogrel and clinical outcomes in patients with unprotected left main disease treated with everolimus-eluting stents

The everolimus-eluting stent (EES) performs better than the first generation drug-eluting stent. Prasugrel compared with clopidogrel in acute coronary syndromes treated invasively is associated with improved clinical outcome and decreased risk of stent thrombosis. The aim of the study was to compare the clinical outcome and degree of platelet aggregation inhibition of patients treated with EES for unprotected left main disease (ULMD) and receiving clopidogrel or prasugrel. Patients receiving an EES for ULMD and with low residual platelet reactivity on clopidogrel or prasugrel treatment were included in the analysis. The primary end point of the study was the composite of cardiac mortality and myocardial infarction at 1 year. The secondary end point was the degree of platelet aggregation inhibition as assessed by light transmittance aggregometry. From January 2009 to December 2011, 252 patients with low residual platelet reactivity on thienopyridine treatment were treated with EES for ULMD. Of these, 104 patients received clopidogrel and 148 received prasugrel. The primary end point rate was lower in the prasugrel group compared with clopidogrel group: 1.3% and 9.6%, respectively (p = 0.002). Residual platelet reactivity was less in the prasugrel group compared with clopidogrel group (adenosine diphosphate 10 μmol/L 37 ± 17% and 45 ± 15%, respectively, p <0.001). At multivariate analysis, prasugrel treatment was related to the primary end point (hazard ratio 0.17; 95% confidence interval 0.04 to 0.77, p = 0.022). In conclusion, in patients treated with EES for ULMD, prasugrel compared with clopidogrel is associated with increased platelet aggregation inhibition and a better clinical outcome.

Impact of aspirin dosing on the effects of P2Y12 inhibition in patients with acute coronary syndromes

The discovery of the antiplatelet effect of low-dose aspirin led to the hugely successful strategy of dual antiplatelet therapy in patients with acute coronary syndromes (ACS). Increasing the dose of aspirin beyond 75-100 mg has never been shown to offer additional efficacy in ACS patients but could possibly increase the risk of bleeding. In the Platelet Inhibition and Patients Outcome (PLATO) study, higher doses of aspirin appeared to neutralise the additional benefit of the potent P2Y12 inhibitor ticagrelor compared to clopidogrel (Circulation 124: 544-554, 2011). However, higher doses of aspirin have not been shown to have an adverse interaction with the potent P2Y12 inhibition provided by prasugrel and double-dose clopidogrel (Journal of the American College of Cardiology, 2013, in press; N Engl J Med 363: 930-942, 2010). This potentially suggests that the mechanism for this interaction is not related to the inhibition of platelet P2Y12 receptors or could simply be a chance finding.

Antiplatelet effect of thienopyridine (clopidogrel or prasugrel) pretreatment in patients undergoing primary percutaneous intervention for ST elevation myocardial infarction

Although previous retrospective studies have suggested the clinical benefits of clopidogrel pretreatment in patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI), the antiplatelet effect of thienopyridines during a narrow door-to-balloon time frame has not been evaluated. Seventy-nine consecutive patients with STEMI were treated with either 600 mg of clopidogrel (n = 49) or 60 mg of prasugrel (n = 30) loading on admission. All patients underwent PPCI with a door-to-balloon time of 48 ± 20 minutes. Adenosine diphosphate (ADP)-induced platelet aggregation (PA) was determined by light transmission aggregometry before thienopyridine loading, at PPCI, and after 72 hours. Baseline ADP-induced PA was comparable in clopidogrel- and prasugrel-treated patients (79 ± 10% vs 76 ± 9%, p = 0.2). Although ADP-induced PA was reduced significantly in both clopidogrel- and prasugrel-treated patients (p <0.01 for both), it was significantly lesser in prasugrel-treated patients (63 ± 18% vs 74 ± 12%, p = 0.002). Yet, <50% of the prasugrel-treated patients achieved adequate platelet inhibition (ADP-induced PA <70%) at PPCI. Prasugrel-treated patients, compared with clopidogrel-treated patients, were more likely to have Thrombolysis In Myocardial Infarction myocardial perfusion grade of ≥2 (79% vs 49%, p = 0.01), lower Thrombolysis In Myocardial Infarction frame count (10.2 ± 5.7 vs 13.6 ± 7.2, p = 0.03), and a numerically greater incidence of early ST-segment resolution >50% (26 of 30 [87%] vs 35 of 49 [71%], p = 0.1), suggesting better myocardial reperfusion. In conclusion, overall, prasugrel compared with clopidogrel pretreatment resulted in greater platelet inhibition at PPCI, but even with prasugrel, only <50% of the patients achieved early adequate platelet response.

Ticagrelor versus prasugrel in diabetic patients with an acute coronary syndrome. A pharmacodynamic randomised study

Optimal P2Y12 receptor blockade is critical to prevent ischaemic recurrence in patients undergoing percutaneous coronary intervention (PCI). We aimed to compare the level of platelet reactivity (PR) inhibition achieved by prasugrel and ticagrelor loading dose (LD) in diabetic acute coronary syndrome (ACS) patients undergoing PCI. We performed a single-center prospective open-label randomised trial. Patients with diabetes mellitus undergoing PCI for an ACS were randomised to receive prasugrel 60 mg or ticagrelor 180 mg. The primary endpoint of the study was the level of platelet reactivity (PR) assessed between 6 and 18 hours post-LD using the VASP index. We randomised 100 diabetic patients undergoing PCI for an ACS. No difference was observed in baseline characteristics between the two groups. In particular, the rate of patient receiving insulin therapy was identical (25 vs 28.6%; p =0.7). Ticagrelor achieved a significantly lower PR compared to prasugrel loading dose (17.3 ± 14.2 vs 27.7 ± 23.3%; p=0.009). In addition the rate of high on-treatment platelet reactivity, defined by a VASP ≥50%, tend to be lower in the ticagrelor group although the difference did not reach statistical significance (6 vs 16%; p=0.2). The rate of low on treatment PR was identical (60 vs 54%; p=0.8). The present study demonstrates that ticagrelor LD is superior to prasugrel LD to reduce PR in ACS patients with diabetes mellitus. Whether the higher potency of ticagrelor could translate into a clinical benefit should be investigated.

Effect on Platelet Reactivity From a Prasugrel Loading Dose After a Clopidogrel Loading Dose Compared With a Prasugrel Loading Dose Alone

Background—

Adding a prasugrel loading dose (LD) to a clopidogrel LD could be desirable because clopidogrel may fail to provide adequate levels of platelet inhibition in patients with acute coronary syndrome undergoing percutaneous coronary intervention.

Methods and Results—

The pharmacodynamic response of prasugrel 60 mg LD alone was compared with prasugrel 60 mg or 30 mg added ≤24 hours to clopidogrel 600 mg in Transferring from Clopidogrel Loading Dose to Prasugrel Loading Dose in Acute Coronary Syndrome Patients study—a multicenter, randomized, double-blind, double-dummy, 3-arm, parallel, active-comparator controlled study. Two hundred eighty-two patients were randomized to 3 LD strategies: placebo plus prasugrel 60 mg, clopidogrel 600 mg plus prasugrel 60 mg, or clopidogrel 600 mg plus prasugrel 30 mg. Platelet function was assessed using VerifyNow P2Y12 Reaction Units (PRU) immediately before prasugrel LD, and 2, 6, 24, and 72 hours after prasugrel LD in 149 patients with evaluable platelet function studies. At 6 hours after the prasugrel 60 mg LD, the least squares mean (95% confidence interval) difference between placebo/prasugrel 60 mg and clopidogrel 600 mg/prasugrel 60 mg (primary outcome) was 22.2 (−11.0 to 55.5; P =0.19; least squares mean PRU 57.9 versus 35.6, respectively). For clopidogrel 600 mg/prasugrel 30 mg (least squares mean PRU, 53.9), the difference was 3.9 (−28.2 to 36.1; P =0.81) versus placebo/prasugrel 60 mg. No significant differences in PRU were observed at any time point across the 3 groups. There were few bleeding events observed regardless of treatment.

Conclusions—

Platelet reactivity with prasugrel 60 mg LD added to clopidogrel 600 mg LD was not significantly different compared with prasugrel 60 mg LD alone in acute coronary syndrome patients undergoing percutaneous coronary intervention.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01115738.

Consensus and update on the definition of on-treatment platelet reactivity to adenosine diphosphate associated with ischemia and bleeding

Dual antiplatelet therapy with aspirin and a P2Y12 receptor blocker is a key strategy to reduce platelet reactivity and to prevent thrombotic events in patients treated with percutaneous coronary intervention. In an earlier consensus document, we proposed cutoff values for high on-treatment platelet reactivity to adenosine diphosphate (ADP) associated with post-percutaneous coronary intervention ischemic events for various platelet function tests (PFTs). Updated American and European practice guidelines have issued a Class IIb recommendation for PFT to facilitate the choice of P2Y12 receptor inhibitor in selected high-risk patients treated with percutaneous coronary intervention, although routine testing is not recommended (Class III). Accumulated data from large studies underscore the importance of high on-treatment platelet reactivity to ADP as a prognostic risk factor. Recent prospective randomized trials of PFT did not demonstrate clinical benefit, thus questioning whether treatment modification based on the results of current PFT platforms can actually influence outcomes. However, there are major limitations associated with these randomized trials. In addition, recent data suggest that low on-treatment platelet reactivity to ADP is associated with a higher risk of bleeding. Therefore, a therapeutic window concept has been proposed for P2Y12 inhibitor therapy. In this updated consensus document, we review the available evidence addressing the relation of platelet reactivity to thrombotic and bleeding events. In addition, we propose cutoff values for high and low on-treatment platelet reactivity to ADP that might be used in future investigations of personalized antiplatelet therapy.

Assessing post-treatment platelet reactivity: a focus on patient selection and setting

Dual antiplatelet therapy is critical to inhibit platelet reactivity in order to prevent ischemic recurrences in stented patients. However, studies have observed a variable blockade of the P2Y12 adenosine diphosphate receptor between patients following clopidogrel intake. This interindividual variability in the biological response is not uncommon with clopidogrel (about 50%) and even prasugrel (20%). High on-treatment platelet reactivity (HTPR) is correlated with thrombotic events following percutaneous coronary intervention. Several studies suggested that tailoring of antiplatelet therapy based on platelet reactivity (PR) monitoring could safely reduce the rate of major adverse cardiovascular events in HTPR patients. In addition, low on-treatment PR was recently associated with bleeding events both in patients treated with prasugrel and clopidogrel. Of importance, bleedings are associated with a poor prognosis in stented patients. Overall, the potential of PR monitoring to individualize antiplatelet therapy might benefit stented patients by reducing both ischemic and bleeding risks. However, such strategies remain to be evaluated in adequately designed large-scale randomized clinical trials.

Clinical and laboratory significance of defective P2Y(12) pathway function in patients with myeloproliferative neoplasms: a pilot study

BACKGROUND

Patients with myeloproliferative neoplasms (MPN) have an increased risk for thrombosis and bleeding and show a defect in adenosine diphosphate (ADP)-induced platelet aggregation. This risk of thrombosis is further increased in MPN patients bearing the JAK2V617F mutation. Two ADP receptors, P2Y1 and P2Y12, are present on platelets. Although the pattern of defective ADP-induced platelet aggregation in MPN suggests an abnormality in the P2Y12 pathway, no previous studies have specifically evaluated P2Y12 function in MPN or the relationship between P2Y12 function and the JAK2V617F mutation.

METHODS

Forty-one MPN patients were enrolled, including 24 with essential thrombocythemia (ET), 16 with polycythemia vera (PV) and 1 with primary myelofibrosis. Platelet P2Y12 function in MPN was evaluated by flow-cytometric measurement of the phosphorylation of vasodilator-stimulated phosphoprotein (VASP). Clinical data were collected by review of medical records. JAK2V617F mutation was detected by allele-specific polymerase chain reaction. JAK2V617F allele burden was measured by the pyrosequencing method.

RESULTS

In patients with MPN, platelet P2Y12 function determined by VASP platelet reactivity index (PRI) was inversely correlated with platelet and white blood cell (WBC) counts. In subgroup analysis, PRI was inversely correlated with platelet and WBC counts in PV. PRI was also inversely correlated with platelet counts in ET, but the correlation of PRI and WBC counts did not reach statistical significance. Eight of the 41 patients had a history of thrombosis and only 2 had a bleeding history. Neither thrombosis nor bleeding patients were found to have significantly different PRIs. JAK2V617F mutation data were available in 35 cases. PRI was not different between JAK2V617F mutation and wild-type patients but PRI had a trend towards an inverse correlation with JAK2V617F allele burden for patients with mutations.

CONCLUSIONS

The present study provides the first explicit demonstration of a defect in the P2Y12 pathway in platelets of patients with MPN. Furthermore, platelet P2Y12 function, assayed by VASP, is inversely correlated with platelet and WBC counts in patients with MPN. Platelet P2Y12 function also appears to be inversely correlated with JAK2V617F allele burden. This compromised P2Y12 function may be a novel mechanism for the bleeding tendency associated with extreme thrombocytosis in MPN.

Effect of CYP2C19*2 and *17 genetic variants on platelet response to clopidogrel and prasugrel maintenance dose and relation to bleeding complications

The present study was performed to compare the influence of cytochrome P459 2C19 (CYP2C19) *2 and *17 genetic variants on the platelet response to clopidogrel and prasugrel maintenance therapy and to assess the relation between platelet reactivity and bleeding complications. A total of 730 patients were included (517 patients treated with clopidogrel 150 mg/day and 213 discharged with prasugrel 10 mg). Platelet reactivity was assessed at 1 month with the platelet reactivity index vasodilator-stimulated phosphoprotein (PRI VASP). High on-treatment platelet reactivity was defined as PRI VASP >50% and low on-treatment platelet reactivity (LTPR) as PRI VASP <20%. The patients were classified according to their genotypes as poor metabolizers (*2/non *17), intermediate metabolizers (*2/*17 or non *2/non *17) and ultrametabolizers (non *2/*17). At 1 month, the prasugrel response was significantly better than the clopidogrel response in all groups of patients, with a lower incidence of high on-treatment platelet reactivity but a greater incidence of LTPR, regardless of the genetic variants. The genetic distribution had a significant effect on the mean PRI VASP values, the incidence of high on-treatment platelet reactivity, and LTPR with both clopidogrel and prasugrel (p <0.05 for all). LTPR identified a group of patients at a greater risk of bleeding (odds ratio 4.8, 95% confidence interval 2.7 to 8.3; p <0.0001). In conclusion, the present study showed that both clopidogrel and prasugrel have genetic modulation by CYP2C19 *2 and *17 alleles and that prasugrel provides greater platelet inhibition, regardless of the genotypes. In addition, LTPR was associated with a greater risk of bleeding.

Comparison of prasugrel and ticagrelor loading doses in ST-segment elevation myocardial infarction patients: RAPID (Rapid Activity of Platelet Inhibitor Drugs) primary PCI study

OBJECTIVES

This study sought to compare the action of prasugrel and ticagrelor in ST-segment elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PPCI).

BACKGROUND

It has been documented that prasugrel and ticagrelor are able to provide effective platelet inhibition 2 h after a loading dose (LD). However, the pharmacodynamic measurements after prasugrel and ticagrelor LD have been provided by assessing only healthy volunteers or subjects with stable coronary artery disease.

METHODS

Fifty patients with STEMI undergoing PPCI with bivalirudin monotherapy were randomized to receive 60 mg prasugrel LD (n = 25) or 180 mg ticagrelor LD (n = 25). Residual platelet reactivity was assessed by VerifyNow at baseline and 2, 4, 8, and 12 h after LD.

RESULTS

Platelet reactivity units (PRU) 2 h after the LD (study primary endpoint) were 217 (12 to 279) and 275 (88 to 305) in the prasugrel and ticagrelor groups, respectively (p = NS), satisfying pre-specified noninferiority criteria. High residual platelet reactivity (HRPR) (PRU ≥240) was found in 44% and 60% of patients (p = 0.258) at 2 h. The mean time to achieve a PRU <240 was 3 ± 2 h and 5 ± 4 h in the prasugrel and ticagrelor groups, respectively. The independent predictors of HRPR at 2 h were morphine use (odds ratio: 5.29; 95% confidence interval: 1.44 to 19.49; p = 0.012) and baseline PRU value (odds ratio: 1.014; 95% confidence interval: 1.00 to 1.03; p = 0.046).

CONCLUSIONS

In patients with STEMI, prasugrel showed to be noninferior as compared with ticagrelor in terms of residual platelet reactivity 2 h after the LD. The 2 drugs provide an effective platelet inhibition 2 h after the LD in only a half of patients, and at least 4 h are required to achieve an effective platelet inhibition in the majority of patients. Morphine use is associated with a delayed activity of these agents. (Rapid Activity of Platelet Inhibitor Drugs Study, NCT01510171).

Prasugrel monitoring and bleeding in real world patients

The aim of this study was to evaluate platelet reactivity and 30-day bleeding events in patients treated with prasugrel 10 mg after acute coronary syndromes. A total of 444 patients with acute coronary syndromes treated with percutaneous coronary intervention and prasugrel 10 mg/day were monitored by measurement of the vasodilator-stimulated phosphoprotein (VASP) index 2 to 4 weeks after hospital discharge. Platelet reactivity was also assessed using the VerifyNow P2Y(12) assay and light transmission aggregometry. Bleeding events (per the Bleeding Academic Research Consortium [BARC] definition) and ischemic events (death, myocardial infarction, and definite stent thrombosis) were collected over 30 days of follow-up. Two thirds of the patients presented with ST-segment elevation myocardial infarctions, 28.8% had diabetes, and 12.4% were aged >75 years. High on-treatment platelet reactivity according to 3 prespecified definitions (VASP index ≥ 50%, platelet reactivity ≥ 235 P2Y(12) reaction units, and residual platelet reactivity ≥ 46.2%) was found in 6.8%, 3.4%, and 3.2% of patients, respectively. Obesity (body mass index >30 kg/m(2)) and multivessel disease were the only independent factors associated with high on-treatment platelet reactivity (p = 0.006 and p = 0.045, respectively). At 30 days, there was no major bleeding complication (BARC grade 3 or 5), and 1.6% of patients had recurrent ischemic events. Nuisance bleeding (BARC grade 1) and minor bleeding (BARC grade 2) occurred in 14.2% (n = 63) and 2.5% (n = 11) of patients, respectively, but were not predicted by VASP index. In conclusion, patients with acute coronary syndromes receiving maintenance doses of prasugrel have low rates of HPR and ischemic events within the first month. Minor or minimal bleeding is frequent, but not major bleeding. VASP was poorly correlated with the risk for minor or minimal bleeding.

Pharmacotherapeutic Considerations for the Use of Prasugrel and Ticagrelor to Reduce Stent Thrombosis in Patients With Acute Coronary Syndrome

Despite the improvement in stent technology, stent thrombosis (ST), a potentially catastrophic event, still occurs. Among several risk factors for ST, high on-treatment platelet reactivity to clopidogrel has been demonstrated to play a role, occurring in about one-third of the patients. In order to overcome this limitation, prasugrel and ticagrelor, newer P2Y12 inhibitors, have been developed and approved for clinical use. Two large clinical trials, TRial to assess Improvement in Therapeutic Outcomes by optimizing platelet inhibitioN with prasugrel-thrombolysis in myocardial infarction (TRITON-TIMI) 38 and Study of Platelet Inhibition and Patient Outcomes (PLATO), evaluated these drugs in patients with acute coronary syndrome (ACS), showing a significant improvement in efficacy end points (including a prominent reduction in ST occurrence) compared to clopidogrel. In contrast, the TRILOGY ACS trial found no benefit with prasugrel compared to clopidogrel in patients with medically treated ACS. The aim of this review is to consider decision-making strategies between prasugrel and ticagrelor in daily clinical practice.

Randomized Assessment of Ticagrelor Versus Prasugrel Antiplatelet Effects in Patients with ST-Segment–Elevation Myocardial Infarction

Background—

Ticagrelor and prasugrel provide stronger platelet inhibition compared with clopidogrel. Direct pharmacodynamic comparison between them has not yet been reported in ST-segment–elevation myocardial infarction patients.

Methods and Results—

In a prospective, single-center, single-blind study, 55 out of 117 (47%) screened consecutive ST-segment–elevation myocardial infarction patients undergoing primary percutaneous coronary intervention were randomized to either ticagrelor 180 mg loading followed by 90 mg bid, or prasugrel 60 mg loading followed by 10 mg od for 5 days. Platelet reactivity (PR) was assessed with the VerifyNow P2Y12 function assay and the Multiplate Analyzer at 0, 1, 2, 6, 24 hours, and 5 days postrandomization. The primary end point, PR with VerifyNow at hour 1, did not differ significantly between patients randomized to ticagrelor versus prasugrel (257.3 P2Y12 reaction unit [PRU], 95% CI 230.8–283.8 versus 231.3 PRU, 95% CI 205.3–257.4; P =0.2). PR did not differ at 2, 6, and 24 hours, although at day 5 it was lower with ticagrelor than prasugrel (25.6 PRU, 95% CI 12.3–38.9 versus 50.3 PRU, 95% CI 36.4–64.1; P =0.01). At hour 2, high on-treatment PR rates (cutoff 208 PRU) were 46.2% and 34.6% for ticagrelor and prasugrel, respectively, decreased significantly thereafter, whereas did not differ significantly between the 2 agents at all the time points of the study.

Conclusions—

In patients with ST-segment–elevation myocardial infarction undergoing primary percutaneous coronary intervention, both ticagrelor and prasugrel exhibit an initial delay in the onset of their antiplatelet action. Ticagrelor did not appear superior to prasugrel in reducing PR during the first 24 hours of ST-segment–elevation myocardial infarction.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01463163.

Platelet reactivity in diabetic patients undergoing coronary stenting for acute coronary syndrome treated with clopidogrel loading dose followed by prasugrel maintenance therapy

BACKGROUND

Diabetes has been identified as a risk factor for impaired clopidogrel response, and these patients might have greater benefit with new P2Y12 blockers such as prasugrel. The present study was designed to assess response to thienopyridine in diabetic patients undergoing PCI for ACS.

METHODS AND RESULTS

107 diabetic patients undergoing PCI for ACS were included and treated by clopidogrel 600 mg loading dose and switched to prasugrel 10mg daily after PCI. Platelet reactivity was assessed by PRI VASP. High-on-treatment platelet reactivity (HTPR) was defined by PRI VASP>50% and Low-on-treatment platelet reactivity (LTPR) as PRI VASP below the 75th percentile (PRI VASP<20%). After clopidogrel, mean PRI VASP was 47 ± 21% and 54 patients (50%) were non responders. At one month, mean PRI VASP on prasugrel 10mg daily was 31 ± 13%, 9 patients (8%) had HTPR and 23 patients (22%) had LTPR. In multivariate analysis, factors associated with platelet reactivity were waist circumference for HTPR on clopidogrel and body weight for HTPR and LTPR on prasugrel. 10 patients (9%) suffered from BARC bleeding complications. Patients with bleeding complications had significantly lower PRI VASP values: 22 ± 9 vs. 32 ± 13, p=0.02 and ROC curves identified a cut-off value of VASP=28% to predict bleeding complications.

CONCLUSION

The present study confirmed that many diabetic patients treated with clopidogrel for ACS have inadequate platelet inhibition. Switch to prasugrel is effective with acceptable safety in this specific population. We observed a significant relationship between on-treatment platelet reactivity and bleeding complications.

Relationship between post-treatment platelet reactivity and ischemic and bleeding events at 1-year follow-up in patients receiving prasugrel

BACKGROUND

Post-treatment platelet reactivity (PR) is associated with ischemic and bleeding events in patients receiving P2Y12 receptor antagonists.

OBJECTIVES

We aimed to study the relationship between post-treatment PR after a 60-mg loading dose (LD) of prasugrel and 1-year thrombotic and bleeding events.

METHOD

Patients were prospectively included in this multicenter study if they had a successful percutaneous coronary intervention (PCI) for acute coronary syndrome (ACS) and received prasugrel. The platelet reactivity index (PRI) was measured using the Vasodilator-Stimulated Phosphoprotein index (VASP) after a prasugrel LD. Endpoints included the rate of thrombotic events and bleeding events at 1 year.

RESULTS

Among the 301 patients enrolled, 9 (3%) were lost to follow-up at 1 year. The rates of thrombotic and bleeding events at 1 year were of 7.5% and 6.8%, respectively. Receiver-operating curve (ROC) analysis demonstrated an optimal cut-off value of 53.5% of PRI to predict thrombotic events at 1 year. Using this cut-off value we observed that patients exhibiting high on-treatment platelet reactivity (HTPR) had a higher rate of thrombotic events (22.4% vs. 2.9%; P < 0.001). In parallel the optimal cut-off value of PRI to predict bleeding was 16%. Patients with a PRI ≤ 16% had a higher rate of bleeding events compared with those with a PRI > 16% (15.6% vs. 3.3%; P < 0.001). In multivariate analysis, the PRI predicted both thrombotic and bleeding events (OR: 1.44, 95% confidence interval [CI]: 1.2-1.72; P < 0.001 and OR: 0.75, 95% CI: 0.59-0.96; P = 0.024 [respectively, per 10% increase]).

CONCLUSION

Platelet reactivity measurement after a prasugrel LD predicts both ischemic and bleeding events at 1 year follow-up for ACS patients undergoing PCI.

Antiplatelet therapy for patients with diabetes mellitus and acute coronary syndrome

In diabetes mellitus, platelet hyperreactivity is common and may contribute to the high incidence of cardiovascular disease; dual antiplatelet therapy reduces the risk of recurrence. Prasugrel or ticagrelor provides a greater, more consistent antiplatelet effect than clopidogrel. Prasugrel provides greater clinical benefit than clopidogrel in patients with diabetes (hazard ratio [HR], 0.70; P<0.001) versus those without diabetes (HR, 0.86; P=0.02), due to greater reductions in cardiovascular events and no increased major bleeding. Similar clinical benefits are seen with ticagrelor versus clopidogrel in patients with and without diabetes. Evidence suggests that prasugrel/aspirin may provide particular advantages for patients with diabetes mellitus.

Stability-Indicating LC Method for the Determination of Prasugrel Hydrochloride in Pharmaceutical Dosage Form

A simple, rapid and precise method was developed for the quantitative estimation of prasugrel hydrochloride in pharmaceutical dosage form. A chromatographic separation of prasugrel and its degradants was achieved with Zorbax XDB C₈, 150 × 4.6 mm, 3.5μm analytical column using aqueous solution of 0.05 M ammonium acetate pH 4.5 with acetic acid-acetonitrile (40:60 v/v). The instrumental settings include flow rate of 1.0 ml/min, column temperature at 30°C and detector wavelength of 254 nm using a photodiode array detector. Theoretical plates for prasugrel were 7023. Tailing factor for prasugrel was 1.11. Prasugrel was exposed to thermal, photolytic, hydrolytic and oxidative stress conditions, and the stressed samples were analyzed by the proposed method. Peak homogeneity data of prasugrel was obtained using photodiode array detector in the stressed sample chromatograms, which demonstrated the specificity of the method for the estimation in presence of degradants. The described method showed excellent linearity over a range of 10–300 μg/ml for prasugrel. The correlation coefficient is 0.999. The relative standard deviation of peak area for six measurements is always less than 2%. Overall, the proposed method was found to be suitable and accurate for quantitative determination and stability study of prasugrel in pharmaceutical dosage form.

Stent thrombosis in a clopidogrel nonresponder

Stent thrombosis is a known complication of percutaneous coronary intervention (PCI) following coronary stent deployment. Dual antiplatelet therapy is standard of care following PCI, however, recent studies demonstrate marked variability in platelet response to clopidogrel. This case study explores the management of a clopidogrel nonresponder who presented with recurrent stent thrombosis despite traditional pharmacologic management.

Prasugrel versus tirofiban bolus with or without short post-bolus infusion with or without concomitant prasugrel administration in patients with myocardial infarction undergoing coronary stenting: the FABOLUS PRO (Facilitation through Aggrastat By drOpping or shortening Infusion Line in patients with ST-segment elevation myocardial infarction compared to or on top of PRasugrel given at loading dOse) trial

OBJECTIVES

The authors sought to compare the effect on inhibition of platelet aggregation (IPA) of prasugrel therapy versus tirofiban bolus with or without a post-bolus short drug infusion in ST-segment elevation myocardial infarction (STEMI) patients.

BACKGROUND

The degree and rapidity of IPA after prasugrel alone with or without concomitant glycoprotein IIb/IIIa inhibition in STEMI patients is unknown.

METHODS

A total of 100 STEMI patients randomly received prasugrel 60 mg versus 25 μg/kg tirofiban bolus with or without post-bolus 2-h infusion of tirofiban, with or without concomitant prasugrel. IPA at light transmission aggregometry was performed throughout 24 h. The primary endpoint was IPA stimulated with 20 μmol/l adenosine diphosphate (ADP) at 30 min.

RESULTS

At 30 min, patients in the prasugrel group showed a significantly lower IPA to 20 μmol/l ADP stimulation as compared with tirofiban-treated patients (36 ± 35 vs. 87 ± 31, p < 0.0001). Similarly, patients taking prasugrel showed a suboptimal degree of platelet inhibition for at least 2 h compared with tirofiban patients. Post-bolus tirofiban infusion was necessary to maintain a high level of IPA beyond 1 h after bolus administration if concomitant clopidogrel was given, whereas the bolus-only tirofiban and concomitant prasugrel led to the higher and more consistent IPA levels after both ADP and thrombin receptor-activating peptide stimuli than either therapy alone.

CONCLUSIONS

Our study shows that prasugrel administration leads to a suboptimal IPA for at least 2 h in STEMI patients. Yet, prasugrel, given in association with a bolus only of glycoprotein IIb/IIIa inhibitor, obviates the need of post-bolus infusion and almost completely abolishes residual variability of IPA after treatment. (Facilitation through Aggrastat By drOpping or shortening Infusion Line in patients with ST-segment elevation myocardial infarction compared to or on top of PRasugrel given at loading dOse [The FABOLUS PRO trial]; NCT01336348).

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.

Atopaxar: a review of its mechanism of action and role in patients with coronary artery disease

Platelet activation and aggregation is a complex and key process in thrombus formation after the rupture of an atherosclerotic plaque, which can lead to an acute coronary syndrome. Aspirin, an irreversible inhibitor of thromboxane A2 synthesis, in combination with an inhibitor of P2Y12 ADP platelet receptors (clopidogrel, prasugrel or ticagrelor), represents the current standard of care of antiplatelet therapy for patients with acute coronary syndrome and in those patients undergoing percutaneous coronary intervention. Despite the benefit of these agents, the risk of thrombotic events and bleeding complications may still occur while on such antiplatelet treatment regimens, thus representing an important limitation. Thrombin is one of the most important platelet activators. The inhibition of thrombin-mediated platelet activation by means of protease-activated receptor-1 inhibitors represents an attractive therapeutic option for patients with atherothrombotic disease processes. This article provides an overview on atopaxar (E5555), an orally active protease-activated receptor-1 antagonist that has recently completed Phase II clinical investigation.

Management of acute coronary syndrome: achievements and goals still to pursue. Novel developments in diagnosis and treatment

Acute coronary syndromes contribute a substantial part of the global disease burden. To realize a reduction in mortality and morbidity, the management of patients with these conditions involves the integration of several different approaches. Timely delivery of appropriate care is a key factor, as the beneficial effect of reperfusion is greatest when performed as soon as possible. Innovations in antithrombotic therapy have also contributed significantly to improvements in the prevention of ischaemic complications. However, with the use of such treatment, an increase in the risk of bleeding is inevitable. Therefore, the greatest challenge is now to obtain an optimal balance between the prevention of ischaemic complications and the risk of bleeding. In this regard, identification of patients at highest risk of either one is essential.

Off-Target Platelet Activation in Macaques Unique to a Therapeutic Monoclonal Antibody

AMG X, a human neutralizing monoclonal antibody (mAb) against a soluble human protein, caused thrombocytopenia, platelet activation, reduced mean arterial pressure, and transient loss of consciousness in cynomolgus monkeys after first intravenous administration. In vitro, AMG X induced activation in platelets from macaque species but not from humans or baboons. Other similar mAbs against the same pharmacological target failed to induce these in vivo and in vitro effects. In addition, the target protein was known to not be expressed on platelets, suggesting that platelet activation occurred through an off-target mechanism. AMG X bound directly to cynomolgus platelets and required both the Fab and Fc portion of the mAb for platelet activation. Binding to platelets was inhibited by preincubation of AMG X with its pharmacological target or with anti-human Fc antibodies or by preincubation of platelets with AMG X F(ab′)2 or human immunoglobulin (IVIG). AMG X F(ab′)2 did not activate platelets. Thus, platelet activation required both recognition/binding of a platelet ligand with the Fab domain and interaction of platelet Fc receptors (i.e., FcγRIIa) with the Fc domain. These findings reflect the complexity of the mechanism of action of mAbs and the increasing awareness of potential for unintended effects in preclinical species.

Phenotyping vs. genotyping for prediction of clopidogrel efficacy and safety: the PEGASUS-PCI study

BACKGROUND

Prognostic values of genotyping and phenotyping for assessment of clopidogrel responsiveness have been shown in independent studies.

OBJECTIVES

To compare different assays for prediction of events during long-term follow-up.

METHODS

In this prospective cohort study polymorphisms of CYP2C19*2 and CYP2C19*17 alleles, vasodilator-stimulated phosphoprotein phosphorylation (VASP) assay, multiple electrode aggregometry (MEA), cone and platelet analyser (CPA) and platelet function analyser (PFA-100) were performed in 416 patients undergoing percutaneous coronary intervention. The rates of events were recorded during a 12-month follow-up.

RESULTS

Platelet aggregation by MEA predicted stent thrombosis (2.4%) better (c-index = 0.90; P < 0.001; sensitivity = 90%; specificity = 83%) than the VASP assay, CPA or PFA-100 (c-index < 0.70; P > 0.05; sensitivity < 70%; specificity < 70% for all) or even the CYP2C19*2 polymorphism (c-index < 0.56; P > 0.05; sensitivity = 30%; specificity = 71%). Survival analysis indicated that patients classified as poor responders by MEA had a substantially higher risk of developing stent thrombosis or MACE than clopidogrel responders (12.5% vs. 0.3%, P < 0.001, and 18.5% vs. 11.3%, P = 0.022, respectively), whereas poor metabolizers (CYP2C19*1/*2 or *2/*2 carriers) were not at increased risks (stent thrombosis, 2.7% vs. 2.5%, P > 0.05; MACE, 13.5% vs. 12.1%, P = 0.556). The incidence of major bleedings (2.6%) was numerically higher in patients with an enhanced vs. poor response to clopidogrel assessed by MEA (4% vs. 0%) or in ultra-metabolizers vs. regular metabolizers (CYP2C19*17/*17 vs. CYP2C19*1/*1; 9.5% vs. 2%). The classification tree analysis demonstrated that acute coronary syndrome at hospitalization and diabetes mellitus were the best discriminators for clopidogrel responder status.

CONCLUSIONS

 Phenotyping of platelet response to clopidogrel was a better predictor of stent thrombosis than genotyping.

Response variability to clopidogrel: is tailored treatment, based on laboratory testing, the right solution?

Clopidogrel is an antithrombotic prodrug, whose active metabolite inhibits platelet function by irreversibly binding to the platelet receptor for adenosine diphosphate, P2Y(12). Wide inter-individual variability of response to clopidogrel has been reported in several studies: a significant proportion of treated patients (about one-third) exhibit a suboptimal inhibition of platelet function. Genetic and environmental factors that influence the absorption and/or the extent of metabolism of clopidogrel to its active metabolite account for the observed variability of response. Tailored treatment based on the results of laboratory tests of platelet function has been proposed as a solution to this problem, which has important clinical implications. Although it is often considered a desirable evolution of modern medicine, tailored treatment based on laboratory tests is actually an old remedy (of yet unproven efficacy, in the case of antiplatelet therapy) for the problem of response variability to antithrombotic drugs with unpredictable bioavailability. When possible, the use of alternative drugs with more uniform and predictable bioavailability, and with favourable profiles in terms of risk/benefit and cost-benefit ratios should be preferred. Moreover, tailored treatment with laboratory tests must be validated in randomized clinical trials before its implementation can be recommended. We still need to identify and standardize the laboratory test for this purpose, as well as answer basic questions on its clinical utility and cost-effectiveness, before tailoring clopidogrel therapy based on laboratory tests can be recommended in clinical practise.

Evolving role of platelet function testing in coronary artery interventions

The substantial reduction in ischemic events provided by the dual antiplatelet regimen with aspirin and clopidogrel is well documented in patients with acute coronary syndrome and patients undergoing percutaneous coronary intervention. Recently the variable response to the antiplatelet agents has received considerable attention after several “boxed warnings” on clopidogrel. This led to intense controversy on pharmacokinetic, pharmacodynamic, and pharmacogenomic issues of antiplatelet drugs, especially clopidogrel. Research use of platelet function testing has been successfully validated in identifying new antiplatelet drugs like prasugrel and ticagrelor. These platelet function assays are no longer regarded just as a laboratory phenomenon but rather as tools that have been shown to predict mortality in several clinical trials. It is believed that suboptimal response to an antiplatelet regimen (pharmacodynamic effect) may be associated with cardiovascular, cerebrovascular, and peripheral arterial events. There has been intense controversy about this variable response of antiplatelet drugs and the role of platelet function testing to guide antiplatelet therapy. While the importance of routine platelet function testing may be uncertain, it may be useful in high-risk patients such as those with diabetes mellitus, diffuse three vessels coronary artery disease, left main stenosis, diffuse atherosclerotic disease, and those with chronic renal failure undergoing percutaneous coronary intervention. It could also be useful in patients with suspected pharmacodynamic interaction with other drugs to assure the adequacy of platelet inhibition. While we wait for definitive trials, a predictive prognostic algorithm is necessary to individualize antiplatelet therapy with P2Y12 inhibitors based on platelet function assays and genetic testing.