Viewpoint: Paradoxical excess mortality in the PLATO trial should be independently verified

The PLATO trial revealed excess all-cause (4.5%) and vascular (4.0%) mortality after experimental pyrimidine, ticagrelor, and even higher death rates (5.9% and 5.1%, respectively) after clopidogrel, which have never been seen in any previous acute coronary syndrome (ACS) trial. The Food and Drug Administration (FDA) conducted, and recently released the ticagrelor review outlining some paradoxical mortality patterns in PLATO, including the existence of alive patient, who initially was reported dead. The drug was recently approved in Europe, but repeatedly delayed in the USA. The objective of this viewpoint article was to evaluate extremely high death rates in PLATO by scrutinising FDA-released evidence, and comparing mortality patterns in recent ACS trials. These data were first presented as the analytical report submitted to the FDA on October 26, 2010. The available evidence suggest that mortality rates in PLATO, so as death benefit of ticagrelor over clopidogrel are extreme, despite incomplete follow-up, short duration of the trial, frequent preloading with clopidogrel, and gross mismatch between conventional average myocardial infarction rates but disproportionally frequent vascular fatalities, and heavily imbalanced sepsis-related deaths. In contrast to the overall PLATO results, the deaths rates in the USA were much lower (3.2% vs. 3.8%) not only favouring clopidogrel, but more importanly matching very well with identical rates in TRITON (3.2%), and one-year ACUITY (3.6%-3.9%) fatalities. Since the «play of chance» cannot explain these discrepancies due to excess death rates in both PLATO arms, and considering that study sponsor self-monitored sites in most countries, but not in the USA, the mortality data are questionable, and should be independently virified. It was concluded that excess mortality rates and delayed timing of the benefit onset in PLATO do not match with any recent ACS trial, and do not look natural. Reevaluation of the survival, especially driven from the several high-volume sponsor monitored sites in Eastern Europe may reveal discrepancies between those reported in PLATO and actual vital records. Future practice of self monitoring in pivotal indication-seeking clinical trials should be completely banned.

Effects of ticagrelor on neointimal hyperplasia and endothelial function, compared with clopidogrel and prasugrel, in a porcine coronary stent restenosis model

BACKGROUND

Several investigations have been conducted to evaluate the off-target effects of ticagrelor. The aim of the present study was to evaluate the off-target effects of ticagrelor such as neointimal formation and endothelial function after drug-eluting stent implantation in a porcine restenosis model.

METHODS

A total of 30 pigs were randomly allocated based on the following P2Y₁₂ inhibitor: (1) clopidogrel 300mg loading plus 75mg maintenance (n=10); (2) prasugrel 60mg loading plus 10mg maintenance (n=10); (3) ticagrelor 180mg loading plus 180mg maintenance (n=10). In each group, zotarolimus-eluting stents were implanted in the proximal portion of the left anterior descending artery and left circumflex artery. One month after stenting, the animals underwent follow-up angiography, endothelial function assessment, optical coherence tomography (OCT) and histopathological analysis.

RESULTS

Regarding vasomotor responses to acetylcholine infusion, there were significant vasoconstrictions to maximal acetylcholine infusion in the clopidogrel and prasugrel group compared with those in the ticagrelor group. The mean neointimal area were significantly lower in the ticagrelor group (1.0±0.3 by OCT, 0.9±0.3 by histology), than in the clopidogrel (1.8±0.7, p=0.003, 1.6±0.8, p=0.030) and prasugrel (1.8±0.5, p=0.001, 1.5±0.5, p=0.019) groups. Percentages of moderate to dense peri-strut inflammatory cell infiltration were significantly lower in the ticagrelor group (9.0%) compared with the clopidogrel (17.3%, p<0.001) and prasugrel groups (15.7%, p=0.002). There were no significant differences in all findings between clopidogrel and prasugrel groups.

CONCLUSIONS

Compared to clopidogrel and prasugrel, ticagrelor reduced neointimal formation, endothelial dysfunction, and peri-strut inflammation.

Similar Impact of Clopidogrel or Ticagrelor on Carotid Atherosclerotic Plaque Inflammation

BACKGROUND

Platelets play an important role in inflammation. Inhibitors of the P2Y₁₂ receptor, which is involved in platelet activation, may have a direct effect on carotid atherosclerotic plaque inflammation.

HYPOTHESIS

We compared the effects of clopidogrel and ticagrelor therapy for carotid atherosclerotic plaque inflammation using ¹⁸ F-fluorodeoxyglucose ( ¹⁸ FDG) positron emission tomography (PET) imaging.

METHODS

Fifty patients with acute coronary syndrome and ≥1 ¹⁸ FDG uptake in the carotid artery (target-to-background ratio [TBR] ≥1.6) were randomized to either clopidogrel or ticagrelor groups. Of these, 46 completed PET examinations at baseline and at 6 months. The primary endpoint was the percent change in TBR of the index vessel at the most diseased segment (MDS).

RESULTS

Baseline characteristics were similar between the 2 groups. At 6-month follow-up, low-density lipoprotein cholesterol and C-reactive protein significantly decreased in both groups (P < 0.001). The TBR of the index vessel and aorta significantly decreased in both groups (P < 0.01). The percent change in the MDS TBR of the index vessel was numerically but not significantly lower in the clopidogrel group than in the ticagrelor group (-9.5 ± 14.6% vs -13.5 ± 19.3%; P = 0.427). Likewise, the percent change in the whole-vessel TBR of the index vessel was not different between the 2 groups (P = 0.166). Similar findings were observed for changes in the MDS TBR (P = 0.412) or whole-vessel TBR of the aorta (P = 0.363).

CONCLUSIONS

Carotid atherosclerotic plaque inflammation significantly decreases to a similar degree following 6 months of either clopidogrel or ticagrelor treatment.

Inferiority of ticagrelor in the PHILO trial: Play of chance in East Asians or nightmare confirmation of PLATO-USA?

Long-awaiting PHILO trial, conducted in 2011-2012 has been submitted and published late in 2015. In contrast to overall PLATO results, but similar to PLATO-US cohort, PHILO revealed numerical inferiority of ticagrelor with regard to death, myocardial infarction, stroke, and bleeding over clopidogrel. Hence, we comprehend the PHILO results in light of the PLATO-US evidence. To assess the PHILO (n=801) outcomes, applied statistics, and trial conduct, matching them with the PLATO-US (n=1413) patients. The Asian, predominantly Japanese ticagrelor patients had worsened outcomes even when compared to the negative American cohort with regard to death (OR=1.44 (PHILO) vs. 1.17 (PLATO-US); myocardial infarction (OR=1.63 vs. 1.38); and composite primary endpoint (OR=1.60 vs. 1.27); but not for stroke (OR=1.51 vs. 1.75). Moreover, in contrast to the trend in PLATO-US (OR=1.11; CI=0.84-1.48, p=0.46), PHILO revealed significant excess of PLATO-defined composite of major and minor bleeding events (OR=1.83; CI=1.27-2.63,p=0.0014). PLATO-defined "net clinical benefit" in PHILO was also significantly (OR=1.61; CI=1.11-2.34, p=0.0145) inferior for ticagrelor. The "number needed to harm" suggests that for every 29 PHILO patients treated for 12months with ticagrelor instead of clopidogrel, one will suffer an additional major bleeding event. Finally, unexplained premature closure of PHILO just after 200-210days mean drug exposure, and short 240days mean follow-up seems deliberate and concerning with regard to unblinding. Aside from some information censoring, early trial closure, and creative statistics, Asian ticagrelor patients did consistently worse in PHILO, than even in the negative PLATO-US cohort. Especially alarming is a significant bleeding inferiority justifying a necessity for a separate outcome-driven low-dose ticagrelor trial in Asian post-PCI patients. This strategy was successfully implemented with the low-dose prasugrel in Japan. Regulatory authorities in Asia may consider conducting an independent review of PHILO dataset to ensure adequate ticagrelor safety.

Dyspnea and reversibility of antiplatelet agents: ticagrelor, elinogrel, cangrelor, and beyond

CONTEXT

Oral reversible platelet P2Y12 receptor inhibitors (ticagrelor and elinogrel) cause double-digit rates of dyspnea, while irreversible oral antiplatelet drugs (aspirin, ticlopidoine, clopidogrel, and prasugrel) or intravenous glycoprotein IIb/IIIa inhibitors (abciximab, eptifibatide, or tirofiban) do not increase the incidence of dyspnea in randomized trials. Dyspnea after oral reversible antiplatelet agents remains unexplained. A transfusion-related acute lung injury (TRALI) hypothesis has been proposed. The dyspnea risks after cangrelor, an intravenous reversible antiplatelet agent, are not well defined but may offer a universal mechanism linking TRALI, dyspnea, and reversible platelet inhibition.

OBJECTIVE

We analyzed safety data from recent head-to-head randomized trials with reversible antiplatelet agents (ticagrelor, elinogrel, and cangrelor) compared to irreversible (clopidogrel/placebo) comparators.

RESULTS

All three reversible antiplatelet agents cause excess dyspnea. In contrast to the high double-digit rates after oral ticagrelor or elinogrel, the dyspnea risks after intravenous cangrelor were smaller (<2%) but still consistently and significantly higher than in the corresponding control arms.

CONCLUSIONS

The clinical utility of reversible antiplatelet strategies has been challenged. Despite a potential advantage of fewer bleeding events during heart surgery, reversible antiplatelet agents carry the risk of potential autoimmune reactions manifesting as dyspnea. Repeated binding and unbinding cycles, impaired platelet turnover, and lung sequestration or apoptosis of overloaded destructive platelets are among the potential mechanism(s) responsible for dyspnea after reversible antiplatelet agents.

Antiplatelet and anticoagulant strategies in acute coronary syndrome: where we are in 2013

Multiple antiplatelet and anticoagulant therapies are available for the treatment of acute coronary syndromes. The combination of agents should be tailored to the individual patient carefully considering the balance between ischemic and bleeding risk, as well as the planned revascularization strategy. Despite multiple large-scale, rigorously designed and conducted randomized controlled trials, it can be difficult to select the correct pharmacotherapy for each patient and many unanswered questions remain, such as the safety and optimal doses of differing combinations of antiplatelet/anticoagulant therapy, as well as the timing and duration of therapies. In addition, the headline results of many trials report improved efficacy outcomes at the cost of increased bleeding risk; however, very few show a clear mortality benefit. It is therefore difficult to weigh up the risk–benefit profile of emerging therapies.

A critical overview on ticagrelor in acute coronary syndromes

Until a few years ago, the mainstay of anti-platelet therapy in patients with acute coronary syndrome (ACS) was the combination of aspirin and clopidogrel, a P2Y12 receptor inhibitor. However, current clinical practice has now changed with the introduction of ticagrelor, a more potent cardiovascular drug than clopidogrel, without the limitations related to clopidogrel therapy. In this review, we provide a critical overview of ticagrelor in ACS, highlight the results with ticagrelor in several subgroups of patients and discuss the future trials.

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.

P2Y12 platelet inhibition in clinical practice

Platelet adhesion, activation and aggregation play a pivotal role in atherothrombosis. Intracoronary atherothrombosis is the most common cause of the development of acute coronary syndrome (ACS), and plays a central role in complications occurring around percutaneous coronary intervention (PCI) including recurrent ACS, procedure-related myocardial infarction or stent thrombosis. Inhibition of platelet aggregation by medical treatment impairs formation and progression of thrombotic processes and is therefore of great importance in the prevention of complications after an ACS or around PCI. An essential part in the platelet activation process is the interaction of adenosine diphosphate (ADP) with the platelet P2Y12 receptor. The P2Y12 receptor is the predominant receptor involved in the ADP-stimulated activation of the glycoprotein IIb/IIIa receptor. Activation of the glycoprotein IIb/IIIa receptor results in enhanced platelet degranulation and thromboxane production, and prolonged platelet aggregation. The objectives of this review are to discuss the pharmacological limitations of the P2Y12 inhibitor clopidogrel, and describe the novel alternative P2Y12 inhibitors prasugrel and ticagrelor and the clinical implications of the introduction of these new medicines.

Ticagrelor, but not clopidogrel and prasugrel, prevents ADP-induced vascular smooth muscle cell contraction: a placebo-controlled study in rats

INTRODUCTION

Off-target effects of novel antiplatelet agents due to their potential clinical benefits are currently an area of intensive investigation. We aimed to compare the effects of different P2Y(12) antagonists on the reactivity of vascular smooth muscle cells.

MATERIALS AND METHODS

Wistar rats (n=30) were pretreated with an investigated drug or placebo. Clopidogrel (50mg/kg, n=7), prasugrel (10mg/kg, n=7), ticagrelor (10mg/kg, n=7) or placebo (n=9) were administered orally 12 and 2 hours before experiments. Constrictions of rat tail arteries induced with a stable analogue of adenosine diphosphate (2-MeS-ADP), phenylephrine and arginine vasopressin were measured as an increase in perfusion pressure. Effects of ticagrelor were assessed in the presence of ticagrelor (1μM/L) added to the perfusion solution as this drug reversibly inhibits the P2Y(12) receptor.

RESULTS

Pretreatment with clopidogrel and prasugrel did not inhibit 2-MeS-ADP-induced contraction while ticagrelor did. Experiments employing endothelium-deprived arteries provided similar results. Clopidogrel and prasugrel did not influence concentration-response curves in the presence of neither phenylephrine nor arginine vasopressin. The curves obtained for both vasopressors in the presence of ticagrelor and 2-MeS-ADP were shifted to the right with a significant reduction in the maximal response.

CONCLUSIONS

Oral administration of ticagrelor, in contrast to clopidogrel and prasugrel, prevents adenosine diphosphate-induced contraction of vascular smooth muscle cells in a rat model. Both the clinical significance and detailed mechanism of our findings warrant further investigation.

Comparison of differential expression of P2Y₁₂ receptor in culprit coronary plaques in patients with acute myocardial infarction versus stable angina pectoris

P2Y₁₂ receptor antagonists may have pleiotropic benefits. Little is known, however, about the expression of P2Y₁₂ receptors in coronary atherosclerotic plaques. We investigated the expression of P2Y₁₂ receptor in coronary atherectomy tissues retrieved from patients with acute myocardial infarction (AMI) or stable angina pectoris (SAP). Tissue specimens were collected from 35 patients with AMI and 19 with SAP who underwent directional coronary atherectomy. Specimens were analyzed immunohistochemically using antibodies specific to P2Y₁₂ receptor and to markers of endothelial cells, macrophages, and smooth muscle cells. The 2 groups had similar baseline clinical characteristics. Plaque types were more likely to be cellular in the AMI group. The proportion of areas immunopositive for α-smooth muscle actin was smaller but those positive for CD31 and CD68 were larger in the AMI than in the SAP group. In addition, the relative area immunopositive for P2Y₁₂ receptor was significantly larger for AMI than SAP (1.1 ± 0.9% vs 0.5 ± 0.4%, respectively, p < 0.001). P2Y₁₂ receptor positivity coincided with areas positive for CD31 and α-smooth muscle actin. In conclusion, P2Y₁₂ receptor is present in coronary atherosclerotic plaques and is increased in culprit plaques of patients with AMI. P2Y₁₂ receptor may play a role in plaque destabilization.

Platelet inhibition by adjunctive cilostazol versus high maintenance-dose clopidogrel in patients with acute myocardial infarction according to cytochrome P450 2C19 genotype

OBJECTIVES

The aim of this study was to assess the degree of platelet inhibition by adjunctive cilostazol in patients with acute myocardial infarction (AMI) according to hepatic cytochrome P450 2C19 (CYP2C19) genotype.

BACKGROUND

Although adjunctive cilostazol intensifies platelet inhibition in AMI patients, it is not established whether this regimen can be free from the effect of CYP2C19 loss-of-function variants (*2/*3).

METHODS

We randomly assigned 126 AMI patients with available CYP2C19 genotyping to receive adjunctive cilostazol (triple group; n = 64) or high maintenance-dose (MD) clopidogrel of 150 mg/day (high-MD group; n = 62). Using conventional aggregometry and VerifyNow (Accumetrics Inc., San Diego, California), platelet reactivity was measured at pre-discharge and 30-day follow-up. Primary endpoint was change in maximal platelet aggregation (ΔAgg(max)) between pre-discharge and 30-day follow-up. High on-treatment platelet reactivity (HPR) was defined as 20 μmol/l adenosine diphosphate-induced maximal platelet aggregation (Agg(max)) >59%.

RESULTS

In noncarriers, despite numerically greater inhibition by adjunctive cilostazol, changes in platelet measures and the rate of HPR did not significantly differ between the 2 groups. In carriers, ΔAgg(max) after 5 and 20 μmol/l adenosine diphosphate stimuli was significantly higher in the triple (n = 39) versus high-MD group (n = 38) (21.8 ± 13.9% vs. 9.0 ± 13.3%, p < 0.001, and 24.2 ± 17.2% vs. 7.7 ± 15.5%, p < 0.001, respectively). Likewise, changes in late platelet aggregation and P2Y12 reaction unit were consistently greater in the triple versus high-MD group. Fewer patients in the triple group met the criteria of HPR at 30-day follow-up than in the high-MD group (15.4% vs. 44.7%, p = 0.005).

CONCLUSIONS

Compared with high-MD clopidogrel, adjunctive cilostazol significantly enhances platelet inhibition and reduces the rate of HPR, especially in AMI patients with CYP2C19 loss-of-function variants. (Adjunctive Cilostazol Versus High Maintenance-Dose Clopidogrel in Acute Myocardial Infarction (AMI) Patients According to CYP2C19 Polymorphism [ACCELAMI2C19]; NCT00915733).

Cytochrome 2C19 polymorphism and response to adjunctive cilostazol versus high maintenance-dose clopidogrel in patients undergoing percutaneous coronary intervention

BACKGROUND

Among patients treated with clopidogrel, carriers of the cytochrome P450 (CYP) 2C19 loss-of-function allele have shown increased platelet reactivity and higher rates of ischemic events. Although adjunctive cilostazol to dual antiplatelet therapy (or "triple antiplatelet therapy") intensifies platelet inhibition, it remains unknown whether triple antiplatelet therapy after percutaneous coronary intervention can achieve adequate platelet inhibition in patients with the CYP2C19 mutant allele.

METHODS AND RESULTS

CYP2C19 genotyping for *1, *2, and *3 was performed in 134 high-risk patients undergoing elective percutaneous coronary intervention. After measurement of preprocedural platelet reactivity, patients were randomly assigned to receive either adjunctive cilostazol 100 mg twice daily (triple group; n=69) or high maintenance-dose (MD) clopidogrel of 150 mg daily (high-MD group; n=65). Using light transmittance aggregometry and the VerifyNow P2Y(12) assay, platelet reactivity was assessed before the index procedure and at 30-day follow-up. The primary end point was absolute change in maximal platelet aggregation (ΔAgg(max)) according to CYP2C19 genotyping. High posttreatment platelet reactivity was defined as 5 μmol/L ADP-induced maximal platelet aggregation >50%. In noncarriers of the CYP2C19*2/*3 mutant allele, ΔAgg(max) values after 5 and 20 μmol/L ADP stimuli did not differ significantly between the triple (n=22) versus the high-MD group (n=22) (23.6±21.6% versus 16.6±15.4%, P=0.224 and 26.4±22.2% versus 18.6±14.9%, P=0.174, respectively). Absolute changes in late platelet aggregation and P2Y(12) reaction unit were not different between the groups. The rate of high posttreatment platelet reactivity at 30-day follow-up also was comparable between the triple versus the high-MD group (4.5% versus 13.6%, P=0.607). In carriers of at least 1 CYP2C19*2/*3 mutant allele, the triple group (n=47) showed greater values of ΔAgg(max) after addition of 5 μmol/L (25.8±16.8% versus 11.1±19.8%, P<0.001) and 20 μmol/L ADP (26.3±16.0% versus 11.5±16.3%, P<0.001) compared with the high-MD group (n=43). Likewise, absolute changes in late platelet aggregation and P2Y(12) reaction unit were consistently greater in the triple versus the high-MD group. Fewer patients in the triple group met the criteria of high posttreatment platelet reactivity at 30-day follow-up compared with the high-MD group (6.4% versus 37.2%, P<0.001).

CONCLUSIONS

Among high-risk patients undergoing elective percutaneous coronary intervention, adjunctive cilostazol can achieve consistently intensified platelet inhibition and reduce the risk of high posttreatment platelet reactivity irrespective of CYP2C19 genotyping.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01012193.