A Prospective Observational Study on Gastric Endoscopic Submucosal Dissection under Continuous Administration of Antithrombotic Agents

Background: This study aimed to assess the completion rate and postoperative bleeding incidence of endoscopic submucosal dissection (ESD) for gastric tumors under continuous antithrombotic therapy. Methods: A prospective observational study was conducted including 88 patients with 100 gastric lesions who underwent gastric endoscopic submucosal dissection (ESD) and received continuous antithrombotic therapy. Additionally, retrospective data on gastric ESD in 479 patients with 534 lesions who did not receive antithrombotic therapy were collected for comparison. Results: The en bloc resection rates (100% in the continuous antithrombotic therapy group vs. 100% in the non-antithrombotic therapy group) and complete resection rates (97.0% vs. 96.3%, respectively) were high and comparable between the groups. No significant differences were found in the specimen size or procedure time. Perforation rates were low (0% vs. 2.3%, respectively) and were not significantly different between the groups. However, postoperative bleeding occurred significantly more frequently in the continuous antithrombotic therapy group (10.2% vs. 4.2%, respectively) than in the non-antithrombotic therapy group. The subgroup analysis revealed a higher incidence of postoperative bleeding in patients receiving thienopyridine derivatives. Conclusions: Continuous administration of antithrombotic agents, especially thienopyridines, increased the risk of postprocedural hemorrhage following gastric ESD. These findings support the need for careful consideration of pharamcological management before ESD, aligning with the current guidelines.

Selective Oxidation of Clopidogrel by Peroxymonosulfate (PMS) and Sodium Halide (NaX) System: An NMR Study

A selective transformation of clopidogrel hydrogen sulfate (CLP) by reactive halogen species (HOX) generated from peroxymonosulfate (PMS) and sodium halide (NaX) is described. Other sustainable oxidants as well as different solvents have also been investigated. As result of this study, for each sodium salt the reaction conditions were optimized, and four different degradation products were formed. Three products were halogenated at C-2 on the thiophene ring and have concomitant functional transformation, such as N-oxide in the piperidine group. A halogenated endo-iminium product was also observed. With this condition, a fast preparation of known endo-iminium clopidogrel impurity (new counterion) was reported as well. The progress of the reaction was monitored using nuclear magnetic resonance spectroscopy as an analytical tool and all the products were characterized by 1D-, 2D-NMR and HRMS.

Biocatalytic Syntheses of Antiplatelet Metabolites of the Thienopyridines Clopidogrel and Prasugrel Using Fungal Peroxygenases

Antithrombotic thienopyridines, such as clopidogrel and prasugrel, are prodrugs that undergo a metabolic two-step bioactivation for their pharmacological efficacy. In the first step, a thiolactone is formed, which is then converted by cytochrome P450-dependent oxidation via sulfenic acids to the active thiol metabolites. These metabolites are the active compounds that inhibit the platelet P2Y₁₂ receptor and thereby prevent atherothrombotic events. Thus far, described biocatalytic and chemical synthesis approaches to obtain active thienopyridine metabolites are rather complex and suffer from low yields. In the present study, several unspecific peroxygenases (UPOs, EC 1.11.2.1) known to efficiently mimic P450 reactions in vitro—but requiring only hydroperoxide as oxidant—were tested for biocatalytic one-pot syntheses. In the course of the reaction optimization, various parameters such as pH and reductant, as well as organic solvent and amount were varied. The best results for the conversion of 1 mM thienopyridine were achieved using 2 U mL⁻¹ of a UPO from agaric fungus Marasmius rotula (MroUPO) in a phosphate-buffered system (pH 7) containing 5 mM ascorbate, 2 mM h⁻¹ H₂O₂ and 20% acetone. The preparation of the active metabolite of clopidogrel was successful via a two-step oxidation with an overall yield of 25%. In the case of prasugrel, a cascade of porcine liver esterase (PLE) and MroUPO was applied, resulting in a yield of 44%. The two metabolites were isolated with high purity, and their structures were confirmed by MS and MS² spectrometry as well as NMR spectroscopy. The findings broaden the scope of UPO applications again and demonstrate that they can be effectively used for the selective synthesis of metabolites and late-state diversification of organic molecules, circumventing complex multistage chemical syntheses and providing sufficient material for structural elucidation, reference material, or cellular assays.

The Discovery and Development of Thienopyrimidines as Inhibitors of Helicobacter pylori That Act through Inhibition of the Respiratory Complex I

The successful treatment of Helicobacter pylori infections is becoming increasingly difficult due to the rise of resistance against current broad spectrum triple therapy regimens. In the search for narrow-spectrum agents against H. pylori, a high-throughput screen identified two structurally related thienopyrimidine compounds that selectively inhibited H. pylori over commensal members of the gut microbiota. To develop the structure-activity relationship (SAR) of the thienopyrimidines against H. pylori, this study employed four series of modifications in which systematic substitution to the thienopyrimidine core was explored and ultimately side-chain elements optimized from the two original hits were merged into lead compounds. During the development of this series, the mode of action studies identified H. pylori's respiratory complex I subunit NuoD as the target for lead thienopyrimidines. As this enzyme complex is uniquely essential for ATP synthesis in H. pylori, a homology model of the H. pylori NuoB-NuoD binding interface was generated to help rationalize the SAR and guide further development of the series. From these studies, lead compounds emerged with increased potency against H. pylori, improved safety indices, and a good overall pharmacokinetic profile with the exception of high protein binding and poor solubility. Although lead compounds in the series demonstrated efficacy in an ex vivo infection model, the compounds had no efficacy in a mouse model of H. pylori infection. Additional optimization of pharmacological properties of the series to increase solubility and free-drug levels at the sequestered sites of H. pylori infection would potentially result in a gain of in vivo efficacy. The thienopyrimidine series developed in this study demonstrates that NuoB-NuoD of the respiratory complex I can be targeted for development of novel narrow spectrum agents against H. pylori and that thienopyrimines can serve as the basis for future advancement of these studies.

Design, Molecular Modeling and Synthesis of Metal-Free Sensitizers of Thieno Pyridine Dyes as Light-Harvesting Materials with Efficiency Improvement Using Plasmonic Nanoparticles

Considering the thiophene unit as an electron-rich heterocycle, it is investigated with the aim of elucidating its potential efficiency for solar cell application. With the introduction of active substituents such as COOEt, CONH₂ and CN into the thiophene segment, three novel thieno pyridine sensitizers (6a–c), based on donor-acceptor D-π-A construction, are designed and synthesized. The effect of the anchoring groups is investigated based on their molecular orbital’s (MO’s) energy gap (E_g). The electrostatic interaction between the synthesized dyes and metal nanoparticles, namely gold, silver and ruthenium, is believed to improve their performance as organic sensitizers. The dye-sensitized solar cells (DSSCs) are manufactured using the novel diazenyl pyridothiophene dyes, along with their metal nanoparticles conjugates as sensitizers, and were examined for efficiency improvement. Accordingly, using this modification, the photovoltaic performance was significantly improved. The promising results of conjugate (6b/AgNPs), compared with reported organic and natural sensitizers (J_SC (1.136 × 10⁻¹ mA/cm²), V_OC (0.436 V), FF (0.57) and η (2.82 × 10⁻²%)), are attributed to the good interaction between the amide, methyl, amino and cyano groups attached to the thiophene pyridyl scaffolds and the surface of TiO₂ porous film. Implementation of a molecular modeling study is performed to predict the ability of the thiophene moiety to be used in solar cell applications.

A thienopyridine, CB-20, exerts diuretic activity by inhibiting urea transporters

Urea transporters (UTs) are transmembrane proteins selectively permeable to urea and play an important role in urine concentration. UT-knockout mice exhibit the urea-selective urine-concentrating defect, without affecting electrolyte balance, suggesting that UT-B inhibitors have the potential to be developed as novel diuretics. In this study, we characterized a novel compound 5-ethyl-2-methyl-3-amino-6-methylthieno[2,3-b]pyridine-2,5-dicarboxylate (CB-20) with UT inhibitory activity as novel diuretics with excellent pharmacological properties. This compound was discovered based on high-throughput virtual screening combined with the erythrocyte osmotic lysis assay. Selectivity of UT inhibitors was assayed using transwell chambers. Diuretic activity of the compound was examined in rats and mice using metabolic cages. Pharmacokinetic parameters were detected in rats using LC-MS/MS. Molecular docking was employed to predict the potential binding modes for the CB-20 with human UT-B. This compound dose-dependently inhibited UT-facilitated urea transport with IC50 values at low micromolar levels. It exhibited nearly equal inhibitory activity on both UT-A1 and UT-B. After subcutaneous administration of CB-20, the animals showed polyuria, without electrolyte imbalance and abnormal metabolism. CB-20 possessed a good absorption and rapid clearance in rat plasma. Administration of CB-20 for 5 days did not cause significant morphological abnormality in kidney or liver tissues of rats. Molecular docking showed that CB-20 was positioned near several residues in human UT-B, including Leu364, Val367, and so on. This study provides proof of evidence for the prominent diuretic activity of CB-20 by specifically inhibiting UTs. CB-20 or thienopyridine analogs may be developed as novel diuretics.

Benefit and Risk of Prolonged DAPT After Coronary Stenting in Women

BACKGROUND

Women may derive differential benefit from prolonged DAPT (dual antiplatelet therapy) after coronary stenting than men. We assessed whether the risks/benefits of prolonged DAPT differ between women and men.

METHODS AND RESULTS

The DAPT study was a randomized double-blind, placebo-controlled trial comparing continued thienopyridine versus placebo beyond 12 months after coronary stenting. We compared rates of myocardial infarction, stent thrombosis, major adverse cardiovascular and cerebrovascular events, and bleeding by sex and randomized treatment. Of 11 648 patients, women (N=2925) were older, with higher prevalence of diabetes mellitus and lower rates of acute coronary syndrome than men. At 12 to 30 months, women had similar adjusted ischemic and bleeding events as men. The effects of continued thienopyridine therapy did not differ significantly by sex for stent thrombosis (women: hazard ratio [HR], 0.54; 95% confidence interval [CI], 0.22-1.36; men: HR, 0.26; 95% CI, 0.15-0.44; interaction P=0.17), myocardial infarction (women: HR, 0.75; 95% CI, 0.50-1.14; men: HR, 0.46; 95% CI, 0.36-0.60; interaction P=0.052), major adverse cardiovascular and cerebrovascular events (women: HR, 0.87; 95% CI, 0.62-1.22; men: HR, 0.70; 95% CI, 0.58-0.85; interaction P=0.26), and bleeding (women: HR, 1.45; 95% CI, 0.88-2.40; men: HR, 1.78; 95% CI, 1.28-2.49; interaction P=0.50).

CONCLUSIONS

Women had similar late risks of ischemia and bleeding as men after coronary stent procedures.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov . Unique identifier: NCT00977938.

High interindividual variability in plasma clopidogrel active metabolite concentrations in healthy cats is associated with sex and cytochrome P450 2C genetic polymorphism

Clopidogrel response variability has been identified in cats. In humans, evidence suggests that variable clopidogrel active metabolite (CAM) generation is the primary explanation for clopidogrel response variability with differences in body weight, sex, and variable metabolism of clopidogrel primarily due to polymorphisms of the gene encoding cytochrome P450 (CYP) 2C19 as some proposed mechanisms. The aim of this study was to evaluate whether variation in CAM concentrations exists in healthy cats and what the cause of such variation might be. Nineteen healthy cats were given 18.75 mg clopidogrel by mouth. Blood was collected 2 hr later. Plasma CAM concentrations were measured using high performance liquid chromatography and tandem mass spectrometry. Clopidogrel metabolism was estimated by calculating CAM metabolic ratio. DNA was collected, and feline CYP2C genotyping was performed. The cats demonstrated high interindividual variation of plasma CAM concentrations. Approximately 69% of this interindividual variation was primarily explained by differences in clopidogrel metabolism as measured by CAM metabolic ratio with some influence by sex but not by weight. A single nucleotide polymorphism was identified in the feline CYP2C gene that explained in part individual differences in CAM metabolic ratio and CAM plasma concentrations.

Reversibility of platelet P2Y12 inhibition by platelet supplementation: ex vivo and in vitro comparisons of prasugrel, clopidogrel and ticagrelor

Essentials Successful outcome of platelet transfusion depends on specific antiplatelet therapy in use. We assessed if ticagrelor, clopidogrel or prasugrel impacts on donor platelet activity ex vivo. Ticagrelor and/or its active metabolite in plasma or bound to platelets can inhibit donor platelets. This might compromise the effectiveness of platelet transfusion therapy.

SUMMARY

Background Platelet transfusion is the conventional approach to restore platelet function during acute bleeds or surgery, but successful outcome depends on the specific antiplatelet therapy. Notably ticagrelor is associated with inadequate recovery of platelet function after platelet transfusion. We examined whether plasma and/or platelets from ticagrelor-treated patients influence donor platelet function, in comparison with clopidogrel and prasugrel. Methods Platelet transfusion was mimicked ex vivo by mixing naïve donor platelet-rich plasma (PRP) or gel-filtered platelets (GFP) in defined proportions with PRP, plasma or GFP from cardiovascular patients receiving standard care including medication with prasugrel, clopidogrel or ticagrelor (n = 20 each). Blood was taken 4 h after the previous dose. HLA2/HLA28 haplotyping let us distinguish net (all platelet) and individual patient/donor platelet reactivity in mixtures of patient/donor platelets, measured by flow cytometry analysis of ADP-induced fibrinogen binding and CD62P expression. Results ADP responsiveness of donor platelets was dramatically reduced by even low (10%) concentrations of PRP or plasma from ticagrelor-treated patients. Clopidogrel and prasugrel were associated with more modest donor platelet inhibition. GFP from ticagrelor-treated patients but not patients receiving clopidogrel or prasugrel also suppressed donor GFP function upon mixing, suggesting the transfer of ticagrelor from patient platelets to donor platelets. This transfer did not lead to recovery of ADP responsiveness of patient's platelets. Conclusion Collectively, these observations support the concept that ticagrelor and/or its active metabolite in plasma or bound to platelets can inhibit donor platelets, which might compromise the effectiveness of platelet transfusion therapy.

Patients with cirrhosis who have coronary artery disease treated with cardiac stents have high rates of gastrointestinal bleeding, but no increased mortality

BACKGROUND

Patients with coronary artery disease (CAD) treated with stents require dual antiplatelet therapy (DAPT). For cirrhotics, who often have varices and coagulopathy, it is not clear if the risk of gastrointestinal bleeding (GIB) should preclude use of DAPT.

AIM

To compare GIB and mortality rates in cirrhotics with CAD treated medically or with stents.

METHODS

Using institutional databases, we identified patients with cirrhosis and CAD treated with stents or medical therapy between January 2000-September 2015. Primary outcomes were GIB and mortality.

RESULTS

We identified 148 cirrhotics with CAD; 68 received stents (cases), 80 were treated with medical therapy (controls). Cases and controls had similar demographics, comorbidities, MELD scores and clinical presentation; DAPT was used in 98.5% of cases vs 5% of controls. The incidence of GIB was significantly higher in cases than controls (22.1% vs 5% at 1 year, P=.003; 27.9% vs 5% at 2 years, P=.0002), whereas all-cause mortality was similar (20.6% vs 21.3%). No patient required surgery or angiography for GIB, and no known patients died due to GIB. Multivariate analysis revealed use of a proton pump inhibitor (PPI) was highly protective against GIB (OR=0.26, 95%CI=0.08-0.79).

CONCLUSIONS

CAD treatment with stents in our cirrhotics was associated with a significantly increased risk of GIB, but no adverse effects on survival. Although it remains unclear whether the cardiovascular benefits of stents outweigh the GIB risk, our findings suggest that DAPT should not be withheld from stented cirrhotics for fear of GIB. Moreover, the use of a PPI should be strongly considered.

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.

Meta-analysis of randomized controlled trials on efficacy and safety of extended thienopyridine therapy after drug-eluting stent implantation

BACKGROUND

The potential benefits and risks of extended thienopyridine therapy beyond 12 months after drug-eluting stent (DES) implantation remain unclear.

METHODS

Randomized controlled trials (RCTs) were searched in PubMed, EMBASE, the Cochrane Library and China National Knowledge Infrastructure databases. The adverse clinical endpoints were compared between 12 months group (aspirin alone) and >12 months group (additional thienopyridine plus aspirin after 12-month dual antiplatelet therapy). Odds ratios (ORs) with 95% confidence intervals (95% CIs) were used as summary statistics. A random-effect model was used in the meta-analysis process.

RESULTS

Finally, three RCTs incorporating 16,265 participants were included in this meta-analysis. The results indicated that the incidences of myocardial infarction (1.55% vs. 2.90%; OR =0.58; 95% CI, 0.40-0.84; P=0.004) and stent thrombosis (0.32% vs. 0.98%; OR =0.35; 95% CI, 0.20-0.62; P<0.001) in the >12 months group were significantly lower than the 12 months group. However, compared to the 12 months group, the extended thienopyridine therapy markedly increased the risk of bleeding events (2.09% vs. 1.28%; OR =1.64; 95% CI, 1.23-2.17; P<0.001). The risks of stroke (0.78% vs. 0.84%; P=0.67) and cardiac death (0.94% vs. 0.89%; P=0.61) were similar between the two groups.

CONCLUSIONS

The synthesis of available evidence indicates that a regimen of extended thienopyridine therapy beyond 12 months may significantly reduce the risks of myocardial infarction and stent thrombosis but increase the risk of bleeding events in the patients who have received DESs implantation.

Design, Synthesis and Pharmacological Evaluation of Novel Piperlongumine derivatives as Potential Antiplatelet Aggregation Candidate

A series of novel piperlongumine derivatives (4a-i, 6a-i) were designed and synthesized. The inhibitory activities of platelet aggregation induced by ADP and AA in vitro have been evaluated by bron turbidimetry and liver microsomal incubated assay. The assay results show that compounds 4e and 6e exhibited remarkable potency to that of the positive control piplartine and aspirin.

Use of thienopyridine prior to presentation with non-ST-segment elevation acute coronary syndrome and association with safety and efficacy of vorapaxar: insights from the TRACER trial

BACKGROUND

Vorapaxar is effective in the prevention of secondary atherothrombotic events, although the efficacy/safety balance appears less favorable in the treatment of patients with non-ST-segment elevation (NSTE) acute coronary syndrome (ACS). We hypothesized that patients with NSTE ACS already receiving thienopyridine prior to the ACS event may show differential efficacy/safety effects with vorapaxar vs. placebo added to their standard care.

METHODS

We studied 12,944 patients from the Thrombin Receptor Antagonist for Clinical Event Reduction in Acute Coronary Syndrome (TRACER) trial with respect to thienopyridine use before admission for the index NSTE ACS event. The primary endpoint was a composite of cardiovascular death, myocardial infarction, stroke, rehospitalization for ischemia, and urgent revascularization. The key secondary endpoint was a composite of cardiovascular death, myocardial infarction, and stroke. Safety endpoints were bleeding complications.

RESULTS

Only 1513 patients (11.7%) were receiving thienopyridine before admission for the index NSTE ACS event. In these patients, Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) moderate/severe bleeding occurred in 5.7% treated with vorapaxar and 5.3% treated with a placebo (hazards ratio (HR) 1.10, 95% confidence interval (CI) 0.70-1.71); in thienopyridine-naïve patients, the rates were 5.7% and 4.1%, respectively (HR 1.32, 95% CI 1.11-1.57; P_int=0.45). GUSTO severe bleeding in the prior thienopyridine group occurred in 0.5% of patients treated with vorapaxar and 1.3% of patients treated with placebo (HR 0.34, 95% CI 0.09-1.30); in thienopyridine-naïve patients, the rates were 2.0% and 1.0%, respectively (HR 1.89, 95% CI 1.36-2.62; P_int=0.01). No interaction was observed between vorapaxar efficacy and prior thienopyridine use on the primary (adjusted P_int=0.53) or key secondary endpoints ( P_int=0.61).

CONCLUSIONS

TRACER was largely conducted in thienopyridine-naïve patients with unknown tolerance to multiple antiplatelet treatments. Patients receiving thienopyridine before the index event may have had an attenuated increase in bleeding when adding vorapaxar, whereas concomitantly adding vorapaxar and thienopyridine in naïve patients may have uncovered a latent susceptibility to bleeding.

Hypersensitivity reactions to modern antiplatelet and anticoagulant drugs

Anticoagulation and antiplatelet drugs are among the most commonly used medical drugs. In addition to the long-established heparins, hirudins, coumarins and antiplatelet drugs such as acetylsalicylic acid, numerous novel and predominantly synthetic pharmacologic agents have come onto the market in recent years. These new agents act at various sites in coagulation and have significantly broadened treatment options. Whilst immunological hypersensitivity reactions are on the whole rare, they have a considerable impact on patient management when they do occur. The present overview discusses the currently known hypersensitivity reactions to anticoagulant and antiplatelet agents, with particular attention to the newer substance classes including P2Y₁₂ inhibitors, glycoprotein IIb/IIIb receptor antagonists, direct factor Xa inhibitors and direct thrombin inhibitors.

Coronary stent thrombosis with vorapaxar versus placebo: results from the TRA 2° P-TIMI 50 trial

BACKGROUND

Vorapaxar, a novel thrombin receptor antagonist, reduces cardiovascular death and recurrent thrombotic events when added to standard antiplatelet therapy in patients with stable atherosclerotic vascular disease.

OBJECTIVES

The goal of this study was to test the hypothesis that treatment with vorapaxar reduces the rate of coronary stent thrombosis (ST) in stable patients with a history of coronary stenting.

METHODS

TRA 2° P-TIMI 50 (Trial to Assess the Effects of Vorapaxar in Preventing Heart Attack and Stroke in Patients With Atherosclerosis-Thrombolysis In Myocardial Infarction 50) was a multinational, randomized, double-blind, placebo-controlled trial of vorapaxar in stable patients with prior myocardial infarction, peripheral arterial disease, or stroke. We evaluated the rates of definite ST as adjudicated by a central events committee using Academic Research Consortium (ARC) criteria.

RESULTS

A total of 26,449 patients were randomized, with 14,042 (53%) having a history of a coronary stent implantation before randomization, and an additional 449 patients receiving a coronary stent during the trial (total 14,491). During follow-up (median 2.5 years), there were 152 definite ST events, with the majority (92%) occurring late or very late. Vorapaxar reduced ARC definite ST (1.1% vs. 1.4%, hazard ratio [HR]: 0.71, 95% confidence interval [CI]: 0.51 to 0.98; p = 0.037). The reduction was consistent, regardless of time from percutaneous coronary intervention, history of diabetes, use of drug-eluting stents, and use of dual antiplatelet therapy (DAPT) at randomization. Vorapaxar increased GUSTO moderate/severe bleeding (HR: 1.57, 95% CI: 1.26 to 1.94; p < 0.001).

CONCLUSIONS

The rate of ARC definite ST in stable patients, the majority of whom were receiving DAPT, was approximately 1.4% at 3 years. In stable patients with coronary stenting receiving standard antiplatelet therapy, vorapaxar administered for long-term secondary prevention significantly reduced ARC definite ST, including very late ST. (Trial to Assess the Effects of Vorapaxar [SCH 530348; MK-5348] in Preventing Heart Attack and Stroke in Patients With Atherosclerosis [TRA 2° P-TIMI 50] [P04737]; NCT00526474).

Detecting a thienopyridine effect by platelet reactivity assessment and its implications for risk stratification

BACKGROUND

On-treatment platelet reactivity (OTR) is a predictor of clinical outcomes in patients receiving thienopyridine therapy.

OBJECTIVE

To assess whether point-of-care platelet reactivity testing can discriminate between patients who have and have not received a thienopyridine.

PATIENTS/METHODS

This was an analysis of a randomized, multicenter, pharmacodynamic trial. Subjects with coronary artery disease treated with aspirin were randomly assigned to clopidogrel 75 mg daily or prasugrel 10 mg daily for 7 days. Platelet reactivity assessment with the VerifyNow P2Y12 test was performed before study drug admistration and 24 h after the final dose. Optimal cut-offs for a detectable drug effect were identified by the use of receiver operating characteristic curve analysis.

RESULTS

A total of 54 subjects were enrolled and completed the study. The c-statistic for the identification of a thienopyridine effect was highly significant (0.93, P < 0.001), including for the clopidogrel and prasugrel groups considered separately (P < 0.001 for both). The optimal cut-off was < 213 P2Y12 reaction units (PRU), which provided a sensitivity of 80% and a specificity of 98%. This cut-off provided a sensitivity of 58% and a specificity of 100% for a clopidogrel effect, and a sensitivity of 100% and specificity of 96% for a prasugrel effect.

CONCLUSIONS

OTR of < 213 PRU is highly specific for exposure to either clopidogrel or prasugrel. This may be useful in the management of thienoypridine-treated patients who require surgery. Furthermore, this diagnostic cut-off is similar to levels of OTR that have been associated with ischemic events in thienopyridine-treated patients, supporting the contention that a lack of drug effect is the mechanistic basis for the prognostic relationship between OTR and clinical outcomes.

Pharmacogenetics in the Community Pharmacy: Thienopyridine Selection Post-Coronary Artery Stent Placement

INTRODUCTION

Although antiplatelet therapy is a mainstay of post-percutaneous coronary intervention therapy, pharmacogenetic (PGt) considerations of therapy are often ignored despite related Food and Drug Administration warnings. Pharmacists are well situated to provide PGt guidance, and the community pharmacy is one setting where PGt testing, interpretation, and recommendations can take place to ensure optimal therapeutic outcomes.

CASE REPORT

A 65-year-old man who had a myocardial infarction that was treated with PCI and stent placement was determined by a community pharmacist to be a candidate for PGt testing to ensure optimal antiplatelet therapy. The patient was seen in the pharmacy as a part of a medication therapy management encounter and underwent genetic testing. Results of the genetic testing indicated the need for modification of therapy. The community pharmacist interpreted the results and made the appropriate recommendation to the cardiologist who in turn modified antiplatelet therapy appropriately.

CONCLUSION

This case describes the potential for collaboration between pharmacists and physicians to optimize antiplatelet therapy through PGt testing. Points of consideration for others looking to implement related PGt services are also discussed.

Platelet function normalization after a prasugrel loading-dose: time-dependent effect of platelet supplementation

BACKGROUND

Hemostatic benefits of platelet transfusions in thienopyridine-treated acute coronary syndrome (ACS) patients may be compromised by residual metabolite in circulation.

OBJECTIVES

To estimate the earliest time after a prasugrel loading-dose when added platelets are no longer inhibited by prasugrel's active metabolite.

METHODS

Baseline platelet reactivity of healthy subjects (n=25, 30 ± 5 years, 68% male) on ASA 325 mg was tested using maximum platelet aggregation (MPA, ADP 20 μm) and VerifyNow(®) P2Y12 and was followed by a 60 mg prasugrel loading-dose. At 2, 6, 12 and 24 h post-dose, fresh concentrated platelets from untreated donors were added ex-vivo to subjects' blood, raising platelet counts by 0% (control), 40%, 60% and 80%. To estimate the earliest time when prasugrel's active metabolite's inhibitory effect on the added platelets ceases, platelet function in supplemented samples was compared across time-points to identify the time when effect of supplementation on platelet function stabilized (i.e. the increase in platelet reactivity was statistically similar to that at the next time-point).

RESULTS

Supplemented samples showed concentration-dependent increases in platelet reactivity vs. respective controls by both MPA and VerifyNow(®) at all assessment time-points. For each supplementation level, platelet reactivity showed a sharp increase from 2 to 6 h but was stable (P=NS) between 6 and 12 h.

CONCLUSIONS

The earliest measured time when supplemented platelets were not inhibited by circulating active metabolite of prasugrel was 6 h after a prasugrel loading-dose. These findings may have important implications for prasugrel-treated ACS patients requiring platelet transfusions during surgery.

Antiplatelet therapy in acute coronary syndromes: focus on ticagrelor

The use of antiplatelet agents, specifically the thienopyridines, has become a standard of care in the approach to the patient presenting with an acute coronary syndrome. These drugs irreversibly inhibit the platelet by permanently binding to the surface P2Y12 receptor and blocking the downstream fibrinogen cross-linking between platelets, which leads to aggregation and thrombus. However, currently available therapeutic choices are limited by potential interaction with other medications, slow hepatic conversion to active metabolite, genetic resistance, and narrow therapeutic safety margin. In order to overcome these disadvantages, there has been an interest in developing alternatives to thienopyridines. Recent investigations have included ticagrelor, a reversible inhibitor of the P2Y12 platelet receptor, which appears to have overcome several drawbacks of the current thienopyridines. Its unique pharmacokinetic and pharmacodynamic profiles result in an inhibition of platelet aggregation that is rapid, high, consistent, and less susceptible to interpatient variability than currently available P2Y12 inhibitors. In addition, ticagrelor offers a potential mortality advantage not apparent with current agents. Although questions regarding the nature, magnitude, and clinical significance of several observed adverse effects (dyspnea and ventricular pauses) remain unanswered, it appears that ticagrelor may represent a significant advancement over currently available oral antiplatelet agents.

A multiple dose study of prasugrel (CS-747), a novel thienopyridine P2Y12 inhibitor, compared with clopidogrel in healthy humans

AIMS

This double-blind, placebo-controlled trial was designed to evaluate the pharmacodynamics, pharmacokinetics, safety, and tolerability of prasugrel (CS-747, LY640315), a novel thienopyridine P2Y(12) ADP receptor antagonist compared with clopidogrel, during multiple oral dosing in healthy subjects.

METHODS

Thirty subjects received placebo, prasugrel 5 mg, 10 mg, or 20 mg, or clopidogrel 75 mg orally, daily for 10 days. Platelet aggregation, bleeding time, and prasugrel metabolites were measured and adverse events were recorded.

RESULTS

Inhibition of ADP-induced platelet aggregation reached steady state by day 3 following prasugrel 10 and 20 mg compared with 5 days for clopidogrel 75 mg or prasugrel 5 mg. Compared with placebo, at 24 h after the last dose of study drug, inhibition of platelet aggregation using (20 microm) ADP was significantly higher in the prasugrel 10 mg group (58.2 +/- 4.9% vs. 9.2 +/- 4.0%, P < 0.001) with no difference in the clopidogrel group (15.7 +/- 6.8% vs. 9.2 +/- 4.0%, P = 0.78). With 5 microm ADP, inhibition of platelet aggregation with prasugrel 10 mg and clopidogrel 75 mg was significantly higher than with placebo (prasugrel 10 mg, 70.5 +/- 4.7%; clopidogrel 75 mg, 36.5 +/- 9.0%; vs. placebo, 11.3 +/- 5.1%; P < 0.0001 and P = 0.02). On day 10 at 4 h postdose, bleeding time was prolonged with prasugrel 10 mg (prasugrel 10 mg, 706 +/- 252 s vs. placebo, 221 +/- 38 s, P = 0.05) but not with clopidogrel (283 +/- 56 s, P = 0.98). There were no clinically significant bleeding events, serious adverse events, or discontinuations of the study drug.

CONCLUSIONS

Compared with clopidogrel 75 mg, prasugrel 10 mg and 20 mg daily for 10 days resulted in more rapid, more consistent, and higher levels of platelet inhibition.

Anti-angiogenic effects of the thienopyridine SR 25989 in vitro and in vivo in a murine pulmonary metastasis model

Neovascularisation is a key step in tumour growth and establishment of distant metastases. We have recently demonstrated that the thienopyridine SR 25989 an enantiomer of the anti-aggregant clopidogrel (Plavix) lacking anti-aggregant activity, inhibits endothelial cell proliferation in vitro by increasing the expression of endogenous thrombospondin-1, a natural potent inhibitor of angiogenesis. The anti-angiogenic effect of SR 25989 was further assessed in vitro in a quantitative assay of angiogenesis comprising a fragment of rat aorta embedded in a fibrin gel and in vivo in a pulmonary metastatic model using C57BL/6 mice inoculated in the foot pad with the highly metastatic melanoma cell line B16 F10. SR 25989 induced a dose dependent inhibition of spontaneous microvessel development in vitro reaching half maximal inhibition at around less than 50 microM and caused platelet derived growth factor induced angiogenesis to regress as a function of thienopyridine concentration. In vivo, SR 25989 did not alter significantly the growth rate of the primary tumour in the foot pad and did not inhibit development of inguinal nodes which appeared after amputation. However, the number and size of lung metastases were reduced in treated animals when examined at the time of sacrifice. In addition, the few metastases over 1 mm3 did not show any neovascularisation, as confirmed by negative von Willebrand immunostaining and in contrast to intense vascularisation seen in metastases developed by control mice. These results confirm that SR 25989 possesses potent anti-angiogenic properties and is able to inhibit metastatic dissemination and growth. The lack of effect on the primary tumour and inguinal nodes illustrates the complexity of the mechanisms involved in tumoural neo-angiogenesis and points out the possibility for distinct processes leading to neovascularisation in primary tumour as opposed to metastases.

Antiplatelet action of R-99224, an active metabolite of a novel thienopyridine-type G(i)-linked P2T antagonist, CS-747

1. CS-747 is a novel thienopyridine-type platelet ADP inhibitor which lacks in vitro activity. This study examined pharmacological profiles of R-99224, a hepatic metabolite of CS-747. 2. R-99224 produced a concentration-dependent inhibition of in vitro platelet aggregation in washed human platelets (0.03 - 1 microg ml(-1)), which was relatively specific to ADP compared to collagen and thrombin. 3. R-99224 (0.1 - 3 microg ml(-1)) also elicited a similar inhibition of ADP-induced aggregation in rat platelets. The inhibition by R-99224 (10 microg ml(-1)) persisted even after platelets were washed three times. Intravenous injection of R-99224 (0.1 - 3 mg kg(-1)) to rats resulted in a dose-dependent inhibition of ex vivo ADP-induced platelet aggregation. 4. R-99224 (0.1 - 100 microM) decreased binding of [(3)H]-2-methylthio-ADP ([(3)H]-2-MeS-ADP), a stable ligand for platelet ADP receptors, to washed human platelets. The inhibition by R-99224 reached a plateau at a concentration of 3 microM (1.4 microg ml(-1)), but complete inhibition was not achieved even at the highest concentration used (100 microM). 5. R-99224 (10 microM) in combination with ARL-66096 (0.3 microM), an ATP analogue-type G(i)-linked P2T receptor antagonist, produced no additional inhibition of [(3)H]-2-MeS-ADP binding. In contrast, [(3)H]-2-MeS-ADP binding was completely abolished by R-99224 (10 microM) in combination with A3P5PS (300 microM), a selective P2Y(1) antagonist, suggesting that R-99224 selectively binds to the G(i)-linked P2T receptor. 6. R-99224 (0.01 - 3 microg ml(-1)) inhibited ADP-induced [(125)I]-fibrinogen binding to human platelets in a concentration-dependent manner. R-99224 (0.1 - 1 microg ml(-1)) also inhibited the ADP-induced decrease in cyclic AMP levels in PGE(1)-stimulated platelets, whereas the agent did not affect ADP (10 microM)-induced Ca(2+) mobilization. 7. These findings suggest that R-99224 is a selective and irreversible antagonist of G(i)-linked P2T receptors and that R-99224 is a responsible molecule for in vivo actions of CS-747.

Results of the Ticlid or Plavix Post-Stents (TOPPS) trial: do they justify the switch from ticlopidine to clopidogrel after coronary stent placement?

In the Ticlid or Plavix Post-Stents (TOPPS) trial, 1016 patients undergoing successful coronary stent placement were randomized to receive aspirin and either ticlopidine or clopidogrel. In this trial, the dosages and regimens of ticlopidine and clopidogrel resembled more closely those used in most catheterization laboratories than did the two previous randomized trials comparing ticlopidine and clopidogrel. The results of the TOPPS trial support the current practice of substituting ticlopidine for clopidogrel in stent patients.