Clopidogrel Resistance: Identifying and Overcoming a Barrier to Effective Antiplatelet Treatment

Tongue diagnostic parameters-based diagnostic signature in coronary artery disease patients with clopidogrel resistance after percutaneous coronary intervention

BACKGROUND

Credible diagnostic stratification remains a challenge for coronary artery disease patients with clopidogrel resistance after percutaneous coronary intervention. Tongue diagnostic parameters-based diagnostic signatures might predict clopidogrel resistance.

METHODS

Clinical and tongue diagnostic parameters data were obtained from coronary artery disease patients with clopidogrel resistance after percutaneous coronary intervention patients and then analyzed. Tongue diagnostic parameters-based diagnostic signatures were developed through univariate and multivariate logistic regression analysis. The diagnostic prediction was assessed using a receiver operating characteristic curve.

RESULTS

A total of 101 patients were consecutively identified. Then, tongue diagnostic parameters were identified as significantly associated with clopidogrel resistance diagnosis and were combined with risk factors to develop a model. The receiver operating characteristic curve analysis showed that tongue diagnostic parameters-based diagnostic signatures performed well in diagnosing clopidogrel resistance with an area under the receiver operating characteristic curve value of 0.819.

CONCLUSIONS

This study identified a novel tongue diagnostic parameters-based diagnostic signature to reliably distinguish clopidogrel resistance diagnosis in coronary artery disease patients undergoing percutaneous coronary intervention. Further larger, multicenter prospective studies are desired to validate this model.

Ticagrelor versus Clopidogrel in the Dual Antiplatelet Regimen for Unruptured Intracranial Aneurysm Treated with Stent-Assisted Coil Embolization: A Single-Center Cohort Study

BACKGROUND

Dual antiplatelet therapy (DAPT) of aspirin plus clopidogrel is commonly used in patients with unruptured intracranial aneurysms treated with stent-assisted coil (SAC) embolization. However, the unpredictable clopidogrel efficacy of the 5%-55% nonresponders limits its use. Ticagrelor, as a potential alternative of clopidogrel, is an antiplatelet agent with low resistance rates but uncertain efficacy and safety in these patients.

METHODS

A single-center cohort study was performed to compare the efficacy and safety of ticagrelor with clopidogrel in the DAPT regimen in patients with unruptured intracranial aneurysms and treated with SAC. The patients with clopidogrel resistance identified as inadequate adenosine diphosphate inhibition rate determined by thromboelastography were treated with ticagrelor instead, and both drugs achieved adequate suppression of platelet aggregation when stents were implanted. The occurrence of major adverse cardiovascular and cerebrovascular events (MACCE) and bleeding events was recorded through 6 months follow-up.

RESULTS

Data from 86 patients with 99 unruptured intracranial aneurysms and treated by SAC with clopidogrel were compared with those from 108 patients with 111 aneurysms and treated with ticagrelor. Neither the baseline characteristics nor the incidence of the MACCE or bleeding events differed between the groups. Ticagrelor exerted significantly higher adenosine diphosphate inhibition rate than that of the clopidogrel. Multivariable logistic regression analysis showed that the incidence of MACCE was related to hematocrit and fibrinogen levels.

CONCLUSIONS

Ticagrelor seemed to be as effective and safe as clopidogrel for SAC in unruptured intracranial aneurysms. Hematocrit and fibrinogen levels were independent risk factors for the incidence of MACCE.

The Use of Thromboelastography in Percutaneous Coronary Intervention and Acute Coronary Syndrome in East Asia: A Systematic Literature Review

Dual antiplatelet therapy (DAPT), alongside percutaneous coronary intervention (PCI), is central to the prevention of ischemic events following acute coronary syndrome (ACS). However, response to therapy can vary due to several factors including CYP2C19 gene variation, which shows increased prevalence in East Asian populations. DAPT responsiveness can be assessed using techniques such as light transmission aggregometry (LTA), VerifyNow^® and thromboelastography with the PlateletMapping^® assay, and there is increasing focus on the utility of platelet function testing to guide individualized treatment. This systematic literature review of one English and three Chinese language databases was conducted to evaluate the evidence for the utility of thromboelastography in ACS/PCI in East Asia. The search identified 42 articles from the English language and 71 articles from the Chinese language databases which fulfilled the pre-determined inclusion criteria, including 38 randomized controlled trials (RCTs). The identified studies explored the use of thromboelastography compared to LTA and VerifyNow in monitoring patient responsiveness to DAPT, as well as predicting ischemic risk, with some studies suggesting that thromboelastography is better able to detect low DAPT response than LTA. Other studies, including one large RCT, described the use of thromboelastography in guiding the escalation of DAPT, with some evidence suggesting that such protocols reduce ischemic events without increasing the risk of bleeding. There was also evidence suggesting that thromboelastography can be used to identify individuals with DAPT hyporesponsiveness genotypes and could potentially guide treatment by adjusting therapy in patients depending on responsiveness.

Identification of the Antithrombotic Mechanism of Leonurine in Adrenalin Hydrochloride-Induced Thrombosis in Zebrafish via Regulating Oxidative Stress and Coagulation Cascade

Thrombosis is a general pathological phenomenon during severe disturbances to homeostasis, which plays an essential role in cardiovascular and cerebrovascular diseases. Leonurine (LEO), isolated from Leonurus japonicus Houtt, showes a crucial role in anticoagulation and vasodilatation. However, the properties and therapeutic mechanisms of this effect have not yet been systematically elucidated. Therefore, the antithrombotic effect of LEO was investigated in this study. Hematoxylin-Eosin staining was used to detect the thrombosis of zebrafish tail. Fluorescence probe was used to detect the reactive oxygen species. The biochemical indexes related to oxidative stress (lactate dehydrogenase, malondialdehyde, superoxide dismutase and glutathione) and vasodilator factor (endothelin-1 and nitric oxide) were analyzed by specific commercial assay kits. Besides, we detected the expression of related genes (fga, fgb, fgg, pkcα, pkcβ, vwf, f2) and proteins (PI3K, phospho-PI3K, Akt, phospho-Akt, ERK, phospho-ERK FIB) related to the anticoagulation and fibrinolytic system by quantitative reverse transcription and western blot. Beyond that, metabolomic analyses were carried out to identify the expressions of metabolites associated with the anti-thrombosis mechanism of LEO. Our in vivo experimental results showed that LEO could improve the oxidative stress injury, abnormal platelet aggregation and coagulation dysfunction induced by adrenalin hydrochloride. Moreover, LEO restored the modulation of amino acids and inositol metabolites which are reported to alleviate the thrombus formation. Collectively, LEO attenuates adrenalin hydrochloride-induced thrombosis partly via modulating oxidative stress, coagulation cascade and platelet activation and amino acid and inositol metabolites.

CD31 Mimetic Coating Enhances Flow Diverting Stent Integration into the Arterial Wall Promoting Aneurysm Healing

BACKGROUND AND PURPOSE

Beyond aneurysmal occlusion, metallic flow diverters (FDs) can induce an adverse endovascular reaction due to the foreignness of metal devices, hampering FD endothelialization across the aneurysm neck, and arterial healing of intracranial aneurysms. Here, we evaluated the potential benefits of an FD coating mimicking CD31, a coreceptor critically involved in endothelial function and endovascular homeostasis, on the endothelialization of FDs implanted in vivo.

METHODS

Nitinol FD (Silk Vista Baby) and flat disks were dip-coated with a CD31-mimetic peptide via an intermediate layer of polydopamine. Disks were used to assess the reaction of endothelial cells and blood elements in vitro. An aneurysm rabbit model was used to compare in vivo effects on the arterial wall of CD31-mimetic-coated (CD31-mimetic, n=6), polydopamine-coated (polydopamine, n=6), and uncoated FDs (bare, n=5) at 4 weeks post-FD implantation. In addition, long-term safety was assessed at 12 weeks.

RESULTS

In vitro, CD31-mimetic coated disks displayed reduced adhesion of blood elements while favoring endothelial cell attachment and confluence, compared to bare and polydopamine disks. Strikingly, in vivo, the neoarterial wall formed over the CD31-mimetic-FD struts at the aneurysm neck was characteristic of an arterial tunica media, with continuous differentiated endothelium covering a significantly thicker layer of collagen and smooth muscle cells as compared to the controls. The rates of angiographic complete occlusion and covered branch arterial patency were similar in all 3 groups.

CONCLUSIONS

CD31-mimetic coating favors the colonization of metallic endovascular devices with endothelial cells displaying a physiological phenotype while preventing the adhesion of platelets and leukocytes. These biological properties lead to a rapid and improved endothelialization of the neoarterial wall at the aneurysm neck. CD31-mimetic coating could therefore represent a valuable strategy for FD biocompatibility improvement and aneurysm healing.

Pharmacokinetic, pharmacodynamic, and pharmacogenetic assays to monitor clopidogrel therapy

Clopidogrel is the most common and widely used antiplatelet agent for patients with coronary artery disease following confirmation by electrocardiographic studies. The nonresponsiveness of patients to clopidogrel and the possibility of testing for clopidogrel resistance by platelet function assays (PFA) are contentious issues. Light transmission aggregometry (LTA) is considered as the gold standard test among all PFA. In this review, the most commonly used PFA used for monitoring the effect of clopidogrel, LTA, vasodilator-stimulated phosphoprotein assay phosphorylation, rotational thromboelastometry (ROTEM) delta and ROTEM platelet, thromboelastography, PFA-100, VerifyNow P2Y12 assay, Multiplate analyzer, Plateletworks assay and pharmacogenetic studies, are comparatively discussed including their principles of action, advantages, and disadvantages. VerifyNow P2Y12 assay can be accepted as the ideal point of care test out of the discussed assays. However, modified assays are required which could overcome the limitations associated with currently available assays.

Failure of platelet function analyser 200 to demonstrate clinical clopidogrel resistance in a patient undergoing intracranial vascular stenting

A patient undergoes intracranial stent insertion for stent-assisted coiling of a basilar tip aneurysm and left middle cerebral artery aneurysm. A flow diverting stent is also placed across an anterior communicating artery aneurysm. Prior to the procedure, the patient takes dual antiplatelet medications, being aspirin and clopidogrel. Because of the concern regarding in-stent thrombus and thromboembolic complications related to intracranial stenting and the high rate of clopidogrel resistance, preoperative platelet function testing (PFT) was undertaken to ensure platelet inhibition. In this case, PFT was performed on a platelet function analyser which demonstrated platelet inhibition. Ten days following the procedure, the patient represented with thromboembolic stroke. Repeat PFT performed with whole blood impedance aggregometry and despite full medication compliance demonstrated clopidogrel resistance. Clopidogrel was then ceased and prasugrel commenced. This case demonstrates the importance of appropriate platelet inhibition in patients with intracranial stents and the controversy surrounding PFT.

Reduction of Preoperative Waiting Time before Urgent Surgery for Patients on P2Y12 Inhibitors Using Multiple Electrode Aggregometry: A Retrospective Study

P2Y₁₂ inhibitor discontinuation is essential before most surgical interventions to limit bleeding complications. Based on pharmacodynamic data, fixed discontinuation durations have been recommended. However, as platelet function recovery is highly variable among patients, a more individualized approach based on platelet function testing (PFT) has been proposed. The aim of this retrospective single-centre study was to determine whether PFT using whole blood adenosine diphosphate–multiple electrode aggregometry (ADP–MEA) was associated with a safe reduction of preoperative waiting time. Preoperative ADP–MEA was performed for 29 patients on P2Y₁₂ inhibitors. Among those, 17 patients underwent a coronary artery bypass graft. Twenty one were operated with an ADP–MEA ≥ 19 U (quantification of the area under the aggregation curve), and the waiting time was shorter by 1.6 days (median 1.8 days, IQR 0.5–2.9), by comparison with the current recommendations (five days for clopidogrel and ticagrelor, seven days for prasugrel). Platelet function recovery was indeed highly variable among individuals. With the 19 U threshold, high residual platelet inhibition was associated with perioperative platelet transfusion. These results suggest that preoperative PFT with ADP–MEA could help reduce waiting time before urgent surgery for patients on P2Y₁₂ inhibitors.

MGB Block ARMS Real-Time PCR for Diagnosis of CYP2C19 Mutation in a Chinese Population

Background:

CYP2C19 is an important genetic factor modulating clopidogrel dose requirement.

Objective:

Therefore, a simple and economic genotyping method for predicting the clopidogrel dose of patients would be useful in clinical applications.

Methods:

In this study, the MGB blocker ARMS real-time PCR contained two forward primers, two MGB blockers and a common reverse primer have been used for CYP2C19*2, *3 and *17 substitutions.

Results:

Results showed that heterozygotes and homozygotes of CYP2C19*2, *3 and *17 could be distinguished by the MGB blocker ARMS real-time PCR successfully. In the Chinese population, patients with allele frequencies of CYP2C19*2, *3, and *17 are 18.43%, 3.03% and 0.76%, respectively.

Conclusion:

This study indicates that the MGB blocker ARMS real-time PCR will be a simple, economical method for the rapid detection of SNPs in CYP2C19.

Prevalence of clOpidogrel 'resIstaNce' in a selected population of patients undergoing elective percutaneous coronary intervention at a tertiary cardiovascular centre in Trinidad: the POINT pilot study

Objectives

This novel, pilot study aimed to assess the estimated prevalence of high on-treatment platelet reactivity (HPR) in Trinidad and Tobago.

Methods

Patients (n=40) who were awaiting elective percutaneous coronary intervention on maintenance dual antiplatelet therapy (DAPT) with aspirin 81 mg daily and clopidogrel 75 mg or loaded at least 48 hours prior were recruited. Platelet reactivity with the VerifyNow P2Y12 assay (Accriva Diagnostics, San Diego, California, USA) was assessed prior to cardiac catheterisation.

Results

60.7% (17/28) of the South Asian (Indo-Trinidadians) patients had HPR, whereas 14.3% (1/7) of Africans and 40% (2/5) of mixed ethnicity had HPR. There was a significant association between HPR (P2Y12 reaction units >208) and ethnicity with South Asians (Indo-Trinidadians) (OR 5.4; 95% CI 1.18 to 24.66, p=0.029).

Conclusions

This pilot study serves to introduce the preliminary observation that the estimated prevalence of HPR is considerably higher within the heterogeneous population in Trinidad at 50% as compared with predominantly Caucasian studies. Furthermore, the HPR is significantly higher in South Asians (Indo-Trinidadians) (>60% of patients) which has severe clinical repercussions considering the cardiovascular disease pandemic. Clopidogrel may not be a satisfactory or optimal antiplatelet agent in this subgroup, and therefore, another more potent antiplatelet such as ticagrelor should be used instead. Further large-scale studies are imperative to confirm these findings. (Funded by the University of the West Indies, St. Augustine; POINT ClinicalTrials.gov number, NCT03667066.).

Ligustrazine inhibits platelet activation via suppression of the Akt pathway

Aberrant activation of platelets has a critical role in thrombotic vascular events, including atherosclerosis, arterial thrombosis and myocardial infarction. The process of platelet activation is associated with multiple intracellular signaling pathways, including the phosphoinositide 3‑kinase/AKT serine/threonine kinase (Akt) pathway. The well‑known medicinal herb Rhizoma Ligusticum Wallichii (RLW) has long been used in China to clinically treat various cardiovascular disorders. As the most pharmacologically active component of RLW, ligustrazine has been demonstrated to possess a potent antiplatelet activity. However, the precise mechanisms mediating the bioactivities of ligustrazine have not been thoroughly elucidated. The present study evaluated the effects of ligustrazine hydrochloride (LH; the clinical‑grade form of ligustrazine) on platelet activation and investigated the underlying molecular mechanisms. In vitro and ex vivo platelet activation models were used, established by stimulating rat platelet‑rich plasma either with the platelet activator adenosine diphosphate (ADP) or with the specific Akt pathway activator insulin‑like growth factor‑1 (IGF‑1). The results demonstrated that treatment with LH significantly and dose‑dependently inhibited ADP‑induced platelet aggregation, in addition to thromboxane A2 (TXA2) secretion and intracellular Ca2+ mobilization in platelets, in vitro and ex vivo. In addition, LH markedly suppressed ADP‑induced Akt phosphorylation in vitro and ex vivo. Furthermore, LH markedly inhibited IGF‑1‑induced Akt phosphorylation, platelet aggregation, TXA2 formation and Ca2+ mobilization in vitro. Finally, LH was able to reverse adrenaline‑induced shortening of bleeding time. Taken together, these results suggested that ligustrazine possesses a broad range of antiplatelet activities without apparent hemorrhagic side-effects, and suppression of Akt signaling may be one of the mechanisms by which ligustrazine exerts its antiplatelet activities.

Clopidogrel non-responsiveness in patients undergoing percutaneous coronary intervention using the VerifyNow test: frequency and predictors

Objectives

Stent thrombosis and death after percutaneous coronary intervention (PCI) can be caused by a phenomenon known as clopidogrel non-responsiveness which has been shown to occur in approximately 5%–44% of patients. We investigated the responsiveness of clopidogrel in an Iraqi series of cases. Our aim was to determine for the first time the frequency and predictors of clopidogrel non-responsiveness among Iraqi patients with ischaemic heart disease undergoing PCI.

Methods

The study was conducted at the Cardiac Catheterization Center, Baghdad Teaching Hospital, Medical City, from January to May 2014, and included patients who presented for PCI. A platelet aggregation test was performed for those patients using the VerifyNow system.

Results

A total of 115 patients (mean age: 58.3±10.1 years; male sex: 73.9%) were included in the study. 18.3% of the study population were clopidogrel non-responders, which was comparable with the results of a Chinese study (20.28%, P=0.796) but contrasted with other reports from Jordan, Brazil and Thailand. The major independent predictive factor for non-responsiveness in our report was diabetes mellitus (OR 5.96, 95% CI 2.23 to 13.71; P=0.001), followed by hypertension (OR 4.135, P=0.035), obesity (OR 3.44, P=0.037) and male sex (OR 3.039, P=0.045). Previous use of clopidogrel (OR 0.17, P=0.02) and younger age (OR 0.72, P=0.026) were identified as protective factors.

Conclusions

In this study, 18.3% of patients were non-responders to clopidogrel and the major independent predictive factors for non-responsiveness were diabetes mellitus, hypertension, obesity and male sex.

Prevalence and risk factors of clopidogrel non-response among Saudi patients undergoing coronary angiography

OBJECTIVES

To estimate the prevalence of clopidogrel non-response and identify its risk factors among Saudi patients. 

METHODS

This cross-sectional study was conducted at Prince Sultan Cardiac Center, Riyadh, Kingdom of Saudi Arabia between January and June 2013, to assess the degree of platelet inhibition using the VerifyNow assay (Accumetrics, San Diego, CA, USA) after receiving clopidogrel standard loading dose. Clopidogrel resistance was defined as ≤15% platelet inhibition or greater than 213 P2Y12 reaction units (PRU). 

RESULTS

Three hundred and four patients were included in the study. The mean age was 60.3 ± 11.4 years, and 73% were males. Clopidogrel doses were 300 mg (57%), 600 mg (27%), and 75 mg (16%). All patients used aspirin (81 mg in 94%). Approximately 66% (200/304) showed in vitro clopidogrel non-response, 54% had low platelet inhibitions, and 61% had high post-loading PRU. Using multivariate regression analysis that included all significant characteristics; only diabetes (odds ratio [OR]: 2.36, 95% confidence interval [CI]: 1.30-4.27, p=0.005) and higher preloading PRU (OR: 2.39, 95% CI: 1.40-4.11, p=0.002) remained significantly associated with higher clopidogrel non-response while myocardial infarction (OR: 0.34, 95% CI: 0.15-0.81, p=0.014) remained significantly associated with lower clopidogrel non-response. The associations of morbid obesity and diuretics use with higher clopidogrel non-response were slightly attenuated.  

CONCLUSION

Our findings indicate a high rate of clopidogrel in-vitro non-response among Saudi patients undergoing coronary angiography.

Association of thrombelastographic parameters with post-stenting ischemic events

BACKGROUND AND PURPOSE

Thrombelastography (TEG) is widely used for the measurement of platelet function. However, few studies have investigated the TEG parameters in patients receiving extracranial or intracranial artery stenting for ischemic cerebrovascular disease. This study sought to describe the association of TEG parameters before the procedure with post-procedural ischemic events after extracranial or intracranial artery stenting.

METHODS

Patients in whom stenting was performed for extracranial or intracranial artery stenosis (70-99%) were recruited into the study. Blood samples were obtained for TEG to assess platelet function before stenting. The primary endpoint was ischemic stroke or transient ischemic attack in the territory of the stented artery.

RESULTS

A total of 218 patients were included in the study. During a mean follow-up period of 132 days (range 98-226 days), 18 (8.3%) primary endpoint events were recorded. Compared with patients without ischemic events, the ADP-induced platelet-fibrin clot strength (MA_ADP) was significantly higher (41.57±15.10 vs 33.50±13.86, p=0.020) and the ADP inhibition rate (ADP%) was significantly lower in patients with ischemic events (39.54±23.15 vs 55.29±24.43, p=0.009). Multivariate analysis identified MA_ADP and ADP% as significant independent predictors of subsequent ischemic events with HRs of 1.036 and 0.965, respectively. From receiver operating characteristic curve analysis, MA_ADP >49.95 mm had the best predictive value of ischemic events.

CONCLUSIONS

Our study suggests that TEG parameters MA_ADP and ADP% are associated with subsequent ischemic events in patients with extracranial or intracranial stents.

CLINICAL TRIAL NUMBER

NCT01925872.

Aspirin and clopidogrel alter core temperature and skin blood flow during heat stress

Antithrombotic therapy with oral aspirin (ASA) or clopidogrel (CLO) (Plavix; Bristol-Myers Squibb, Bridgewater, NJ) is associated with an attenuated skin vasodilator response and a greater rate of rise in core temperature in healthy, middle-age individuals during passive heating in a water perfused suit.

PURPOSE

The present double-blind, crossover study examined the functional consequences of 7 d of low-dose ASA (81 mg·d) versus CLO (75 mg·d) treatment in 14 healthy, middle-age (50-65 yr) men and women during passive heating in air (40 min at 30°C, 40% relative humidity) followed by exercise (60% V˙O2peak).

METHODS

Oral temperature (Tor) was measured in the antechamber (23.0°C ± 0.1°C) before entering a warm environmental chamber. After 40 min of rest, subjects cycled on a recumbent cycle ergometer for up to 120 min. Esophageal temperature (Tes) and laser Doppler flux were measured continuously, and the latter was normalized to maximal cutaneous vascular conductance (%CVCmax).

RESULTS

Before entry into the environmental chamber there were no differences in Tor among treatments; however, after 40 min of rest in the heat, Tes was significantly higher for ASA and CLO versus placebo (37.2°C ± 0.1°C, 37.3°C ± 0.1°C, vs 37.0°C ± 0.1°C, both P < 0.001), a difference that persisted throughout exercise (P < 0.001 vs placebo). The mean body temperature thresholds for the onset of cutaneous vasodilation were shifted to the right for both ASA and CLO during exercise (P < 0.05).

CONCLUSION

ASA and CLO resulted in elevated core temperatures during passive heat stress and shifted the onset of peripheral thermoeffector mechanisms toward higher body temperatures during exercise heat stress.

Ginsenoside Rg1 inhibits platelet activation and arterial thrombosis

INTRODUCTION

Derived from the root of Panax ginseng C.A.Mey, Panax notoginsenosides (PNS) is a widely used herbal medicine to treat atherothrombotic diseases in Asian medicine. Ginsenoside Rg1 is one of the main compounds responsible for the pharmaceutical actions of PNS. As platelets play pivotal roles in atherothrombogenesis, we therefore studied the effect of Rg1 on platelet activation and its underlying mechanisms.

MATERIALS AND METHODS

Human platelets are obtained from healthy subjects. Platelet activation and the inhibition of Rg1 were assessed by Born aggregometer, flow cytmetry, flow chamber and western blot. The in vivo thrombosis model was induced by 10% FeCl3 on mesenteric arterioles of wild type B57/b6 mice.

RESULTS

Rg1 significantly inhibited platelet aggregation induced by thrombin, ADP, collagen and U46619, e.g., aggregation rate stimulated by 0.1UmL(-1) thrombin was decreased 46% by Rg1. Rg1 also reduced thrombin (0.1UmL(-1))-enhanced fibrinogen binding and P-selectin expression of single platelet by 81% and 66%, respectively. Rg1 affected αIIbβ3-mediated outside-in signaling as demonstrated by diminished platelet spreading on immobilized fibrinogen. Rg1 also decreased the rate of clot retraction in platelet rich plasma. Furthermore, Rg1 decreased platelet adhesion on collagen surface under a shear rate correlated to the arterial flow (1000s(-1)) by approximately 70%. Western blot showed that Rg1 potently inhibited ERK phosphrylation. The in vitro findings were further evaluated in the mouse model of in vivo arterial thrombosis, and Rg1 was found to prolong the mesenteric arterial occlusion time (34.9±4.1min without and 64.3±4.9min with Rg1; p<0.01).

CONCLUSIONS

Rg1 inhibits platelet activation via the inhibition of ERK pathway, and attenuates arterial thrombus formation in vivo.

Thienopyridines resistance and recovery of platelet function after discontinuation of thienopyridines in cardiac surgery patients

OBJECTIVES

Patients who undergo cardiac operations under the effects of thienopyridines have a greater risk of major postoperative bleeding, transfusions and surgical revision due to bleeding. Discontinuation of thienopyridine is suggested but an adequate recovery period following discontinuation is still under debate, with opinions ranging from 3 to 7 days. The aim of this study was to assess the rate of recovery of thienopyridine-resistant patients and the time taken for resumption of platelet function after discontinuation of thienopyridine, in the setting of patients scheduled for cardiac operations.

METHODS

This was a retrospective study, based on 344 patients screened for platelet aggregation before cardiac operations. All the patients received thienopyridines within 7 days prior to the test. Multiple electrode aggregometry adenosine diphosphate test was used to assess platelet aggregation before the operation.

RESULTS

Thienopyridine resistance rate was 28%. Patients receiving clopidogrel had a significantly higher rate (32%) of resistance, compared with those receiving ticlopidine (14%) and thienopyridine resistance was significantly associated with platelet count (P = 0.006). The time taken to recover platelet function after thienopyridine discontinuation was variable between individuals; the only factor associated with a faster recovery time was the serum bilirubin value (P = 0.002). Platelet aggregation values high enough to avoid major bleeding were reached 3 days after discontinuation (95% confidence interval: 2-4 days); however, a complete recovery of platelet function was reached only after 8 days (95% confidence interval: 7-9 days).

CONCLUSIONS

Patient-specific factors determine the effectiveness of thienopyridine treatment and platelet function recovery rate. Among these, platelet count (for thienopyridine resistance) and serum bilirubin values (for platelet function recovery rate) should be considered.

Effect of premedication method and drug resistance of antiplatelet agent on periprocedural thromboembolic events during coil embolization of an unruptured intracranial aneurysm

Objective

A retrospective review of premedication method and drug resistance of aspirin and clopidogrel in association with thromboembolic events during and after coil embolization of an unruptured intracranial aneurysm was conducted.

Methods

Our premedication policy for coil embolization of an unruptured intracranial aneurysm has changed from administration of the loading dose before the procedure (i.e. loading group) to repeated administration of the maintenance dose for several days (i.e. preparation group). The loading group (27 patients with 29 aneurysms) and the preparation group (30 patients with 35 aneurysms) were compared for identification of the effect of premedication method on periprocedural thromboembolic events. The results of drug response assays of the preparation group were analyzed with respect to periprocedural thromboembolic events.

Results

No statistically significant difference in incidence of thromboembolic events was observed between the loading group and the preparation group. Analysis of the results of the drug response assay showed high prevalence (56.7%, 73.3%) of clopidogrel resistance and relatively low prevalence (6.7%) of aspirin resistance. Patients who had thromboembolic events tended to have lower responsiveness to both aspirin and clopidogrel than patients without it.

Conclusion

The method of antiplatelet premedication does not affect the rate of periprocedural thromboembolic events in coil embolization for treatment of an unruptured intracranial aneurysm. Nevertheless, considering the high prevalence of drug resistance, it is reasonable to premedicate antiplatelet agents in the preparation method for the drug response assay. Use of a higher dose of aspirin and clopidogrel or addition of an alternative drug (cilostazol or triflusal) can be applied against antiplatelet agent resistance. However, because the hemorrhagic risk associated with this supplementary use of antiplatelet agent has not been well-documented, the hemorrhagic risk and the preventive benefit must be weighed.

Impaired bioavailability and antiplatelet effect of high-dose clopidogrel in patients after cardiopulmonary resuscitation (CPR)

PURPOSE

Bioavailability of clopidogrel in the form of crushed tablets administered via nasogastric tube (NGT) has not been established in patients after cardiopulmonary resuscitation. Therefore, we performed a study comparing pharmacokinetic and pharmacodynamic response to high loading dose of clopidogrel in critically ill patients after cardiopulmonary resuscitation (CPR) with patients scheduled for elective coronary angiography with stent implantation.

METHODS

In the NGT group (nine patients, after cardiopulmonary resuscitation, mechanically ventilated, therapeutic hypothermia), clopidogrel was administered in the form of crushed tablets via NGT. Ten patients undergoing elective coronary artery stenting took clopidogrel per os (po) in the form of intact tablets. Pharmacokinetics of clopidogrel was measured with high-performance liquid chromatography (HPLC) before and at 0.5, 1, 6, 12, 24 h after administration of a loading dose of 600 mg. In five patients in each group, antiplatelet effect was measured with thrombelastography (TEG; Platelet Mapping) before and 24 h after administration.

RESULTS

The carboxylic acid metabolite of clopidogrel was detected in all patients in the po group. In eight patients, the maximum concentration was measured in the range of 0.5-1 h after the initial dose. In four patients in the of NGT group, the carboxylic acid metabolite of clopidogrel was undetectable and in the remaining patients was significantly delayed (peak values at 12 h). All patients in the po group reached clinically relevant (>50 %) inhibition of thrombocyte adenosine diphosphate (ADP) receptor after 24 h compared with only two in the NGT group (p = 0.012). There was a close correlation between peak of inactive clopidogrel metabolite plasmatic concentration and inhibition of the ADP receptor (r = 0.79; p < 0.001).

CONCLUSION

The bioavailability of clopidogrel in critically ill patients after cardiopulmonary resuscitation is significantly impaired compared with stable patients. Therefore, other drugs, preferentially administered intravenously, should be considered.