Effectiveness of Platelet Function Analyzer-100 for Laboratory Detection of Anti-Platelet Drug-Induced Platelet Dysfunction

Genotype-guided dual antiplatelet therapy in cerebrovascular disease: assessing the risk and benefits for ethnic populations

INTRODUCTION

Cerebrovascular disease is a leading cause of morbidity and mortality in the world and antiplatelet therapy is a main pharmacologic means of secondary prevention. Clinical information has accumulated about benefit of dual antiplatelet therapy in certain clinical scenarios, genetic causes of antiplatelet resistance and its effect on clinical outcomes, and ethnic and geographic distributions of genetic polymorphisms.

AREAS COVERED

This review covers literature related to the pharmacogenomics of antiplatelet agents with a focus on ethnic variability, antiplatelet resistance, and dual antiplatelet therapy in cerebrovascular disease.

EXPERT OPINION

Selecting patients for dual antiplatelet therapy and specific agents require consideration of multiple factors. Ethnic factors should be considered in certain circumstances, but additional research is needed to determine the generalizability of the findings.

Resistance on the Latest Oral and Intravenous P2Y12 ADP Receptor Blockers in Patients with Acute Coronary Syndromes: Fact or Myth?

Novel P2Y12 ADP receptor blockers (ADPRB) should be preferred in dual-antiplatelet therapy in patients with acute coronary syndrome. Nevertheless, there are still patients who do not respond optimally to novel ADP receptor blocker therapy, and this nonoptimal response (so-called "high on-treatment platelet reactivity" or "resistance") could be connected with increased risk of adverse ischemic events, such as myocardial re-infarction, target lesion failure and stent thrombosis. In addition, several risk factors have been proposed as factors associated with the phenomenon of inadequate response on novel ADPRB. These include obesity, multivessel coronary artery disease, high pre-treatment platelet reactivity and impaired metabolic status for prasugrel, as well as elderly, concomitant therapy with beta-blockers, morphine and platelet count for ticagrelor. There is no literature report describing nonoptimal therapeutic response on cangrelor, and cangrelor therapy seems to be a possible approach for overcoming HTPR on prasugrel and ticagrelor. However, the optimal therapeutic management of "resistance" on novel ADPRB is not clear and this issue requires further research. This narrative review article discusses the phenomenon of high on-treatment platelet reactivity on novel ADPRB, its importance in clinical practice and approaches for its therapeutic overcoming.

Design, synthesis, and biological evaluation of low-toxic lappaconitine derivatives as potential analgesics

The C₁₈-diterpenoid alkaloid lappaconitine (LA) is a non-addictive analgesic used in China. The toxicity (LD₅₀ = 11.7 mg/kg) limits its application. Two series of LA derivatives, including amides and sulfonamides (1-93), were designed and synthesized by modification on their C4 acetamidobenzoate side chains in this work. In vivo analgesic activity and toxicity of all derivatives were evaluated, and the structure-activity relationship was summarized. Six lead compounds (35, 36, 39, 49, 70, and 89) exhibited approximate analgesic activity to LA but with significantly reduced toxicity. The therapeutic index of these compounds is 14-30 times that of LA. In vivo metabolism study of the lead compounds 39, 49, 70, and 89 were conducted by UPLC-MS^E, indicating the reason for the low toxicity of the potential derivatives might be they are difficult to metabolize to toxic metabolite N-deacetyllappaconitine compared to LA. The effects of lead compounds on sodium channels and hERG channels were also studied by ion channel reader (ICR) which further revealed their analgesic and toxicity-attenuating mechanisms. Sodium channel assay revealed that the analgesic mechanism of these lead compounds was inhibiting the Na_v 1.7 channels. Taken together, compound 39 was provided as a new analgesic lead compound with significantly low toxicity and comparable activity to LA.

Platelet reactivity testing in peripheral artery disease

DISCLAIMER

In an effort to expedite the publication of articles related to the COVID-19 pandemic, AJHP is posting these manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time.

PURPOSE

Oral antiplatelet therapy is routinely used to prevent adverse cardiovascular events in patients with peripheral artery disease (PAD). Several laboratory tests are available to quantify the degree of platelet inhibition following antiplatelet therapy. This article aims to provide a review of the literature surrounding platelet functional testing in patients with PAD receiving oral P2Y12 inhibitors and to offer guidance to clinicians for the use and interpretation of these tests.

SUMMARY

A literature search of PubMed and the Web of Science Core Collection database was conducted. All studies that performed platelet function testing and reported clinical outcomes in patients with PAD were included. Evaluation of the data suggests that, among the available testing strategies, the VerifyNow platelet reactivity unit (PRU) test is the most widely used. Despite numerous investigations attempting to define a laboratory threshold indicating suboptimal response to antiplatelet therapy, controversy exists about which PRU value best correlates with cardiovascular outcomes (ie, mortality, stent thrombosis, etc). In the PAD literature, the most commonly used PRU thresholds are 208 or higher and 235 or higher. Nonetheless, adjusting antiplatelet regimens based on suboptimal P2Y12 reactivity values has yet to be proven useful in reducing the incidence of adverse cardiovascular outcomes. This review examines platelet function testing in patients with PAD and discusses the interpretation and application of these tests when monitoring the safety and efficacy of P2Y12 inhibitors.

CONCLUSION

Although platelet functional tests may be simple to use, clinical trials thus far have failed to show benefit from therapy adjustments based on test results. Clinicians should be cautioned against relying on this test result alone and should instead consider a combination of laboratory, clinical, and patient-specific factors when adjusting P2Y12 inhibitor therapy in clinical practice.

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.

Platelet function testing in patients with post-operative tonsillectomy bleeding may be a useful early identifier of inherited platelet function disorders

BACKGROUND

Post-tonsillectomy bleeding is the most frequent complication of tonsillectomy. Inherited platelet function disorders have an estimated prevalence of 1 per cent. Any association between post-tonsillectomy bleeds and undiagnosed inherited platelet function disorders has not been investigated before.

OBJECTIVES

To assess the prevalence of inherited platelet function disorders in a cohort of post-tonsillectomy bleed patients.

METHODS

An observational cohort study was conducted using hospital digital records. Platelet function analyser 100 ('PFA-100') closure time was tested on post-tonsillectomy bleed patients who presented to hospital.

RESULTS

Between 2013 and 2017, 9 of 91 post-tonsillectomy bleed patients who underwent platelet function analyser 100 testing (9.89 per cent) had positive results. Five patients (5.49 per cent) had undiagnosed inherited platelet function disorders. Four patients had false positive results secondary to a non-steroidal anti-inflammatory drug effect (specificity of 95.3 per cent) proven by repeat testing six weeks later, off medication. The false negative rate was 0 per cent.

CONCLUSION

The prevalence of inherited platelet function disorders in our post-tonsillectomy bleed cohort is five-fold higher than in the general population. Platelet function analyser 100 testing when patients present with a post-tonsillectomy bleed allows management of their inherited platelet function disorder.

Comprehensive platelet phenotyping supports the role of platelets in the pathogenesis of acute venous thromboembolism - results from clinical observation studies

Background

The pathogenesis of arterial and venous thrombosis is in large part interlaced. How much platelet phenotype relates to acute venous thromboembolism (VTE) independent of the underlying cardiovascular profile is presently poorly investigated.

Methods

Platelet count and mean platelet volume (MPV), platelet aggregation in whole blood and platelet rich plasma (PRP), platelet-dependent thrombin generation (TG) and platelet surface activation markers were measured under standardized conditions. Machine learning was applied to identify the most relevant characteristics associated with VTE from a large array (N = 58) of clinical and platelet-related variables.

Findings

VTE cases (N = 159) presented with lower platelet count and MPV vs controls (N = 140). Whole blood aggregation showed shorter collagen/Epinephrine closure times in cases, particularly within acetylsalicylic acid (ASA) users. Within ASA users, higher PRP aggregation after adenosine diphosphate (ADP), epinephrine, collagen and arachidonic acid was observed in cases vs controls. Within non-ASA and/or subjects on anticoagulants, cases presented with lower aggregation after ADP and collagen vs controls. Lower platelet-dependent TG, higher CD63 on resting and lower PAC-1 expression after collagen/ADP in-vitro stimulated platelets further characterized VTE cases vs controls, independent of therapy. Lasso regression analysis identified 26 variables associated with VTE of which 69% were platelet-related.

Interpretation

Comprehensive phenotyping of platelet function identified a large proportion of low responders to ASA in VTE cases. Lower platelet-dependent TG and lower platelet reactivity after ex-vivo stimulation characterized the “platelet exhausted syndrome” in cases. Finally, from a large array of covariates including clinical risk factors, platelet biomarkers comprised 69% of all selected variables differentiating VTE cases vs controls.

Funding

German Federal Ministry of Education and Research, CTH-Mainz and Bayer AG.

Platelet Mapping by Thromboelastography and Whole Blood Aggregometry in Adult Patients Supported by Mechanical Circulatory Support Device on Aspirin Therapy

Patients on mechanical circulatory support (MCS) devices are placed on aspirin and may require platelet function testing (PFT) to monitor the adequacy of therapy. Routine laboratory PFT is performed using whole blood aggregation (WBA) which typically has a long turnaround time (4-5 hours) and may not be readily available. By contrast, platelet mapping by thromboelastography (TPM) can provide results within 45 minutes. The objective of this study was to compare the results of TPM with WBA. We compared platelet mapping maximal amplitude (MA) by TPM with that of arachidonic acid (AA) to WBA with AA by impedance. We analyzed paired samples where both TPM and WBA were available. Of 45 paired samples, 34 were from 29 MCS patients and 11 were from non-MCS patients. When applying institutional interpretation guidelines with an MA_Activator cutoff of ≤40 mm, WBA_AA vs TPM MA_AA in non-MCS and MCS patients correlated well with an accuracy of 100 and 94.4%, respectively. MA_Activator >40 had poor correlation with an accuracy of 37.5%. Irrespective of MA_Activator value, TPM AA inhibition expressed in percent of inhibition had poor accuracy. When used with proper guidelines for interpretation, specifically when MA_Activator ≤ 40 mm, TPM is a suitable and reliable test to use for MCS patients on aspirin.

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.

Changes in and significance of platelet function and parameters in Kawasaki disease

Kawasaki disease (KD) is a systemic febrile, inflammatory vascular disease of unknown etiology. The coronary artery abnormality (CAA) caused by KD has become the most commonly acquired heart disease in children. Initial treatment of intravenous immunoglobulin (IVIG) can reduce the incidence of CAA. Thrombocytosis is common during the course of KD, but changes in and significances of platelet function and parameters are unclear. In this study, we enrolled 120 patients, including 40 patients with KD, 40 febrile controls, and 40 afebrile controls. The platelet function was assessed using the platelet function analyzer (PFA)-200. Platelet parameters, including platelet count (PLT), mean platelet volume (MPV), platelet distribution width (PDW), and platelet hematocrit (PCT) were measured. In the febrile period, the PDW and MPV were lower in KD patients (P < 0.05). The platelet function did not change significantly during the febrile period of KD but weakened in the defervescence phase. No significant differences between the CAA and normal groups, and between IVIG resistance and response groups. The diagnostic cutoff value of the PDW level for predicting KD was 10.85 fL with a sensitivity of 55% and a specificity of 77.5% (area under curve (AUC) = 0.690, 95% confidence interval (CI): 0.574–0.806, P < 0.01). Besides, the MPV level was 9.55 fL with sensitivity of 75% and specificity of 70% (AUC = 0.733, 95%CI: 0.620–0.846, P < 0.001). This is the first longitudinal study of platelet function changes in KD patients using PFA-200. Besides, lower PDW and MPV may be available markers for early diagnosis of KD.