Monitoring aspirin treatment in patients with thrombocytosis: Comparison of the platelet function analyzer (PFA)-100 with optical aggregometry

Identification of High Platelet Reactivity Despite ADP P2Y 12 Inhibitor Treatment: Two Populations in the Vasodilator-Stimulated Phosphoprotein Assay and Variable PFA-P2Y Shapes of Curve

Introduction  Response to ADP P2Y ₁₂ receptor inhibition by clopidogrel can be evaluated by various techniques. Here, we compared a functional rapid point-of-care technique (PFA-P2Y) with the degree of biochemical inhibition assessed by the VASP/P2Y ₁₂ assay. Methods  Platelet response to clopidogrel was investigated in 173 patients undergoing elective intracerebral stenting (derivation cohort n  = 117; validation cohort n  = 56). High platelet reactivity (HPR) was defined as PFA-P2Y occlusion time <106 seconds or VASP/P2Y ₁₂ platelet reactivity index (PRI) >50%. Results  In the derivation cohort, receiver operator characteristics analysis for the ability of PFA-P2Y to detect biochemical HPR showed high specificity (98.4%) but poor sensitivity (20.0%) and a very low area under the curve (0.59). The VASP/P2Y ₁₂ assay revealed two coexisting platelet populations with different levels of vasodilator-stimulated phosphoprotein (VASP) phosphorylation: a fraction of highly phosphorylated, inhibited platelets and another of poorly phosphorylated, reactive platelets. Analysis of the PFA-P2Y curve shape revealed different types, categorized by time of occlusion (<106 seconds, 106 to 300 seconds, >300 seconds), and pattern (regular, irregular, and atypical). Noteworthy, curves with late occlusion and permeable curves with an irregular or atypical pattern correlated with VASP-PRI >50% and smaller sizes of the inhibited platelet subpopulation. Considering the PFA-P2Y shape of the curve for the detection of HPR improved sensitivity (72.7%) and preserved specificity (91.9%), with a rather high AUC (0.823). The validation cohort confirmed the VASP/P2Y ₁₂ assay data and the usefulness of considering the PFA-P2Y curve shape. Conclusion  In patients treated with acetylsalicylic acid and clopidogrel for 7-10 days, the VASP/P2Y ₁₂ assay reveals two coexisting subpopulations of differentially inhibited platelets, whose relative sizes predict global PRI and distinct PFA-P2Y curve patterns, indicating incomplete clopidogrel efficacy. The detailed analysis of both VASP/P2Y ₁₂ and PFA-P2Y is necessary for optimal detection of HPR.

Laboratory assessment of the anticoagulant activity of dabigatran

BACKGROUND

Our aim was to identify laboratory assays in order to assess the anticoagulant effects of dabigatran etexilate (DE).

METHODS

Twenty patients with nonvalvular atrial fibrillation treated on DE (110 mg per os twice daily) and 20 on acenocoumarol were studied. Conventional coagulation tests, endogenous thrombin potential (ETP), thromboelastometry (ROTEM), epinephrine-induced light transmission aggregometry (LTA), and Hemoclot Thrombin Inhibitors (HTI) were performed in all patients.

RESULTS

In ROTEM analysis, the lysis index at 60 minutes was significantly lower in patients receiving DE (P = .011). In LTA, patients on DE showed decreased aggregation compared to those on acenocoumarol, marginally insignificant (P = .068). Regarding ETP, acenocoumarol affected thrombin generation more than dabigatran (area under the curve [AUC], P < .001), while statistically significant associations were detected between dabigatran levels, as determined by the HTI assay, and almost all parameters of ETP assay (AUC, P < .001).

CONCLUSION

The role of ETP in estimating anticoagulant activity of dabigatran possibly requires further research.

Changes in response to antiaggregatory treatment in patients with myeloproliferative neoplasms: a sequential study using multiple electrode aggregometry

In the present study, we used multiple electrode aggregometry (MEA) to investigate the response to aspirin and clopidogrel treatment, and its potential changes over a long-time disease course in patients with myeloproliferative neoplasms (MPNs). arachidonic acid (ASPI), ADP, and thrombin receptor activating peptide (TRAP) tests were performed at two timepoints between 32-50 months in 21 patients with MPN and 1-46 months in 29 controls. We further checked the medical records of the participants to identify a potential correlation of changes in the treatment response with clinical events. In MPN, four out of 13 patients treated with 100 mg of aspirin, no patients receiving 50 mg of aspirin, and one out of five clopidogrel-treated patients showed a therapeutic antiplatelet effect. In the subsequent examinations, five patients changed from response to nonresponse or vice versa. Initial nonresponse and changes from an initial response to nonresponse were observed in six patients with thrombotic events. In the controls, 25 out of 26 aspirin-treated patients and two out of three clopidogrel-treated patients showed an initially adequate in-vitro response. Except from one patient changing from initial aspirin nonresponse to response, all controls showed a stable response state. One control with two ischemic strokes showed a nonresponse to clopidogrel. In conclusion, MEA detects the response to antiaggregatory treatment, as well as its changes during the disease course in patients with MPN. An initial or subsequent nonresponse was observed in patients with thrombotic events.

Preparation and evaluation of oral controlled-release cilostazol formulation: pharmacokinetics and antithrombotic efficacy in dogs and healthy male Korean participants

Objectives

To prepare oral controlled-release cilostazol formulations and evaluate their pharmacokinetics and pharmacodynamics in dogs and humans compared with a commercial twice-daily immediate-release formulation (Pletal), thereby showing the potential for the development of an improved once-daily cilostazol formulation.

Methods

Six different controlled-release preparations were formulated using a micronized cilostazol, solubilizer/absorption enhancer and erodible hydrogel. In-vitro drug release profiles were tailored by varying hydrogel viscosity. Pharmacokinetics and pharmacodynamic (antithrombotic) efficacy were evaluated in beagle dog model of arterial thrombosis. Finally, their pharmacokinetics and pharmacodynamics were also evaluated in healthy human volunteers after single and multiple oral administrations.

Key findings

Hydrogel viscosity-dependent sustained drug release profiles were observed with zero-order release kinetics during 8–12 h. In dogs and humans, compared with Pletal, prolonged drug absorption profiles were observed in the two controlled-release formulations studied. In dogs, the controlled-release formulations showed greater antithrombotic efficacy than twice-daily Pletal. In humans, the antithrombotic efficacy of the selected once-daily cilostazol formulation was equivalent to that of twice-daily Pletal after single and multiple administrations.

Conclusions

The prepared oral controlled-release cilostazol formulation may provide prolonged drug absorption and sufficient therapeutic efficacy, potentially serving as an oral once-daily cilostazol formulation to improve patient compliance.

Assessment of the response to acetylsalicylic acid in patients with myeloproliferative neoplasms by whole blood assays: a comparison of the PFA-100 with multiple electrode aggregometry

Since thrombotic and haemorrhagic complications are the most important causes of morbidity and mortality in myeloproliferative neoplasms (MPN), establishing valid techniques for the monitoring of antiaggregatory treatment would be beneficial. The aim of this study was to assess the aspirin responsiveness in patients with MPN by multiple electrode aggregometry (MEA) and the PFA-100, to determine the concordance rate between the two techniques and to examine a potential clinical impact. Twenty-two consecutive outpatients with polycythaemia vera and essential thrombocythaemia receiving long-time treatment with 100 mg of aspirin were included and clinically re-evaluated within six months after study entry. All subjects were identified as aspirin responders using the PFA-100, whereas only nine (41%) study participants were detected as responders by MEA. The difference in the response rates was statistically highly significant (p < 0.0001). The median aggregation result was 55.5 U (8-123) in the ASPI test, and the median PFA-100 closure time (CT) was 300 sec (221 to 300) in the COL-EPI test. Within the clinical observation period no thrombotic or haemorrhagic events occurred in the study population. In this study we concluded that MEA and the PFA-100 are suitable devices for the detection of a response to aspirin treatment in patients with MPN, but differ significantly in the response rates and thus show a low concordance rate.

Direct evidence for normalization of platelet function resulting from platelet count reduction in essential thrombocythemia

Essential thrombocythemia is characterized by persistent elevation and functional disturbances of platelets. Both the platelet function analyzer-100 (PFA-100) collagen-epinephrine (CEPI) cartridge and aggregometry with epinephrine are considered sensitive and valid methods in detecting abnormal platelet function in essential thrombocythemia. We attempted to confirm that restoration of abnormal platelet function results from platelet count reduction in essential thrombocythemia, by using these two methods. Thirty-nine essential thrombocythemia patients were divided into two groups on the basis of their platelet count. Group A participants (n = 20) exhibited platelet counts greater than 500 × 10/l, whereas group B participants (n = 19) had platelet counts below this limit. Hematological parameters, plasma von Willebrand factor (vWF) antigen and activity levels were assessed. Platelet function was analyzed by the PFA-100 and light transmission aggregometry with epinephrine, collagen, and ADP. The point mutation JAK2 V617F was identified and its effect on platelet function tests was also investigated. By using logistic regression analysis, white blood cell count, vWF activity level, and the measurements of aggregation in response to epinephrine were significantly different between the two groups. Epinephrine-induced aggregation retained the statistical significance in the multivariable procedure (P : 0.002). PFA-100 CEPI closure times were lower - but not statistically significant - in group B. Neither the JAK2 V617F positivity nor different cytoreductive treatments had any influence on ex-vivo platelet function tests. Our findings demonstrate normalization of platelet function resulting from platelet count reduction in essential thrombocythemia and reinforce the concept of lowering platelet counts in these patients.

Evaluation of platelet function and pharmacological platelet inhibition in patients with myeloproliferative disorders using multiple electrode aggregometry

BACKGROUND

The aim of this study was to describe platelet aggregation characteristics by multiple electrode aggregometry (MEA) and to evaluate MEA for its potential to detect platelet dysfunction and response to anti-aggregatory drugs in patients with myeloproliferative disorders (MPD).

METHODS

We compared the platelet response to arachidonic acid (ASPI test), adenosine diphosphate (ADP test) and thrombin receptor activating peptide (TRAP test) in hirudin-anticoagulated blood of 55 patients with polycythaemia vera and essential thrombocythaemia and 75 controls.

RESULTS

Comparing MPD patients and controls no statistically significant difference indicative of platelet dysfunction was found in MPD patients. Analysis of covariance revealed platelet- and leukocyte count as a significant influencing factor on MEA function. Furthermore we could demonstrate that ASA and clopidogrel treatment results in a statistically significant lower ASPI (Controls: p<0.0001, MPD: p<0.0001) and ADPtest value (MPD: p=0.00125) compared to untreated patients thereby validating the method for monitoring of anti-aggregatory therapy.

CONCLUSION

In this study MEA was confirmed as a valid method for monitoring of ASA and clopidogrel treatment in patients with MPD and normal control subjects. The platelet and leukocyte count were identified as major influencing factors on MEA aggregation tests both in MPD patients and controls. No functional platelet abnormalities were detected in MPD patients.

The role of the Platelet Function Analyzer (PFA)-100 and platelet aggregometry in the differentiation of essential thrombocythemia from reactive thrombocytosis

INTRODUCTION

The most crucial component of all diagnostic criteria for essential thrombocythemia (ET) has been the exclusion of reactive thrombocytosis (RT). Our aim was to evaluate the diagnostic performance of the PFA-100 collagen-epinephrine (CEPI) cartridge test and epinephrine-induced aggregometry individually, but mainly combined, in the differentiation of ET from RT.

MATERIALS AND METHODS

26 patients with ET and 25 with RT were studied. Platelet function was analyzed by the PFA-100 and by light transmission aggregometry with epinephrine and ADP. The JAK2 mutational status was identified and hematological parameters, plasma von Willebrand factor antigen and activity levels were also assessed.

RESULTS

The sensitivity (Se), specificity (Sp), positive predictive value (PPV), and the negative predictive value (NPV) of PFA-100 CEPI vs epinephrine-induced aggregometry in the differentiation of ET from RT were estimated as follows: Se (%): 78.9 vs 84.6, Sp (%): 92.0 vs 96.0, PPV (%): 88.2 vs 95.7, NPV (%): 85.2 vs 85.7, respectively. When both of these methods were combined, a lower sensitivity of 68.4%, but a specificity of 100% was attained. The PPV observed with this double abnormal combination was 100% and the NPV 80.6%. Lastly, when we assessed the abnormality for either CEPI CT or epinephrine-induced aggregometry, the sensitivity was 100%, the specificity 88.0%, PPV 86.4% and NPV 100%. Thus, an abnormal combination was strongly suggestive of ET, while normal results with both methods excluded ET.

CONCLUSIONS

If our results are replicated by further studies, these two methods could be used very effectively as adjunct markers in the differentiation between ET and RT.