Lack of association between the P2Y12 receptor gene polymorphism and platelet response to clopidogrel in patients with coronary artery disease

INTRODUCTION: Clopidogrel inhibits the ADP subtype P2Y(12) receptor. Recently, polymorphisms of this receptor have been associated with different degrees of platelet aggregation in healthy volunteers and have been suggested to modulate clopidogrel response. However, the role of gene sequence variations of the P2Y(12) receptor in patients treated with clopidogrel has not yet been assessed. MATERIALS AND METHODS: The T744C polymorphism of the P2Y(12) receptor gene was assessed in 119 patients: 36 undergoing coronary stenting receiving a 300 mg loading dose (Group A) and 83 on long-term clopidogrel (75 mg/day) treatment (Group B). Patients were divided into 2 subgroups according to the presence or absence of the C allele: carriers (CT heterozygotes and CC homozygotes) and non-carriers (TT homozygotes). Platelet aggregation, assessed by light transmittance aggregometry following ADP, collagen, TRAP and epinephrine stimuli, and platelet activation (GP IIb/IIIa activation and P-selectin expression), assessed by whole blood flow cytometry in ADP and TRAP-stimulated platelets, were performed. Platelet function was assessed at baseline and 4 and 24 h following clopidogrel loading dose in Group A and when patients where on clopidogrel treatment for at least 1 month in Group B. RESULTS: The genotype distribution of Group A was: 22/36 (61.1%) non-carriers and 14/36 (38.9%) carriers of the C allele; Group B: 57/83 (68.7%) non-carriers and 26/83 (31.3%) carriers of the C allele. There were no differences between groups for all the assessed platelet function assays. CONCLUSIONS: The T744C polymorphism of the P2Y(12) receptor gene does not modulate platelet response to clopidogrel either in the early or long-term phases of treatment. This specific gene polymorphism alone is therefore unlikely to be the cause of variability in individual response to antiplatelet therapy.     

The P2Y1 receptor is normal in a patient presenting a severe deficiency of ADP-induced platelet aggregation.

ADP is a key stimulus inducing platelet shape change and aggregation, a rise in internal calcium and inhibition of adenylyl cyclase. These signaling pathways are thought to be activated by three independent receptors, but to date only the P2Y1 receptor responsible for calcium mobilization and the ionotropic P2X1 receptor have been identified. We report here the characteristics of the P2Y1 receptor in a patient presenting a selective deficiency of ADP-induced aggregation. Cloning of the P2Y1 gene revealed that the patient's DNA and mRNA were normal. Pharmacological studies showed that the P2Y1 receptor was expressed and functional in patient's platelets. Hence, the P2Y, receptor is not the cause of the impaired ADP-induced platelet aggregation in this patient. The P2X1 mRNA was also found to be present and normal. These findings add evidence to previous observations suggesting that a third P2 receptor coupled to adenylyl cyclase may be involved in ADP-induced platelet aggregation.     

Pharmacodynamic assessment of a novel P2Y12 receptor antagonist in Japanese patients with coronary artery disease undergoing elective percutaneous coronary intervention

Introduction

Numerous reports have shown that prasugrel shows a rapid and consistent antiplatelet effect among European and US patients. Previous studies suggest that prasugrel might be expected to achieve an adequate antiplatelet effect in healthy Asian subjects, even at lower doses than those assessed in the TRITON-TIMI 38 study. In this study, the antiplatelet effect of prasugrel was evaluated in Japanese coronary artery disease (CAD) patients undergoing percutaneous coronary intervention (PCI).

Methods and results

Eighty-four patients were randomized into four treatment groups: prasugrel 10/2.5 mg (loading dose [LD]/maintenance dose [MD]), 15/3.75 mg or 20/5 mg, and clopidogrel 300/75 mg. The LD of each regimen was administered the day before PCI, followed by 28-day MD on aspirin background therapy (81-100 mg). Antiplatelet effects were evaluated by light transmission aggregometry and VASP assay.The mean inhibition of platelet aggregation (IPA) induced by 20 μM of adenosine diphosphate at 4 hours after LD was higher among the prasugrel 10/2.5 mg, 15/3.75 mg and 20/5 mg groups compared with the clopidogrel group (12.3%, 20.9%, 29.8% vs. 8.4%, respectively). The proportion of subjects with an IPA of < 10% on Day 28 was lower among the prasugrel 15/3.75 mg, and 20/5 mg groups than in the clopidogrel group (0%, 6.3% vs. 15.8%, respectively). No “major” or “clinically relevant non-major” bleeding was observed.

Conclusions

Prasugrel 15 mg LD/3.75 mg MD or higher doses was well tolerated and achieved a more rapid, higher and consistent antiplatelet effect than clopidogrel in Japanese CAD patients undergoing PCI.     

Platelet aggregation is dependent on platelet count in patients with coronary artery disease

Introduction

Platelet function testing in whole blood is widely used to evaluate the effect of antiplatelet agents, but it is not known whether results are affected by whole blood parameters. This study investigated the importance of platelet count, haematocrit, red blood cells (RBC), and white blood cells in whole blood platelet aggregometry.

Materials and methods

We included 417 patients with coronary artery disease on aspirin mono-therapy and 21 aspirin-naïve healthy individuals. Blood sampling was performed one hour after aspirin ingestion. The antiplatelet effect of aspirin was evaluated using the VerifyNow® Aspirin assay and multiple electrode aggregometry (MEA, Multiplate®) induced by collagen (1.0 μg/mL) and arachidonic acid (1.0 or 0.75 mmol/L). Measurements of whole blood parameters were performed to evaluate the three major cell lines in circulating blood.

Results

In patients, platelet count correlated significantly with platelet aggregation (MEA_collagen, p < 0.0001; MEA_{arachidonic acid}, p < 0.0001; VerifyNow®, p = 0.03). Haematocrit and RBC correlated inversely with MEA induced by collagen (p_haematocrit < 0.001; p_RBC = 0.07) and with VerifyNow® (p_haematocrit < 0.0001; p_RBC < 0.0001), but not with MEA induced by arachidonic acid (p_haematocrit = 1; p_RBC = 0.87). White blood cells correlated significantly with platelet aggregation (MEA_collagen, p < 0.001; MEA_{arachidonic acid}, p < 0.0001; VerifyNow®, p = 0.05). Similar associations were observed in aspirin-naïve healthy individuals.

Conclusions

Whole blood aggregometry is dependent on all major cell lines in whole blood. Importantly, platelet aggregation is significantly associated with platelet count even within the normal range.     

Impact of P2Y12-ADP receptor polymorphism on the efficacy of clopidogrel dose-adjustment according to platelet reactivity monitoring in coronary artery disease patients

Introduction

High on-treatment platelet reactivity (HTPR) after clopidogrel loading dose (LD) is associated with a high risk of thrombotic events after percutaneous coronary intervention(PCI). We have demonstrated that HTPR could be overcome in the majority of cases using LD adjustment resulting in an improved clinical outcome. However this strategy failed in nearly 10% of patients with HTPR. We aimed to determine if P2Y12-ADP receptor polymorphisms were associated with failed dose adjustment.

Materiel and method

Forty-three patients undergoing PCI were included in this prospective study. A VASP index ≥ 50% after a 600 mg LD of clopidogrel defined HTPR. Dose adjustment was performed according to PR monitoring to reach a VASP index < 50%. Genetic polymorphism of the P2Y12-ADP receptor was determined by direct sequencing.

Results

Patients with successful dose-adjustment (SDA) (n = 33) and failed (FDA) (n = 10) dose-adjustment groups were compared. The 2 groups were similar in terms of cardiovascular risk factors including diabetes mellitus (SDA vs FDA: 42 vs 20%; p = 0.3). The prevalence of the H2 allele of the P2Y12-ADP receptor was also similar between the 2 groups (p = 0.3). The H2 allele was found in 6 patients which are all included in the SDA group. After the first 600 mg loading dose of clopidogrel, patients carrying at least one H2 allele had similar VASP index compared to those carrying two copies of the wild type allele (H1) (SDA vs FDA: 44.9 ± 14.9 vs 43.5 ± 10%; p = 0.8).

Conclusion

The present study suggests that the H2 allele of the P2Y12-ADP receptor is not involved in clopidogrel failed dose adjustment according to platelet reactivity monitoring.     

Comparison of platelet fibronectin, ADP-induced platelet aggregation and serum total nitric oxide (NOx) levels in angiographically determined coronary artery disease

INTRODUCTION: Coronary thrombosis is an important determinant of prognosis in patients with acute coronary syndromes. Fibronectin is also found in platelets within the alpha secretory granules and secreted following platelet stimulation by a variety of agonist. Available data suggest that expression of platelet fibronectin on the cell surface may indicate a role in platelet aggregation and adhesion to fibrin thrombi and connective tissue. Clear evidence has emerged that a concerted action of nitric oxide (NO) generated by either endothelial or platelet NO synthases regulates platelet activation, causing inhibition of adhesion and aggregation. The aim of the present study was determining and correlating the serum total NO (NOx), platelet fibronectin and ADP-induced platelet aggregation levels in coronary artery disease (CAD) patient subgroups. MATERIALS AND METHODS: A total of 43 coronary artery disease patients were included in this study. Peripheral blood samples from patients with coronary artery disease were obtained from the Department of Cardiology. Platelet aggregation tests with adenosine diphosphate (ADP) were analyzed by using aggregometer. Platelet fibronectin concentrations were determined by enzyme-linked immunosorbent assay (ELISA). Serum total nitric oxide (NOx) levels were determined by colorimetric method. RESULTS: In patients with double-vessel disease, platelet fibronectin levels were found to be significantly higher than no-vessel disease (p<0.001), single-vessel disease (p<0.01) and triple-vessel disease (p<0.001). In addition, in patients with single-vessel disease platelet fibronectin levels significantly higher than no-vessel disease (p<0.05). We could not find any significant differences in ADP-induced platelet aggregation and serum NOx values between CAD patient subgroups. There was a positive correlation between platelet fibronectin levels and severity of disease (r=0.315, p<0.05).     

Association between platelet P2Y12 haplotype and risk of cardiovascular events in chronic coronary disease

INTRODUCTION: A positive association was recently described between P2Y12 platelet receptor H1 and H2 haplotypes and peripheral artery disease. We tested the described P2Y12 receptor haplotypes in a group of patients with coronary artery disease. STUDY DESIGN AND METHODS: The P2Y12 platelet receptor H1 and H2 haplotypes was tested in a group of 540 patients enrolled in the Medical, Angioplasty, or Surgery Study II (MASS II), a randomized trial comparing treatments for patients with coronary artery disease (CAD) and preserved left ventricular function. After a 3-year follow-up period, the incidence of the composite end point of cardiac death, myocardial infarction, and refractory angina requiring revascularization was determined in the H1/H1, H1/H2 and H2/H2 haplotype groups. We used Student's t-test and the chi-square test to analyze the differences among groups and Kaplan-Meier method to calculate survival curves. Risk was assessed with the use of a Cox proportional-hazards model. RESULTS: The frequency of haplotypes among studied patients were 410 (75.9%) H1/H1, 119 (22.0%) H1/H2 and 11 (2.1%) H2/H2. The baseline clinical characteristics, mean clinical follow-up time and received treatment of each genotype group were similar. We did not disclose any association between haplotype groups regarding the incidence of any of the studied cardiovascular end-points. CONCLUSION: This is the first report studying the association of P2Y12 platelet receptor H1 and H2 haplotype and cardiovascular events. Our findings do not provide evidence for a strong association between H1/H1 and H1/H2 haplotypes and a increased risk of cardiovascular events in a population with CAD. Future works should address the role of the H2/H2 haplotype as a genetic marker for cardiovascular events.     

Intravascular microaggregation and in vitro platelet aggregation in coronary artery disease

The amount and protein composition of heparin precipitable fraction (HPF), and the plasma concentrations of fibrinogen, fibronectin, alpha 1-acid glycoprotein, alpha 1-antitrypsin, haptoglobin and C-reactive protein (CRP) were determined in healthy subjects as well as during the course of acute myocardial infarction (AMI). In all samples tested, HPF consisted nearly exclusively of fibrinogen and fibronectin. In the small precipitates from healthy subjects, approximately equal amounts of these two proteins were recovered. During the first days of AMI, plasma fibrinogen increased 2-3 fold. At the same time, however, the amount of HPF increased 5-10 fold. This increase was associated with increased precipitation of fibrinogen, whereas no simultaneous increase in fibronectin was found. In fact, a slight drop in plasma as well as HPF-fibronectin was regularly observed during this period. During the following week HPF returned to normal values, whereas the plasma fibrinogen remained elevated. No satisfactory explanation for this discrepancy can be offered at present. Thus, no evidence could be provided that other acute phase proteins than fibrinogen itself were involved. Some experiments, however, indicated qualitative changes in the fibrinogen participating in the HPF precipitation. Further studies are necessary to clarify this point. Such studies are in progress.     

Inhibition of ADP-induced platelet aggregation by dipyrone in patients with acute myocardial infarction

ADP induced platelet aggregation was investigated in 48 patients within three days of the first signs of acute myocardial (AMI). Thirty six of them received 1 gram of dipyrone. Twelve patients who did not receive dipyrone served as controls. Platelet aggregation was found severely inhibited in 11 patients who had received dipyrone up to 12 hours before investigation and moderately inhibited among 25 patients who were given the drug 12-24 hours prior to the investigation. All the patients with AMI who did not receive dipyrone, exhibited a state of hyperaggregability evidenced by the presence of a second phase of aggregation even with 0.5 microM ADP. The inhibitory activity of dipyrone on the second phase of platelet aggregation resembles that of other non steroidal anti-inflammatory drugs.     

Reduced platelet response to aspirin in patients with coronary artery disease and type 2 diabetes mellitus

Introduction

Diabetes mellitus is complicated by accelerated atherosclerosis, resulting in an increased risk of coronary artery disease (CAD) and thrombosis. Despite the proven benefits of aspirin, previous studies indicate a reduced cardiovascular protection from aspirin in diabetic patients. We aimed to investigate whether diabetes mellitus influenced the platelet response to aspirin in patients with CAD.

Materials and Methods

Platelet aggregation and activation were evaluated during aspirin treatment in 85 diabetic and 92 non-diabetic patients with CAD. Adherence to aspirin was carefully controlled. All patients had CAD verified by coronary angiography and were taking 75 mg non-enteric coated aspirin daily.

Results

Diabetic patients showed significantly higher levels of platelet aggregation compared to non-diabetic patients evaluated by VerifyNow^® Aspirin (p = 0.03) and Multiplate^® aggregometry using arachidonic acid (AA) 0.5 mM (p = 0.005) and 1.0 mM (p = 0.009). In addition, platelet activation determined by soluble P-selectin was significantly higher in diabetics compared to non-diabetics (p = 0.005). The higher AA-induced aggregation was associated with higher levels of HbA_1c. Compliance was confirmed by low levels of serum thromboxane B₂ (below 7.2 ng/mL). Diabetics had significantly higher levels of serum thromboxane B₂ (p < 0.0001).

Conclusions

Diabetic patients with CAD had significantly higher levels of both platelet aggregation and activation compared to non-diabetic patients with CAD despite treatment with the same dosage of aspirin. These findings may partly explain the reduced cardiovascular protection from aspirin in diabetic patients.     

Comparison of VASP-phosphorylation assay to light-transmission aggregometry in assessing inhibition of the platelet ADP P2Y12 receptor

There is need to improve platelet function testing to monitor the response to antiplatelet drugs. We compared flow-cytometric analysis of intraplatelet vasodilator-stimulated phosphoprotein phosphorylation (VASP-P) to light-transmission aggregometry for the detection of drug-induced in-vitro inhibition of the platelet P2Y12 ADP receptor on 22 healthy subjects (10 males, 12 females, 28.5 +/- 6.6 years). The platelet reactivity index (PRI) of VASP was calculated both from mean fluorescence intensity (MFI) and percent of fluorescence-positive platelets in the presence of PGE1 with or without ADP (10 microM). Platelet aggregation was induced by ADP (1.25, 2.5 and 5 microM). Cangrelor, a competitive inhibitor of the P2Y12 receptor, preincubated 5 minutes, induced a concentration-dependent inhibition of platelet ADP-receptor function in both tests. Indeed PRI (%) based on either MFI or percent platelets gated were highly correlated with each other (r = 0.97, p %lt; 0.0001) and with aggregation induced by ADP. The IC50 of cangrelor against each of the three ADP concentrations used in aggregometry increased from 5.8 +/- 3.4 nM to 23.1 +/- 4.0 nM and to 98 +/- 25 nM, respectively. The IC50 of cangrelor based on VASP-P was within the same range (25.5 +/- 7.7 nM). No correlation was observed between IC50 values of cangrelor and ADP concentrations giving 50% effect (EC50) in the absence of the drug. However, at 10 nM cangrelor seven subjects could be identified by the VASP-P assay as " low responders " to the drug (PRI > 50%), and six of them also had an aggregation response to 5 micro M ADP > 50%. These six subjects showed the lowest ADP EC50 values in the absence of the drug, possibly reflecting high sensitivity of their platelet P2Y12 receptors to ADP. In conclusion, both the VASP-P assay and light-transmission aggregometry detect in a comparable way in-vitro pharmacological inhibition of the platelet P2Y12 ADP receptor and its individual variability.     

Potentiation of platelet aggregation by heparin in human whole blood is attenuated by P2Y12 and P2Y1 antagonists but not aspirin

INTRODUCTION: Unfractionated heparin (UFH) potentiates platelet aggregation induced by some agonists. P2Y12 and P2Y1 receptors play a major role in amplifying platelet aggregation. We assessed the ability of cangrelor, a selective P2Y12 antagonist, A2P5P, a selective P2Y1 antagonist, and aspirin to block the potentiating effects of heparin. MATERIALS AND METHODS: Whole blood from healthy human volunteers was anticoagulated with either hirudin or UFH 10 IU/ml. Some tubes anticoagulated with hirudin also contained UFH 1 or 10 IU/ml. The low-molecular-weight heparin dalteparin was also assessed. Platelet aggregation was performed using whole blood single-platelet counting. Dense granule release was assessed using 14C-5HT-labelled platelets. RESULTS: UFH and, to a lesser extent, dalteparin potentiated platelet aggregation induced by ADP, PAF, 5HT, U46619, epinephrine and TRAP in a concentration-dependent manner but inhibited aggregation induced by collagen. Cangrelor effectively opposed the potentiating effects of heparins on sustained aggregation induced by ADP, PAF, 5HT, U46619 and TRAP but had less effect on epinephrine-induced aggregation, whereas A2P5P was more effective at blocking both the initial phase of ADP-induced aggregation and the aggregation response to epinephrine, reflecting the differences in G protein coupling between the agonist receptors. Aspirin had no effect on potentiation by heparin. Heparins did not increase ADP- or TRAP-induced 14C-5HT release. CONCLUSIONS: Heparins potentiate platelet responses to ADP and numerous other agonists. This potentiation is attenuated by cangrelor and A2P5P, and is not mediated by increased dense granule release. ADP receptor antagonists but not aspirin may have potential therapeutic benefits in counteracting the pro-thrombotic effects of heparins.     

Intracoronary platelet release in patients with and without coronary artery disease

Intracoronary platelet release of beta-thromboglobulin (BTG) was measured in 18 patients with a history of chest pain by analysis of aortic and coronary sinus blood samples in rest and during atrial pacing. Eleven proved to have coronary artery disease, while seven had normal coronary arteriograms and served as controls. In both groups no statistically significant transmyocardial gradient of platelet and plasma BTG content was observed under basal conditions, although the aortic plasma BTG levels in the patients (60.4 +/- 4.1 ng/ml) were significantly (p less than 0.05) higher than in the controls (47.5 +/- 2.6 ng/ml). However, also during atrial pacing no significant gradient could be demonstrated in the patients nor in the controls. It is concluded, that in stable coronary artery disease measurable intracoronary platelet release does not occur in rest nor atrial pacing and, therefore, does not seem to contribute to the development of exercise-induced myocardial ischaemia.     

The effect of clopidogrel besylate and clopidogrel hydrogensulfate on platelet aggregation in patients with coronary artery disease: a retrospective study

Background

Recently several alternative forms of the original clopidogrel hydrogensulfate (CHS) were spread worldwide. A large amount of such drugs turned out to be clopidogrel besylate (CB). Only three studies, involving healthy volunteers, investigated the antiplatelet effect of CB, whereas its attribute remained unexplored in the case of patients with cardiovascular diseases. This retrospective study aimed to evaluate the difference between the antiplatelet effects of two clopidogrel formulas, CHS and CB, on patients with coronary artery diseases.

Methods

Data of 150 patients with previous CHS treatment were investigated. According to the documentations, the CHS therapy was shifted to CB. 94 patients of the selected population received dual antiplatelet therapy, clopidogrel and aspirin. The antiplatelet effects of CHS and CB were compared by ADP induced platelet aggregation measurements using light transmission aggregometry.

Results

Irrespective of the therapeutic combinations the performed statistical investigations failed to show significant difference (p = 0.30) between the effect of CB (AGGmax_CB: 27.6 ± 13.7%) or CHS (AGGmax_CHS: 29.0 ± 15.3%) on the ADP induced platelet aggregation. Insignificant deviations were found in both forms of clopidogrel salts, either in the lack (AGGmax_CB : 32.5 ± 14,2%; AGGmax_CHS: 34,0 ± 16,1%; p = 0,29) or in the presence of aspirin (AGGmax_CB: 24.7 ± 12,5%; AGGmax_CHS: 26,0 ± 14,1%; p = 0,31).

Conclusion

Our results indicated that both CB and CHS had an identical inhibitory effect on ADP induced platelet aggregation in patients with cardiovascular diseases. Moreover their efficiency showed no overall significant difference in the case of dual antiplatelet therapy with aspirin as well. However there might be an inter- and intraindividual variability between the two clopidogrel formulas.     

Optical platelet aggregation versus thromboxane metabolites in healthy individuals and patients with stable coronary artery disease after low-dose aspirin administration

IntroductionAspirin reduces cardiovascular events in patients with coronary artery disease (CAD), but studies report a highly variable response to aspirin, often referred to as ‘aspirin low-responsiveness’. We investigated whether 75 mg of daily non-enteric coated aspirin would completely inhibit the platelet cyclooxygenase-1 activity to a comparable extent in healthy individuals and stable CAD patients.MethodsWe assessed serum thromboxane B₂ (S-TxB₂), urinary 11-dehydro-TxB₂ (U-TxM) and arachidonic acid-induced optical platelet aggregometry (OPA) in 44 CAD patients on aspirin and in 22 healthy individuals before and after aspirin. OPA was performed in duplicate for four consecutive days during aspirin treatment after one week of treatment. Compliance was optimized by face-to-face interviews and pill counting and confirmed by S-TxB₂ measurements.ResultsAspirin inhibited S-TxB₂ > 99% in healthy individuals (median 1.1 ng/mL, interquartile range (IQR) = 0.8;1.9 after aspirin) and in patients, S-TxB₂ was reduced to a similar level (0.9 ng/mL (0.7;1.5)). Healthy individuals had a median U-TxM of 278.5 pg/mg creatinine (229.5;380.0) before aspirin and 68.5 pg/mg creatinine (59.0;99.7) on aspirin corresponding to an average 74% inhibition of the endogenous TxA₂ biosynthesis. In patients median U-TxM was 67.5 pg/mg creatinine (54.0;85.5). Seven study participants (11%) were aspirin low-responders according to OPA, but none had S-TxB₂ in the highest quartile.ConclusionsLow-dose aspirin suppressed S-TxB₂ to comparable levels in CAD patients and healthy individuals. Despite an almost complete inhibition of S-TxB₂, some participants were low-responders according to OPA. Thorough compliance control and use of thromboxane-specific assays are important when measuring platelet response to aspirin.     

Intrinsic platelet reactivity before P2Y12 blockade contributes to residual platelet reactivity despite high-level P2Y12 blockade by prasugrel or high-dose clopidogrel. Results from PRINCIPLE-TIMI 44

It was the objective of this study to determine whether the intrinsic platelet response to adenosine diphosphate (ADP) before thienopyridine exposure contributes to residual platelet reactivity to ADP despite high level P2Y12 blockade by prasugrel (60 mg loading dose [LD]), 10 mg daily maintenance dose [MD]) or high-dose clopidogrel (600 mg LD, 150 mg daily MD). High residual platelet function during clopidogrel therapy is associated with poor clinical outcomes. It remains unknown whether the relationship between platelet reactivity prior to treatment with clopidogrel (300 mg LD, 75 mg daily MD) and residual on-treatment platelet reactivity is maintained after more potent P2Y12 inhibition. PRINCIPLE-TIMI 44 was a randomised, double-blind, two-phase crossover study of prasugrel compared with high-dose clopidogrel in 201 patients undergoing cardiac catheterisation for planned percutaneous coronary intervention. ADP-stimulated platelet-monocyte aggregates, platelet surface P-selectin and platelet aggregation were measured pre-treatment, during LD (6 h and 18-24 h) and MD (15 d). Correlations of pre-treatment to on-treatment values were determined by Spearman rank order. Prasugrel resulted in greater platelet inhibition than high-dose clopidogrel for each measure. However, for both drugs, pre-treatment reactivity to ADP predicted 6 h, 18-24 h and 15 day reactivity to ADP (correlations 0.24-0.62 for platelet-monocyte aggregates and P-selectin). In conclusion, a patient's intrinsic platelet response to ADP before exposure to thienopyridines contributes to residual platelet reactivity to ADP despite high level P2Y12 blockade with high-dose clopidogrel or even higher level P2Y12 blockade with prasugrel. Patients who are hyper-responsive to ADP pre-treatment are more likely to be hyper-responsive to ADP on-treatment, which may be relevant to therapeutic strategies.     

The use of the VerifyNow P2Y12 point-of-care device to monitor platelet function across a range of P2Y12 inhibition levels following prasugrel and clopidogrel administration

Variability in response to antiplatelet agents has prompted the development of point-of-care (POC) technology. In this study, we compared the VerifyNow P2Y12 (VN-P2Y12) POC device with light transmission aggregometry (LTA) in subjects switched directly from clopidogrel to prasugrel. Healthy subjects on aspirin were administered a clopidogrel 600 mg loading dose (LD) followed by a 75 mg/d maintenance dose (MD) for 10 days. Subjects were then switched to a prasugrel 60 mg LD and then 10 mg/d MD for 10 days (n = 16), or to a prasugrel 10 mg/d MD for 11 days (n = 19). Platelet function was measured by LTA and VN-P2Y12 at baseline and after dosing. Clopidogrel 600 mg LD/75 mg MD treatment led to a reduction in P2Y(12) reaction units (PRU) from baseline. A switch from clopidogrel MD to prasugrel 60 mg LD/10 mg MD produced an immediate decrease in PRU, while a switch to prasugrel 10 mg MD resulted in a more gradual decline. Consistent with the reduction in PRU, device-reported percent inhibition increased during both clopidogrel and prasugrel regimens. Inhibition of platelet aggregation as measured by LTA showed a very similar pattern to that found with VN-P2Y12 measurement, irrespective of treatment regimens. The dynamic range of VN-P2Y12 appeared to be narrower than that of LTA. With two different thienopyridines, the VN-P2Y12 device, within a somewhat more limited range, reflected the overall magnitude of change in aggregation response determined by LTA. The determination of the clinical utility of such POC devices will require their use in clinical outcome studies.