Impact of timing from blood sampling to pharmacodynamic assessment on measures of platelet reactivity in patients treated with P2Y12 receptor inhibitors.

Several platelet function tests (PFT) are available to assess the pharmacodynamic (PD) effects of P2Y12 inhibitors. However, there are technical variances between PFT, and P2Y12 inhibitors differ in pharmacological properties. Manufactures of PFT recommend a time-frame within which assessments needs to be executed. However, if the timing from blood sampling to processing affects PD results is unknown. We conducted a prospective study assessing the impact of timing from blood sampling to processing on PD measures using three different PFT. We studied 60 aspirin-treated patients with coronary artery disease (CAD) on maintenance P2Y12 inhibiting therapy [clopidogrel 75 mg/day (n=20), prasugrel 10 mg/day (n=20) and ticagrelor 90 mg bid (n=20)]. PD assessments (trough levels) were performed by VerifyNow P2Y12 (VN), light transmittance aggregometry (LTA) and vasodilator-stimulated phosphoprotein (VASP) at 30 minutes, 2 and 4 hours post-sampling; VASP was also performed at 24 hours. P2Y12 reaction units (PRU) by VN significantly decreased over time with all P2Y12 inhibitors (clopidogrel p<0.001; prasugrel p=0.016; ticagrelor p<0.001). PRU at 30 minutes and 2 hours were similar, but decreased at 4 hours. LTA showed consistent findings with VN. Conversely, PD measures as assessed by VASP were stable over time (p>0.1 for all P2Y12 inhibitors). In conclusion, in CAD patients on maintenance therapy with P2Y12 inhibitors, timing from blood sampling to processing significantly influences PD measures as assessed by VN and LTA, but not by VASP.

A head-to-head pharmacodynamic comparison of prasugrel vs. ticagrelor after switching from clopidogrel in patients with coronary artery disease: results of a prospective randomized study.

AIMS: Pharmacodynamic (PD) studies comparing prasugrel and ticagrelor have reached inconsistent findings. Therefore, a comprehensive investigation comparing the PD effects of prasugrel vs. ticagrelor after switching from clopidogrel therapy, exploring both loading dose (LD) and maintenance dose (MD) regimens represented the aim of this study. METHODS AND RESULTS: Patients (n = 110) with coronary artery disease were randomized to prasugrel (60 mg LD/10 mg MD q.d.) or ticagrelor (180 mg LD/90 mg MD b.i.d) therapy for 1 week. Pharmacodynamic assessments were conducted using three assays (vasodilator-stimulated phosphoprotein, VerifyNow P2Y12, and light transmittance aggregometry, LTA) at baseline, 30 min, 2, 24 h, and 1 week. The impact of initiating ticagrelor MD 12 vs. 24 h after LD administration was also assessed. Switching clopidogrel-treated patients to an LD of prasugrel or ticagrelor was associated with a reduction in platelet reactivity at 30 min and was sustained at all time points up to 1 week with the MD (P < 0.001 for all assays). Platelet reactivity was similar with prasugrel and ticagrelor with all assays at 30 min, 2 h, and 1 week (P > 0.05 for all time points), with the exception of LTA at 30 min (lower with prasugrel; P = 0.003). At 24 h, platelet reactivity was lower among patients initiating ticagrelor MD after 12 vs. 24 h post-LD. Rates of high platelet reactivity (HPR) were markedly reduced and similar between groups. CONCLUSION: Prasugrel and ticagrelor exert similar levels of P2Y12 inhibition achieving more potent PD effects and reduced HPR rates compared with clopidogrel which are reached promptly following LD and sustained with MD. CLINICALTRIALSGOV IDENTIFIER: NCT01852175.

Effects of dabigatran on the cellular and protein phase of coagulation in patients with coronary artery disease on dual antiplatelet therapy with aspirin and clopidogrel. Results from a prospective, randomised, double-blind, placebo-controlled study.

There is growing interest in understanding the effects of adding an oral anticoagulant in patients on dual antiplatelet therapy (DAPT). Vitamin K antagonists (VKAs) and clopidogrel represent the most broadly utilised oral anticoagulant and P2Y12 receptor inhibitor, respectively. However, VKAs can interfere with clopidogrel metabolism via the cytochrome P450 (CYP) system which in turn may result in an increase in platelet reactivity. Dabigatran is a direct acting (anti-II) oral anticoagulant which does not interfere with CYP and has favourable safety and efficacy profiles compared with VKAs. The pharmacodynamic (PD) effects on platelet reactivity and clot kinetic of adjunctive dabigatran therapy in patients on DAPT are poorly explored. In this prospective, randomised, double-blind, placebo-controlled PD study, patients (n=30) on maintenance DAPT with aspirin and clopidogrel were randomised to either dabigatran 150 mg bid or placebo for seven days. PD testing was performed before and after treatment using four different assays exploring multiple pathways of platelet aggregation and fibrin clot kinetics: light transmittance aggregometry (LTA), multiple electrode aggregometry (MEA), kaolin-activated thromboelastography (TEG) and turbidimetric assays. There were no differences in multiple measures of platelet reactivity investigating purinergic and non-purinergic signaling pathways assessed by LTA, MEA and TEG platelet mapping. Dabigatran significantly increased parameters related to thrombin activity and thrombus generation, and delayed fibrin clot formation, without affecting clot structure or fibrinolysis. In conclusion, in patients on DAPT with aspirin and clopidogrel, adjunctive dabigatran therapy is not associated with modulation of profiles of platelet reactivity as determined by several assays assessing multiple platelet signalling pathways. However, dabigatran significantly interferes with parameters related to thrombin activity and delays fibrin clot formation.

Impact of Escalating Loading Dose Regimens of Ticagrelor in Patients With ST-Segment Elevation Myocardial Infarction Undergoing Primary Percutaneous Coronary Intervention: Results of a Prospective Randomized Pharmacokinetic and Pharmacodynamic Investigation.

OBJECTIVES: The goal of this study was to assess the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of escalating ticagrelor loading dose (LD) regimens in primary percutaneous coronary intervention (PPCI). BACKGROUND: Patients with ST-segment elevation myocardial infarction undergoing PPCI frequently have suboptimal platelet inhibition in the early hours after ticagrelor LD. The use of high ticagrelor LD regimens has been hypothesized to optimize platelet inhibition in PPCI. METHODS: This was a prospective, randomized study of escalating ticagrelor LD regimens (180 mg, 270 mg, or 360 mg) in PPCI (N = 52). PK/PD analyses were performed before and 30 min, 1, 2, 4, 8, and 24 h post-LD. PK assessments included exposure to ticagrelor and its metabolite (AR-C124910XX). PD assessments included P2Y12 reaction units (PRU) measured by VerifyNow P2Y12 and platelet reactivity index (PRI) measured by vasodilator-stimulated phosphoprotein (VASP). RESULTS: Platelet reactivity was elevated during the first 2 h post-LD. There were no differences in PRU between groups during the study time course (p = 0.179). There were no significant differences in PRU levels across groups at all time points, except at 1 h (p = 0.017) where platelet reactivity was lowest with a 270-mg LD. No differences were found between the 180-mg and 360-mg groups (primary endpoint; p > 0.999). High on-treatment platelet reactivity rates were not different across groups, except at 1 hour (p = 0.038). Parallel PD findings were observed with VASP-PRI. PK analysis showed a delay in ticagrelor absorption and generation of AR-C124910XX, irrespective of dose. Although morphine was associated with a delay in ticagrelor PK/PD, it was not an independent predictor of high on-treatment platelet reactivity. CONCLUSIONS: ST-segment elevation myocardial infarction patients undergoing PPCI frequently exhibit impaired response to ticagrelor in the early hours after drug administration, which cannot be overcome by increasing LD regimens. These PD findings are largely attributed to an impaired PK profile, indicating a delay in drug absorption compared with that reported in stable clinical settings. (High Ticagrelor Loading Dose in STEMI; NCT01898442).

Pharmacodynamic Effects of Ticagrelor Dosing Regimens in Patients on Maintenance Ticagrelor Therapy: Results From a Prospective, Randomized, Double-Blind Investigation.

OBJECTIVES: The aim of this study was to assess the impact of ticagrelor dosing regimens on pharmacodynamic (PD) profiles in patients on maintenance ticagrelor therapy. BACKGROUND: Many patients on maintenance P2Y12-inhibiting therapies may require coronary revascularization procedures, raising a common clinical question with regard to the dosing regimen of the P2Y12-inhibiting agent to be used. To date, investigations assessing dosing regimens of P2Y12 receptor inhibitors in patients on maintenance therapy have been only assessed with thienopyridines, but not with ticagrelor. METHODS: This was a prospective, randomized, double-blind, placebo-controlled study assessing the PD effects of 2 dosing regimens of ticagrelor in patients on standard aspirin and ticagrelor maintenance therapy. A total of 60 patients were randomized to either 90 mg (maintenance dose [MD] group) or 180 mg (loading dose [LD] group) dose of ticagrelor. PD assessments were conducted at 3 time points (baseline, 1 h and 4 h). PD assessments were defined according to the platelet reactivity index (PRI) (vasodilator-stimulated phosphoprotein phosphorylation assay), P2Y12 reaction unit (VerifyNow P2Y12 assay) and adenosine diphosphate-induced platelet aggregation by light transmittance aggregometry. RESULTS: There were no differences in baseline levels of platelet reactivity with all assays. Intergroup comparisons by means of repeated-measures analysis adjusted for baseline PRI values showed that the LD group had significantly lower PRI levels compared with the MD group during the overall study time course (p = 0.031). Consistent findings were found for P2Y12 reaction unit (p = 0.026) and light transmittance aggregometry (p = 0.004). Intragroup comparisons showed that a more prompt and sustained platelet inhibitory effect was achieved more consistently with an LD regimen compared with a MD regimen. CONCLUSIONS: In patients on maintenance ticagrelor therapy, a 180-mg LD regimen of ticagrelor is associated with more potent and prompt platelet inhibition compared with a 90-mg MD. (Impact of Ticagrelor Re-Load Pharmacodynamic Profiles; NCT01731041).

Role of thromboelastography and rapid thromboelastography to assess the pharmacodynamic effects of vitamin K antagonists.

Thromboelastography (TEG) measures the effects of antithrombotic agents by assessing global functional clotting status by evaluating the viscoelastic properties of in vitro clot formation. Recently, rapid TEG (r-TEG), which uses tissue factor in addition to standard kaolin to accelerate activation of the clotting cascade, has been proposed to obtain more immediate results. The correlation between results of TEG or r-TEG with international normalized ratio (INR) in patients on vitamin K antagonist (VKA) therapy has not been explored and represents the aim of this study. Patients on chronic therapy with VKAs (n = 100) were included in an observational prospective pharmacodynamic study. The correlation between TEG parameters, in particular markers of thrombus generation [Reaction time (R), maximum rate of thrombus generation (MRTG), and time to maximum rate of thrombus generation (TMRTG)], and INR values as well as the concordance between these parameters and therapeutic INR ranges were evaluated. In addition, in a subgroup of subjects (n = 17), the correlation of r-TEG parameters with TEG parameters and INR values was also assessed. No correlation was found between INR and TEG parameters of thrombus generation, in particular between INR and R (r = 0.189, p = 0.06), MRTG (r = -0.027, p = 0.79), and TMRTG (r = 0.188, p = 0.06). Further, no concordance was found between these parameters and recommended INR ranges. Significant Spearman correlations were found between INR and activated clotting time (rS = 0.546, p < 0.001), r-R (rS = 0.572, p = 0.017), and r-TMRTG (rS = 0.510, p = 0.037), but not r-MRTG (rS = 0.131, p = 0.617). Results were obtained in 24 ± 6 versus 12 ± 4 min with TEG and r-TEG, respectively (p < 0.001). In patients on chronic VKA therapy, TEG is not a useful tool to evaluate VKA anticoagulant effect, compared with standard INR measurements. However, r-TEG parameters of thrombus generation correlate with INR levels, suggesting a possible role of this assay for measuring more expeditiously anticoagulant treatment effects.

Cigarette smoking and antiplatelet effects of aspirin monotherapy versus clopidogrel monotherapy in patients with atherosclerotic disease: results of a prospective pharmacodynamic study.

Smokers have a greater relative benefit of clopidogrel therapy compared with nonsmokers, likely attributed to its enhanced pharmacodynamic (PD) effects. However, to date, all PD studies have been conducted in patients on dual antiplatelet therapy with aspirin and clopidogrel, and it is unknown whether clopidogrel monotherapy can offer more effective antithrombotic effects compared with aspirin alone among smoking patients. Sixty aspirin-treated (81 mg/day) patients with vascular disease, classified as nonsmokers, light smokers, and heavy smokers according to cotinine serum levels, were enrolled. Patients were switched to clopidogrel (75 mg/day) monotherapy for 7-10 days. PD assessments were performed before and after switch by multiple electrode aggregometry (MEA) and kaolin-activated thromboelastography (TEG). Complete PD data were obtained in 57 patients (nonsmokers, n = 27; light smokers, n = 13; heavy smokers, n = 17). On treatment platelet reactivity following MEA, adenosine diphosphate (ADP) + prostaglandin E1 (PGE1) and thrombin receptor-activating peptide (TRAP) stimuli were significantly lower among heavy smokers following switch to clopidogrel. A significant inverse effect was observed with MEA arachidonic acid (ASPI), while neutral findings were shown with MEA collagen (COLL) stimulus. Thrombin and fibrin activity assessed by clot generation parameters were all nonsignificantly different but showed trends towards enhanced antithrombotic activity with clopidogrel among heavy smokers. In heavy smokers with vascular disease manifestations, clopidogrel is associated with enhanced platelet inhibitory effects, affecting purinergic and non-purinergic pathways, compared with aspirin as measured by MEA. Moreover, among smokers, clopidogrel offers trends towards enhanced effects on parameters of clot generation measured by TEG.