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.

Pharmacodynamic Effects of Switching From Prasugrel to Ticagrelor: Results of the Prospective, Randomized SWAP-3 Study.

OBJECTIVES: This study sought to assess the pharmacodynamic (PD) effects of switching to ticagrelor patients who were treated with prasugrel after undergoing percutaneous coronary intervention in the setting of an acute coronary syndrome. BACKGROUND: In clinical practice, there is a frequent need to switch between P2Y12 receptor inhibitors. However, concerns on drug interactions have emerged when switching therapies. To date, the PD effects of switching from prasugrel to ticagrelor have yet to be investigated. METHODS: This was a prospective, randomized, open-label, 3-arm, parallel-design study conducted in patients (n = 82) on maintenance dual antiplatelet therapy with aspirin (81 mg QD) and prasugrel (10 mg QD). Patients were randomized to continue prasugrel 10 mg QD or switch to ticagrelor 90 mg bid, with or without a 180 mg loading dose (LD), for 1 week. PD assessments included P2Y12 reaction units (PRU) by VerifyNow, platelet reactivity index by vasodilator-stimulated phosphoprotein (VASP), and platelet aggregation by light transmittance aggregometry (LTA) at a total of 6 time points: baseline, 2 h, 4 h, 24 h, 48 h, and 1 week after randomization. RESULTS: After switching to ticagrelor, PRU levels decreased as early as 2 h after drug administration. Mean PRU levels remained low during the study time course, without evidence of drug interactions. The primary endpoint of noninferiority of ticagrelor (2 arms combined) versus prasugrel measured by PRU at 1 week was met (least squares mean difference: -18; 95% confidence interval: -41 to 5). There was no increase in rates of high on-treatment platelet reactivity (PRU >208), which were overall very low throughout the study time course. Similar levels of platelet reactivity were observed irrespective of the use of a ticagrelor LD. Parallel findings were observed with VASP and LTA. CONCLUSIONS: Switching from prasugrel to ticagrelor leads to transiently higher levels of platelet inhibition, irrespective of the use of a LD, without evidence of drug interactions. (Pharmacodynamic Evaluation of Switching From Prasugrel to Ticagrelor [SWAP3]; NCT02016170).

Ventricular Tachycardia Precipitated by the Use of the Diet Supplement Hydroxycut Gummies.

BACKGROUND: Dietary supplements have a long history of causing adverse effects. Ventricular arrhythmias have not been described with Hydroxycut Gummies. OBJECTIVE: To report a case of ventricular arrhythmia after prolonged use of a popular dietary supplement, Hydroxycut Gummies. CASE REPORT: An 18-year-old female with no significant past medical history presented with life-threatening ventricular arrhythmia following about 10 days of use of Hydroxycut Gummies, a legal dietary supplement previously unreported to cause this complication. The patient received external cardioversion due to progressive decline in mental status and persistent hypotension and was initiated on intravenous procainamide at an outside hospital. Left ventricular ejection fraction was 45% to 50%, and cardiac MRI showed no definite finding of infarct, myocarditis, or fibrosis. Beta-blocker therapy was initiated, and there was a progressive reduction in ventricular arrhythmia burden with an improvement of symptoms over the next few days. Two and a half months after the initial hospitalization, follow-up Holter monitor revealed occasional accelerated idioventricular rhythm events and a significant reduction in, but still occasional, long monomorphic ventricular tachycardia events. None of the ingredients listed in this product have been associated with cardiac dysrhythmias in the literature. One phytochemical potentially in the product is alpha-quinidine, which could be the cause of the adverse event. However, there was no other identifiable etiology for the ventricular tachycardia, which resolved after the discontinuation of supplement and the addition of beta-blocker therapy. CONCLUSION: Hydroxycut Gummies should be considered a probable cause of this patient's arrhythmia given the lack of another etiology and a Naranjo Scale score of 6.

Impact of aspirin dose on adenosine diphosphate-mediated platelet activities. Results of an in vitro pilot investigation.

Different aspirin dosing regimens have been suggested to impact outcomes when used in combination with adenosine diphosphate (ADP) P2Y12 receptor antagonists. Prior investigations have shown that not only aspirin, but also potent ADP P2Y12 receptor blockade can inhibit thromboxane A2-mediated platelet activation. The impact of aspirin dosing on ADP mediated platelet activities is unknown and represents the aim of this in vitro pilot pharmacodynamic (PD) investigation. Twenty-six patients with stable coronary artery disease on aspirin 81 mg/day and P2Y12 naïve were enrolled. PD assessments were performed at baseline, while patients were on 81 mg/day aspirin and after switching to 325 mg/day for 7 ± 2 days with and without escalating concentrations (vehicle, 1, 3, and 10 µM) of prasugrel's active metabolite (P-AM). PD assays included flow cytometric assessment of VASP to define the platelet reactivity index (PRI) and the Multiplate Analyzer (MEA) using multiple agonists [ADP, ADP + prostaglandin (PGE1), arachidonic acid (AA), and collagen]. Escalating P-AM concentrations showed incremental platelet P2Y12 inhibition measured by VASP-PRI (p<0.001). However, there were no differences according to aspirin dosing regimen at any P-AM concentration (vehicle: p=0.899; 1 µM: p=0.888; 3 µM: p=0.524; 10 µM: p=0.548). Similar findings were observed in purinergic markers assessed by MEA (ADP and ADP+PGE1). P-AM addition significantly reduced AA and collagen induced platelet aggregation (p<0.001 for all measures), irrespective of aspirin dose. In conclusion, aspirin dosing does not appear to affect PD measures of ADP-mediated platelet reactivity irrespective of the degree of P2Y12 receptor blockade. P2Y12 receptor blockade modulates platelet reactivity mediated by alternative activators.