Comparison between hirudin and citrate in monitoring the inhibitory effects of P2Y12 receptor antagonists with different platelet function tests

Abstract

To cite this article: Pittens CACM, Bouman HJ, van Werkum JW, ten Berg JM, Hackeng CM. Comparison between hirudin and citrate in monitoring the inhibitory effects of P2Y12 receptor antagonists with different platelet function tests. J Thromb Haemost 2009; 7: 1929-32. Dual treatment with aspirin and clopidogrel is currently the therapy of choice in the prevention of recurrent cardiovascular events following coronary stent implantation. However, not all patients benefit equally from this antiplatelet regimen, as inadequate suppression of platelet aggregation by clopidogrel and/or aspirin -also referred to as Ôhigh on-treatment platelet reactivityÕ or Ôantiplatelet therapy resistanceÕ -is associated with worsened clinical outcome. The prevalence of this phenomenon varies widely, and is highly dependent on the type of platelet function test and the type of anticoagulant that is being used [1,2].ÔClassicÕ light transmission aggregometry (LTA), using ADP as agonist, is considered to be the reference standard platelet function test for determining the effectiveness of clopidogrel. Its use in daily practice is, however, not viable, owing to important limitations [3]. To overcome these limitations, various wholeblood platelet function assays designed to evaluate the efficacy of P2Y12 receptor antagonism have been introduced to the commercial market.Trisodium citrate dihydrate is the preferred anticoagulant agent for platelet function testing, as it has been in use for more than 40 years. However, measurements in citrate do not resemble physiologic conditions, as citrate inhibits coagulation by chelating calcium. This could result in an underestimation or overestimation of the true inhibitory effects of P2Y12 receptor antagonists in vivo. Other anticoagulants, such as hirudin and D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (PPACK), prevent coagulation of blood by direct inhibition of thrombin, thereby maintaining physiologic calcium levels [4]. This approach might therefore mimic the in vivo situation of platelet function more precisely than anticoagulation with citrate. Previous studies on this issue have demonstrated a generally higher magnitude of ADP-induced platelet aggregation in blood anticoagulated with citrate than in blood anticoagulated with PPACK or hirudin when measured with classic LTA [5][6][7].The manufacturers of the multiple-electrode aggregometry (MEA) assay strongly recommend the use of hirudin instead of citrate as an anticoagulant agent. Two recent publications reported a reduced area under the MEA curve, which indicates a lower magnitude of platelet aggregation, when platelet function was measured in citrated blood than when it was measured in hirudin-anticoagulated blood [8,9]. This finding is opposite to the results obtained with classic LTA when measurements are made in citrate vs. PPACK (or hirudin) [5,7]. For the whole-blood assays determining the efficacy of P2Y12 receptor antagonists, no information regarding the effects of anticoagulants other than citrate on the test performan...

A New Reversible and Potent P2Y12 Receptor Antagonist (ACT-246475): Tolerability, Pharmacokinetics, and Pharmacodynamics in a First-in-Man Trial

“…However, by chelating calcium, citrate reduces the free calcium levels in the blood samples thus interfering with the platelet aggregation process. Previous studies have reported a potential underestimation of the %IPA of P2Y 12 inhibitors due to higher platelet aggregation values obtained in citrate than with other anticoagulants [25]. The selection of optimal doses of P2Y 12 inhibitors to be tested during clinical development is based on targeting %IPA values between 70 and 90 %.…”

“…By chelating calcium, citrate reduces the free calcium levels in the samples and interferes with the platelet aggregation processes. Napsagatran is a direct thrombin inhibitor and prevents blood coagulation without affecting free calcium levels [25,26].…”

Assessment of Multiplate platelet aggregometry using citrate, heparin or hirudin in Rhesus macaques

“…Mean aggregation values for heparin and hirudin were significantly different from citrate, though they did not differ from one another in aggregation (Figure 2). Again, this could be due to the calcium-chelating effects of citrate [17], which are not observed with heparin or hirudin. This was further supported by the observation that mean AUC for heparin and hirudin were not significantly different from one another.…”

Platelet function tests for the monitoring of P2Y12 inhibitors

“…The performance characteristics of this product have not been established.) This new test cartridge is intended to measure the effect of clopidogrel on platelet function [38].…”