Effect of Drotrecogin alfa (activated) on platelet receptor expressionin vitro

Abstract

Thrombocytopenia is a common problem in critically ill patients, which is associated with increased mortality. Recently, Drotrecogin alfa (activated) (recombinant human activated protein C (APC)) was shown to reduce mortality in patients with severe sepsis. Only minimal effect of APC on coagulation markers was demonstrated. Nevertheless, low platelet count was identified as a risk factor for bleeding with use of this drug. We conducted this study to evaluate possible influence of APC on in vitro expression of platelet receptors at therapeutic and supra-therapeutic concentrations. Blood samples of volunteers and patients with severe sepsis were adjusted with APC to final concentrations of 0.045 microg mL(-1) APC (APC-45, therapeutic dose) and 0.225 microg mL(-1) APC (APC-225, five-fold therapeutic dose), respectively. The activation of platelets was mediated by two different agonists. APC had no significant influence on platelet activation, with or without stimulation at both concentrations. In group APC-225, CD62P showed a non-significant decrease. This in vitro study demonstrates that therapeutic plasma concentrations of Drotrecogin alfa (activated) have neither influence on expression of platelet activation markers nor on platelet-granulocyte complexes in blood of volunteers and patients with severe sepsis. Thus, a direct drug-platelet interaction seems unlikely.

Comparative Response of Platelet fV and Plasma fV to Activated Protein C and Relevance to a Model of Acute Traumatic Coagulopathy

“…Efficacy of aPC at nanomolar concentrations has been shown to be reduced in the presence of platelets but not phospholipid alone [54], and aPC is ineffective at inhibiting both platelet adhesion and fibrin formation in blood flow models except at extreme superphysiological concentrations (16 µg/ml; 285 nM) [55]. aPC has also been shown to be incapable of affecting activation of platelets by thrombin-receptor-agonist-peptide-6 (TRAP) or ADP at DrotAA pharmacological doses (45 ng/ml; 790 pM) and even five-fold higher concentrations [56], while activation of platelets by arachadonic acid, ADP, and collagen was unaltered even at very high aPC doses (10 µg/ml; 178 nM), although that extreme concentration did inhibit activation of platelets by recombinant tissue factor [57]. It has been hypothesized that timing is key; if sufficient aPC is allowed to interact with fVa and/or fVIIIa prior to their involvement in prothrombinase/tenase complex activity, its anticoagulant function may be enhanced as these complexes provide some protection from aPC proteolysis [58]–[60].…”

Anticoagulant properties of drotrecogin alfa (activated) during hemofiltration in patients with severe sepsis

“…The lack of an additional effect of heparin on filter survival is not surprising since the anti-thrombotic effect of DrotAA is not enhanced by the addition of heparin [ 8 ]. However, since epoprostenol is a potent inhibitor of platelet function and DrotAA does not seem to have a direct inhibitory effect on platelet aggregation [ 9 ], one might have expected prolongation of filter survival during treatment with both DrotAA and epoprostenol.…”