The protease-activated receptor-1 (PAR-1) is critically involved in the co-activation of coagulation and inflammatory responses. Vorapaxar is a reversible, orally active, low molecular weight, competitive antagonist of PAR-1.We investigated the effects of PAR-1 inhibition by vorapaxar on the inflammatory response, the activation of coagulation, fibrinolysis and endothelium during experimental endotoxemia. In this randomized, double blind, crossover trial, 16 healthy volunteers received a bolus infusion of 2 ng/kg lipopolysaccharide (LPS) ± placebo/vorapaxar with a washout period of 8 weeks. Vorapaxar dosing was guided by thrombin receptor-activating peptide-6-induced whole blood aggregometry. Participants received 10 mg vorapaxar or placebo as an initial dose and, depending on the aggregometry, potentially an additional 10 mg. Goal was > 80% inhibition of aggregation compared with baseline. Vorapaxar significantly reduced the LPS-induced increase in pro-thrombin fragments F1 + 2 by a median of 27% (quartiles: 11–49%), thrombin–anti-thrombin concentrations by 22% (–3 to 46%) and plasmin–anti-plasmin levels by 38% (23–53%). PAR-1 inhibition dampened peak concentrations of tumour necrosis factor -α, interleukin-6 and consequently C-reactive protein by 66% (−11–71%), 50% (15–79%) and 23% (16–38%), respectively. Vorapaxar decreased maximum von Willebrand factor levels by 29% (26–51%) and soluble E-selectin concentrations by 30% (25–38%) after LPS infusion. PAR-1 inhibition did not affect thrombomodulin, soluble P-selectin and platelet factor-4 concentrations.

PAR-1 inhibition significantly reduced the activation of coagulation, fibrinolysis, the inflammatory response and endothelial activation during experimental human endotoxemia.