Direct thrombin inhibitors are not equally effective in vivo against arterial thrombosis: In vivo evaluation of DuP714 and Argatroban in a porcine angioplasty model and comparison to r-hirudin

Background: Qualitative differences in antithrombotic efficacy between thrombin inhibitors may be explained by the affinity for which they bind thrombin. This affinity is inversely proportional to the inhibitory constant for the agent (Ki). Thrombin inhibitors, DuP714 (Ki = 10^{- 11}) and argatroban (Ki = 10^{- 8}), were compared to our previous studies with r-hirudin (Ki = 10^{- 13}). Methods and results: Prior to balloon angioplasty, thirty pigs randomly received DuP714 (0.1 mg/kg bolus and 0.6 mg/kg/h infusion; n = 8), argatroban (0.2 mg/kg/min. continuous infusion; n = 9), or saline (n = 17). Injured arterial segments were measured for ¹¹¹In-platelet and ¹²⁵I-fibrin(ogen) deposition and the incidence of macroscopic thrombus. In DuP714-treated animals, platelet and fibrin(ogen) deposition were significantly lower than controls in both carotid (10 ± 2 vs. 62 ± 18 and 20 ± 4 vs. 74 ± 6) and coronary (10 ± 4 vs. 160 ± 63 and 17 ± 3 vs. 86 ± 22) arteries (p < 0.005). In contrast, platelet and fibrin(ogen) deposition were similar when comparing argatroban to saline in carotid (41 ± 20 vs. 40 ± 9 and 71 ± 5 vs. 49 ± 7) and coronary (92 ± 33 vs. 151 ± 45 and 114 ± 37 vs. 89 ± 38) arteries (p = 0.82 and 0.38, respectively). Compared to argatroban, fibrin(ogen) (p < 0.001) and coronary platelet deposition (p < 0.05) were significantly reduced in animals treated with DuP714 with no significant difference in carotid platelet deposition (p = 0.10). Neither inhibitor prevented macroscopic thrombosis. In previous studies with r-hirudin in this model, platelet deposition was limited to a monolayer with complete inhibition of macroscopic thrombus. Conclusions: Direct thrombin inhibitors do not equally prevent arterial thrombosis. Qualitative differences may be explained in part by the affinity for which they bind thrombin.