Effect of higher concentrations of RO318220 on platelet-supported thrombin generation. Thrombin generation assays were performed in the presence of 1 nM factor Xa and 2 nM factor Va, with aspirin-treated, washed, and gel-filtered platelets preincubated with vehicle or either (A) increasing concentrations of RO318220 or (B) 100 μM RO318220 (open symbols) and activated with either α thrombin (0.2 U/mL; A, ▦; B, •) or SFLLRN (50 μM; A, ▪; B, squares). Thrombin generation was assayed by S-2238 hydrolysis as described in “Materials and methods.” Means and standard errors were derived from 4 (A) or 3 (B) experiments.