aDabi-Fab binds to dabigatran and reverses its effect in vitro. (A) The orally available double prodrug dabigatran etexilate (1) is converted into the active form dabigatran (2), which is able to bind reversibly to the catalytic site of thrombin. The hapten (3) was used as immunogen for antibody generation. (B) Immobilized mouse antibodies were analyzed for binding to a hapten-peroxidase conjugate, which was competed off by increasing concentrations of soluble dabigatran. As a representative example, 2 dabigatran-specific antibodies together with a negative control, mAb, are shown. Complete inhibition is observed at a dabigatran concentration >10nM. (C) The prolonged clotting time with addition of dabigatran (7nM) in vitro in a thrombin clotting assay was reversed in a concentration-dependent manner by the mouse antibody (clone 22), the chimeric Fab, and the humanized Fab, aDabi-Fab without a loss in potency. Data are represented as mean of 3 determinations.