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The new oral anticoagulants have demonstrated efficacy and safety in preventing stroke in patients with atrial fibrillation; however, one feature they all share is the lack of a specific antidote in cases of emergency. A humanized antibody fragment (Fab) against dabigatran is currently in development.
Binding affinity and on– and off–rates for Fab:dabigatran interactions were tested (mean ± SD, n=3). Inhibition of glucuronidated dabigatran was tested using diluted thrombin time assay. Any thrombotic activity of the Fab was tested as fibrinopeptide A (FPA) generation in the absence or presence of an existing clot. Pharmacokinetics (PK) was determined by measuring functional and sum dabigatran and total Fab in the rat (n=3). Dabigatran etexilate (DE), 30 mg/kg, or warfarin, 3 mg/kg, was given to rats every 8 hrs to induce bleeding in a rat tail bleeding model. Increasing Fab doses were given to test for bleeding time (BT) reversal (n=4–6).
Binding affinity of Fab to dabigatran was 2 pM, with a rapid kon (7.3 ±6.4×105/Ms) and slow koff (1.5 ±1.4×10–6/s). The IC50 of dabigatran inhibition by Fab was 3.5 nM and IC50 of dabigatran metabolite inhibition was 2nM in human plasma. Addition of up to 3 mg/mL Fab did not increase FPA generation in presence of a preformed clot or in plasma. PK of the Fab in rats had a short initial t1/2 of 0.24 h and longer terminal t1/2 of 5.8 h. Clearance was low (1.95 mL/min/kg) and steady–state volume of distribution small (0.0688 L/kg). PK of the Fab was not affected by dabigatran. DE (30 mg/kg p.o.) given in 8 hr intervals achieved steady state levels of 1500 nM (~750 ng/mL), and resulted in ~2–fold increase of tail cut BT. There was a rapid, dose–dependent decrease in BT after i.v. injection of Fab. Anticoagulation (clotting ex vivo) was also reversed. Treating rats with warfarin (0.5 mg/kg p.o.) over 3 days resulted in a 2–fold elevation of BT. Addition of similar doses of Fab had no effect on reversing this elevated BT.
The Fab is specific and selective for dabigatran and reversed DE–induced blood loss in rats, correlating with reversal of ex vivo clotting tests. This agent holds promise for reversing dabigatran–induced anticoagulation and bleeding effects.
Moderated Poster Contributions
Poster Sessions, Expo North
Sunday, March 10, 2013, 3:45 p.m.–4:30 p.m.
Session Title: Preclinical and Translational Research
Abstract Category: 52. TCT@ACC–i2: Translation and Pre–clinical Research
Presentation Number: 2111M–237
- 2013 American College of Cardiology Foundation