Partial factor IXa inhibition with TTP889 for prevention of venous thromboembolism: an exploratory study

Summary.  Background:  Inhibitors of factor (F) IXa show potent antithrombotic activity with a low risk of bleeding in preclinical models. We investigated the anticoagulant potential of oral TTP889, a small molecule that inhibits up to 90% of FIXa activity at therapeutic doses, using a clinical model of extended prophylaxis in hip fracture surgery (HFS). Methods:  In this multicenter, randomized, double-blind study, 261 patients received oral TTP889 (300 mg once daily) or placebo starting 6–10 days after HFS, and standard thromboprophylaxis for 5–9 days. Treatment was continued for 3 weeks and all patients then underwent mandatory bilateral venography. The primary efficacy outcome was venous thromboembolism (VTE; venographic or symptomatic deep vein thrombosis or pulmonary embolism) during treatment, and it was evaluated centrally by an independent adjudication panel. The main safety outcome was bleeding (major, clinically relevant non-major, and minor events). Results:  Two hundred and twelve patients with an evaluable venogram were included in the efficacy analysis. The primary efficacy outcome occurred in 32.1% (35/109) of patients who had been allocated TTP889, and 28.2% (29/103) of patients on placebo ( P  =   0.58). There were no major bleeding events, and only two clinically relevant non-major bleeding events with TTP889. Conclusion:  Partial FIXa inhibition with TTP889 300 mg daily was not effective for extended prevention of VTE after standard prophylaxis for up to 9 days. Coupled with the low incidence of bleeding episodes, this suggests a lack of antithrombotic potential. Further investigation of TTP889 in different clinical settings is needed.
(Clinical trial registration information URL: http://www.clinicaltrials.gov . Unique identifier: NCT00119457) .