Alnylam reports fatal thrombotic event in fitusiran extension

Alnylam Pharmaceuticals Inc. (NASDAQ:ALNY) reported a fatal thrombotic event in an open-label, international Phase II extension trial that prompted the company and partner Sanofi (Euronext:SAN; NYSE:SNY) to suspend dosing in all clinical trials of hemophilia candidate fitusiran (ALN-AT3, SAR439774). Alnylam said it will meet with FDA and conduct additional analyses to implement risk mitigation, enhanced safety monitoring and improved bleed management into the program.

The death occurred in a hemophilia A patient without inhibitors treated with fitusiran in the extension. Alnylam said the patient was initially diagnosed with subarachnoid hemorrhage on the basis of CT imaging after complaining of a severe headache. After a 14-day hospitalization while receiving Factor VIII concentrate 2-3 times daily, the patient died from a subsequent cerebral edema. Upon review of the patient's CT scans, 3 independent neuro-radiologists determined that the initiating event was not a subarachnoid hemorrhage but rather cerebral venous sinus thrombosis, which Alnylam considers to be "possibly related" to fitusiran. Given the revised diagnosis, Alnylam suspended dosing of fitusiran to investigate the safety event...