Alnylam Suspends Fitusiran Dosing due to Thrombotic Event in Phase 2 open-label extension study

The WFH was saddened to learn of the death of a hemophilia A patient taking part in the Phase II trial of fitusiran, in development by Alnylam. On behalf of the entire bleeding disorder community, our condolences go out to the family of this individual.

The press release states: “Alnylam recently became aware of a fatal serious adverse event (SAE) that occurred in a patient with hemophilia A who was receiving fitusiran in the Phase 2 OLE study. Approximately nine days prior to hospital admission, he developed exercise-induced right hip pain that was treated with a total of three doses of factor VIII concentrate (31-46 IU/kg) on three separate days. Four days prior to admission, when the patient received his third dose of factor, he developed a severe headache. While he was initially suspected of having viral meningitis, the patient was diagnosed with subarachnoid hemorrhage on the basis of CT imaging, and treated with factor VIII concentrate administered two to three times daily. Over a 14-day hospitalization, his medical condition worsened despite the administration of factor and the patient died from subsequent cerebral edema. The initial diagnosis of subarachnoid hemorrhage was reported by the investigator as not related to fitusiran. For a more complete understanding, the Company initiated further investigation of the SAE, including review of the patient’s CT scans by three independent neuro-radiologists, who all confirmed on September 1, 2017, that the initiating event was a cerebral venous sinus thrombosis, and not a subarachnoid hemorrhage. As a result of this new information, Alnylam suspended dosing in fitusiran studies in order to further investigate the safety event, now considered to be possibly related, and to develop a risk mitigation plan. The Company also notified study investigators and global regulatory authorities.”

The full press release from Alnylam is available at

The WFH will follow developments and provide updates as they become available.