RARE Daily

Sanofi Genzyme Halts Dosing in Global Hemophilia Trial to Investigate New Adverse Events

November 6, 2020

Rare Daily Staff

Sanofi Genzyme initiated a voluntary sponsor-led global dosing hold on its full clinical development program for fitusiran due to the identification of new adverse events, according to a joint statement issued by the World Federation of Hemophilia, European Haemophilia Consortium, and the National Hemophilia Foundation.

Hemophilia is a hereditary bleeding disorder caused by a genetic mutation that results in inadequate levels of thrombin, an enzyme that causes clotting. Fitusiran is an experimental RNAi therapy that is administered once a month. It targets antithrombin, a protein that inactivates certain enzymes involved in coagulation. Fitusiran is designed to lower levels of antithrombin with the goal of promoting sufficient thrombin generation to restore hemostasis and prevent bleeding in patients with hemophilia A or B.

In a statement to Endpoints News, Sanofi said that it had voluntarily paused dosing and enrollment in the ongoing fitusiran clinical studies on Friday October 30 to allow investigation of reports of non-fatal thrombotic events in patients in the trials.

It is not the first time that studies of fitusiran have been halted due to thrombotic events. Fitusiran was originally developed by Alnylam, which partnered with Sanofi Genzyme to develop it in 2014. In September 2017, Alnylam halted dosing in ongoing trials of fitusiran following the death of a 78-year-old man with hemophilia A in the mid-stage open label extension. The U.S. Food and Drug Administration lifted the hold a few months later after reaching agreement on new clinical risk mitigation measures, and soon after, the partners restructured their deal and Sanofi Genzyme acquired full rights to the drug.

“Sanofi is currently engaging with regulatory authorities and assessing relevant trial data,” the company told Endpoints in a statement. “During this pause in dosing and enrollment, all other trial-related activities will continue. As you may be aware, patients enrolled in fitusiran clinical trials often have other health issues and various co-morbidities, which may be complicated by the current COVID-19 pandemic.”


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