Sanofi, Alnylam’s hemophilia med fitusiran is on hold—again

Sanofi, Alnylam’s hemophilia med fitusiran is on hold—again

Sanofi hit pause on the development program for fitusiran, its Alnylam-partnered RNA-silencing hemophilia treatment, thanks to new side effects seen in clinical trials, a trio of hemophilia organizations announced on Friday.

The company voluntarily placed the global dosing hold after “the identification of new adverse events,” according to a joint statement from the World Federation of Hemophilia, European Hemophilia Consortium and the National Hemophilia Foundation on Friday.

Sanofi picked up the global rights to fitusiran in 2018 when the French pharma and Alnylam retooled a development deal that had previously divided fitusiran and the now-approved amyloidosis drug Onpattro (patirsiran) along geographic lines. It is developing fitusiran for hemophilia A and B.

This isn’t the first time the program has been paused for safety. Fitusiran ran into an FDA clinical hold in 2017 after a patient with hemophilia A died from a thrombotic event—or blood clot—in a phase 2 study. Alnylam suspended dosing in the trial and worked on a strategy to improve safety monitoring and mitigate the risk of fatal blood clots affecting more patients.

Sanofi announced long-term data from that phase 2 study in June of this year, showing the drug staved off bleeding episodes for up to 57 months, or nearly five years.

People with hemophilia A make a faulty version of a blood clotting factor called factor VIII, or too little of it, while people with hemophilia B make a defective version of factor IX. These patients receive frequent infusions of these clotting factors, often multiple times a week, to control bleeding.

Given once a month as an injection just under the skin, fitusiran targets antithrombin, a protein that prevents blood clotting. The hope is that lowering antithrombin levels will boost levels of thrombin, an enzyme that causes blood to clot.

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