Wolfgang Miesbach: Discussing Model-Informed Precision Dosing of Fitusiran at EAHAD 2026
Wolfgang Miesbach, Professor of Medicine at Frankfurt University Hospital, shared on LinkedIn:
”At the start of his oral EAHAD 2026 presentation, Guy Young asked whether anyone had ever heard of the FDA approving a dose that had never been tested in phase 3 – and then explained that this is exactly the case for fitusiran 10 mg, where approval was based on modelling and simulation rather than direct trial experience.
Fitusiran uses siRNA to lower antithrombin (AT), rebalance thrombin generation and provide prophylaxis for people with haemophilia A or B, with or without inhibitors; the AT‑based dose regimen (AT‑DR) targets an AT window of 15–35% to balance efficacy and thrombosis risk.
In ATLAS‑OLE, around 11.7% of participants on the 20 mg Q2M regimen discontinued treatment because AT levels fell <15%, despite dose‑de‑escalation steps.
Population PK/PD modelling and simulations (N=1358 virtual participants) tested a new, lower 10 mg Q2M or QM dose to “rescue” those with AT <15% while keeping them within the 15–35% target range.
Adding the 10 mg regimens reduced the proportion of simulated patients with AT <15% to <1% and cut predicted discontinuations from 11.7% to ~0.66%, while maintaining most patients within the desired AT window.
For me, this work is a powerful example of how model‑informed precision dosing can refine the benefit–risk profile of rebalancing therapies, helping more people with haemophilia stay safely on fitusiran with as few injections as possible.”

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