FDA Approves Fesilty, Novel Agent for Acute Bleeding Episodes, in Congenital Fibrinogen Deficiency

The FDA has approved a novel fibrinogen concentrate, fibrinogen, human-chmt (Fesilty; Grifols) for the treatment of pediatric and adult patients with congenital fibrinogen deficiency (CFD), including hypo- or afibrinogenemia, who experience acute bleeding episodes. The approval was announced in a news release by Grifols, which intends for the drug to be made available during the first half of 2026.¹

“With the approval of [fibrinogen, human-chmt], we are excited to be able to provide US health care providers and patients with CFD a safe, effective, and reliable treatment for acute bleeding episodes—when every minute counts,” Roland Wandeler, president of Grifols Biopharma, said in the news release.¹

What is Congenital Fibrinogen Deficiency?

CFD is a very rare inherited blood disorder that leads to abnormal blood clotting. Fibrinogen is a key protein necessary for blood to clot that is produced in the liver; patients with CFD have a deficiency in the function or amount of fibrinogen in the body. When the variant is passed down from only 1 parent, a patient may have reduced levels of fibrinogen, called hypofibrinogenemia. Afibrinogenemia is when the variant gene is passed down from both parents, leading to a complete lack of fibrinogen.^1,2

While individuals who experience problems with the specific function of their fibrinogen often do not exhibit symptoms, those with reduced or lacking fibrinogen may experience a series of bleeding complications. This can include bleeding in the joints, heavy bleeding following injury or surgery, and easy bruising. People with reduced levels of fibrinogen bleed less often, and the bleeding is not as severe compared with patients with a complete lack of fibrinogen.²

Are Treatments Available, and Where Does Fibrinogen, Human-chmt, Fit in the Paradigm?

Treatment options for episodes of this rare disorder are limited, necessitating research into novel alternatives. Standard treatments for low fibrinogen levels include fresh frozen plasma—which is the liquid portion of the blood that contains clotting factors—cryoprecipitate, or fibrinogen concentrate. Despite these options, patients with CFD often experience excessive bleeding complications, including gastrointestinal bleeding or brain bleeding, which can be severe or fatal.^1,2

Fibrinogen, human-chmt, is a human blood coagulation factor product. The product is highly purified and contains a precisely defined amount of fibrinogen, which enables a predictable but rapid restoration of fibrinogen levels. It differs from standard of care treatments, which often include additional proteins and components that are not necessary for fibrinogen replacement. Furthermore, these treatments often require large infusion volumes to achieve adequate fibrinogen levels, which could be burdensome for patients.^1,2

Safety and Efficacy of Human Fibrinogen Concentrate

In a prospective, multinational, open-label, single-arm interventional pharmacokinetic/pharmacodynamic (PK/PD) clinical trial (NCT02065882), investigators observed significant efficacy and safety in patients with CFD treated with fibrinogen, human-chmt, previously called BT524. The trial was divided into phase 1, which focused on the single-dose PK/PD of BT524, and phase 3, which evaluated the efficacy and safety of BT524 as an on-demand treatment or prophylaxis of bleeding events (multiple doses).^3,4

A total of 27 patients were treated with the human fibrinogen concentrate. Incremental in vivo recovery (IVR) of fibrinogen activity was 1.88 mg/dL per mg/kg. Maximum clot firmness (MCF) significantly increased 1 hour following the infusion of BT524 in adults (mean change, 11.1 mm; 95% CI, 9.33–14.47; P < .0001). There was a similar increase in pediatric patients, in which the mean MCF increase ranged from 9.3 to 16.5 mm. Importantly, this increase was maintained for up to 8 hours.³

Regarding safety, a total of 31 treatment-emergent adverse events (AEs) were reported in 55.6% of patients. For AEs specifically related to treatment, there was a very low incidence. On the boxed label for fibrinogen, human-chmt, there are contraindications listed for patients who have severe hypersensitivity reactions, including anaphylaxis, to the drug or any of its components.¹

REFERENCES

1. Grifols receives US FDA approval for new fibrinogen concentrate, FESILTYTM (fibrinogen, human-chmt). News Release. Grifols. Released December 19, 2025. Accessed December 19, 2025. https://www.grifols.com/en/view-news/-/news/grifols-receives-us-fda-approval-for-new-fibrinogen-concentrate-fesiltytm-fibrinogen-human-chmt

2. Congenital fibrinogen deficiency. MedlinePlus [Internet]. Bethesda (MD): National Library of Medicine (US). Last Updated February 3, 2025. Accessed December 19, 2025. https://medlineplus.gov/ency/article/001313.htm

3. Khayat CD, Boejm H, Aigner S, et al. Evaluation of pharmacokinetics, efficacy, and safety of a new human fibrinogen concentrate in patients with congenital fibrinogen deficiency. Blood. 2024;144(1):1221. doi:10.1182/blood-2024-198116

4. Pharmacokinetic, efficacy, and safety of BT524 in patients with congenital fibrinogen deficiency. ClinicalTrials.gov Identifier: NCT02065882. Last Updated July 3, 2025. Accessed December 19, 2025. https://www.clinicaltrials.gov/study/NCT02065882