Recent studies have shown that pharmacokinetic (PK)-guided extended half-life (EHL) factor VIII can improve joint health in patients with hemophilia A. However, some patients experience suboptimal joint outcomes despite optimized PK-guided therapy. Low-dose emicizumab has emerged as a potential option for improving bleeding control and joint health in patients who do not respond adequately to PK-guided EHL factor VIII.

The objectives of the study is to compare clinical bleeding outcomes, joint health, cartilage biomarkers, and musculoskeletal ultrasound findings (HEAD-US) in hemophilia A patients in Thailand during PK-guided EHL factor VIII therapy and after switching to low-dose emicizumab.

Eighteen patients with hemophilia A from King Chulalongkorn Memorial Hospital, Thailand, aged 8-28 years, who were receiving PK-guided EHL factor VIII were enrolled. Patients with a Hemophilia Joint Health Score (HJHS) ≥ 12 were switched to low-dose emicizumab. A loading dose of 2 mcg/kg was administered, followed by dosing every 2 weeks during the first month and every 4 weeks thereafter. Clinical bleeding, annual bleeding rate (ABR), annual joint bleeding rate (AJBR), HJHS, cartilage biomarkers, and musculoskeletal ultrasound findings (HEAD-US) were evaluated every 4 months for up to 8 months after switching.

Inclusion Criteria:

• hemophilia A patients aged 3-30 years who received treatment with PK-guided EHL Factor VIII for more than 8 months

Exclusion Criteria:

• hemophilia A patients with presence of factor VIII inhibitors