Sequential Use of Monthly Low Dose Emicizumab and Factor VIII Concentrate Prophylaxis Among Patients with Hemophilia a: A Case Series Report

Introduction: The effectiveness of monthly low dose emicizumab of 1.0 to 2.0 mg/kg has been reported among patients with and without inhibitor. However, their trough level of emicizumab was rather low ranging from 5.9 to 11.9 mg/mL and breakthrough bleeding episodes often occurred at the 4 ^th week after administering emicizumab. Moreover, non-exposure to factor VIII is one concern among patients receiving emicizumab prophylaxis. Therefore, the study aimed to evaluate the effectiveness of sequential use of monthly low dose emicizumab and factor VIII concentrate prophylaxis among patients with hemophilia A.

Methods: Patients with hemophilia A without inhibitor were recruited. Sequential use of monthly low dose emicizumab in the first week and factor VIII concentrate in the 4 ^th week was provided. Patients were closely monitored concerning the number and sites of bleeding episode, cause of bleeding from spontaneous or trauma-related conditions and the amount of additional factor VIII concentrate to treat breakthrough bleeding episodes. Also, the comparison of quality of life, hemophilia joint health score (HJHS), hemophilia early arthropathy detection by ultrasound (HEAD-US) and ultrasonography of bilateral elbows, knees and ankles before and after prophylaxis was conducted.

Results: Five male patients (4 adults, 1 boy) with hemophilia A (severe 2, moderate 3) without inhibitor were enrolled in the study with the mean (SD) age of 26.8 (15.5) years. They encompassed low bleeding risk circumstances including avoidance of contact sports and high velocity activities. Four adults initially received episodic treatment and subsequent low dose prophylaxis at 15-20 units/kg twice weekly but breakthrough bleeding episodes frequently occurred. The only boy also received low dose prophylaxis at 14 units/kg once weekly at the age of 5.9 years and increased to twice weekly one month later due to frequent spontaneous bleeding at the right knee. However, the difficulty in venous access created constraint in achieving adequate prophylaxis. Therefore, all patients were switched to receive the whole vial of emicizumab at the monthly low dose ranging from 1.14 to 1.25 mg/kg without 4-loading doses for 2 years and sequential use of median (IQR) monthly low dose emicizumab of 1.50 (1.31, 1.65) mg/kg in the first week and factor VIII concentrate 15 units/kg twice weekly in the 4 ^th week in the third year. The duration of follow-up in the third year was 6 months.

The results revealed the median (interquartile range, IQR) trough level of plasma emicizumab concentration at the 4 ^th weeks before factor VIII administration determined by a modified one stage factor VIII assay using emicizumab calibrator was maintained at 8.5 (6.2,10.8) µg/mL. The median (IQR) APTT of all patients at 6-month prophylaxis of 25.7 sec (25.3, 26.0) was shortened compared with a baseline of 66.9 sec (54.3, 105.1) demonstrating the presence of emicizumab and the likely absence of anti-emicizumab antibodies. Also, no inhibitor to factor VIII clotting activity was detected among all patients before and after prophylaxis.

Their median (IQR) annual bleeding rate significantly decreased from baseline of 30.0 (13, 36.5) to 5.0 (3, 12.5) in the first year, 1.0 (0.5, 8.5) in the second year and 1 (0, 3) in the third year of prophylaxis with p-values of 0.043. Impressively, zero annual bleeding rate in the third year of the current study was found among 2 patients while 2 patients exhibited one episode of trauma-related bleeding at the ankle and one patient had frequent epistaxis from high PM 2.5 in his hometown. Ultimately, all patients achieved annual spontaneous joint bleeding rate ≤1 episode during a 6-month period of sequential use of emicizumab and factor concentrate prophylaxis. In addition, quality of life, HJHS, HEAD-US and ultrasonography study were improved in all studied patients.

Factor VIII concentrate was helpful in preventing bleeding especially at the 4 ^th week after administering emicizumab and providing other biological activities beyond hemostasis related to bone remodeling, dysregulated macrophage polarization and inflammatory processes among studied patients.

Conclusion: The sequential use of monthly low dose emicizumab and factor VIII concentrate prophylaxis showed effectiveness with annual spontaneous joint bleeding rate ≤1 episode among all studied patients. The musculoskeletal system and quality of life were also improved.