Pharmacokinetics of Factor VIII Level in Patients Hemophilia A in Relation to Clinical and Radiological Outcomes

Abstract Background The benefit of pharmacokinetics (PK) -guided dosing is that both prophylactic and “on demand” dosing will be based on actual FVIII trough and peak levels instead of current FVIII estimates based on body weight and in-vivo recovery based dosing. Knowledge will increase with regards the relationship between FVIII level and bleeding in individual patients. The dose and frequency of factor VIII for patients on prophylaxis should only be reduced if clinically justified and impact should be monitored with regard to bleeding events, bleeding pattern and joint status. Objective To assess the trough and peak level of factor VIII in patients with hemophilia A on low dose prophylaxis and its impact on the clinical and radiological joint status. Patients and Methods A cross sectional study was performed in Ain-Shams University, Pediatrics Hospital, Hemophilia Clinic. It included 25 children and adolescents with hemophilia A on prophylactic factor VIII during the period from September 2018 to August 2019. Factor VIII used was recombinant 3rd generation with a dose of 45 IU/Kg/week rounded to the nearest 500IU. Trough level of factor VIII was done before prophylactic dose and peak level was done one hour postinfusion through chromogenic assay using STAGO-Immuno-Def VIII reagent. Clinical joint score and Functional Independence Score of Hemophilia (FISH) were done. Radiological joint scores were done using conventional x-ray, ultrasound and MRI. Cut-off level of trough levels was studied at 1% and 1%-5% of factor VIII. Results Patients were classified into 3 groups,4 patients (21.1%) had trough level <1%, 13 patients (68.4%) had trough level between 1%-5%, 2 patients (10.5%) had trough level > 5%. No significant difference between trough level of factor VIII and clinical joint scores and FISH scores of patients. Median score of the worst joint of patients with trough level >5% was 5 in comparison to 8 and 7 in patients with trough level 1%-5% and <1% respectively. Mean FISH of patients with trough level >5% was 9.50 ± 2.12 in comparison to 12.92 ± 5.41 and 11.00 ± 3.56 for patients with troughs 1%-5% and <1% that was respectively. Comparison between groups with different trough level of factor VIII according to X-ray scores of patients showed no significant difference Conclusion Low trough levels alone did not warrant intensification of the prophylaxis regimen; rather, the dose and dosing frequency should be adjusted based on individual’s bleeding pattern and many other factors as shown in our study the insignificant relation between trough levels of factor VIII and clinical and radiological outcomes.. More frequent factor VIII monitoring and incorporation into population based PK are warranted.