An in vivo assessment of factor VIII concentrates

G. Rock, P. Tittley and V. Fuller

Replacement therapy for patients with hemophilia A requires that a specific dose of factor VIII be administered. Generally, these calculations involve the use of the manufacturer's stated dose in an equation. We have assessed factor VIII concentrates by in vitro techniques and found a considerable discrepancy (35%) between the stated and the measured contents. Confirmation of this discrepancy was obtained by in vivo assessment where posttransfusion recoveries corresponded to the measured rather than the stated contents of the vial. The half-disappearance time ranged from five to eight hours. The data suggest that constant monitoring of factor VIII preparations is necessary to ensure optimal treatment of patients with hemophilia A and help to explain the recent efforts by the Office of Biologics to achieve standardization.