von Willebrand Factor/Factor VIII Concentrate (Humate-P®) Is Safe and Effective in the Prevention of Perioperative Bleeding in Patients with Very Low von Willebrand Factor: Ristocetin Cofactor (VWF:RCo).

Optimal dosing to prevent excessive surgical bleeding in von Willebrand Disease (VWD) was investigated in an open-label study of replacement therapy with a von Willebrand factor/factor VIII concentrate (VWF/FVIII, Humate-P®). This analysis focused on the subset of patients with very low VWF, defined as those with baseline VWF:RCo levels of <12 IU/dL. Of a total of 35 patients, 17 had very low levels of VWF:RCo; of these 17 “severe” VWD patients, 12 had type 3 VWD, one each had types 1, 2A or 2B, and 2 had type 2M VWD. Previous pharmacokinetic data in each patient was utilized to calculate pre-operative and immediate postoperative doses to raise plasma VWF:RCo and FVIII to 80–100 IU/dL for major surgery and 50–60 IU/dL for minor and oral surgery; subsequent doses were adjusted based on VWF:RCo levels. Eleven patients underwent major surgery including orthopedic, gynecologic and plastic surgery, and multiple tooth extractions; 4 had minor surgery and 2 had single tooth extractions. Hemostatic efficacy was assessed by investigators as excellent, good, moderate/poor, or none immediately after the surgery, 24 hours after the last VWF/FVIII infusion and 14 days post-op. Expected and actual estimated blood loss (EBL) was compared, transfusions recorded and adverse events (AEs) documented. The median loading dose was higher among subjects with severe VWD types (71 IU/kg, range 39 to 135) compared with non-severe VWD (44 IU/kg, range 17 to 121). Subjects with severe VWD types also used higher total doses (median: 280 IU/kg, range 63 to 859) and had longer treatment duration (6 days, range 1–26) than subjects with non-severe VWD types (median total dose: 208 IU/kg, range 79 to 1699; and treatment duration: 4.5 days, range 2–19). Hemostasis was rated as effective (good or excellent efficacy) in 15/17 (88.2%) patients immediately postoperatively, in 17/17 (100%) patients 24 hours after the last infusion (primary endpoint), and in 17/17 (100%) patients 14 days postoperatively. A bleeding related serious AE occurred in one patient; she had hemorrhage post-hysteroscopic resection of uterine fibroids followed by hysterectomy; actual EBL exceeded expected EBL and hemostatic efficacy was considered moderate/poor immediately post-op but good/excellent at the other time points. Three other surgery-related hemorrhagic events were mild in the severe VWD types; in the non-severe VWD patients, 1 severe, 1 moderate and 2 mild hemorrhagic adverse events were reported; none of these were considered to be related to poor efficacy of the drug. No thromboembolic complications or changes in viral titers were observed in the study. We conclude that patients with very low baseline VWF levels can safely undergo both major and minor surgery with VWF/FVIII concentrate when dosing is calculated to achieve and maintain hemostatic VWF levels based on VWF:RCo monitoring. It is important to base therapeutic decisions on the severity of disease as assessed by baseline plasma VWF and FVIII levels as well as VWD type.