OBJECTIVES:  Prior literature has suggested that the B domain of FVIII may play a role in the rate of FVIII inactivation (Krenov 2006).  Faster inactivation of recombinant B domain-deleted factor VIII (BDD-rFVIII) could affect efficacy during prophylaxis,  potentially leading to increased risk for breakthrough bleeds and higher FVIII utilization.  The objective of this analysis was to use real world data to determine whether patients treated with BDD-rFVIII had higher annual FVIII utilization than matched patients treated with full-length rFVIII (FL-rFVIII). METHODS:  Retrospective analysis of a large, US specialty pharmacy database was conducted using 2006/2007 data.  Patients who were not receiving Immune Tolerance Therapy, had at least six months of prescription activity, and did not switch brands or treatment regimens were selected.  BDD-rFVIII patients were matched with up to 5 FL-rFVIII patients based on treatment regimen (on-demand and prophylaxis), hemophilia severity and age.  The annualized number of international units (IU) dispensed per kilogram was compared between both rFVIII groups using a Wilcoxon Matched Pairs Test.  Subgroup analysis was performed by treatment regimen.  RESULTS:  Twenty-two BDD-rFVIII patients met the inclusion criteria and were matched to 104 FL-rFVIII patients.  Median annual IU/kg consumed for all BDD-rFVIII and FL-rFVIII patients was 3630 and 3054 respectively (p=0.20).  Subgroup analysis showed a statistically significant difference observed when comparing patients on a prophylactic treatment regimen.  Here, BDD-rFVIII patients consumed a median of 6204 IU/kg per year while matched FL-rFVIII patients utilized a median of 4118 IU/kg (p=0.03).  This difference could not be attributed to a higher prescribed prophylaxis dose. CONCLUSIONS:  This analysis shows that BDD-rFVIII-treated patients were associated with utilizing more IU/kg/year of FVIII while on a prophylactic regimen than matched FL-rFVIII-treated patients.  Further research is required to determine whether greater utilization of BDD-rFVIII during prophylaxis is associated with increased risk of breakthrough bleeds.