BACKGROUND: Standard of care for bleed prevention in patients with severe congenital hemophilia A is continuous prophylaxis with factor VIII (FVIII), typically administered intravenously 2-3 times per week in the home setting. Nonfactor prophylaxis and gene therapy are emerging novel prophylaxis strategies for hemophilia A, and it is important to compare their health economics with that of FVIII prophylaxis. Current data on resource utilization and costs in the adult hemophilia A prophylaxis population are limited, and a structured approach to analyze annual costs in these patients using administrative claims data has not been previously reported. OBJECTIVE: To assess health care resource utilization and costs of continuous FVIII prophylaxis in commercially insured adults with hemophilia A without inhibitors. METHODS: Administrative claims records from beneficiaries covered by major selfinsured companies in the United States from January 1999 through March 2017 (OptumHealth Care Solutions) were queried, and records for adult patients (aged 18-64 years) diagnosed with hemophilia A who received FVIII were extracted. Three criteria were defined to distinguish patients most likely to be managed with continuous FVIII prophylaxis from those on episodic treatment based on the frequency and timing of FVIII claims over a 12-month period of continuous enrollment: (1) having ≥ 4 FVIII claims, (2) having ≥ 6 FVIII claims, or (3) having no gaps > 60 days between FVIII claims. Patients with evidence of bypassing agent use were excluded. Health care resource utilization and costs were assessed for all patients with any FVIII use and for patients defined as being managed with continuous FVIII prophylaxis based on each criterion. RESULTS: The analysis included 189 patients with a diagnosis code for hemophilia A (ICD 9-CM code 286.0; ICD-10-CM code D66) from January 1999 through March 2017 who had at least 12 months of continuous enrollment and at least 1 noninpatient/nonemergency department claim for FVIII concentrate (any type) during their last 12 months of continuous enrollment (overall cohort). Within the overall cohort, 118, 94, and 61 patients met the criteria for FVIII prophylaxis based on the first, second, and third definitions, respectively. Per patient mean (SD) total health care costs for the overall cohort was $287,055 (306,933). For patients meeting criteria 1 through 3, per patient costs ranged from $407,752 (321,036) to $551,645 (302,841). FVIII concentrate accounted for over 90% of costs, with mean (SD) annual FVIII costs of $264,777 (292,423) in the overall cohort and $384,197 (303,826), $433,029 (313,711), and $531,098 (297,142) among patients meeting the respective definitions for prophylaxis. CONCLUSIONS: This analysis highlights the substantial economic burden associated with managing adults with hemophilia A on FVIII prophylaxis, where per patient mean total annual health care costs ranged from $407,752 to $551,645. Over 90% of such costs were attributable to FVIII concentrate dispensed. DISCLOSURES: This study was funded by BioMarin Pharmaceutical, which was involved in protocol development, analysis plan development, data interpretation, manuscript preparation, and publication decisions. All authors contributed to protocol development, analysis plan development, data interpretation, and manuscript development. All authors maintained control over the final content. Sammon, Solari, Kim, and Hinds are employees and shareholders of BioMarin Pharmaceutical. Cook, Sheikh, and Chawla are employees of Analysis Group, a consulting company that was contracted by BioMarin Pharmaceutical to conduct this study and develop the manuscript. Croteau has received professional fees from BioMarin Pharmaceutical, Bayer, CSL Behring, Genentech, and Pfizer. Thornberg has received professional fees from BioMarin Pharmaceutical, Genentech, Novo Nordisk, Sanofi, and Spark Therapeutics, as well as research funding from Novo Nordisk and Sanofi.