Safety and Efficacy Profile of rAHF-PFM for Immune Tolerance Induction as Assessed In 3 Clinical Trials (PUP ITI, PRE-PAIR, and PAIR).

Development of neutralizing antibodies to FVIII is the most serious complication in the management of hemophilia A today. Eradication of the inhibitor with ITI therapy is a common treatment practice however, there are few reports of controlled studies, and much of the current ITI experience is reported from international registries and small site-based case studies. A previous case-series demonstrated successful tolerance in 9/12 (75%) patients using ADVATE [Antihemophilic Factor (Recombinant) Plasma/Albumin Free Method] (rAHF-PFM). Data on the safety and efficacy of rAHF-PFM in ITI therapy have now been formally captured in the recently completed Previously Untreated Patient (PUP-ITI) study, a retrospective chart review (PRE-PAIR), and an ongoing Prospective ADVATE ITI Registry (PAIR).

To provide a critical assessment of the safety and efficacy of rAHF-PFM in ITI therapy through a review of the cumulative data from PUP-ITI, PRE-PAIR, and PAIR.

PUP study was a prospective, multicenter, open-label, clinical study in PUPs <6 years of age with severe or moderately severe hemophilia (FVIII level ≤2%) who underwent on-demand or prophylactic treatment with rAHF-PFM. Subjects who developed inhibitors against rAHF-PFM could enter the PUP-ITI study and receive ITI. PRE-PAIR was a multicenter, retrospective, chart review of PTPs of any age and any severity of hemophilia A with history of ITI with rAHF-PFM. PAIR is an ongoing non-interventional safety surveillance registry of subjects prescribed rAHF-PFM for ITI. In all three studies, the choice of ITI regimen was at the discretion of the investigator; however, for the PUP-ITI study, the ITI regimen was based on site-specific ITI data and/or institutional guidelines, or as described in peer reviewed literature. The primary endpoints for PUP-ITI and PRE-PAIR were the success rate of ITI. The PAIR report was an interim safety assessment that did not examine efficacy endpoints. For PUP-ITI and PRE-PAIR, the definitions of success required the subject to have achieved 2 consecutive negative inhibitor test results and if data available, demonstrated normalized FVIII recovery. For PRE-PAIR, partial success was defined as achieving negative titer but without normalized recovery.

In PUP-ITI, a total of 11 subjects initiated ITI; 3 withdrew and 8 completed ITI. In PRE-PAIR, 35 subjects were enrolled, 30 of which were evaluable per protocol. Of these 30 subjects, 20 had moderately severe to severe hemophilia A (FVIII ≤2%), and high-titer (>5 BU) inhibitor. As of Sept 4, 2010, 18 subjects had been enrolled in PAIR and were included in an interim safety assessment. Over all 3 studies, most commonly prescribed initial dose regimen in subjects with high inhibitor titer prior to initiation of ITI was 100 IU/kg QD (17/37 [46%]), followed by 200 IU/kg QD (11/37 [30%]), and any dose at a frequency of <1/day (9/37 [24%]). In the low titer inhibitor subjects the most commonly prescribed regimen were various doses with a frequency of <1/day (13/22 [59%] subjects). Of the 11 subjects in the PUP study who participated in the PUP-ITI study, 3 withdrew and 8 (72.7%) achieved success (95% CI: 43.4%, 90.3%). All 8 subjects (100%) achieved success, with 1^st negative titer at a median time of 1.8 months (0.0 - 4.1 months) and the 2^nd negative titer at 3.0 months (1.1 – 9.0 months). In PRE-PAIR, sum of complete and partial success rates gave a total success rate of 76.7% (23/30) in subjects who met inclusion criteria (95% CI: 59.1, 88.2%). During these 3 studies, there were no SAEs related to rAHF-PFM ITI therapy and 6 non-serious AEs in 3 subjects considered to be related to rAHF-PFM (diarrhea, vomiting, pain following bleed, mild urticaria, and mild fever).

In 2 clinical studies of rAHF-PFM therapy in ITI treatment, rAHF-PFM was found to be efficacious in a variety of dosing regimens reflective of current standards of practice in hemophilia care. Overall success rates ranged from 72.7% in PUP-ITI to 76.7% in PRE-PAIR. Success rates in these 2 rAHF-PFM studies are similar to those reported in published literature. In all 3 ITI studies, there were no product related SAEs and 6 non-serious AEs in 3 subjects considered to be related to rAHF-PFM, suggesting that rAHF-PFM used for ITI has a similar risk profile established in routine clinical use. These data suggest that ITI treatment with rAHF-PFM was both effective and safe.

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