An Individualized Approach to Treating Pups with Severe Hemophilia a: Which Factors Correlate with the Low Rate of Inhibitor Development?

Introduction:Development of inhibitors to replacement factor VIII (FVIII) remains a significant challenge to the management of previously untreated patients (PUPs) with severe hemophilia A. Although several determinants have been associated with the risk of inhibitor development, the impact of treatment approach remains controversial. Here we report our experience with an individualized approach to managing PUPs at a single hemophilia treatment center (HTC) in Germany.

Methods:PUPs with severe hemophilia A (FVIII:C <1%) treated at the Gerinnungszentrum Rhein-Ruhr (GZRR), Germany, between January 2013 and June 2021 were followed prospectively. Our treatment approach includes early prophylactic physiotherapy, pdFVIIIconcentrate for at least the first 50 exposure days (EDs), tailored prophylaxis with individualized dose escalation according to bleeding tendency, and avoidance of prolonged on-demand treatment by avoiding treatment of minor bleeds or hematomas. Potential bleeds were examined by a hemophilia specialist and a decision made as whether to treat with pdFVIII based on the bleed location and severity. Ultrasound was performed every 3-6 months to check for joint bleeds. Where on-demand treatment was necessary, we used a high initial dose of 60-80 IU/kg with the aim of reducing the need for subsequent doses. Non-urgent surgical procedures were postponed and venous access system implants were avoided within the first 100 EDs. Inhibitor levels were measured using the modified Bethesda assay every 3-4 EDs until ED 100, and every 3 months thereafter for 2 years.

Results:Data from 28 consecutive caucasian PUPs were collected. Fourteen (50%) patients had a F8 gene mutation associated with a high risk for inhibitor development. At the time of data cut-off 23 patients had received over 50 EDs of FVIII treatment, with 21 patients having over 100 EDs; the remaining patients had up to 45 EDs.Of the 28 patients, 27 started prophylaxis within the first 10 EDs. The initial prophylaxis schedule was tailored to each patient and ranged from 21 IU/kg every 10 days up to 40 IU/kg twice per week. One patient was treated on-demand for an intracranial bleed from ED 1-100. Only 3 spontaneous bleeds in 3 patients were treated; 25 patients (89%) remained free of spontaneous bleeds during prophylaxis. All three spontaneous bleeds were treated successfully with FVIII ± tranexamic acid. None of the 28 patients developed inhibitors.

Discussion:Our approach to managing PUPs includes treatment with pdFVIII for at least the first 50 EDs, during which we treat bleeds only where necessary and use high doses to minimize further infusions. We had no cases of inhibitor development in our prospective cohort of 28 patients. In contrast, between 2003 and 2012, four of nine (44%) PUPs treated at our center developed inhibitors during the first 20 EDs, with two patients developing low-titer and two high-titer inhibitors. At that time we used recombinant FVIII (rFVIII) for prophylaxis in most patients and were less selective about which bleeds to treat with FVIII. Our individualized management approach, choice of pdFVIII and restricted use of FVIII for on-demand treatment therefore appear to correlate with a reduction in inhibitor incidence at our center. We usually switch patients from pdFVIII to rFVIII after at least 50 EDs due to the lower administration volume. Given the low rate of inhibitor development reported for PUPs treated with human cell line-derived rFVIII, there is a rationale to consider starting PUPs on human cell line-derived rFVIII.

Conclusion:Our data support the position, that the use of an individualized management approach minimizes the risk of inhibitor development and raise important questions about how different aspects of treatment approach could impact outcomes in PUPs with severe hemophilia A.