The standard therapy for patients with haemophilia is prophylactic treatment with replacement factor VIII (FVIII) or factor IX (FIX). Patients who develop inhibitors against FVIII/FIX face an increased risk of bleeding, and the likelihood of early development of progressive arthropathy, alongside higher treatment‐related costs. Bypassing agents can be used to prevent and control bleeding, as well as the recently licensed prophylaxis, emicizumab, but their efficacy is less predictable than that of factor replacement therapy. Antibody eradication, by way of immune tolerance induction (ITI), is still the preferred management strategy for treating patients with inhibitors. This approach is successful in most patients, but some are difficult to tolerise and/or are unresponsive to ITI, and they represent the most complicated patients to treat. However, there are limited clinical data and guidelines available to help guide physicians in formulating the next treatment steps in these patients. This review summarises currently available treatment options for patients with inhibitors, focussing on ITI regimens and those ITI strategies that may be used in difficult‐to‐treat patients. Some alternative, non‐ITI approaches for inhibitor management, are also proposed.

Haemophilia A and haemophilia B are congenital X-linked bleeding disorders caused by deficiency of coagulation factor VIII (FVIII) and IX (FIX), respectively. The preferred treatment option for patients with haemophilia is replacement therapy. For patients with severe disease, prophylactic replacement of coagulation factor is the treatment of choice; this has been shown to reduce arthropathy significantly, reduce the frequency of bleeds and improve patients’ quality of life. Prophylaxis with standard recombinant factor requires regular intravenous infusion at least two (FIX) to three (FVIII) times a week. Recombinant FVIII and FIX products with an extended half-life are in development, or have been recently licensed. With reported mean half-life extensions of 1.5–1.8 times that of standard products for FVIII and 3–5 times that of standard products for FIX, these products have the potential to address many of the unmet needs of patients currently treated with standard factor concentrates. For example, they may encourage patients to switch from on-demand treatment to prophylaxis and improve the quality of life of patients receiving prophylaxis. Indeed, extended half-life products have the potential to reduce the burden of frequent intravenous injections, reducing the need for central venous lines in children, promote adherence, improve outcomes, potentially allow for more active lifestyles and, depending on the dosing regimen, increase factor trough levels. Members of the Zürich Haemophilia Forum convened for their 19th meeting to discuss the practicalities of incorporating new treatments into the management of people with haemophilia. This review of extended half-life products considers their introduction in haemophilia treatment, including the appropriate dose and schedule of infusions, laboratory monitoring, patient selection, safety considerations, and the economic aspects of care.

Progress in hemophilia therapy has been remarkable in the first 20 years of the third millennium, but the innovation began with the description the fractionation of plasma in 1946. The first concentrates followed the discovery of FVIII in the cryoprecipitate of frozen plasma and FIX in the supernatant in the early 1960s, which led to the initial attempts at replacement therapy. Unfortunately, the lack of screening methods for viral pathogens resulted in people with hemophilia (PWH) receiving concentrates contaminated by hepatitis A virus, hepatitis C virus, and human immunodeficiency virus, as these concentrates were made from large industrial pools of plasma derived from thousands of donors. Fortunately, by 1985, viral screening methods and proper virucidal techniques were developed that made concentrates safe. Increasingly pure products followed the introduction of chromatography steps with monoclonal antibodies in the production process. The problem of immunogenicity of exogenously administered concentrates has not yet had a complete solution. The development of alloantibodies against FVIII in about 25– 35% of PWH is the most serious adverse effect of replacement therapy. The next major advance followed the cloning of the F8 gene and later the F9 genes, which paved the way to produce concentrates of factors obtained by the recombinant DNA technology. The injected FVIII and FIX molecules had a relatively short circulating half-life in the plasma of people with hemophilia A and B, approximately 12 and 18 hours, respectively. The ability to prolong the plasma half-life and extend the interval between injections followed the application of methods to conjugate the factor molecule with the fragment crystallizable of IgG1 or albumin or by adding polyethylene glycol, which has led to an increase in the half-life of concentrates, especially for rFIX. The next frontier in hemophilia therapy is the application of durable and potentially curative therapies such as with gene addition therapy. Experiments in hemophilia B have demonstrated durable responses. Unfortunately, the results with gene therapy for hemophilia A have not been as remarkable and the durability must still be demonstrated. Nonetheless, the long-term safety, predictability, durability, and efficacy of gene therapy for hemophilia A and B remain an open question. At present, only healthy adult PWH have been enrolled in gene therapy clinical trials. The application of gene therapy to children and those with pre-existing antibodies against the delivery vector must also be studied before this therapy becomes widespread.

von Willebrand disease (VWD) is the most common inherited bleeding disorder and is due to quantitative and/or qualitative defects of von Willebrand factor (VWF). Despite the improved knowledge of the disease, detailed data on VWD types requiring specific treatments have not been reported thus far. To determine the number and types of VWD requiring therapy with desmopressin (DDAVP) and/or VWF/FVIII concentrates in Italy, a national registry on VWD (RENAWI) was organized. Only 16 of 48 centers included VWD in the RENAWI with diagnoses performed locally. Patients with uncertain results were retested by two expert laboratories using multimeric analysis and mutations of the VWF gene. A total of 1234 of 1529 (81%) cases satisfied the inclusion criteria and could be classified as VWD1 (63%), VWD2A (7%), VWD2B (6%), VWD2M (18%), VWD2N (1%), and VWD3 (5%). VWD types were also confirmed by DNA analyses and occur in young adults (83%), mainly in women (58%). Mucosal bleedings (32 to 57%) are more frequent than hematomas (13%) or hemarthrosis (6%). Most patients were exposed to an infusion trial with desmopressin (DDAVP) and found responsive with the following rates: VWD1 (69%), VWD2A (26%), VWD2M (29%), and VWD2N (71%). However, DDAVP was not always used to manage bleeding in all responsive patients and VWF/FVIII concentrates were given instead of or together with DDAVP in VWD1 (30%), VWD2A (84%), VWD2B (62%), VWD2M (63%), VWD2N (30%), and VWD3 (91%). Data of the RENAWI showed that correct VWD identification and classification might be difficult in many Italian centers. Therefore, evidence-based studies should be organized only in well-characterized patients tested by laboratories that are expert in the clinical, laboratory, and molecular markers of VWD.