Abstract
Inhibitors are the most serious side effect of haemophilia treatment; they occur in 25-30 % of all patients with severe haemophilia A. Over the last 2 decades, conflicting data on the impact of clotting products have been published. Due to small studies of selected cases, appreciation of the impact of any particular product has been difficult. Moreover, the emphasis on inhibitor testing has led to increased detection of low-titre inhibitors (to >10 %), while the percentage of high-titre inhibitors is still around 20 %. Other non-genetic risk factors, such as dosing and intensive treatment, are able to increase individual inhibitor risk. Early prophylaxis might reduce inhibitor risk. Well-defined large PUP studies including products should be considered. This can only be achieved in collaboration with all stakeholders. In conclusion, while the impact of FVIII products on inhibitor development is large, presently the actual impact of any specific product is unclear.