Answering relevant research questions via careful observation of clinical practice: a fresh look at the old way forward.

Although many aspects of inhibitor development have been elucidated, the role of switching FVIII product concentrate in the risk of inhibitors development in previously treated patients is still under discussion. To provide their contribution, Aznar et al [9] transparently showed the numerous different brands used over time and the number of patients treated with one or another class of concentrates in their center. This way of inclusively reporting data as generated in routine clinical practice would need to be adopted more broadly among hemophilia treater and scientists. Strength and limitations of the approach are discussed.

Switching clotting factor concentrates: considerations in estimating the risk of immunogenicity.

The development of neutralizing antibodies to factor VIII (FVIII) is the most serious complication of therapy for haemophilia A. There is now excellent documentation that a large number of both genetic and environmental factors contribute to the risk of FVIII inhibitor incidence. One of the environmental factors that has been proposed as an influence on this complication is the occurrence of FVIII product switching. There are only a small number of clinical studies that have addressed this question, and thus, the amount of objective information available to assess this association is limited. In this review, in addition to summarizing past evidence pertinent to this subject, we present the results of a complementary strategy, a Delphi analysis, to add to the considerations of product switching and FVIII immunogenicity. With the imminent arrival in the clinic of several new FVIII products, the haemophilia community must be prepared to collect prospectively controlled data to better address this important management issue.