Previously treated patients (PTP), who have not developed an inhibitor (inh) so far, are considered to be tolerant to factor VIII and at low risk for inh development. Therefore inh detection in a PTP should raise concerns about the concomitant variables such as product neo-antigenicity or way of application.

In our own center we recently detected the new development of a high responding inh to factor VIII in a 58 year old patient with severe haemophilia A. To find out about the current situation regarding inh development in PTP in Germany, we conducted a retrospective study.

A questionnaire was sent to 99 haemophilia treating physicians, so far 46 of them answered.

24 PTP-inh were registered during the last 5 years. Patients had at least 20 ED and/or one change of factor concentrate. Age (9 months to 70 years, median 35), severity of haemophilia A (16 severe, 2 moderate, 6 mild), exposure days (ED 6 to >1500, median 37) and genotype (4 intron-22-inversions, 3 large deletions, 2 missense mutations, 1 stop mutation, 1 insertion, 1 small deletion, 11 unknown) were recorded.

8 different factor VIII concentrates were given during inh development (5 plasma derived, 3 recombinant). Way of application (16 bolus infusion, 3 continuous infusion, 5 times both), infused amount until inh development (3000 IU to >1 mio IU), inh characteristic (15 HR, 9 LR), concomitant diseases and medication were registered.

In conclusion it became obvious that inh in PTP are still a serious and underestimated problem in haemophilia treatment today.

Our patient numbers are still too small to draw conclusions concerning given F VIII products or way of application. Secondly data showed that there is a variety of PTP definitions in Germany, referring to age of pat, number of ED and former change of product. A definition from the SSC of the ISTH for PTP would be helpful. The continuous use of the German register for drug side effects would make it easier to evaluate data in the future. A prospective, not product related study should be conducted.

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