Purity of factor VIII product and incidence of inhibitors in previously untreated patients with haemophilia A

It has been suggested that ultrapure clotting factor products carry a great er risk for inhibitor development in patients with haemophilia. We compared the incidence of inhibitors in 59 previously untreated patients (PUPs) wit h severe haemophilia (endogenous factor VIII < 0.01 U L-1) A, who were init ially treated with cryoprecipitate or intermediate purified products, with that in 22 patients exclusively treated with monoclonally purified and reco mbinant factor VIII. Persistent inhibitors were those with 1 Bethesda unit per mt or more, on more than one occasion, combined with a decrease in reco very. Incidences of persistent inhibitors were 17% (10/59) for patients who were treated with cryoprecipitate or intermediate-purity products and 9% ( 2/10) for monoclonally purified and recombinant factor VIII. Transient inhi bitors appeared to develop earlier during treatment with ultrapure products as compared to treatment with intermediate/low-purity products. In conclus ion, ultrapure products appear not to carry a higher risk for inhibitor dev elopment.