Disappearance of factor VIII:C antibodies in patients with haemophilia A upon frequent administration of factor VIII in intermediate or low dose.

In 18 haemophilia A patients with antibodies against factor VIII:C (F VIII:c) the effect of regular treatment with factor VIII (F VIII) in intermediate or low dose was studied. All patients with previous maximal F VIII:c antibody levels between 5 and 60 Bethesda Units per millilitre (BU/ml) showed a decrease of antibody level and normal F VIII recovery within 1-2 months. From nine patients with previous maximal antibody levels above 60 BU/ml four showed a decrease of antibody level within 2-26 months. In four young patients F VIII prophylactic therapy was started or continued as soon as there was evidence of F VIII:c antibody activity. In three of these patients F VIII recovery normalized within a few months.