Time course of factor VIII clotting activities and inhibitor levels. Factor VIII clotting activities (○) are shown as average baseline (B) or trough levels 24 hours after factor VIII concentrate (except for month 5 at 2 hours and month 8 at 12 hours postinfusion) or as clotting activities 1 hour post DDAVP (•, at 5 and 11 months). Inhibitor titers (□) are also indicated. Zero time is taken as first detection of the inhibitor with subsequent follow-up for 1 year shown. Factor VIII doses were 50 U/kg per day until month 4 when it was increased to twice daily then, after 6 weeks, reduced to 25 U/kg twice daily.