Factor VIII inhibitors: in vivo decrease of inhibitory activity during calcium infusion.

The effect of parenteral calcium on altering the activity of factor VIII inhibitors has been studied in three patients, two nonhemophiliacs and one hemophiliac. The patients were studied during both intravenous calcium infusion, factor VIII replacement, and combinations thereof. When compared to factor VIII replacement alone, a greater diminution of inhibitory activity was noted whenever calcium was infused prior to and during factor VIII replacement. This was demonstrated by both conventional coagulation assays and an agarose gel method. These observations could have therapeutic implications and may aid in further understanding the relationship of calcium to factor VIII and its inhibitor.