One-third of patients with severe
factor XI (FXI) deficiency caused by homozygosity for null alleles develop inhibitor
antibodies following exposure to plasma. Haemostasis during surgery is achievable in such patients by recombinant
activated factor VII (
rFVIIa) at doses used in
haemophilia A patients with an inhibitor to FVIII. However,
thrombosis has occurred in three of 12 such patients. In this study we discerned whether low-dose
rFVIIa would secure haemostasis and cause no
thrombosis in patients with severe FXI deficiency and an inhibitor during surgery. In vitro, a very low concentration of
rFVIIa (0.24 microg/ml) induced
thrombin generation in FXI-deficient plasma quite similarly to 1.9 microg/ml (a concentration that is achieved in patients with
haemophilia A and inhibitor after infusion of 80 microg/kg). Based on this finding, a protocol was designed for four patients with severe FXI deficiency and an inhibitor or
immunoglobulin A deficiency who underwent five major
surgical procedures. This included administration of
tranexamic acid from two hours before surgery until seven to 14 days after, and single infusion of low-dose
rFVIIa. No excessive
bleeding or
thrombosis were observed. In conclusion, a single low dose of
rFVIIa and
tranexamic acid secure normal haemostasis in patients with severe FXI deficiency who can not receive blood products.