A circulating factor V inhibitor: possible side effect of treatment with streptomycin

A potent inhibitor of factor V was discovered in a middle aged woman shortly after streptomycin therapy. The patient suffered from severe bleeding over a period of 10 days and the inhibitor was demonstrable for 6 weeks. By use of specific antisera the anticoagulant was found to be of an IgG nature. In agar electrophoresis the inhibitor mowed with the immunoglobulin fraction and was separable from factor V activity in the pathological plasma although no factor V activity was demonstrable in untreated patient plasma. It is suggested that this method should be used to distinguish between cases of inhibitors in patients with congenital factor V deficiency and cases of transient inhibitors in patients with normal factor V production.