Intravenous nanofiltered human C1 inhibitor concentrate (Cinryze®) is used as a direct replacement of deficient levels of plasma C1 inhibitor in patients with hereditary angioedema (HAE). In clinical trials in patients with HAE (including some patients who were pregnant), treatment with intravenous Cinryze® 1000 U effectively relieved HAE attacks. Pre-procedural prevention with the agent reduced the incidence of HAE attacks during and after a variety of dental, surgical or interventional diagnostic procedures. Routine preventative treatment every 3 or 4 days with the agent reduced the number and severity of HAE attacks. In clinical trials, intravenous Cinryze® was well tolerated, with no cases of viral transmission being reported.