Hereditary angioedema: increased number of attacks after frequent treatments with C1 inhibitor concentrate.

OBJECTIVE: C1 inhibitor concentrate is regarded as effective and safe in treating acute attacks of hereditary angioedema caused by C1 inhibitor deficiency. This study investigated the course of disease in 3 women treated frequently with C1 inhibitor concentrate.
METHODS: Three women are described who received C1 inhibitor concentrate for the treatment of acute attacks of hereditary angioedema and experienced an increase in the frequency of attacks during that treatment period. In a control group of 24 patients aged more than 60 years with hereditary angioedema, the natural course of disease was determined.
RESULTS: The 3 women (ages 50, 69, and 72 years) had received C1 inhibitor concentrate for 27, 18, and 22 years, respectively, for acute abdominal and skin attacks. Before this treatment, all attacks were severe. The treatment was always effective: The attacks were mild, and the duration of the attacks was shortened. During the treatment period, the number of attacks increased slowly but continuously, starting at the onset of treatment and paralleling the course of treatment. At the end of the observation period, the number of attacks increased by 4-fold, 12-fold, and 5-fold in the 3 women, respectively. No factors known to increase the frequency of attacks in hereditary angioedema were found in these patients. The control group did not show a similar increase in attacks during a comparable period of time.
CONCLUSION: A possible explanation for the increase in the frequency of attacks may lie in the large number of injections of C1 inhibitor concentrate.