BACKGROUND Plasma-derived C1-inhibitor (C1-INH) concentrates (pdC1-INH) have been used as safe and effective treatments for hereditary angioedema with C1-INH deficiency (C1-INH-HAE) for >30 years. Notwithstanding this, sporadic reports and a study into the high-dose therapy of neonates with C1-INH concentrate administered in an off-label indication raised concerns that this drug might increase the risk of thromboembolism. OBJECTIVE To investigate the incidence of thromboembolism and the background of the risk factors related to treatment with pdC1-INH. METHODS Our retrospective cohort study of 144 patients with C1-INH-HAE compared the incidence of thromboembolism and its risk factors in patients who received pdC1-INH with those who did not receive pdC1-INH as well as with those treated with danazol or with tranexamic acid. RESULTS During the observation period (29 years), 104 of the 144 subjects received pdC1-INH. The average dose per treatment was 573.59 IU. None of the patients used an indwelling central venous catheter. Multiple risk factors for thromboembolism were identified in 93 of the 104 patients treated with pdC1-INH. The incidence rate of thromboembolism was 0.0019/100 person-years in patients treated with pdC1-INH, whereas it was 0.0211/100 person-years in the not-treated group. CONCLUSION Our cohort study did not find any evidence for an increased risk of thromboembolism during treatment with pdC1-INH, despite the presence of multiple predisposing factors.
