Large Predominance of Off-Label Prescriptions of C1-Inhibitor Concentrates and Icatibant in a Real-Life Setting: A Retrospective Clinical Study

C1-inhibitor (C1INH) concentrates and the selective bradykinin B2 receptor antagonist icatibant are approved only for treating hereditary angioedema with C1INH deficiency. Yet, they are regularly prescribed off label in other types of bradykinin-mediated angioedema including angiotensin-converting enzyme inhibitor (ACEi)-related and undetermined angioedema. We conducted a retrospective chart review of inpatient prescriptions of C1INH concentrates and icatibant between 2016 and 2020 in the University Hospital of Angers. The first outcome was the proportion of prescriptions with explicit indication. Then, we determined the compliance of prescriptions with European Medicines Agency approvals and the French bradykinin-mediated angioedema reference center guidelines. Finally, we estimated the economic impact of inappropriate prescribing. The therapeutic indication was explicit in 90.4% of prescriptions (n = 66/73). Only 17.8% of prescriptions were for hereditary angioedema with C1INH deficiency, while 31.5% were for ACEi-related and 28.7% for undetermined angioedema. However, most off-label prescriptions were consistent with the French bradykinin-mediated angioedema reference center guidelines (73.3%). We estimated that 13% of drug expenditures were potentially excessive. The predominance of off-label prescriptions may be explained by the infrequency of hereditary angioedema and the absence of approved alternatives in other types of bradykinin-mediated angioedema. Most attacks were related to ACEis. Epinephrine was rarely prescribed as first-line therapy in attacks of unknown origin. Given the high prices of these drugs, we advocate the development of a readily available management algorithm of angioedema to reduce inappropriate prescriptions in our center. In addition, we think that the drug prescription circuit should be redesigned to ensure the traceability of prescribed vials in the dispensing areas.