Is Intramuscular Administration of Recombinant Human C1-Inhibitor an Alternative for the Treatment of Acute Attacks in Patients with Hereditary Angioedema?

RATIONALE: Recombinant human C1-inhibitor (rhC1-INH) is registered for intravenous treatment of hereditary angioedema (HAE) attacks in adults and adolescents. In some cases, patients have compromised veins and/or difficulties accessing medical facilities.

METHODS: Data collected from five different HAE Type 1 patients, who use off-label on-demand (OD) intramuscular (IM) administration of rhC1-INH. After discussion of all ethical implications, the dose used per administration was either 1 or 2 vials (reconstituted in 10 mL WFI, each) injected IM in different locations (m. gluteus maximus or m. quadriceps femoris). Patient diaries were analyzed, which included documentation for pain by the visual analogue scale (VAS).

RESULTS: The data showed good efficacy of the initiated OD IM approach. The time to IM treatment was shorter in comparison to the usually delayed IV administration (40/77, 17/50, 29/55, 29/59, 89/123 min IM/IV). VAS (pain) for OD IM rhC1-INH injection was comparable to IV (1.57/1.36, 0.55/0.53, 1.66/1.16, 1.18/0.83, 1.53/0.96 IM/IV) and comparable IM administration (1.5, 0.5, 1.5, 1.0, 1.0). Two peripheral attacks required a second rhC1-INH dose (administered IV). Mild bruises and transitory edema at the injection sites were observed in 2/53 injections. No other adverse events were reported from any of the subjects.

CONCLUSIONS: Intramuscular application of rhC1-INH OD seems to be safe and effective, demonstrating an alternative to the intravenous route of application. 2100U rhC1-INH can be successfully reconstituted in 10 ml WFI and the intramuscular administration showed no adverse effects (except local pain). VAS (pain) for IM administration is comparable to IV and a comparable IM injection.