Angiotensin-converting enzyme inhibitors (ACE-Is), prescribed most often to treat hypertension, have been used extensively since the 1980s. Additional indications for their use include heart failure, diabetes mellitus, chronic kidney disease, and post-myocardial infarction. It is estimated that up to 40 million patients take ACE-Is worldwide. C1-INH is a serine protease inhibitor that is normally found in the blood. Its primary function is the regulation of the complement and contact system pathways by binding irreversibly to target proteases. It additionally inhibits the fibrinolytic, clotting, and kinin pathways.31 Patients with the hereditary forms of AE (HAE) tend to have lower quantitative or functional levels of C1-INH. This results in decreased suppression of plasma kallikrein and factor XIIa leading to cleavage of high molecular weight kininogen to form increased circulating levels of bradykinin. Bradykinin binds to bradykinin 2 receptors resulting in separation of endothelial vascular cells and extravasation of fluid manifesting clinically as angioedema. Conestat alfa (Ruconest®) is a recombinant human C1-INH that has been purified from the breast milk of genetically modified rabbits. It is a single-chain soluble glycoprotein that is made of 478 amino acids. Administering conestat alfa increases the amount of C1-INH in these patients, repleting their levels, and acting as a treatment for AE due to C1-INH deficiency. Conestat alfa has been studied on asymptomatic patients with HAE and was shown to dose-dependently increase the level of functional C1-INH. Additionally, it was shown to restore the level of the complement C4 protein, which is also decreased in these patients. Since the same pathophysiological pathway is involved in patients with ACE-I-induced AE, it is reasonable to hypothesize its effectiveness in the treatment of patients with acute attacks.

This phase III clinical trial is being conducted to assess the benefits of emergency administration of intravenous (IV) conestat alfa to treat ACE-I-induced AE during an ED visit. This will be a multi-center, randomized, double-blind, two-armed, placebo-controlled trial. It will enroll 24 patients at two clinical sites in the United States. The population will consist of adult patients (≥ 18 years of age) who present to the ED with acute ACE-I-induced AE of the head and/or neck. Eligible patients will be enrolled in the study and randomized at a ratio of 1:1 to either the active treatment or placebo groups. The treatment group will receive intravenous conestat alfa at a fixed dose of 4200 International Units (IU) IV along with usual ED care at the discretion of the clinical care team, which may include epinephrine, H1 and/or H2-antihistamines, and corticosteroids. The placebo group will receive the same volume of an isotonic, sterile, normal saline (pH 5.5 ± 0.3) solution without any preservatives via IV injection, in addition to the usual care. Fixed dosing was chosen for this study rather than weight-based dosing as is used for treatment of acute attacks of hereditary angioedema because it is hypothesized that higher doses may have greater efficacy in ACE-I-induced AE and is safe to administer.32 A second fixed dose (4200 IU) of open label study drug will be administered 2 hours after the initial dose as a rescue medication if the subject has not experienced symptom relief (based upon TOSR evaluation). Additional doses of study drug or placebo will not be used. The rationale behind the dosage is based on the fact that 4200 IU is the maximum dose irrespective of patient weight. A second dose of the same amount is recommended if symptoms persist.

The primary objective is to compare the Time to Onset of Symptom Relief (TOSR) of conestat alfa compared to placebo in the treatment of ACE-I-induced AE. The secondary objective is to evaluate the efficacy of conestat alfa compared to placebo in Time to Meeting Discharge Criteria (TMDC), based on investigator-assessment of upper airway symptoms. The study will also compare the proportion of patients in each arm who 1) are hospitalized for any level of care 2) are admitted to the intensive care unit (ICU) and 3) requiring airway intervention (e.g., intubation, cricothyrotomy, or tracheotomy). Safety and tolerability of conestat alfa treatment will also be assessed.

Inclusion Criteria:

1. Age 18 years or older 2. Currently being treated with an ACE-I and presenting with presumed ACE-I-induced AE involving the head and/or neck region as determined by the clinical team 3. ACE-I-induced AE of the head and/or neck region of at least moderate severity within 24 hours of onset (must be sufficiently less than 24 hours to allow study drug to be administered within the same time frame) 4. AE that is at least moderate in severity for no less than one of the AE-associated airway symptoms (difficulty breathing, difficulty swallowing, voice changes, tongue swelling)32 5. Be able to provide informed consent or obtain informed consent from a legally appointed representative

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Exclusion Criteria:

1. History of anaphylaxis, hypersensitivity, or allergic reactions to rabbits/rabbit-derived products and C1-INH preparations 2. Urticaria present during the current illness 3. AE thought by the clinical team to be due to any other etiology i.e., HAE (types I, II, and HAE with normal C1-INH), acquired AE, allergic/histaminergic AE 4. History of recent trauma, abscess, infection, local inflammation, local tumor, postoperative or post-radiogenic edema, salivary gland disorders, and non-ACE-I drug-induced AE 5. Family history of recurrent AE 6. History of AE prior to ACE-I therapy initiation 7. Last dose of ACE-I taken more than 72 hours before the onset of AE symptoms 8. History of a major systemic disease that is not well controlled (left to the study team's discretion) 9. Anyone requiring immediate airway intervention according to the clinical team, such as endotracheal intubation 10. Women who are pregnant or breast-feeding (pregnancy must be ruled out by a negative test with the exception of those who have undergone total hysterectomy, bilateral oophorectomy, or are 2 years post-menopausal) 11. Concurrent participation in other investigational drug studies 12. Treatment with other targeted therapeutic agents for HAE (ecallantide/icatibant/C1-INH/fresh frozen plasma) 13. In the opinion of the investigator, there is adequate response to the usual care treatments (epinephrine, H1 and/or H2 antihistamine, corticosteroids) within one hour before dosing of the study drug 14. Prisoners 15. Non-English speaking

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Data will be published. Raw data will be provided upon request as appropriate.

Study will enrol over 12 months and data analysis and publication 0ver 6 to 12 months. Data will be available after publication of the study

Contact the Protocol Chair Jonathan Bernstein or Co-PIs Drs. Joseph Moellman or Gentry Wilderson

The study will be conducted as a double-blind, placebo-controlled trial. The appearance of the prefilled device containing placebo will be indistinguishable from those containing conestat alfa. The blinding will be maintained throughout the duration of the study for the subject. As such, only investigators and study staff blinded to the treatment assignments will be responsible for monitoring the patient and assessing efficacy and safety outcomes.