Hereditary angioedema with C1 esterase inhibitor deficiency is a rare genetic condition that causes unpredictable episodes of severe swelling. Managing this challenging disorder requires a combination of strategies aimed at preventing attacks, treating sudden flare-ups when they occur, and improving the overall quality of life for those affected.

How Treatment Goals Are Shaped by the Nature of the Disease

The main aim when treating hereditary angioedema with C1 esterase inhibitor deficiency is to reduce the frequency and severity of swelling attacks that can affect different parts of the body. These episodes are not just uncomfortable—they can be dangerous, especially when they involve the throat or airways, where swelling can lead to life-threatening breathing problems. Because every person with this condition experiences attacks differently, treatment plans need to be tailored to match individual needs, taking into account how often attacks happen, where swelling tends to occur, and how severely the condition affects daily life.^[1]

Treatment is also influenced by the patient’s age and life circumstances. Children, adolescents, and adults may need different approaches, and certain life events such as pregnancy, dental procedures, or planned surgeries require special preparation to prevent attacks. The unpredictable nature of hereditary angioedema means that treatment must address both sudden emergencies and long-term prevention. While some patients experience attacks every one to two weeks, others may have longer intervals between episodes, making it essential for healthcare providers to work closely with each patient to develop a personalized management strategy.^[2]

Over the years, medical societies and expert groups have developed clinical guidelines to help doctors decide which treatments to use and when. These guidelines are based on research and clinical experience, but they also recognize that hereditary angioedema is a complex condition where one approach does not fit all. Alongside standard therapies that have been used for years, researchers continue to explore new treatments through clinical trials, offering hope for more effective options in the future.^[1]

Standard Approaches to Managing Hereditary Angioedema

The traditional treatment of hereditary angioedema with C1 esterase inhibitor deficiency revolves around three main strategies: managing acute attacks when they happen, preventing attacks before they start, and taking special precautions before situations that might trigger swelling, such as dental work or surgery. Each of these strategies uses different types of medications that work in specific ways to address the underlying problem—the lack of functional C1 esterase inhibitor protein in the blood.^[4]

For acute attacks, the goal is to stop the swelling as quickly as possible. The most direct way to do this is by replacing the missing or non-functioning C1 esterase inhibitor protein. Several products derived from human blood plasma are available for this purpose. These include medications known by brand names such as Berinert, Cinryze, and Haegarda. Berinert is given intravenously and is approved for treating sudden attacks of any severity, including those affecting the abdomen, face, and throat. Patients can be trained to administer these infusions at home, which allows for faster treatment when symptoms begin.^[15]

Another class of medications used during acute attacks are bradykinin receptor antagonists. A medication called icatibant (Firazyr) works by blocking the action of bradykinin, a substance that accumulates when C1 inhibitor is deficient and causes blood vessels to leak fluid into surrounding tissues, leading to swelling. Icatibant is given as a subcutaneous injection—a shot under the skin—and can provide relief within a couple of hours. It is designed for self-administration, giving patients the ability to treat attacks quickly without needing to visit a hospital.^[13]

A third type of acute treatment involves blocking plasma kallikrein, an enzyme that plays a key role in producing bradykinin. Ecallantide (Kalbitor) is a plasma kallikrein inhibitor given by subcutaneous injection. However, this medication carries a warning because it can cause serious allergic reactions, including anaphylaxis, so it must be administered by a healthcare professional who can monitor the patient for adverse effects.^[13]

For long-term prevention of attacks, doctors often prescribe medications that either reduce the production of the substances that cause swelling or replace the missing C1 inhibitor on a regular schedule. Attenuated androgens, such as danazol, have been used for decades to prevent attacks. These hormones work by increasing the liver’s production of C1 inhibitor. While effective, they come with significant side effects, especially for women, including weight gain, unwanted hair growth, changes in menstrual cycles, and potential liver problems. Because of these concerns, androgens are generally used at the lowest effective dose, and patients require regular monitoring.^[10]

An alternative preventive medication is tranexamic acid, an antifibrinolytic agent that helps stabilize the formation of C1 inhibitor. It is less effective than androgens but has fewer side effects, making it a useful option for some patients, particularly children and women who cannot tolerate androgens.^[10]

More recently, C1 esterase inhibitor concentrates have been approved for routine prophylaxis. Cinryze is given intravenously every three to four days, while Haegarda is administered subcutaneously with a similar schedule. These products directly replace the deficient protein and have become a preferred option for many patients because they address the root cause of the disease without the hormonal side effects of androgens.^[15]

When patients with hereditary angioedema need to undergo procedures that could trigger an attack—such as dental extractions, endoscopy, or surgery—doctors typically administer a dose of C1 inhibitor concentrate beforehand as a preventive measure. This approach, known as short-term prophylaxis, significantly reduces the risk of post-procedural swelling and has become standard practice in managing these patients.^[1]

The duration of therapy varies widely. Acute treatments are used only when symptoms appear and are stopped once the attack resolves, typically within one to three days. Prophylactic therapies, on the other hand, may continue for months or years, depending on how frequently the patient experiences attacks and how well they tolerate the medication. Doctors regularly reassess the need for ongoing prevention and adjust treatment based on changes in attack frequency and severity.^[1]

Innovative Therapies Being Tested in Clinical Trials

While standard treatments have greatly improved the lives of people with hereditary angioedema, researchers continue to develop and test new therapies that could offer even better control of the disease. Clinical trials are essential in this process, as they allow scientists to evaluate the safety and effectiveness of experimental drugs before they become widely available. These trials are conducted in phases, each with a specific purpose.^[13]

Phase I trials focus on safety. Researchers give the new treatment to a small group of healthy volunteers or patients to see if it causes any harmful side effects and to determine the appropriate dose. Phase II trials expand the study to a larger group of patients with the disease to test whether the treatment actually works—whether it reduces attack frequency, shortens attack duration, or improves other clinical measures. Phase III trials compare the new treatment with existing therapies or a placebo in large groups of patients across multiple locations to confirm its benefits and monitor for rare side effects.^[13]

One promising class of drugs being studied involves monoclonal antibodies that target specific proteins in the pathway that leads to bradykinin production. Lanadelumab (Takhzyro) is an example that has already completed clinical trials and received approval in many countries. This medication is a monoclonal antibody that inhibits plasma kallikrein, similar to ecallantide, but is designed for long-term prevention rather than acute treatment. It is given as a subcutaneous injection every two weeks or, in some cases, once a month. Clinical studies have shown that patients receiving lanadelumab experienced a significant reduction in attack frequency—some had their attacks reduced by as much as 87 percent compared to placebo. The medication also has a favorable safety profile, with the most common side effect being mild reactions at the injection site.^[12]

Another innovative approach involves gene therapy and small interfering RNA technology. Berotralstat (Orladeyo) is an oral medication—a pill taken once daily—that inhibits plasma kallikrein inside the body’s cells. This is the first oral prophylactic treatment for hereditary angioedema, offering convenience for patients who prefer not to receive injections. Phase III trials demonstrated that berotralstat reduced attack rates by about 44 percent compared to placebo. The most common side effects included mild gastrointestinal symptoms such as nausea and abdominal discomfort. Berotralstat represents an important advancement because it can be taken at home without the need for refrigeration or special handling, unlike many other biologics.^[12]

More recently, research has focused on RNA interference therapy. Donidalorsen is an investigational drug that uses this technology to reduce the production of prekallikrein, the precursor to plasma kallikrein, directly at the genetic level. By silencing the gene responsible for making this protein, the drug can lower the amount of kallikrein available to trigger bradykinin production. Early-phase clinical trials have shown promising results, with patients experiencing fewer attacks and longer attack-free periods. Donidalorsen is administered as a subcutaneous injection once a month, and the effects can last for several weeks after each dose. This approach is particularly exciting because it addresses the problem upstream, potentially offering longer-lasting protection with less frequent dosing.^[13]

Another experimental therapy is garadacimab (Andembry), a monoclonal antibody that inhibits factor XIIa, a different enzyme in the pathway that leads to bradykinin production. By blocking this enzyme, garadacimab prevents the cascade of reactions that result in swelling. Clinical trials are ongoing, but early data suggest that patients treated with garadacimab experience fewer attacks and have a good safety profile. This drug is given as a subcutaneous injection once a month.^[12]

Clinical trials for these new therapies are being conducted in multiple countries, including the United States, several European nations, and other regions around the world. Eligibility for participation in these trials depends on several factors, including the patient’s age, the type of hereditary angioedema they have, their current treatment regimen, and the frequency and severity of their attacks. Patients interested in joining a trial typically need a confirmed diagnosis of hereditary angioedema with C1 inhibitor deficiency and must meet specific criteria set by the study sponsors. Information about ongoing trials is often available through patient advocacy organizations, specialty clinics, and online registries.^[13]

Most Common Treatment Methods

• C1 Esterase Inhibitor Replacement Therapy
  • Berinert: given intravenously to treat acute attacks of all types, including facial, abdominal, and laryngeal swelling; approved for all ages including children under 12 years.^[13]
  • Cinryze: administered intravenously, primarily used for routine prophylaxis but also effective for treating acute attacks; given every three to four days for prevention.^[15]
  • Haegarda: a subcutaneous formulation of C1 inhibitor concentrate used for routine prophylaxis, injected every three to four days to prevent attacks.^[15]
• Bradykinin Receptor Antagonists
  • Icatibant (Firazyr): blocks bradykinin receptors to stop swelling during acute attacks; given as a subcutaneous injection that patients can self-administer; clinical response typically occurs within two hours.^[2]
• Plasma Kallikrein Inhibitors
  • Ecallantide (Kalbitor): inhibits plasma kallikrein to prevent excessive bradykinin generation; used for acute attacks in patients 16 years and older; must be administered by healthcare professionals due to risk of anaphylaxis.^[13]
  • Lanadelumab (Takhzyro): a monoclonal antibody that inhibits plasma kallikrein; used for prophylaxis in patients 2 years and older; given as subcutaneous injection every two to four weeks depending on age and response.^[12]
• Oral Kallikrein Inhibitors
  • Berotralstat (Orladeyo): the first oral prophylactic treatment for hereditary angioedema; inhibits plasma kallikrein; taken once daily at a dose of 150 mg in patients 12 years and older; clinical trials showed approximately 44% reduction in attack rates.^[12]
• Attenuated Androgens
  • Danazol: increases liver production of C1 inhibitor; used for long-term prophylaxis but has significant side effects including weight gain, menstrual changes, and liver toxicity; requires regular monitoring and use of lowest effective dose.^[10]
• Antifibrinolytic Agents
  • Tranexamic acid: stabilizes C1 inhibitor formation; less effective than androgens but has fewer side effects; useful in children and women who cannot tolerate androgens; used for long-term prophylaxis.^[10]
• RNA Interference Therapy (Investigational)
  • Donidalorsen: reduces plasma kallikrein production at the genetic level; given as subcutaneous injection once monthly; early clinical trials show reduction in attack frequency with good safety profile; approved for prophylaxis in patients 12 years and older.^[13]
• Factor XIIa Inhibitors (Investigational)
  • Garadacimab (Andembry): monoclonal antibody that blocks factor XIIa in the contact system pathway; used for prophylaxis; administered subcutaneously once monthly in patients 12 years and older; early trials show reduction in attack frequency.^[12]